Translated Abstract
Numerical Simulation and PIV Measurements of the 3-DComplex Viscous Flow in the Centrifugal Compressor StagesAbstractIn recent years, the study of multistage internal flow has become one of the majorresearch areas in turbomachinery aerodynamics. In comparison with the axialturbomachinery, the internal flow in centrifugal compressors is more complex.Furthermore, many problems concerning the 3D flow structure in centrifugal compressorsare yet to be solved. In this dissertation the research work on 3D flow field in thecentrifugal compressor stages by means of CFD and experimental method was reported.These studies mainly consist of the following aspects:The validation of the numerical simulation with various turbulence models by meansof the NASA Low Speed Centrifugal Compressor is studied. The numerical precisions andconvergence abilities are compared with the algebraic Baldwin-Lomax and three ε − kturbulence models. Additionally, the influences of y+ and grid number on the performanceof ε − k turbulence model are also discussed.On the basis of the stages of the Shenyang Blower Works as an illustrateon, theanalysis of the influence of splitter blade distribution on the flow field and characteristic ofthe impeller is carried out and the results show the reduction of the blockage at the inlet incase of the spllitter blade. It can get more uniform distribution of the velocity at theimpeller outlet when the splitter blade is at the location III. The load at the blade pressureside becomes heavier with the shorter splitter blade. For the different azimuthal distributionof splitter blade, the impeller IBSA gets the highest efficiency. The numerical simulationresults of the flow in the impeller at various tip clearance show that it is possible to get anoptimum value of the tip clearance, which is not zero to make the flow loss minimized andthe modification of the experiential coefficient in the formula was given. The numericalresults show a good agreement with the experimental results for the impellershroud-cutting and the efficiency of the stage with shroud-cutting impeller is higher, whichaffirms the effectiveness of the shroud-cutting in the design. The simulation results of thecompression of the perfect gas and real gas show that the flow parameters at the outlet ofthe impeller in case of real gas is different from that of the impeller for the perfect gas andthe differences are mainly located at the hub and shroud surface of the impeller. The staticpressure coefficient along the bend and the return channel for the perfect gas is higher thanthat for the real gas. The efficiency of the compressor for the real gas is more close to theexperimental data.Another computational analysis of the flow field in a high speed centrifugalcompressor with a backswept unshrouded impeller and the hub vane diffuser is presented.In order to get the optimum hub vane height, the pressure and velocity fields werenumerically simulated for eight kinds of the hub vanes, which are varied as follows: h/b=0西安交通大学博士学位论文iv(vaneless), 0.3, 0.4, 0.5 and 1 (vane). The results show that hub vane diffusers can obtainboth higher pressure recovery and efficiency as compared with the vaneless diffuser andget wider operating range as compared with the vane diffuser. The compressor with the hubvane diffuser of h/b=0.4 can get the best performance. The shroud vane diffuser cancapture the highly tangential flow that is found near the diffuser shroud surface and helpguide it toward the diffuser exit. So the performance of the centrifugal compressor with theshroud vane diffuser is better than that with the hub vane diffuser for the same height of thevane.The flow field from the impeller outlet to the vane diffuser of a centrifugal blower,which is particularly designed for the optical access, has been measured via PIV. Thewhole velocity field is obtained in three planes perpendicular to the axis of impeller, in thehub to shroud direction, at different rotation speed by means of the phase-locked technique.Through further data processing, time-averaged parameters can also be derived. Theso-called “jet-wake” structure is clearly shown at the impeller outlet. In the diffuser, theradial velocity and absolute flow angle are non-uniform, the radial velocity decreases and itbecome more uniform when the radius increase.The significant effect of the flow rate, the rotation speed and the time phase on theflow state is discussed. The velocity distributions at different conditions are given. Themeasurement results show that low velocity locates at the suction side of the diffuser at lowflow rate and it locates at the pressure side at large flow rate. The velocity distributions atdifferent rotation speed are similar. The interaction between the impeller and diffuser in afull period is investigated at the rotation speed of 1000rpm and 1500rpm. The direction andmagnitude of the velocity in the diffuser are changed with the different time phase, and theunsteady flows in the diffuser are affected by the relative position between the impeller anddiffuser.
Translated Keyword
[numerical simulationcentrifugal compressorPIV measurement3d flow]
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