Effect of the Hub Endwall Cavity Flow on the Flow-Field of a Transonic High-Pressure Turbine

Abstract

In high-pressure turbines, a small amount of cold flow is ejected at the hub from the cavity that exists between the stator and the rotor disk. This prevents the ingestion of hot gases into the wheel-space cavity, thus avoiding possible damage. This paper analyzes the interaction between the hub-endwall cavity flow and the mainstream in a high-pressure transonic turbine stage. Several cooling flow ratios are investigated under engine representative conditions. Both time-averaged and time-resolved data are presented. The experimental data is successfully compared with the results of a three-dimensional steady Navier-Stokes computation. Despite the small amount of gas ejected, the hub-endwall cavity flow has a significant influence on the mainstream flow. The Navier-Stokes predictions show how the ejected cold flow is entrained by the rotor hub vortex. The time-resolved static pressure field around the rotor is greatly affected when traversing the non-uniform vane exit flow field. When the cavity flow rate is increased, the unsteady forces on the rotor airfoil are reduced. This is linked to the decrease of vane exit Mach number caused by the blockage of the ejected flow.

Unsteady Strong Shock Interactions in a Transonic Turbine: Experimental and Numerical Analysis

“…Figure 9 shows the rotor suction side velocity distribution at 15% span, midspan, and 85% span for the nom condition. The discrepancy at 15% span has been attributed by Paniagua et al [30] to the stator rim-rotor platform cavity flow ingestion, which has not been simulated in the current CFD study. At 15% span, there is more positive incidence than at midspan.…”

Endwall Heat Transfer for a Turbine Blade With an Upstream Cavity and Rim Seal Leakage

“…It appears that 0.75% MFR causes a slight upstream shift of the saddle point region (in the negative streamwise direction) compared to 0% MFR. Although the limited resolution of oil flow visualization makes it difficult to argue this conclusively, Paniagua, et al [19] observed the same trend for increasing net leakage flow upstream of their transonic rotating turbine blade, and inferred that the leakage increases the size of the horseshoe vortex. Figure 7 shows contours of endwall heat transfer for varying net leakage mass flow ratio from the rim seal with unswirled flow (100% V wh ).…”

Pressure Distortion Effects on Rim Seal Performance in a Linear Cascade

“…Radial overlap seals not only require less purge flow to prevent ingress than axial gap seals but also generate lower aerodynamic losses. Radial injection of the purge flow from an axial gap seal, as shown by Paniagua et al, results in a blockage of the main gas path, altering the degree of reaction at mid-span by 11% in their case [18]. A radial overlap seal however, injects the purge flow along the endwall reducing the mixing losses by minimizing the radial distance the purge flow penetrates the main gas path [13][14][15].…”