Numerical and Experimental Investigation of the Wake Flow Downstream of a Linear Turbine Cascade

Abstract

In turbomachinery the wake flow together with the inherent unsteadiness caused by interaction between stator and rotor has a significant impact on efficiency and performance. The prediction of the wake flow depends largely on the turbulence modeling. Therefore in this study the evolution of a viscous wake downstream of a linear turbine cascade is experimentally and computationally investigated. In a transonic cascade test stand Laser Doppler Velocimeter (LDV) measurements of velocity and turbulent kinetic energy are done in several axial planes downstream of the blade trailing edge. Two different turbulence models are then incorporated into a two-dimensional Navier-Stokes solver to calculate the turbulent wake flow and the results are compared with the experimental data to test the quality of the turbulence models. The large discrepancies between measurement and Calculation are assumed to be caused by the periodic vortex shedding from the blunt trailing edge which is not taken into account by the turbulence models. But further research is needed to resolve this issue.

Numerical and Experimental Investigation of Trailing Edge Vortex Shedding Downstream of a Linear Turbine Cascade

“…In all steady state simulations presented herein, λ was set to 1 and convergence was optimised by using local time-stepping and three multigrid levels. The results of the steady computations are very similar to those presented in detail by Sanz et. al (1998) for an isentropic exit Mach number of M 2,is =0.624 obtained with the same Navier-Stokes code on different computational grids.…”

“…All numerical results predict this trend, but whereas the steady state results show a much narrower wake than the measurements, the width and the location of the wake centre predicted by the unsteady simulations are in better agreement with the experiment. However, all numerical simulations give overly high values for the velocity defect, very similar to the results of Sanz et. al.…”

“…The experiment was carried out in a linear cascade wind tunnel capable of supersonic inlet flow which is described in detail by Sanz et al (1998). The turbine cascade consists of 7 blades as described by Kiock et al (1986).…”

“…The wake flow downstream of the trailing edge is measured with a Laser-Doppler Velocimeter (LDV). The measurement data in the wake are acquired at midspan at three axial planes located downstream of the cascade at x/c ax = 0.037, 0.161 and 0.285 as described by Sanz et al (1998). The first plane is located in the trailing edge region of the wake, where the velocity defect is very large.…”

“…Investigations of the wake flow downstream of a linear turbine cascade by Sanz et. al., (1998) revealed large discrepancies between LDV-measurement and numerical results, obtained with a twodimensional upwind-biased Navier-Stokes solver using two different turbulence models.…”