Research On Flow Resistance Of Combustor Diffusers Based On Boundary Layer Control

Dump diffusers are widely used in aero engine combustors.In order to lower dump diffuser total pressure loss and improve its static pressure recovery,the influences of vortex generators(VGs)on flow separation,static pressure recovery and total pressure loss of the dump diffuser are analyzed.CFD simulation method,Particle Image Velocimetry(PIV)and pressure measurements are used to study such influences.In this paper,a simple dump diffuser model with a dump diffuser is designed for the study of VGs.Then the inlet air flow parameters and flow splits between inner annulus,outer annulus and liner are defined.The divergence angle of inner pre-diffuser wall is designed to be 14° to ensure flow separation in this region.The divergence angle of inner pre-diffuser wall is smaller,which is 6° in this case.Based on such diffuser model,different types of VGs are designed,structural parameters of which include the shape,the skew angle,the length,and distance between the trailing edges.In numerical simulation study,SST k-ω turbulence model is chosen to capture the phenomenon of flow separation.The mesh independency and simulation method are checked.The results show that VGs indeed improve flow separation inside the pre-diffuser,and that the dump diffuser performance is improved.At the same time,VGs in the shape of a triangle show better performance than a rectangle.The VGs skew angle has a great impact on its performance,the optimal value of which is 14°.The performance of VGs is not sensitive to its length or its distance between the trailing edges.However,optimal values of these two parameters are given in this paper,which is 1.5 and 3.0 respectively.Base on numerical simulation,experimental research is carried out on the same model and inlet air flow condition.PIV system is used to capture the flow flied in the pre-diffuser to verify the effectiveness of VGs in flow separation control.Pressure measurements is carried out to calculate the static pressure recovery along the pre-diffuser inner wall as well as the static pressure recovery and total pressure loss of the dump diffuser.The experimental research shows that flow separation does occur in the prediffuser without VGs and flow separation disappears with VGs,the dump diffuser performance improves with the existence of VGs.The total pressure loss measured in experiment is higher than the calculated result,but the changing treads are the same.The influence of different VGs on flow resistance of the dump diffuser in consistent in numerical and experimental research.