2019 Vol. 34, No. 9

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Display Method:
Analysis of rotating instability characteristics in compressor with different tipclearances by POD and DMD methods
2019, 34(9) doi: 10.13224/j.cnki.jasp.2019.09.019
Abstract PDF(4510KB) icon1519 icon1379
Abstract:
Rotating instability(RI) characteristics of a single-stage low-speed compressor were analyzed. Based on the preliminary results of RI characteristics, flow cause and influence with different tip clearances and full passage numerical simulation, two flow field decomposition methods were applied to obtain the flow components, energy proportion and stability of RI modes. The computation results reveal that the first several modes account for a large proportion of energy, make major contributions to the flow field and have stronger stability. With the decrease of tip clearance, the energy and stability of RI modes decrease gradually, while blade rotating and its harmonics become the main components in macro flow field.
Numerical simulation on seal-rotor system with airflow induced vibration
2019, 34(9): 1857-1865. doi: 10.13224/j.cnki.jasp.2019.09.001
Abstract PDF(4628KB) icon1233 icon1215
Abstract:
For the diagnosis of airflow induced vibration fault in the seal, the dynamic model of seal-rotor system was established based on finite element method and Muzynska seal fluid force model. The airflow induced vibration instability law and dynamic characteristics from run-up and run-down processes were studied by numerical simulation method. And the different eccentricities' effects during the case of variable speed and steady speed were also analyzed. The result showed that natural frequency of rotor system was increased by the airflow excitation force, and the amplitude was reduced in resonance zone. The frequency locking phenomenon and combination frequency characteristics appeared by airflow vibration with the speed increase. The phenomenon of hysteresis under run-down conditions was not obvious because of the strong gas flow. Only frequency locking occurred when the eccentricity was small, the combined frequency was observed and enriched with eccentricity increase. The airflow vibration frequency was enhanced and changed suddenly by increasing eccentricity in the process of constant rotating speed.
Failure mechanism of TiN/Ti strength and tough coating under high-speed sand-dust erosion
2019, 34(9): 1866-1872. doi: 10.13224/j.cnki.jasp.2019.09.002
Abstract PDF(2531KB) icon1063 icon1019
Abstract:
Through high-speed continuous erosion test system, high-speed sand-dust erosion tests of stainless steel specimens with or without TiN/Ti strength and tough coating were carried out at different impact angles and sand supplies, and the mass erosion rates of specimens were obtained. The surface and cross-sectional damage morphology of the coating were observed by scanning electron microscopy (SEM), and the failure mechanism of TiN/Ti coatings under different impact conditions was analyzed. The results show that the mass erosion rate of TiN/Ti coatings increases with the increase of impact angle and sand supply. At low impact angle, the cutting action of sand particles is the main reason for the spalling of coatings; at high impact angle, the crack initiation and propagation caused by sand-dust impact lead to massive fragmentation and spalling of coatings. TiN/Ti coating can significantly improve the erosion resistance of stainless steel, especially at low impact angle.At low impact angle, the erosion resistance of stainless steel with coating can be increased by about 5 times, and at high impact angle it can be increased by about 2 times.
Rapid determination method for degradation curve subject to power function
2019, 34(9): 1873-1878. doi: 10.13224/j.cnki.jasp.2019.09.003
Abstract PDF(731KB) icon1157 icon1080
Abstract:
Many degradation curves illustrate a two-stage property where the deterioration is fast in the first stage and then becomes slow in the second stage. For this sort of degradation curves subject to power function, a rapid determination method was proposed, which can fit and extrapolate the complete degradation curve with the test data from fast degradation stage, or adding a small amount of test data from slow degradation stage. Abundant analyses of real applications and Monte Carlo simulations showed that, under this circumstance the obtained curve can also approach the true value, or be more conservative, which is safe and useable in engineering. Rapid determination methods for three-parameter power function degradation curve (rubber aging curve, S -N curve, ε -N curve, light intensity degrading curve of LED, etc) and four-parameter power function degradation curve (stress relaxation curve, creep rupture curve, and so forth) were discussed, corresponding median degradation curve and confidence limit curve with high confidence level and high reliability were further derived. According to the comparative analyses of two real applications, it can be concluded that the proposed method can save about two-third of test time and cost.
Rubbing analysis and structural design for fan blade and case of aero-engine
2019, 34(9): 1879-1887. doi: 10.13224/j.cnki.jasp.2019.09.004
Abstract PDF(4891KB) icon1585 icon1327
Abstract:
Under abnormal loads, there is often a lack of data to describe the rubbing deformation and damage characteristics between the blade tip and the case of the wide-chord fan blade of aero-engines. The traditional theoretical calculation methods have large errors. To solve this problem, an explicit dynamic analytical model for the blade tip rubbing of a wide-chord fan was established. The calculation accuracy of the analytical model was verified by utilizing the test data of wide-chord fan blades and case. Based on the analytical model, sensitivity analysis of simulation parameters were carried out. The rules of blade deformation and case damage after the rubbing of the blade and case were obtained. The results indicate that the blade tip elongation is sensitive to rotor speed,and the increase rate of blade tip elongation is much bigger than the rotor speed.So the blade tip elongation at limited fan blade speed was considered in design. Suitable twist angle is an important factor of safe and dynamic performance demand.In the case inclusive area design, it is necessary to enlarge the safe margin to eliminate the influence of abnormal load. Choosing wear-resistant material with reasonable parameter is helpful to reduce the impact damage from fan blade. The proposed method can improve the accuracy of tip clearance control, and reduce the risk of rubbing and the damage of blade and case caused by rubbing.
Method to determine modified influence exponent of stress gradient considering stress ratio
2019, 34(9): 1888-1894. doi: 10.13224/j.cnki.jasp.2019.09.005
Abstract PDF(1861KB) icon1124 icon1073
Abstract:
A new equation for fatigue life prediction considering the stress ratio was established. The expression introduced a new parameter which reflected the effect of stress ratio on the stress gradient exponent based on the previous fatigue life model with stress gradient. Life prediction and precise checking were carried out using exiting test data of typical alloy. The results showed that the local stress ratio had a considerable influence on the stress gradient exponent. The calculation results of the modified model were more close to the experiment results than the previous model. Predictions of notched specimens for TC4(200 ℃) and GH4169(500, 650 ℃) showed a scatter band within 2.0. Even better, some of the results showed a scatter band within 1.5.
Vibration measurement on compressor rotor blades of aero-engine based on tip-timing
2019, 34(9): 1895-1904. doi: 10.13224/j.cnki.jasp.2019.09.006
Abstract PDF(3248KB) icon1875 icon1263
Abstract:
The theory and data processing method of the non-contact vibration testing system based on blade tip timing were introduced. The system was successfully applied in the blade vibration measurement on the first stage of rotor blades of a turbo-fan engine high pressure compressor, and the blade tip amplitudes and frequencies of the whole blades at resonance were obtained. The displacement-stress conversion ratio from blade tip magnitude to the critical points stress was calculated by the finite element analysis. The vibration character of the whole blades was obtained through the non-contact vibration testing system of the turbo-fan engine. As the thickness of prototypical blades was enlarged by the processing technology, the blades were resonated in the working speed caused by the engine order of 3, which led to the failure of the blades. The vibration character of remodelled blades is very well after promotion of processing technology.
Dynamic characteristics coupled thermal and dynamic loads for labyrinth seal in ultra-supercritical steam turbine
2019, 34(9): 1905-1913. doi: 10.13224/j.cnki.jasp.2019.09.007
Abstract PDF(4047KB) icon1001 icon932
Abstract:
The operating safety of ultra-supercritical steam turbine is seriously affected by steam flow excited vibration in labyrinth seal. The DEFINE_CG_MOTION and DEFINE_PROFILE control macro were used to establish rotor whirl equation. The deformation of seal teeth under thermal and dynamic loads was calculated by Workbench fluid-solid coupling method. So the operating dynamic characteristics in seal were obtained by fast Fourier transform, and the rotor stability was analyzed. The results show that the steam flow can cause the deformation of seal teeth. The temperature made seal teeth length increase by 1%-1.5%, and the pressure and centrifugal effect had little influence on it. Under the action of thermal and dynamic loads, direct stiffness decreased, direct damping increased first and then decreased, cross-coupling stiffness decreased first and then increased, the maximum variation of dynamic coefficient was twice as before. Rotor stability margin decreased sharply in 35-55 Hz, so the rotor was more sensitive to the steam flow excited vibration. Due to the thermal and dynamic loads, the pressure fluctuations concentrated in low frequency range. The circumferential pressure fluctuations in seal could be increased by 18.5 kPa. The dramatic increase of pressure fluctuations in high pressure zone is the main reason for intense steam flow excited vibration.
Rub-impact characteristics of bearing co-cavity turboshaft engine with flexible static parts
2019, 34(9): 1914-1926. doi: 10.13224/j.cnki.jasp.2019.09.008
Abstract PDF(3992KB) icon980 icon1047
Abstract:
In order to study the dynamic characteristics of the rotor system and the vibration response characteristics of the casing for the rotor and stator rub of bearing co-cavity structure, a simplified rotor-casing impact dynamics model was established and solved by the Runge-Kutta method. Simulation results showed that when the rotor and stator were rubbed, the frequency doubling and combined frequency of the rotor appeared in the casing response spectrum. Meanwhile, the amplitude of frequency doubling component increased with the degree of rubbing. The bench experiment of this engine was carried out to verify the validity of the model and conclusion. And it was further verified that there was motion coupling between the two rotors in the bearing co-cavity engine with flexible stator parts by utilizing the rubbing data of a second-generation turboshaft engine experiment without this structure. This work may provide some theoretical basis of the vibration monitoring of the turboshaft engine, and it is also beneficial to the fault diagnosis in the future.
Dynamic modeling and updating for contact interface of rod fastening rotor based on thin-layer element
2019, 34(9): 1927-1935. doi: 10.13224/j.cnki.jasp.2019.09.009
Abstract PDF(2295KB) icon1174 icon1039
Abstract:
In order to study the dynamic characteristics of a rod fastening rotor system with complex contact interfaces, a method for dynamic modeling and updating of a rod fastening rotor system with contact interfaces is developed based on thin layer elements. The contact relationship of the rod fastening rotor parts was simulated by the thin layer element of linear constitutive relationship. Based on modal test data, the connection stiffness of contact interfaces of the rotor parts of pre-tighten status was identified by the hierarchical model updating method, and then the dynamic prediction model of the rod fastening rotor system was established via the identified connection parameters of the thin layer elements. The dynamic predictions of the rod fastening rotor were compared with the experimental data. Results show that the mechanical properties of the contact interfaces under the pre-tightening state of the tie rod can be simulated by using the thin-layer elements with linear constitutive relation, and the normal and tangential stiffness of the contact interfaces can be simulated by modifying elastic modulus of the thin-layer elements. The maximum frequency error and the average frequency relative error between the updated rotor model and the test data were 0.6% and 0.25%, respectively, and the updated model can predict the vibration responses of its actual structure.
Dynamic characteristics of rotor system subjected to pulse detonation aerodynamic loads
2019, 34(9): 1936-1943. doi: 10.13224/j.cnki.jasp.2019.09.010
Abstract PDF(3829KB) icon1290 icon1011
Abstract:
In view of the periodic and unsteady aerodynamic loads of pulse detonation turbine engine(PDTE), finite element method was used to establish a dynamic characteristics calculation model for rotor system of PDTE. On the basis of verifying the accuracy of the calculation model, the effects of periodic and unsteady axial force and torque on the dynamics characteristics of rotor system were studied. The results show that compared with traditional gas turbine engine, the rotor system of PDTE has bending vibration, axial vibration and torsional vibration at the same time. Aerodynamic loads of pulse detonation combustor change bending stiffness of rotor system, but it has little effect on bending vibration in case of reasonable design. Periodic and unsteady axial force causes axial vibration of rotor system, and the axial vibration characteristics are mainly affected by the responses at zero frequency and the first order axial resonance frequency. When PDTE is in service state, the axial reaction force of ball bearing changes direction continuously, which should be considered in the design of ball bearings. Periodic and unsteady torque causes torsional vibration of rotor system, and the first order torsional resonance frequency component is dominant in torsional vibration response.
Nonlinear equivalent modeling method for clamp based on test data
2019, 34(9): 1944-1952. doi: 10.13224/j.cnki.jasp.2019.09.011
Abstract PDF(3836KB) icon1101 icon986
Abstract:
In order to calculate the vibration response of clamp piping system quickly and accurately, a nonlinear equivalent modeling method for clamp was presented based on test data. The finite element model of simple straight pipe system was modified by the test data of modal test to identify the liner stiffness and damping parameters of clamp. The constant force test was carried out for the simple straight pipe system under different excitation levels. The constant force frequency response function was transformed into constant displacement and constant velocity frequency response function by spline interpolation polynomial method, and the nonlinear equivalent stiffness and damping of clamp were further identified. Finally, the equivalent dynamic model of clamp considering nonlinearity was established. The results showed the maximum error between the predicted frequency response functions and the experimental frequency response functions was only -6.9%. It proves that the equivalent dynamic model of clamp can effectively reflect the actual stiffness and damping characteristics of clamp, and has important guiding significance in vibration response analysis of clamp piping system.
Fast response prediction method for bladed disks with contact interfaces
2019, 34(9): 1953-1961. doi: 10.13224/j.cnki.jasp.2019.09.012
Abstract PDF(1444KB) icon896 icon595
Abstract:
A fast prediction method for forced vibration response of bladed disks with contact interfaces was established. This method was exemplified by applying it into a finite element (FE) model of a bladed disk with dovetail joints. The linear part of the finite element model was reduced by means of the modal synthesis method. A reduced model with the total amount of the generalized degree-of-freedoms less than 1/25 that of the full model was set up. Forced response was predicted by employing the harmonic balance method. In this process, the Jacobian acceleration technique proposed in previous research effort was reformulated and improved. It evolved into a improved and fast Jacobian-evaluation method suitable for large-scale non-linear bladed disk models with contact interfaces. Result showed that the response prediction based on the harmonic balance method was more than 400 times faster. Prevailing advantages in computational efficiency and accuracy were fully demonstrated by the simulation results. This can raise the potentiality of acting as a powerful tool for the design and optimization for various dry friction dampers.
Viscosity characteristics of droplet deformation and breakup under shock wave
2019, 34(9): 1962-1970. doi: 10.13224/j.cnki.jasp.2019.09.013
Abstract PDF(2560KB) icon889 icon586
Abstract:
In order to obtain the morphological feature images of different viscous droplets deformed and broken in high-speed airflow, the influence of viscosity in the process of deformation and fracture was quantitatively analyzed, and the high-speed camera direct shooting method was used to study the droplet deformation and crushing process in the horizontal shock tube. The characteristic parameters such as windward surface displacement, lateral deformation width, and crushing time were measured. Results showed that when the viscosity of the droplet was low, the shape of the trail formed by the tail of the droplet was an elongated pointed cone. When the viscosity of the droplet was high, the shape of the trail was corrugated, and the wake of the droplet was more complicated and disordered when the viscosity increased; the windward surface of the droplet was deformed and unstable under the action of the wave, and the "spike" structure was developed; the viscosity of the liquid hindered the deformation and fracture process; the lower viscosity of the drop led to the faster rate of development of Rayleigh-Taylor(RT) instability, and the number of "spikes" increased first and then decreased with the increase of viscosity.
Theoretical and experimental studies of vacuum cooling of liquid nitrogen
2019, 34(9): 1971-1976. doi: 10.13224/j.cnki.jasp.2019.09.014
Abstract PDF(2017KB) icon976 icon603
Abstract:
Considering the total mass change of liquid nitrogen and heat capacity of tank, the mathematical model of vacuum cooling of liquid nitrogen based on the physico-chemical depression, heat transfer coefficient and mass transfer coefficient approach was built. The theoretical results were in satisfactory agreement with the experimental data of making subcooled liquid nitrogen, which indicated the mathematical model could well predict the phase change of liquid nitrogen. The physico-chemical depression of 1.21 K, heat transfer coefficient of 2 942.37 W/(m2·K) and mass transfer coefficient of 0.004 4 m/s respectively were also obtained.
Effect of channel cross sectional shape on flow distribution of hydrocarbon fuel
2019, 34(9): 1977-1987. doi: 10.13224/j.cnki.jasp.2019.09.015
Abstract PDF(5450KB) icon699 icon496
Abstract:
The effect of cooling channel cross sectional shape on the flow distribution of hydrocarbon fuel in SCRamjet was researched. Parallelogram shape cooling channel was taken as an example to compare with rectangular channel. 3-D modelling of the flow and heat transfer of hydrocarbon fuel in multiple cooling channels under supercritical pressure was done. Under different channel aspect ratios, the parallelogram channel was better both in flow distribution and cooling effect because of the larger heat exchange area. The maximum heated wall temperature fell 226 K at most. Then the angle of the parallelogram channel was also important. Larger angle design led to larger heat exchange area and improved the flow distribution and cooling effect. The maximum heated wall temperature fell 287 K when the channel angle increased from 105° to 150°. The effect of practical headers was also taken into consideration. The parallelogram channel design was validated under the joint influence of U-type headers and non-uniform thermal boundary condition, showing good application value. The results of this work offer possible solution to the cooling channel design of SCRamjet.
Scaling method of turbofan engine nacelle under icing test
2019, 34(9): 1988-2000. doi: 10.13224/j.cnki.jasp.2019.09.016
Abstract PDF(8054KB) icon839 icon580
Abstract:
In order to eliminate the constrains of engine icing test on experimental ability and space, an icing scaling law of turbofan engine nacelle icing test was established based on similar requirements such as the airflow field, water droplet impingement and ice accretion characteristics. And there were three airflow velocity selections based on airflow Reynolds number, airflow Weber number and water droplet Weber number respectively, and these three velocity selections can be used to reflect different influencing parameters on icing similarity. The glaze and rime ice accretion conditions of 1/2 sub-scale turbofan engine nacelle model were obtained by this scaling law. And the ice prediction on turbofan nacelle inlet was carried out with numerical simulation, and the similarities of water droplet impingement, ice accretion and runback water characteristics were analysed. Results show that the scaling law based on airflow Weber number and water droplet Weber number can better ensure the similarity of the droplets impingement on the surface of the scale model and the reference model under the glaze ice and rime ice conditions, and the similarity is not affected by the freezing temperature. The variation and limit of the runback water is similar to the reference model. Under different icing conditions, the surface ice accretion of scale model is similar to the reference, and this scaling law can provide a good basis for the subscale nacelle icing test.
Numerical simulation of stratified scavenging two-stroke gasoline engine
2019, 34(9): 2001-2009. doi: 10.13224/j.cnki.jasp.2019.09.017
Abstract PDF(3302KB) icon822 icon515
Abstract:
A three-dimensional model of stratified scavenging engine was established to study the scavenging characteristics and working mechanism of stratified scavenging engine, then three-dimensional CFD software Fluent was used to simulate and analyze the fluid structure with or without stratified scavenging system at rated speed, and the boundary conditions required for its calculation were obtained by one-dimensional simulation calculation of the engine. Results showed that, the stratified scavenging engine used pure air to form a stratification between the fresh mixture and the exhaust gas during operation, a part of the scavenging loss was taken by the pure air, which reduced 15% of unburned hydrocarbon and improved the fuel economy of the engine; the stratified scavenging engine and the non-stratified scavenging engine had a scavenging efficiency of 75%, without significant effect on the scavenging efficiency. The results of the research can provide reference for the design of stratified scavenging engines.
Experiment on structure of premixed flame in annular combustor using OH-PLIF
2019, 34(9): 2010-2017. doi: 10.13224/j.cnki.jasp.2019.09.018
Abstract PDF(4011KB) icon1011 icon557
Abstract:
In view of the combustion characteristics of a micro gas turbine annular combustor, a planar laser induced fluorescence (PLIF) technique was used to investigate the effects of Reynolds number and equivalent ratio on the structural parameters of a methane/air premixed turbulent flame in the annular combustor. Results showed that the OH radical concentration distribution exhibited a ring structure with flame lift and bifurcation phenomena. The instantaneous and average images of OH-PLIF revealed that the flame had the common characteristics of turbulent flow and laminar premixed structure. The quantitative analysis of the characteristic parameters of flame structure showed that when the Reynolds number increased, the flame premixed conical structure was stretched and the interaction between jets was promoted. The conda effect made the inner flame bend towards the inner wall and the flame angle increase. Proper adjustment of the equivalent ratio of premixed flame is beneficial to the stability of flame structure.
Impact of bow shock on tip leakage flow in counter-rotating compressor
2019, 34(9): 2027-2037. doi: 10.13224/j.cnki.jasp.2019.09.020
Abstract PDF(7050KB) icon756 icon551
Abstract:
In order to reveal the impact of the bow shock of downstream rotor on the tip leakage flow of upstream rotor in a counter-rotating compressor, the unsteady numerical simulation of a counter-rotating compressor was conducted with tip clearance of 0.2, 0.5 and 0.8 mm of the upstream rotor, respectively. Results showed that impacted by the sweep of the downstream rotor bow shock, a weak compression wave was formed on the pressure surface near the tail edge of the upstream rotor, which could be weakened gradually with the increase of the leakage flow of the upstream rotor. On the suction surface near the trailing edge of the upstream rotor, a strong compression wave perpendicular to the tangential direction of the blade profile was formed causing the downstream rotor bow shock, and its position was basically not affected by the sizes of tip clearance. Also, the pressure difference between the suction and the pressure surfaces near the tail edge of the upstream rotor increased by the bow shock, which led to the augment of the tip leakage flow, and then the flow loss. With the increase of tip clearance, the motivator of the main frequency of the pressure fluctuation, which was located among the blade tip half-chord region belonging to the leading edge of the upstream rotor, was changed from the channel shock to the tip leakage flow and the main frequency decreased gradually. While the blade tip half-chord region was located at the trailing edge, the pressure fluctuation was mainly dominated by the downstream rotor bow shock, and its main frequency was consistent with the bow shock sweeping.
Research on one-dimensional/three-dimensional coupled modeling for seal and cavity flow of centrifugal compressor
2019, 34(9): 2038-2047. doi: 10.13224/j.cnki.jasp.2019.09.021
Abstract PDF(3362KB) icon737 icon463
Abstract:
In order to reduce the modeling complexity of the centrifugal compressor while ensuring the numerical prediction accuracy, a source term modeling method for the seal and cavity flow of the centrifugal compressor was studied based on the one-dimensional seal leakage calculation instead of the complete seal-cavity modeling. The results showed that the simplified seal and cavity modeling based on source term method could accurately reproduce the overall performance and key flow details obtained by calculation of full seal and cavity modeling, allowing only to impose the boundary conditions of leakage mass flow, total temperature and friction loss source term on the mainstream channel modeling. Compared with the complete modeling, the absolute deviation of the isentropic efficiency predicted by the source term modeling at full operating conditions was less than 0.65%, and the relative performance deviation of the total pressure ratio and the isentropic efficiency was less than 1%. The method could reduce the number of meshes by more than 50% while meeting the accuracy requirement of matching design for downstream components, and also significantly improve the economy and convergence of the calculation. The calculation accuracy of the leakage flow was the most critical factor affecting the accuracy of the performance prediction for the source term modeling method. The coupling modeling could adopt the recommended seal leakage coefficient value of the one-dimensional calculation.
Analysis of transonic axial compressor tip clearance flow field with POD method
2019, 34(9): 2048-2055. doi: 10.13224/j.cnki.jasp.2019.09.022
Abstract PDF(4888KB) icon762 icon510
Abstract:
The unsteady flow phenomenon of a transonic axial compressor NASA Rotor 36 was investigated. Based on the unsteady simulation results, proper orthogonal decomposition (POD) modes and time coefficients were obtained with POD method, and the flow characteristics of the tip clearance flow field at near stall conditions were further analyzed. Results showed that: at near stall condition, the dominant frequency of tip clearance flow field was the tip leakage vortex frequency, about 0.6 times blade passing frequency; the POD mode with higher energy determined the fluctuation frequency and amplitude of tip leakage vortex, and the POD mode with lower energy determined the fine structure of the flow field; the first 5 POD modes reconstructed the flow field very well, providing a theoretical guidance for the establishment of the low-order model.
Reverse thrust calibration test technology of turbofan nacelle simulator
2019, 34(9): 2056-2062. doi: 10.13224/j.cnki.jasp.2019.09.023
Abstract PDF(1754KB) icon744 icon517
Abstract:
To meet the demand of reverse thrust wind tunnel tests for large aircraft, a kind of reverse thrust calibration test technology of turbofan nacelle simulator was developed in China Aerodynamics Research and Development Center. The reverse thrust calibration test platform was constructed in FL-12 low speed wind tunnel. Thrust of the nacelle was measured by the thrust balance. Air-line bridges were used to reduce the impact of air-line tube on the balance. In order to eliminate effects of induction of inlet and exhaust flow of the nacelle on wind tunnel flow and prevent the potentially dangerous re-ingestion of reverse exhaust flow, the wind tunnel test section was blocked by a plate between the inlet and outlet of the nacelle. A reverse thrust calibration test method and a test result correcting method were developed. In ordered to verify reliability of the reverse thrust calibration test technology, a reverse thrust calibration test of a turbine simulator nacelle and a full model reverse thrust wind tunnel test were conducted in FL-12 and FL-13 low speed wind tunnel respectively. The test results indicated that, with the increase of nozzle pressure ratio, the differences between calculation and calibration of mass flow and velocity of the reverse thrust nacelle decreased gradually; the calibration test accuracy was better than 0.5%, which can meet the accuracy need of reverse thrust wind tunnel test.
Intake system optimization study and design for an aircraft piston engine
2019, 34(9): 2063-2070. doi: 10.13224/j.cnki.jasp.2019.09.024
Abstract PDF(3775KB) icon952 icon489
Abstract:
A one-dimensional thermal dynamic model and three dimensional CFD model about the intake pipe for a specific aero-piston engine were established respectively for analyzing intake uniformity. These models verified the phenomenon about intake uniformity when the engine worked under external characteristic condition and figured out the causality of this phenomenon. An intake system was designed. The intake uniformity phenomenon could be improved by taking this intake system. The calculation results showed that: by adopting the new intake system, the engine's intake air non-uniformity decreased from 20% to 6% when the engine was at 5 000 r/min. By using this intake system, the average air intake quality increased by 19% when the engine was at 5 500 r/min, the maximum air intake quality increased by 34.1% and the minimum by 12.9%.
Numerical research on aerodynamic characteristics of shaftless ducted rotor
2019, 34(9): 2071-2080. doi: 10.13224/j.cnki.jasp.2019.09.025
Abstract PDF(5306KB) icon813 icon572
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The unsteady Euler equations for the aerodynamic characteristics of shaftless and traditional ducted rotors were numerically simulated by using the sliding mesh technique based on unstructured meshes. The difference of aerodynamic characteristics between shaftless ducted rotor and traditional ducted rotor was investigated. The effects of center aperture, ducted diffusion angle and ducted airfoil on the aerodynamic characteristics of ducted shaftless rotor were studied. The divergence angle of the ducted rotor ranged from -6°—10°. The ducted airfoils were NACA66, NACA0018 and NACA4415. It was found that the type of ducted airfoil had a great influence on the tension distribution of the shaftless ducted rotor, and the symmetrical airfoil can weaken the low-pressure vortices above the rotor so that the ducted rotor can produce greater tension; the shaftless ducted rotor had better tension performance than the traditional ducted rotor, and its total tension was 1.185 times of the latter when the rotational speed was 18 000 r/min; reducing the central aperture of the shaftless ducted rotor can improve the total tension value, however, the overall energy consumption also increased; the higher proportion of ducted tension means the larger optimal ducted diffusion angle, and the highest proportion of ducted tension in this state.

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