Effect of the relative location of a pocket cavity on heat transfer and flow structures of the downstream endwall with a symmetrical vane

In a gas turbine engine, the low pressure turbine (LPT) and the outlet guide vane (OGV) part are connected in the rear part. The outlet nozzle is designed as a contracted part to increase the ejection velocity and a pocket cavity (PC) is formed at this location. In this research work, the effects of the locations of the PC on the downstream endwall with a symmetrical vane (SV) are investigated and evaluated. The PC is simplified as a triangular groove with a small fillet radius on the pocket edge connecting to the flat surface. The distance ratio (L_d/D) between the PC and the SV is ranging from 1.0 to 3.0 and the case with only the SV is also considered. Heat transfer and flow field characteristics over the tested surfaces are provided. Heat transfer coefficients (HTCs) are measured by steady-state Liquid Crystal Thermography (LCT) with Reynolds number (Re) ranging between 87.6 × 10³ and 21.9 × 10³. Two kinds of turbulence models are used to close the N-S equations for the present flow field, i.e., the unsteady DES simulation and the steady the k-ω SST model. When the PC is placed upstream of the SV, the higher Nu regions around the SV due to the horse-shoe vortices is significantly decreased compared with the SV only case. With the distance ratio between SV and PC becoming larger, the weakening effect of the PC is greatly reduced and the heat transfer distributions around the SV on the endwall are seen to approach those of the SV only case (Case 0) when the distance ratio is extremely large. The PC changes the pattern of flow impingement on the SV and the ejection flow from the PC is greatly enhanced. The ejection flow interacts with the mainstream flow and the flow separates from the endwall when it is approaching the SV. Then, the higher heat transfer around the SV is weakened.