Experimental and Numerical Study of Ejection Characteristics of Circular Lobe Ejector with Bend Mixers

For the purpose of infrared stealth, the lobe and bend exhaust nozzle is required for the turbo shaft engine to eject surrounding cooling air and to change the direction of exhaust jets.The test model used was a set of circular twelve-lobe nozzles with bend mixers.The effects of the mixer bend angles β,the mixer to lobe cross sectional area ratio λ and the cross sectional area ratio σ of the secondary inlet to lobe on ejection ratio φ was studied.The experimental results show that for β=40°,the ejection ratio φ of the bend mixer is the same as that of the cylindrical mixer with the same diameter.For β>40°,the ejection ratioφ relative to the cylindrical mixer decreases significantly.With the increase of the mixer cross sectional area ratio λ,at first the ejection ratio φ increases and then decreases.The maximum ejection ratio φ_maxis less than that of the cylindrical mixer,but the optimal cross sectional area ratio λ_maxis about the same as that of the cylindrical mixer.The ejection ratio φ increases approximately linearly with the cross sectional area ratio σ.Because of the symmetrical feature of the lobe mixer,for simplicity,3D incompressible flow field of half of the mixer was numerically simulated.The calculated wall static pressure coefficients agree well with the measured ones.The numerical results show that the main reason for the significant decrease of the ejection ratio φ when the mixer bend angle is larger than 40° is due to the high static pressure along the bend part of the mixer,and the high static pressure chokes the effective flow passage area.