2017 Vol. 32, No. 9

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Effects of hydrogen addition on burning characteristics of RP-3 kerosene
2017, 32(9): 2049-2054. doi: 10.13224/j.cnki.jasp.2017.09.001
Abstract PDF(999KB) icon1200 icon592
Abstract:
In order to illustrate the effects of hydrogen addition on the combustion characteristics of RP3 kerosene, the laminar burning velocity and Markstein length of RP3 kerosene/hydrogen mixture were investigated experimentally in a constant volume combustion bomb. The experiments were performed at initial pressure of 0.1MPa, initial temperatures of 390,420K and over the equivalence ratios range of 0.8-1.5. The influences of hydrogen addition ratio on the flame structure, laminar burning velocity and Markstein length were investigated. Results showed that some cracks or folds appeared on the flame front in the flame developing process, and the instability of flame increased with the growing hydrogen addition ratio. Increasing the equivalence ratio or the hydrogen addition ratio decreased the Markstein length of RP3 kerosene/hydrogen mixture. Furthermore, with the equivalence ratio increasing from 0.8 to 1.5, the laminar burning velocity of RP-3 kerosene/hydrogen mixture increased initially and then decreased gradually. The highest laminar burning velocity was measured at fuel rich condition (the equivalence ratio was 1.2). At the same time, with the increase of initial temperature or hydrogen addition ratio, the laminar burning velocity of RP-3 kerosene/hydrogen mixture showed an increasing trend.
Design method of equal life on detonation combustor under actual detonation loading
2017, 32(9): 2055-2062. doi: 10.13224/j.cnki.jasp.2017.09.002
Abstract PDF(872KB) icon963 icon493
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According to the equal wall thickness detonation combustor of 60mm inner diameter, the finite element model was established and the real detonation load was applied. The fatigue load spectrum was confirmed as a constant amplitude spectrum. The relationship between the wall thickness and the dynamic magnification factor of detonation combustor was found by calculating analytical model under static loading and finite element model. The wall thickness adjusted itself through the dynamic magnification factor. In the process, target stress was approached by the equivalent stress of the inner wall. On this basis, the design method of equal life detonation combustor was presented. According to the calculation results, the test section of the variable wall detonation combustor was designed and processed. The strain of three measuring points on the outer wall of variable wall thickness was measured; the fatigue life of the inner wall of these three measuring points was estimated, and the maximum error of the fatigue life was 882%. Considering the working conditions error between the test and numerical calculation, the life of these three measuring points was the same, proving the validity of the design method of equal life detonation combustor.
Experiment and numerical simulation of axial incident shock wave reflection and focusing process
2017, 32(9): 2063-2069. doi: 10.13224/j.cnki.jasp.2017.09.003
Abstract PDF(878KB) icon1035 icon514
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To study the effects of the shock wave focusing on the second stage process of the twostage pulse detonation engine by the cavity entrance widths, an experimental system was designed to research axially incident shock focusing on the different cavity entrance widths. And experiment and numerical simulation were carried out to investigate the process and the effects of the reflected shock wave focusing. The schlieren system was used to photograph the structure of the cavity flow field, and the dynamic pressure on the vertex was measured. Strong stabilitypreserving (SSP) RungeKutta method, and weighed essential nonoscillation (WENO) scheme and block structured dynamically adaptive mesh refinement (SAMR) algorithm were adopted to simulate the shock wave reflection, diffraction and focusing process. Good agreement between experiments and numerical results was observed. By analyzing and comparing the shock wave reflection and focusing process under the conditions of the same Mach shock wave through different entrance cavity widths, the enhancement of the reflection and focusing and the increase of the vertex pressure with a smaller width were found. Meanwhile, the jet enhancement was induced by the shock wave focusing.
Experiment on infrared characteristics suppression by component cooling of twodimensional convergentdivergent vectoring nozzle exhaust system
2017, 32(9): 2070-2079. doi: 10.13224/j.cnki.jasp.2017.09.004
Abstract PDF(1493KB) icon1177 icon527
Abstract:
Experiment was conducted to study the distribution of wall temperature and infrared radiation characteristics on twodimensional convergentdivergent (2DCD) vectoring nozzle exhaust system with cone film cooling and nozzle impingementfilm cooling, in three geometric deflection states, namely deflection of 0°, 10°, 20°, and the results were compared with nocooling state. The experimental results showed that film holes with pre dense and after thinning arrangement form can effectively reduce the hot side temperature region size. For cone cooling state，under the conditions of density flow ratio of 08, cooling efficiency reached 45%-63%, the infrared radiation intensity of exhaust system decreased by 20%, in the tail direction ±10°，but due to the cooling air flow injection, the temperature of heat shield wall and nozzle wall increased, and infrared radiation intensity increased by 15%, in 30° detection direction. In nozzle cooling state, convergent section (density flow ratio of 0.25) cooling efficiency reached 19%-33%, the expansion section (density flow ratio of 065) cooling efficiency reached 755%-835%, the side wall sections (density flow ratio of 065) cooling efficiency reached 78%-90%, infrared radiation intensity decreased by more than 30%, in the tail direction 15°-75°, the maximum decrease reached 80% (geometric deflection angle of 20°, detection direction of 30°).
Anisotropic turbulence model applied to rotating channel
2017, 32(9): 2080-2087. doi: 10.13224/j.cnki.jasp.2017.09.005
Abstract PDF(945KB) icon1172 icon494
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An anisotropic kω model adapted to simulate the rotating channel was proposed based on the simplified model of algebraic Reynolds stress equation combined with the turbulent fluctuation data obtained from the direct numerical simulation(DNS) calculation of the full development rotating channel. A rotating straight channel with the inlet Reynolds number of 6000 and the rotation number ranging from 0 to 026 was studied. Results show that the anisotropic kω model is modified by the means of the rotation correction coefficient multiplied by the traditional turbulence viscosity coefficient. The modified model can describe the heat transfer situation of the leading and trailing surfaces in the rotating channel accurately, which is an effective method for anisotropic turbulence model correction. The accurate description of the Reynolds stress ratio is the key to the rotation correction coefficient. The heat transfer effect of the rotating channel is related to the rotation number and the dimensionless distance along the flow direction. The heat transfer effect of leading surface decreases with the increasing rotation number and dimensionless distance. However, the situation of the trailing surface is opposite, that is to say, with the increase of rotation number and dimensionless distance, the heat transfer effect of trailing surface is enhanced.
Numerical analysis of flat plate film cooling characteristics at various streamwise angles based on plasma actuation
2017, 32(9): 2088-2094. doi: 10.13224/j.cnki.jasp.2017.09.006
Abstract PDF(1053KB) icon976 icon511
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Large eddy simulations(LES) were carried out to numerically investigate the effects of streamwise angles on the film cooling performance with and without plasma actuation. Results showed that as the streamwise angle increased, the coolant penetrated deeper into the crossflow, thus the reverse flow region downstream the jet grew in size, and the strength and the liftoff effect of the hairpin vortex increased, resulting in a reduction of film cooling efficiency, but at 90° angle the film cooling efficiency slightly increased since some cold fluid was entrained into its wake. As a result, the film cooling efficiency was the highest at 35°angle and the lowest at 60°angle. Due to the downward momentum of plasma actuation, the penetration of the jet into the crossflow was depressed, the KuttaZhoukowski lift acted by the crossflow and on the head of the hairpin vortex was reduced, and the strength of the mutual induction between the feet of the hairpin vortex was decreased. Accordingly, the evolution and the liftoff effect of the hairpin vortex were suppressed, thus the film cooling efficiency was enhanced and these impacts were more significant at smaller streamwise angle. At the 35° angle the centerline film cooling efficiency increased by 55% at most.
Temperature indicating paint image isotherm extraction algorithm
2017, 32(9): 2095-2099. doi: 10.13224/j.cnki.jasp.2017.09.007
Abstract PDF(867KB) icon1009 icon561
Abstract:
The feature of isotherm in temperature indicating paints (TIP) images was analyzed, four kinds of edge extraction algorithms were experimented and compared, extracting isotherms with Canny edge extraction was suggested and the Kmeans clustering algorithm was used before the edge extraction. The Kmeans clustering and Canny edge extraction were improved. Two methods of choosing the Kmeans initial centers were proposed, which were more suitable for TIP image segmentation. The Canny algorithm to detect isotherms with higher quality was improved. The algorithm could extract clear and continuous isotherms fast. Experimental results show that the algorithm proposed runs well, and satisfies the engineering application needs. Now it has been well applied in TIP automatic temperature interpretation software development.
Combustion characteristics of liquid fuel diffusion flame at capillary oulet
2017, 32(9): 2100-2109. doi: 10.13224/j.cnki.jasp.2017.09.008
Abstract PDF(1216KB) icon1095 icon491
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In order to study the characteristics of micro scale diffusion flame, liquid fuels were chosen for combustion experiment, and the theoretical models were used to estimate the height of the laminar flame. The following results were obtained. The flame size increased with the increase of the volume flow; in the horizontal direction, when the fuel volume flow was more than 50μL/min, a droplet injection occurred because of the incomplete fuel evaporation, and the flame size changed a little; when the capillary was placed vertically, because of the greater influence of buoyancy, the flame height was elongated. Flame oscillation period decreased with the increase of volume flow, and the bigger flame size meant the stronger flame oscillation. Flame oscillation period in vertical direction was smaller than in horizontal direction. With the increase of carbon content, the flame size became larger, and the oscillation was stronger. Kerosene with more carbon content injected fuel around the nozzle, resulting in unstable flame. The flame height was proportional to the Reynolds number of the fuel vapor at nozzle in the vertical direction, Roper model predicted the experimental result best, helping to calculate the laminar diffusion flame height of liquid hydrocarbon fuels in the vertical direction.
Impingement cooling experiment of structured surface with micro-W-shaped ribs
2017, 32(9): 2110-2117. doi: 10.13224/j.cnki.jasp.2017.09.009
Abstract PDF(957KB) icon1067 icon515
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The micro-W-shaped ribs roughened plate in a multiple-jet impingement cooling system was studied by combining the integrated surface with impingement cooling technology. Steady-state experiments and transient thermal liquid crystal testing technology were used to explore the heat transfer characteristics of multiple-jet impingement onto a flat plate and a roughened plate with micro-W-shaped ribs. The impingement spacing ratios were 1.5, 3 and 5. The Reynolds number based on hydraulic diameter ranged from 15000 to 40000. It was concluded from the results that the averaged Nusselt number and pressure loss increased with the Reynolds number, and decreased with the impingement spacing ratio. Compared with the impingement onto the flat plate, the micro-W-shaped ribs roughened plate can increase the averaged Nusselt number by 5.1%-7.3%, when the impingement spacing ratio was 1.5. However, the increase in pressure loss was negligible. When impingement spacing ratio was larger than 3, the enhancement of heat transfer caused by micro-W-shaped ribs was not distinct.
Effects of deflector angle on initiating detonation by shock wave focusing
2017, 32(9): 2118-2124. doi: 10.13224/j.cnki.jasp.2017.09.010
Abstract PDF(1012KB) icon1023 icon471
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In order to investigate the effect of annular jet inlet deflector angle on initiating detonation by shock wave focusing in a twostage pulse detonation engine, initiating detonation with different deflector angles were simulated with H2/O2/N2 mixture. Cold experimental was also carried out on the effect of deflector angle on initiating detonation by shock wave focusing. The results indicate that, as deflector angle increases, the jet collision temperature and jet collison pressure is higher, the jet collision time is earlier and initiating detonation is easier, but the shock wave focusing time remains unchanged when the deflector angle is bigger than 11°. And as deflector angle increases, airflow oscillating frequency in the concave cavity increases and dynamic pressure amplitude at the bottom of the cavity decreases.
Experiment of flow characteristics of coverplate 45° preswirl system
2017, 32(9): 2125-2131. doi: 10.13224/j.cnki.jasp.2017.09.011
Abstract PDF(1117KB) icon1074 icon454
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Flow characteristics of preswirl cavity and rotorstator cavity of a coverplate 45° preswirl system structure were studied experimentally. Static pressure distribution on the stator, total pressure distribution on the mid plane (z/S=0326) and variations of the flow resistance coefficient in cavity and prenozzle discharge coefficient were obtained under high rotation speed. The results show that the pressure distribution in cavity is affected by the flow distribution weakly. The turbulent flow parameter is one of the primary control parameters of flow characteristics. The flow structure in cavity is mainly divided into two parts, the free vortex structures of rotorstator cavity, and the recirculation and low pressure zones in preswirl cavity. The flow resistance coefficient of the cavity rise significantly with the increase of the turbulent flow parameter. The discharge coefficient of preswirl nozzle increases with the increasing pressure ratio of preswirl nozzle.
Threedimensional unsteady numerical simulation and analysis of deployment for cascade thrust reverser
2017, 32(9): 2132-2138. doi: 10.13224/j.cnki.jasp.2017.09.012
Abstract PDF(934KB) icon1125 icon501
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A numerical study was carried out for a cascade thrust reverser of a turbofan engine with bypass ratio of 8, in order to investigate the influences of the thrust reverser deployment with different movement controls on the back pressure of the fan and the force of the blocker door. Results showed that the fluctuation of the fan back pressure increased and the aerodynamic force acted on the blocker door reduced with the delay of the initial rotating time of the blocker door when the total opening time for the thrust reverser was constant. Therefore, for the blocker door, there was a compromise design time for blocker rotation which started at the moment of the transcowl moved 1/3 of the length overall. The total moving time of the thrust reverser from the close point to the deployment had little effect on the pressure at the fan exit and the aerodynamic force on the blocker door. When the deployment of the thrust reverser took place at the emergency cancel of taking off, the fluctuation of the back pressure for the fan was about 20%. It exceeded the allowable values of pressure fluctuation. The maximum force on the blocker door at the emergency cancel of taking off reached 4500N, equaled to four times the normal state.
Application research on supersonic nozzle performance optimization
2017, 32(9): 2139-2144. doi: 10.13224/j.cnki.jasp.2017.09.013
Abstract PDF(862KB) icon990 icon461
Abstract:
With restart global algorithm and Gaussian process(GP) model, supersonic nozzle contour optimization was investigated to improve the flow quality in test section. According to the experimental results in 06m continuous transonic wind tunnel, the optimization problem was defined and the CFD results were verified. The crowding distance notation was introduced to form a restart mechanism for a highly efficient global algorithm. The relationship between design parameters and aerodynamic performances was modeled with Gaussian process model, and used in optimization as a surrogate for the real evaluation procedure to reduce the number of CFD evaluation. Result shows that the optimization framework can improve supersonic nozzle performance efficiently, the root mean square deviation of Mach number in model area falls from 0.012 to 0.001, and axial gradient of Mach number falls from 0.049 to 0.
New embedded grid method for aerodynamic analyses of tiltrotor aircraft
2017, 32(9): 2145-2159. doi: 10.13224/j.cnki.jasp.2017.09.014
Abstract PDF(2568KB) icon993 icon463
Abstract:
To overcome the difficulties in generating high quality integrative structured grids around the tiltrotor aircraft, the multiblock grid strategy and embedded grid method were combined to establish a new embedded grid generation method, which was suitable for aerodynamic interaction analyses of tiltrotor aircraft. On the basis of keeping the interpolation accuracy, the whole grid system composed of the multiblock grids was used to reduce the size of the grids. Firstly, the InverseMap method was introduced for auxiliary localization, and the new multidirectional projection method was proposed to ensure the continuity of the hole boundaries among the multiblock grids. Then, the independent embedded grid strategy was used in completing the combination of the airframe and background grids, and the assistant coordinates were adopted in the identification of the background boundary grids. Compressible RANS (Reynolds averaged NavierStokes) equations with SA(SpalartAllmaras) turbulence model were employed in the bodyfitted region, and Euler equations were chosen to simulate the background region. In the present method, the SPMD (single program, multiple data) model parallel acceleration technology was adopted to improve the computational efficiency. On this basis, Robin airframe was taken as the numerical example to verify the validity of the present CFD method. Then the interaction flowfields of tiltrotor aircraft in different modes were investigated emphatically, and several simulated results (special fountain effect phenomenon in hover, special flowfield in conversion mode, and variations of the aerodynamic characteristics of the tiltrotor aircraft in cruise) were obtained. The proposed embedded grid method and the numerical method were demonstrated to be effective in investigating the aerodynamic configuration of the tiltrotor aircraft, laying a good foundation for analyzing aerodynamic characteristics of the tiltrotor aircraft, with the speedup greater than 50.
Blade vortex interaction acoustic prediction method for rotorbased on aerodynamic/elastic coupling
2017, 32(9): 2160-2169. doi: 10.13224/j.cnki.jasp.2017.09.015
Abstract PDF(1331KB) icon1139 icon480
Abstract:
An engineering method suitable for blade vortex interaction(BVI) airload and acoustic analysis was established based on aerodynamic/elastic coupling. The aerodynamic model includes modified Beddoes wake method and CFD method. Acoustic prediction was based on FfowcsWilliams Hawkings(FWH) equation derived by acoustic analogy, and the elastic blade model was based on finite element method. By applying the established models, the airload and acoustic characteristics of rigid operational load survey(OLS) rotor were calculated under BVI flight state firstly, and the validity of the two aerodynamic models was compared, then the influences of elasticity and time step on HART Ⅱ rotor BVI airload and acoustic were analyzed. The results indicate that the time step adopted in BVI calculation should be no more than 2 degree. Peak acoustic pressure of OLS rotor predicted by CFD is only 60% of experimental data because of inherent numerical dissipation, while the modified Beddoes wake method can address this problem with high computation efficiency. Taking blade elasticity into consideration is beneficial for BVI acoustic prediction accuracy.
Numerical simulation of static and dynamic aerodynamics for flying wing with intake and exhaust effect
2017, 32(9): 2180-2186. doi: 10.13224/j.cnki.jasp.2017.09.017
Abstract PDF(934KB) icon978 icon482
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Based on the computational fluid dynamics (CFD) technique, a twodimensional model was adopted to carry out the simulation. A method to identify combined dynamic derivative was developed and testified with small amplitude oscillation, then three computational models: the model with intake and exhaust effect, the model with ventilating effect and traditional fairing model, were built, furthermore the stable and dynamic aerodynamics of the models was numerically simulated, and the dynamic derivatives were also calculated. Results and their analysis indicate that the method to obtain dynamic derivative is reliable, and compared with faring model, the stable stall angles of attack (AOAs) of the other two models are bigger with increasing lift, drag and pitching moment coefficients, however, the slopes of pitching moment coefficient are almost the same, showing there is no clear difference of static stabilities among the models. Moreover, the absolute value of dynamic derivative of intake and exhaust models is the largest for all the models at the same AOA, showing this model has the largest dynamic damping, the model with ventilating effect takes the second place and the fairing model has the minimum value.
Analysis of thermodynamic cycle for separated flow turbofan engine
2017, 32(9): 2187-2192. doi: 10.13224/j.cnki.jasp.2017.09.018
Abstract PDF(714KB) icon1155 icon522
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The efficiency of separated flow turbofan engine was analyzed based on the definition of gas generator. It proved the existence criterion of the optimum fan pressure ratio and the equivalence of extreme value of the specific thrust, the total efficiency and the specific fuel consumption by theoretical deduction on the basis of the efficiency definitions. This criterion could be used to determine the optimum fan pressure ratio for separated flow turbofan engine in practical design progress. The parametric study results of two different highbypassratio separated flow turbofan engines demonstrated that when the ratio of bypass and primary exhaust velocity equaled to the product of fan and low pressure turbine efficiencies, the overall efficiency and specific thrust reached their maximums and specific fuel consumption reached its minimum, proving the validity of the criterion.
Whole aeroengine vibration coupling dynamics model including modeling of complex ball and roller bearings
2017, 32(9): 2193-2204. doi: 10.13224/j.cnki.jasp.2017.09.019
Abstract PDF(989KB) icon1445 icon524
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The ball and roller bearings were modeled in detail in whole aeroengine vibration model. The 5 DOF (degrees of freedom) model of ball bearing was established, and the bearing forces and moments were deduced under complex deformations of 5DOF. The cylindrical roller bearing was modeled by means of the “section method”, and the bearing force and moments were deduced considering the radial deformation, degree of convexity of cylindrical roller, bearing clearance, and angular deformation due to the bearing inclination. The complex bearing models were combined with the rotor and casing finite element beam model with 6 DOF, the whole aeroengine vibration model including modeling of complex ball and roller bearings was established, and the dynamic responses were solved by the numerical integral method. The aeroengine rig with casings was used to verify the correctness and effectiveness of the model. Compared with the experiment results and showed that, the errors of the first 3 orders natural frequencies were less than 5%, and the mode shapes were fully similar.
Fault sensitivity analysis and fusion technology for vibration features of aero-engine rolling bearings
2017, 32(9): 2205-2218. doi: 10.13224/j.cnki.jasp.2017.09.020
Abstract PDF(1436KB) icon1145 icon580
Abstract:
A method of multifeatures fusion based on normalized Euclidean distance was proposed to meet the requirement of monitoring aeroengine rolling bearing real time condition. Firstly, the bearing fault simulation experiments were carried out while the fault sensitivity of the features before and after fusion was analysed by introducing a quantitative evaluation index of fault sensitivity. Then, the proposed method was compared with the principal component analysis, support vector data description and support vector distribution estimation. Finally, the bearing fatigue accelerated experiment was carried out, and the proposed fusion method was applied to the aeroengine rolling bearing condition monitoring. Experimental results show that compared with principal component analysis, support vector data description and support vector distribution estimation, the fault sensitivity of fusion value based on normalized Euclidean distance is higher. For different types and different stages of the bearing fault, the fusion value obtained by proposed method is more sensitive, which is more suitable to be an index of the bearing condition monitoring, compared with the effective value.
A test method of rotor space bending axis and its test verification
2017, 32(9): 2219-2229. doi: 10.13224/j.cnki.jasp.2017.09.021
Abstract PDF(1261KB) icon792 icon505
Abstract:
A test method of rotor space bending axis was put forward. Firstly, for a practical bended rotor, the bending of each section centroid relative to the rotation center can be obtained by using the eddy current displacement sensors, and the bending degree of different sections of the rotor can be obtained in the same absolute coordinate system. Secondly, the cubic spline function was applied to fit the space geometry center line of rotor, and the threedimensional solid models of the bended rotor were shown by using the OPENGL graphics function, which was called by the Visual C++. Finally, the traditional means of measurement based on the dial indicator were employed to verify the proposed method. The results indicated that, the shaft orbit of each section except for section 1 and section 6 measured by the proposed method were consistent with the shaft orbit of the dial indicator, and circle fitting results were also basically coincident. Whats more, the error range of the circle fitting of section 1 and section 6 were in reasonable agreement. Thus the method is available to investigate the migration.
Friction fault detection methods based on impact signal for plain bearing
2017, 32(9): 2230-2237. doi: 10.13224/j.cnki.jasp.2017.09.022
Abstract PDF(750KB) icon1039 icon437
Abstract:
Aiming at the problem of plain bearing acoustic emission (AE) signal interference seriously, fault signal separation difficulty, friction fault monitoring difficulty, based on the pulse characteristic of impact signal, a method based on shock signals to monitor plain bearing faults was proposed, which established the relation between impulse signal and bearing friction fault. Firstly, the Kmeans singlular value decomposition (KSVD) dictionary was used to capture impact characteristics, and the time of impact pulse generation was determined. In order to sharpen and enhance impact signal, the impact envelope signal was demodulated by the Hilbert envelope. Secondly, the bell pulse parameter was introduced to fit the single impact envelope signal, and the simplified formula of the strength of the impact envelope signal was further deduced, which was applied to the contact friction fault identification of the plain bearing. Finally, the friction fault of plain bearing was simulated by cutting off oil supply channels. Comparing with the traditional characteristics of AE, the proposed algorithm were easier to identify early friction fault and higher computational efficiency and can completly describe bearing friction process. So, the proposed algorithm provides a new way for the plain bearing contact friction fault diagnosis.
Analysis on effect of contact pad gripping rigidity on fretting fatigue life
2017, 32(9): 2238-2242. doi: 10.13224/j.cnki.jasp.2017.09.023
Abstract PDF(679KB) icon912 icon462
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An apparatus with different contact pad gripping rigidity was designed on the basis of single clamp fretting fatigue apparatus. The mechanical models of two apparatuses were developed. By the investigation of the experimental results and numerical analysis, the effect of contact pad gripping rigidity on fretting fatigue damage was discussed. Results indicate that,with the decrease of the contact pad gripping rigidity, the maximum SWT(SmithWatsonTopper) fatigue parameter value remains almost the same and tends to have a symmetrical distribution over contact interface. As a result, the relative slip amplitude and fretting wear decrease correspondingly; the smaller contact pad gripping rigidity of the apparatus means the longer fretting fatigue life.
Loss characteristic of stator under different rotational speeds in transonic stage environment
2017, 32(9): 2243-2252. doi: 10.13224/j.cnki.jasp.2017.09.024
Abstract PDF(1535KB) icon877 icon494
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To investigate the aerodynamic and loss characteristics of stator in transonic stage environment at different rotational speeds, the characteristics of a transonic single stage compressor at 09 times of design rotational speed was obtained by a method of experimental investigation. Detailed numerical results in the stator passage were obtained in a range from 07 to 11 times of design rotational speed with validated numerical methods. The impact mechanism of rotational speed on the stator flow field structure was explored. The association between flow field structure and loss distribution were analyzed. Two kinds of loss criteria were compared, and their guidance to the blade optimized design was given. The results show that, as the rotational speed grows, the flow field structure in the top region of stator getting worse, which changes little in the middle and hub regions. Vortices and pressure gradient perform as the driving forces in the transportation of lowenergy fluid in the flow passage, resulting in the lowenergy fluid gathering, thereby making up a highenergyloss area.
Uncertainty analysis of machining error influence of compressor blade
2017, 32(9): 2253-2259. doi: 10.13224/j.cnki.jasp.2017.09.025
Abstract PDF(785KB) icon1093 icon541
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A numerical method was innovatively presented to achieve uncertainty quantification of airfoil considering the randomness of distribution and magnitude of manufacturing error. Airfoil parameterization achieved by NURBS(nonuniform rational Bspline) method and random sample was generated by Monte Carlo method based on error detection and statistics. And then the Kriging surrogate model was trained to get the influence of machining error on compressor performance. Result shows the influence of profile error is related to the working condition and the loss may increase by 0853% at most. Moreover, the aerodynamic performance is more sensitive to suction surface than to pressure surface. The conclusion can provide more reasonable machining technology requirement and criteria of blade evaluation.
Application of blade tip clearance measurement technology on centrifugal compressor test rigA
2017, 32(9): 2260-2264. doi: 10.13224/j.cnki.jasp.2017.09.026
Abstract PDF(626KB) icon1173 icon445
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Each part consisted of the capacitive blade tip clearance measurement system was introduced. The install method and check method of blade tip clearance measurement on centrifugal compressor test rig were mentioned. While the blade tip clearance on centrifugal compressor test rig was monitored in real time, the blade tip clearance decreased with the increase of speed on inlet, middle and outlet sections. The test safety and test rig integrity were ensured. Relationship between blade tip clearance and speed is able to help to further reduce cold blade tip clearance and gain the optional flow path of centrifugal impeller tip and impeller cover. The application of blade tip clearance measurement technology on centrifugal compressor test rig can help ensure the optimal clearance and also provides important data support.
Unsteady analysis of effect on hydraulic turbine under variable gas content
2017, 32(9): 2265-2272. doi: 10.13224/j.cnki.jasp.2017.09.027
Abstract PDF(1073KB) icon771 icon395
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In order to study the effect of gas content on the internal pressure in hydraulic turbine, CFD technology was used to simulate the flow field in a pump with the specific speed of 845 as turbine, the distribution of gas and the effect of gas content on pressure fluctuation in hydraulic turbine were clarified. Results showed that from volume inlet to impeller outlet, the gas content increased gradually, when the gas content was equal to 02, the gas distribution was not uniform, and in volume outlet and impeller inlet the wake effect was obvious. The gas gathered in impeller outlet, the higher gas rate indicated the more obvious gathering phenomenon. The influence of gas content on the distribution of relative pressure was obvious, the relative pressure of each point in hydraulic turbine decreased with the increase in gas rate. The gas content had little effect on the pressure fluctuation amplitude of the monitored point at the main frequency when the inlet gas content was less than 005, but when the inlet gas content was greater than 005, the effect was obvious. The bigger gas content meant the smaller pressure fluctuation frequency amplitude. In different gas content the main frequencies of pressure fluctuation in turbine volute and impeller were equal to the rotation frequency of the impeller blades.
Numerical simulation and experiment of laminar separation bubble transition and corner separation of compressor stator cascade
2017, 32(9): 2273-2282. doi: 10.13224/j.cnki.jasp.2017.09.028
Abstract PDF(1434KB) icon1287 icon428
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Threedimensional numerical simulation of the controlled diffusion airfoil(CDA) linear cascade in whole range of incidences was implemented by the γ-Reθ transition turbulence model. The numerical results were in good agreement with the experiments. Based on these, the effect of the turbulence intensity and Reynolds number on the laminar separation, transition and corner separation on the blade was studied. Result showed that, the laminar separation bubble can be found when the turbulence intensity was lower than 5%. If the turbulence intensity increased greater than 5%, the laminar separation could be removed totally. However, the transition from laminar to turbulence retained. With the increase of turbulence intensity and Reynolds number, the transition point moved forward. Otherwise, the corner separation on the suction side of cascade reduced a little when the turbulence intensity went up. The corner separation was independent of the Reynolds number.
Identification method of compressor stall inception based on modal wave theory
2017, 32(9): 2283-2290. doi: 10.13224/j.cnki.jasp.2017.09.029
Abstract PDF(949KB) icon1036 icon417
Abstract:
Targeting the shortages of the compressor aerodynamic stall warning that the existing algorithm cannot identify progressivetype stall and spiketype stall inception effectively and multi sensor channels are required for obtaining the amplitude of stall cell, the characteristics of signal during compressor stall development were analyzed. And according to the rotation characteristics of compressor stall signal, the method of circumferential multipath stall inception signal reconstruction was proposed based on singlechannel sensor signal by parallel moving algorithm. The value of signal reconstruction step was discussed. Furthermore, based on the modal wave theory, the stall signal amplitudes of each mode disturbance were obtained by the application of the spatial Fourier transformation on the reconstructed signal. Progressivetype and spiketype stall precursor were identified according to the amplitude variation of low order modes, thus predicting the occurrence of stall. Taking certain compressor as an example for simulation. Results show that as long as the signal reconstruction steps is less than half the time scale of the spike wave, the reconstructed multipath signal can reproduce the development process of circumferential position compressor stall well, the smellier step means more conducive to identifying stall inception. Changes in the amplitude of firstorder modal acquired from modal decomposition can effectively reflect the stall development. The stall inception can be accurately identified in the prestall development by setting reasonable modal amplitude threshold. Therefore, both progressivetype and spiketype stall enable warning based on a single sensor signal.
Decomposition methodology for gear tooth contact analysis
2017, 32(9): 2299-2304. doi: 10.13224/j.cnki.jasp.2017.09.031
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Abstract:
A methodology for gear tooth contact analysis was proposed. The conventional approach of tooth contact analysis was used to solve a system of five nonlinear equations for each contact point, but the numerical stability of the algorithm was weak. In addition, the mathematical models for tooth surface contact and edge contact were not the same; therefore, different systems of five nonlinear equations were required for different mathematical models, causing complex computing process and too many parameters involved therein. This decomposition methodology defined and utilized a concept called instantaneous conjugate contact curve. By constructing instantaneous conjugate contact curve, the transmission errors can be separated effectively and then the contact point and instantaneous contact curve can be located effortlessly. The number of nonlinear equations for searching contact point was reduced from 5 to 2.This mathematic model was also applied to edge contact analysis. So the decomposition methodology was simple, effective and adaptable. At the end, the decomposition methodology was applied to a pair of spiral bevel gears to demonstrate its effectiveness compared with the conventional method. For tooth surfaces contact, contact patterns were identically calculated by the two methods, and the relative difference for the magnitude of transmission errors was about 03″. In the case of edges contact, there were relatively few differences for patterns.

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