Turbulence Modeling for Secondary Flow Prediction in a Turbine Cascade

Abstract

Predictions of secondary flow in an axial turbine cascade have been made using three different turbulence models: mixing length, a one-equation model and a k–ε mixing length hybrid model. The results are compared with results from detailed measurements, not only by looking at mean flow velocities and total pressure loss, but also by assessing how well turbulence quantities are predicted. It is found that the turbulence model can have a big influence on the mean flow results, with the mixing length model giving generally the best mean flow. None of the models give good predictions of the turbulent shear stresses in the vortex region, although the k–ε model gives quite good turbulent kinetic energy values. The one-equation model is the only one to contain a transition criterion. The importance of such a criterion is illustrated, but the present one needs development to give reliable predictions in the complex flow within a blade passage.

Controlling secondary flows in very highly-loaded low-pressure turbine cascades

“…As above, the magnitude of the secondary kinetic energy is over predicted suggesting that the secondary velocities generated within the blade passage are being dissipated too slowly by the turbulence model. This has been observed by other researchers (eg Cleak and Gregory-Smith, 1992)Hartland et al (2000) for the evaluation of their contoured endwall relative to the planar configuration.The simulations ofHartland et al (2000) used a structured grid topology and an algebraic mixing length turbulence model with a wall function.…”

“…Hildebrand and Fottner (1999) showed higher predicted losses in the two dimensional wake and secondary flow using both the k -e and k -u turbulence closure models. Cleak and Gregory-Smith (1992) Hildebrand and Fottner (1999) and Cleak and Gregory-Smith (1992), the over prediction of secondary loss can be partially accounted for by the assumption of a fully turbulent boundary layer on the endwall of the blade passage. It is unclear why the computations of Hjarne et al (2007) under predict the loss without the implementation of a transition model.…”

On Turbulence and its Effects on Aerodynamics of Flow through Turbine Stages

“…The kε turbulence models are appropriate for flows characterized by high adverse pressure and intensive separation. This model allows for a more accurate near wall treatment with an automatic switch from wall function to low-Reynolds number formulation, based on grid spacing see [125][126][127][128].…”

Computational Predictions of Heat Transfer and Film-Cooling for a Turbine Blade With Non-Axisymmetric Endwall Contouring

“…cores and in the blade wake. While the difference might be partially due to limited spatial resolution in the experiment, it has also been shown that eddy-viscosity turbulence models tend to overpredict both secondary and midspan blade wake losses ( [31]). The flat endwall predictions using the realizable k-ε turbulence model (Figure 7c) show poor agreement for both C SKE and C Ptot when compared to the measurements in Figure 7a.…”