| During the flight from take-off to cruising condition,Reynolds number of aero-engine with highload and low-pressure turbine is greatly reduced.Under the condition of low Reynolds number,the fluid in the second half of the blade suction surface is prone to flow separation induced by reverse pressure gradient.Local vibration wall is a kind of active control method which is applied to low Reynolds number flow in outflow.It uses small amplitude unsteady vibration of local surface to restrain airfoil laminar flow separation.It has the advantages of maintaining airfoil geometric integrity and actively controlling energy consumption Low,inhibition of separation ability and so on.In this study,it was applied to the flow control of high load and low pressure turbine.Taking the high load and low pressure turbine blade PAKB as the research object,the flow control mechanism to reduce the loss of low Reynolds number turbine cascade by local vibration wall was explored.Influence of control parameter change on Control effect.In order to solve the problem of laminar flow separation in high load low pressure turbine PAKB cascade under low Reynolds number 25 K,a small size sine vibration convex hull is placed on the suction side of the blade for active flow control.The maximum amplitude of convex hull is 1mm and the frequency is 200 HZ,according to the normal direction of the wall by unscented sine wave unsteady numerical method by two-dimensional straight-type vibration convex hull position and geometric width of the aerodynamic performance of the cascade,the results show that the optimal vibration convex hull position The loss of work of cascade is significantly lower than that of the non-controlled cascade at the peak point of the velocity of suction side of the non-controlled cascade and close to the peak of velocity.However,the performance of the cascade is not improved by the vibration convex hump located downstream of the separation point.When the vibration convex hull is placed in the best position of the suction surface,the influence of the convex hull geometric width on the cascade loss is negligible.Then the control effect of the lattice vibrating wall in the three-dimensional flow field with a leaf height of 20 mm with a Reynolds number of 25 K was studied.The local vibration wall geometry of the point vibration type is a convex hull formed by the superposition of the sine lines in both X and Z directions.According to the effective vibration width and the optimal axial position obtained previously,a control scheme is designed,Point vibration mode local vibration wall control program analysis,and different spacing,different types of array type vibration wall control program analysis.Afterwards,the LES method was used to simulate the control flow field of the lattice-type vibration convex hull,and the results were in good agreement with the RANS results to further analyze the flow mechanism.Finally,the vibration control method of convex hull is applied to the high-speed flow field of T106 A blade.The calculation shows that the vibration hull control method is suitable for high-speed flow field and T106 A airfoil.The results show that under the control of vibrating wall,the change of cascade loss comes from the balance of turbulent wet area reduction,exfoliation vortex scale and shedding vortex mixing loss in the rear of the blade,The point-vibration local vibration wall upstream of the point of separation of the suction surface can greatly reduce the flow loss of the cascade.The pressure wave generated by the vibrating wall converts the large-scale isolated bubbles at the back of the blade into small-scale shedding vortices that change by a certain period to form the "rolling bearing" effect and then uses the interaction between the vortices to promote the crushing of vortex clusters.So that the large-scale isolated bubble covering the back of the leaf disappears,which greatly reduces the turbulence loss in the flow field at the back of the leaf. |
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