Degree

Doctor of Philosophy (PhD)

Department

Mechanical and Industrial Engineering

Document Type

Dissertation

Abstract

To address the issue of variable heat load near the stagnation and the mid-chord region of a modern gas turbine blade, an incremental impingement cooling technique, which is a combination of pin-fin channel and jet impingement, is designed and explored. Large Eddy Simulation (LES), a well-known turbulence model, is used to simulate the coolant flow field and heat transfer. The streamwise (X) and the spanwise spacing (S) of the pin-fin arrangement are 1.074D and 1.625D. The aspect ratio of the pin-fin channel is 0.5D. The diameter (D) of the pin-fin is 2.54 cm. The configuration consists of five rows of the jet with variable jet diameter. All the simulations are done for Reynolds number ranging from 5000 - 21000. The validation of the simulation is done by comparing the numerical and experimental thermal effectiveness and cooling parameter. Effect of four different jet diameter, petite (P) - 0.25D, medium (M) - 0.29d, small (S) - 0.36D, and large (L) - 0.41D, on the flow field and heat transfer is investigated. The velocity field and the turbulent statistics near the upstream and the downstream jet remain self-similar in P configuration, whereas they deviate from self-similarity in L configuration. Although the heat transfer rate of the stagnation region is independent of crossflow in P and L configuration, the heat transfer rate of the downstream area increases with a higher crossflow and presence of L size jet. The stagnation region Nu and overall Nu is dependent on (d/D)-0.68 and (d/D)-0.21, respectively. A systematic study is then conducted to explore the effects of jet hole combination and distribution on heat transfer. A theoretical argument is presented to describe the trend in the distribution of the jet exit velocity in the selected configurations. The hole size combination should contain many P size holes to maximize the overall heat transfer. And to maximize the local cooling parameter, the L size hole should be placed at the desired location. The thermal performance which accounts for both the heat transfer and the pressure drop is higher for SSPSS and PPLPP configurations.

Date

11-6-2019

Committee Chair

Acharya, Sumanta

Available for download on Thursday, October 29, 2020

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