| Gas turbines are widely used in aviation,ships and power generation fields,and have an irreplaceable role in the development of the industry.As one of the core components of gas turbines,the compressor has always been valued by the industry.By continuously increasing the load of the blade,the single-stage pressure ratio of the high-performance compressor is continuously improved,but the higher back pressure gradient makes the blade face more and more serious danger of boundary layer separation,which seriously threatens the efficiency and safety of the compressor.The study found that the periodic wake produced by the upper-stage blade has an inhibitory effect on the separation of the boundary layer of the lower-stage blade,which makes it possible to further improve the lift of the blade.Therefore,the periodic wake of the upper-stage blade in the compressor environment has an effect on the suction surface boundary layer of the lower-stage blade.The complex role of stimuli is very important,but the research in this area at home and abroad is relatively limited,and the interaction under complex conditions has not been fully explained.In this paper,the unsteady wake effect of the flat-plate boundary layer in the compressor-like channel is simulated and experimentally studied by combining large eddy simulation,URANS transient calculation and experiment,combined with FFT and POD method in-depth analysis of the mechanism of wake effect,the main work is as follows:(1)For a flat plate with an effective chord length of 300 mm in a compressor-like counterpressure channel,the boundary layer was measured and numerically verified under stable inflow conditions with different Reynolds numbers and free-flow turbulence degrees.FFT analysis is used to obtain the transition mechanism of the slab boundary layer under the condition of stable incoming flow,and the basic working condition is established for the study of the unsteady interference boundary layer of the wake.The results show that the turbulence intensity has a stronger effect on the state of the laminar separation bubble than the Reynolds number.Compared with the experimental values,the laminar separation bubbles predicted by the LES and transition SST models are both shifted upstream by 0.04 times the chord length.Velocity pulsation induces transition along the exponential growth of the separation shear layer dominated by K-H instability.(2)A surface airfoil with the same effective chord length is designed for a thin airfoil with a relative thickness of 8%,and a large eddy simulation study is carried out under the boundary conditions of 1.5% turbulence degree and 70000 Reynolds number to compare the thin airfoil surface in the same reverse pressure channel.The similarities and differences between the separation bubble and the plate separation bubble are investigated,and the feasibility of using a plate to replace the airfoil surface of the thin airfoil range to study the wake effect is investigated.The results show that compared with the flat plate,the thickness of the surface separation bubble changes very little,the flow direction size decreases by about 5.5%,and the overall position moves downstream by about 12.16%.Because the size change is small,and the offset of the overall position of the separation bubble does not affect the time-averaged results of the wake interference,the feasibility of using a flat plate to replace the airfoil in the thin airfoil range to study the interaction between the boundary layer and the wake has been proved.(3)Under the conditions of 70000 Reynolds number and 0.8 wake reduced frequency,the experimental study of the steady incoming flow condition and the unsteady wake interference condition is carried out.return zone.According to typical compressor parameters and related research,four periodic wake inflow conditions consisting of two Reynolds numbers of 70000 and 150000 and two reduced frequencies of 0.8 and 1.6 were designed,and the flat boundary layer was carried out by using the overlapping grid combined with the transition SST model.Two-dimensional and three-dimensional transient calculations are carried out to study the influence of different Reynolds numbers and reduced frequency wakes on the boundary layer separation transition,and the interference mechanism of the wakes is deeply analyzed with the help of the main frequency extraction of FFT and the flow field decomposition of POD method.The results reveal that the damping effect of the laminar separation shear layer on the wake leads to a lag period of the separation bubble under the interference deformation.The detachment transition is promoted,resulting in a decrease in the time-average size of the detachment bubbles,which is mainly manifested by a large advance of the reattachment point.The pulsation frequency of the separation bubble appeared along the flow direction,and the main frequency shifted from low frequency to high frequency.The spatiotemporal pulsation growth curve of the shear layer obtained based on the Lagrangian trace method and phase averaging shows a significant linearity.(4)For the working condition of 70000 Reynolds number and the reduced frequency of1.6,the three-dimensional URANS calculation is carried out for the vibration parameters of the plate-attached compressor blade with the help of dynamic mesh and UDF technology,and the laminar separation bubble is simultaneously affected by unsteady wake and vibration.Transition mechanisms,and the role of blade vibration in wake interference.Three-dimensional transient vorticity analysis is used to explain the two unstable stages of direct interference and delayed interference formed in the wake interference process,and it is pointed out that the vibration causes the transition region to advance.The higher-order modes of the POD show the large eddy dissipation in the wake near the wall caused by vibration,which weakens the frequency characteristics of the wake.The spatiotemporal pulsation growth curve of the separated shear layer and the wake mixed vortex region exhibits the same linear characteristics as the pure wake interference case,and the curve shows that the shear layer with low pulsation level has a higher pulsation growth rate. |
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