Numerical Simulation of Backward Film Cooling With Fan-Shaped Holes

Abstract

The thermal efficiency of a gas turbine is largely dependent on the turbine inlet temperature (TIT). Modern gas turbines may operate at temperatures as high as 2000K, which is higher than the melting point of the material in use. Hence, thermal protection of gas turbine hot components is a big challenge. Film cooling is the most common cooling technique adopted in this application. In film cooling, coolant is injected at discrete locations along the metal surface, which forms a layer of cool air immediately over the hot surface, thus, protecting it from direct contact with hot mainstream air. The cooling is strong along the centerline of the hole in the downstream region and rapidly decreases over the span-wise direction. The distributed cooling can result in large thermal gradients, inducing thermal stresses in the material. The region with least cooling may lead to a cascade failure of the blade. Film cooling with backward injection holes has been proved to reduce this effect. In the current work, backward coolant injection scheme is explored under fan-shaped holes numerically. Fluent, a commercial CFD software, is used in the current work for numerical simulations. Effects of blowing ratio, injection angle, and turbulence are considered. Numerical results show that fan-shaped holes are better than simple cylindrical holes in terms of both cooling effectiveness and its uniformity. Numerical results are validated with experimental results. The image of temperature fields on cooling surface is captured with an Infrared camera.

Numerical Evaluation on Effects of Upstream Sand-Dune-Shaped Ramp and Backward Coolant Injection on Heat Transfer

“…Over the past decades, film cooling with forward coolant injection was the main focus. Recently, a research group from Lamar University inspired the researches on film cooling with backward coolant injection [7][8][9][10]. These studies provided a clear understanding on the backward injection film cooling.…”

Numerical Investigation on Backward-Injection Film Cooling with Upstream Ramps

“…In actuality, the coolant injection orientation is also a paramount factor that affects the mutual interaction between coolant jets and primary flow, and subsequently the film cooling performance. The backward injection, an opposite scheme to forward injection, was illustrated by Li et al [28] and Subbuswamy et al [29,30] to own a unique interaction feature of jet-in-crossflow, leading to a better jet spreading in the lateral direction but a worse jet spreading along the streamwise direction on the whole. Because backward coolant injection could provide a uniform film cooling in the lateral direction relative to the forward coolant injection, it was suggested to be a possible scheme for weakening the thermal gradients.…”

Effect of backward injection with combined hole on film colling performance

“…The results showed that the backward hole (BH) can improve the film cooling effectiveness with a larger pressure loss penalty. Subbuswamy et al [25] have improved the film cooling effectiveness using backward injection with fan-shaped holes. Park et al [26] combined the forward and backward injection together taking into account the effect of blowing ratios (0.5 to 2.0), the density ratio was set to the unity.…”