Turbulence anisotropy analysis at the middle section of a highly loaded 3D linear turbine cascade using Large Eddy Simulation

Abstract

This study analyzes the flow over a three-dimensional linear low-pressure turbine cascade blade using large eddy simulation at Re = 90,000. The computational model consists of one blade passage with periodic boundaries and synthetic turbulence is generated at the inlet of the domain. Various flow metrics, including isentropic Mach number distribution at mid-span and wake total pressure losses are compared with available experimental data and found to be in good agreement. A more detailed analysis of the turbulence with particular attention to the separation bubble region is subsequently presented. The analysis revealed that the turbulence is in a nearly two-component state very close to the wall region and gradually follows a certain anisotropy trajectory, as the distance from the wall increases. Even in the free-stream region no fully isotropic state is reached, due to large acceleration and flow turning. The results give a new insight into the state of turbulence within the separation region on the blade suction side and emphasize the deficiencies of the Reynolds-averaged Navier Stokes (RANS) turbulence models in reproducing the turbulence anisotropy. This insight is of relevance for the aerodynamic design of turbines, since large parts of the total pressure loss are generated in the separation region.

Large Eddy Simulation of a Low Pressure Turbine Cascade with Turbulent End Wall Boundary Layers

“…Following the overview of the secondary flow system, we now turn to a more detailed analysis of the turbulence close to the suction side of the blade as potential root cause for the discrepancies in the wake losses discussed earlier. For the midspan region, this has already been discussed extensively by Afshar et al (2023) and our results are consistent with their findings. We, therefore, focus on the end wall region.…”

“…Close to the blade, in the statistically two-dimensional part of the flow, the transitional separated shear layer can be observed in the Q-contour (Ⓑ) featuring turbulence distinctively close to the one-component limit, cf. Afshar et al (2023). After transition to turbulence, this area can be found significantly closer to isotropic (3C) turbulence (Ⓒ).…”

Direct numerical simulations of airfoil cascades for the improvement of turbulence models through database generation

“…Afterwards, the distribution of isentropic Mach number M is over the critical region of the blade is shown in Figure 8, along with the total pressure loss profile in the wake of the blade. In both cases, a good agreement with experimental data is obtained, while RANS simulations typically suffer to predict the M is distribution and total pressure loss in the wake, as illustrated by Fard Afshar et al (2023). Not shown here, the outflow angle is also well predicted by these DNS simulations compared to the experiments.…”

A Numerical Test Rig for Turbomachinery Flows Based on Large Eddy Simulations With a High-Order Discontinuous Galerkin Scheme—Part III: Secondary Flow Effects

“…in the wind tunnel [18]. Both mid-span blade loading and the total 93 pressure losses in a plane behind the blade will be shown to be in 94 excellent agreement with the available experimental data [19] and 95 recently published numerical data [15,20]. We assess the mesh in- Since the numerical method used in this paper itself has been 116 extensively described in part 1, we restrain ourselves to the descrip-117 tion of the numerical setup of the MTU T161 (see also [18]).…”

“…The midspan blade loading is shown in Fig. 4 against experimental [19] and numerical [14,15,20] available on sampling error. In the following, we will show 68% 345 confidence intervals for all our LES runs [22].…”