Numerical simulations of flows in centrifugal turbomachinery

Abstract

NomenclatureA quasi-three-dimensional Navier-Stokes analysis h a s been extended and applied t o flows in centrifugal turbomachinery blade rows. The numerical procedure was validated using a radial fan geometry typical of those found in fossil fuels plants and air handling systems. The predicted blade loading and performance characteristics showed excellent agreement with the experimental data. The numerical analysis was then applied t o a low aspect ratio centrifugal impeller. Inviscid and viscous flow simulations were performed at three operating conditions. While steady solutions were obtained in the inviscid flow calculations, the appearance of an oscillating separation bubble on the pressure surface of the impeller necessitated that the viscous flow simulations be time dependent. By comparing the predicted and experimental circumferential distributions of the relative frame velocity and flow angle downstream of the impeller, it was hypothesized that in the experiments the end wall secondary flows energized the impeller suction surface boundary layer, making the flow locally behave like an inviscid fluid. The performance curve generated from the viscous calculations showed satisfactory agreement with the experimental data, while the inviscid calculations overpredicted the performance of the impeller. It was concluded that the physics retained in quasi-three-dimensional analysis are adequate for accurately predicting flow trends in certain types of centrifugal turbomachinery. a et I M 'I P Pr Re v, w P P K P3 P T e R -Speed of sound -Total energy -Rothalpy -Mach number -Total velocity -Radius -Static pressure -Prandtl number -Free stream Reynolds number -tangential and radial components of velocity -Inlet, exit flow angle -Thermal conductivity -First and second coefficients of viscosity -Density -Shear stress -Circumferential angle -Rotational speed Subscripts a -Inviscid L -Laminar quantity N -Normal direction t -Stagnation quantity T -Turbulent quantity u -Viscous r,O 112 -Inletlexit quantity -First derivative with respect to P or 0 Superscripts -Relative frame quantitj 1 Downloaded by NANYANG TECHNOLOGICAL UNIVERSITY on June 14, 2016 | http://arc.aiaa.org |