Turbine Blade Trailing Edge Flow Characteristics at High Subsonic Outlet Mach Number

Abstract

The paper presents an experimental investigationof the effect of the trailing edge vortex shedding on the steady and unsteady trailing blade pressure distribution of a turbine blade at high subsonic Mach number M2,is=0.79 and high Reynolds number RE=2.8×106. The vortex formation and shedding process is visualized using a high-speed schlieren camera and a holographic interferometric density measuring technique. The blade is equipped with a rotatable trailing edge cylinder instrumented side-by-side with a pneumatic pressure tap and a fast response pressure sensor for detailed measurements of the trailing edge pressure distribution. The experiments demonstrate that contrary to the isobaric dead air region demonstrated at low subsonic Mach numbers the data reveal the existence of a highly nonuniform trailing edge pressure distribution with a strong pressure minimum at the center of the trailing edge. This finding is significant for the determination of the base pressure coefficient that is in general measured with a single pressure-sensing hole at the trailing edge center. The paper investigates further the effect of the vortex shedding on the blade rear suction side and discusses the superposition of unsteady effects emanating from the trailing edge and from the neighboring blade. The experimental data are a unique source for the validation of unsteady Navier-Stokes codes.

Elliptic Trailing Edge for a Turbine Blade: Aerodynamic and Aerothermal Effects

“…The CC boundary conditions are exactly the same as those used by Sieverding et al 9) On the other hand, the HC has the same exit isentropic Mach number (M 2;is ) and exit isentropic Reynolds number (Re 2;is ), based on chord length for the ab1 case, as that of the CC. The inlet and exit boundary conditions are calculated using the method of characteristics.…”

“…Figure 4 shows the time-averaged velocity distributions of our computational results for both cases, and the experiment result 9) for the ab1 case. The computational results of the ab1 case agree well with the experimental data.…”

“…The turbine cascade with a circular TE (ab1) is the same as that used in Sieverding et al 9) For the elliptic TE case, we study two shapes: ab0.5, where the elliptic TE major axis is half the TE thickness, and ab2, where the elliptic TE major axis is twice the TE thickness. The circular TE and modified elliptic TE are shown in Fig.…”

“…In the present study, we perform a numerical simulation for the experimental results of Sieverding et al 9,15) and modify the TE geometry to the elliptic shape. We investigate the effect of this modification on the loss and heat transfer coefficient.…”

“…Sondak and Dorney 7) and Manna et al 8) numerically confirmed this distribution using the same cascade and flow conditions as Cicatelli and Sieverding. 6) Sieverding et al 9) conducted experiments at M 2;is ¼ 0:79 on a cascade with half the scale of that used in other research. [6][7][8] They noticed that the TE pressure distribution is non-uniform.…”