A Comparison of Experimental With Computational Results in an Annular Turbine Cascade With Emphasis on Losses

Abstract

Recent discussions in the industrial CFD community have identified a need for guidelines covering the accurate and efficient computation of a range of flow field classes. This paper addresses some of these issues for a standard turbomachinery test case, by investigating the flow through on annular blade row of a generic turbine profile, operating at an exit Mach number of 0.5. The joint experimental and CFD works have focused upon identifying and quantifying the loss sources and loss development. This has been achieved by the acquisition of dense data sets of a known, high and repeatable experimental accuracy, where, concentrating primarily upon the investigation of the secondary flow phenomena, optimised experimental methods have been employed to measure the pressure distributions in the annuls and the development of the flow field, particularly the loss structures, downstream of the trailing edge. On the CFD side, the flow field has been computed using commercial codes. Adopting the loss distribution as a primary marker for the quality of the CFD results, the performance and efficacy of the codes and the implemented viscous models can be assessed. The flow has been computed both 2D and 3D, from inviscid to laminar to turbulent with different turbulence models, with and without transition. According to the model, the flow has been investigated considering a wide range of parameters influencing its turbulent state. Through this study, guidelines concerning numerical smoothing and free-stream turbulence parameters are proposed for the computation of such flows. The need of a transition model within 3D schemes, rather than an improvement of the turbulence model, to predict accurate loss levels has been recognized. However, through the cross analysis of the different computational results, a good estimate of the loss magnitude and distribution is feasible with the currently used models.

Effects of Flow Injection From Outer Casing Upon Turbine Nozzle Vane Flow Field

“…The values for the inlet turbulence intensity and inlet eddy length scale were investigated by performing several simulations combining difference values. A similar study was performed Casciaro et al [10] using the same software. In the present study it was found that Tu=5% and L ε =0.05m presented the best agreement with the experimental data.…”

“…The three-dimensional, steady-state, Reynolds-averaged, compressible Navier-Stokes equations were solved with the CFX-TASCflow 2.10.0 computational code. Several numerical analyses of the flow field inside turbomachinery were performed by using this code, as described by Labrecque et al [9], Casciaro et al [10], von Hoyningen-Huene and Hermeler [11], Casciaro et al [12] and Favaretto [13].…”

Tip-clearance-affected flow fields in a turbine blade row

“…For the no-clearance case (Fig. 6a), the typical features associated with the secondary flow field are seen [13]. Because of the decision to use a constant contour step of 0.5 for all four plots, some of the fine detail of the measured flow field for this case is lost in this figure.…”

“…For a discussion of the use of the exit static pressure distribution as a boundary condition see Section 3.3. An in-depth discussion of the issues relating to the validation of the code can be found in references [13] and [14]. The aim of this paper is to generate an experimental data set for CFD validation data, and it is outside the scope of the paper to discuss all the issues raised by the numerical simulation.…”

“…For the no-clearance case (Fig. 6a), the typical features associated with the secondary flow field are seen [13]. Because of the decision to use a constant contour step of 0.5 for all four plots, some of the fine detail of the measured flow field for this case is lost in this figure . The fact that such a large contour step is required to plot the isolines for the tip clearance cases reflects perfectly the dominant nature of the loss core associated with the tip leakage flow, compared with the zero-clearance secondary flows.…”