Effects of Tip Clearance Gap and Exit Mach Number on Turbine Blade Tip and Near-Tip Heat Transfer

Abstract

It is important to be able to accurately predict the heat transfer distribution over a component when designing the turbine section of an engine. The gas temperature exiting the combustor in many gas turbine engines is above the melting temperature of turbine components. These high gas temperatures can quickly degrade components and cause failure. A detailed heat transfer study on these turbine components is an important input when developing ways to cool them. One such important component is the gas turbine blade, which primarily extracts the energy from the hot combustion gases. To allow for rotation of the blades, a gap exists between the stationary casing and the rotating blades. Unfortunately, leakage flow from the blade pressure side to the suction side dramatically increases the heat load on and around the blade tip surfaces.The objective of this work is to present the heat transfer distribution on the tip and neartip region of a turbine blade under transonic conditions. Tests were performed at a high inlet freestream turbulence level (Tu = 12%). This work seeks to investigate the effects of tip clearance gap and Mach number on heat transfer on and near the blade tip. Thin film heat flux gages that allow for high frequency measurements are used to obtain the heat transfer distribution on the near tip pressure and suction sides. An infrared thermography technique is used to obtain the heat transfer distribution on the blade tip surface.iii PrefaceIn order to get more energy from gas turbine engines, the temperature of the combustion products is continually being increased by designers. These high temperatures will lead to increased degradation of turbine blades unless effective cooling schemes are developed to help protect the blades. A thorough understanding of the heat transfer distribution on the gas turbine blades is essential before sound cooling techniques can be implemented. An especially fragile part of the turbine blade exposed to high heat transfer is the blade tip. The tip gap, between the casing and the blade tip, is where leakage flow escapes from the blade pressure side to the suction side. This leakage flow has been shown to significantly increase the heat load on the blade tip. Designers need to understand the heat transfer distribution, especially on the blade tip, and then subsequently devise the appropriate cooling mechanisms. This study examines the effects of tip clearance gap and exit Reynolds number on the heat transfer distribution on a turbine blade tip and near-tip region.This thesis is organized into two sections that include one research paper that concisely documents the central thrust of this study. The author was primarily responsible for most aspects of the research project from initial test section design to analyzing data. A colleague, Xue Song, was responsible for the post processing of some of the blade tip heat transfer results. The title of the research paper coincides with the title of this thesis. A series of appendices then follow which provide additional in...

Investigation on tip clearance control for the high-pressure rotor of an uncooled vaneless counter-rotating turbine

“…Anto et al. 13 investigated the effects of tip clearance height and exit Mach number on heat transfer coefficient distribution on the tip surface using a transient infrared thermography technique, and showed that the leakage flow imposes a relatively significant sheer effect (flow migration) in a larger tip gap case, which was consistent with the fact that a larger tip gap implies that more leakage flow would enter the tip clearance gap.…”

Recent investigations of shock wave effects and interactions

“…Within the figure, color variations denote tip surface heat flux variations, and greyscale variations denote flow density gradient distributions which were employed in these studies utilized squealer configurations [57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72], partial squealer configurations [61,64,69], and winglet configurations [73,74]. Smooth blade tips were employed by Thorpe et al [75], Green et al [59], Key and Arts [62], O'Dowd et al [76,77], Wheeler et al [78], Zhang et al [55,56], Shyam et al [79], Atkins et al [80], Wheeler and Saleh [70], Anto et al [81], Virdi et al [68], Wheeler and Sandberg [82], Li et al [65], Zhang et al [83], Zhang and He [84], Wang et al [69], Zhou [71], Jung et al [61], Gao et al [85], and Kim et al [64]. Most of these investigations (which involved experimental measurements) employed annular or linear cascades with stationary blades.…”

Effect of unsteady passing wake on the aerodynamic and heat transfer performance of the turbine blade squealer tip

“…Park et al 2 and Acharya et al 3 pointed out that for flat tip and squealer, heat transfer near tip leading edge is higher due to leakage flow reattachment, while heat transfer on tip cavity floor decreases with cavity depth increasing. Anto et al 4 experimentally studied effects of the clearance height and exit Mach number on tip heat transfer characteristics. It was found that tip heat transfer coefficient increases 3% with clearance height increasing from 0.9% to 1.8%, while tip heat transfer coefficient increases 39% with exit Mach number changing from 0.85 to 1.05.…”