Semester

Spring

Date of Graduation

2017

Document Type

Problem/Project Report

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Andrew C Nix

Committee Co-Chair

John M. Kuhlman

Committee Member

Cosmin Dumitrescu

Abstract

The boundary layer region of a flow is a primary area of interest when analyzing the effects of various flow phenomena, heat transfer, and skin friction near an immersed object's surface. Characterizing this region yields a proper understanding of mass, momentum, and energy transfer to or from the region near the immersed body surface. Such characterization includes the boundary layer height, displacement, and momentum boundary layer thicknesses among many attributes. These factors offer a description of the flow for a laminar state, but also must include length scales, turbulence intensities, and distribution of turbulent kinetic energy to fully describe a boundary layer in the turbulent regime. This investigation will experimentally find these boundary layer characterization parameters for four scenarios. Two independent flow variations will be introduced and their effects upon the boundary layer examined and compared to previous and theoretical data. The first two scenarios examine the effects of wall suction on and off and the resulting effect on a non-tripped laminar boundary layer. The last two scenarios maintain the cases of suction on and off but introduce a turbulence generator within the boundary layer in order to trip the boundary layer to a turbulent state. Confirmation of turbulence and to what degree the flow is turbulent is found through calculating the turbulence intensity and length scale. This investigation is experimentally conducted in the West Virginia University Turbine Aerodynamic and Advanced Cooling (TAAC) Wind Tunnel facility, which has been recently recommissioned by the author. Pitot-static and hotwire anemometry were used to record data. Freestream turbulence was controlled by a passive turbulence generator and held constant for each scenario. It was found that a non-tripped flow with no suction yielded a boundary layer height of 1.045 inches taken 9.625 inches downstream of the turbulence grid location. Once suction is introduced, this height reduces to 0.795 inches. Similarly, suction decreased the boundary layer height for the tripped boundary flow from 2.25 inches to 1.17 inches. Due to the way the investigation originally defined the boundary layer height at 99% freestream conditions, conclusions yield that resolutely maintaining this definition slightly deviates this investigation's results from prior benchmarked data prior to facility recommissioning. However, general trends in boundary layer parameters are consistent, and turbulence intensities along with turbulent length scales from the tripped flow scenario validate a turbulent boundary layer. Turbulence intensities and other boundary layer characteristics detail for the non-tripped flow scenarios, which assume a laminar boundary layer, more closely align instead with a transitional flow regime as opposed to a completely laminar one as assumed. Understanding the influence of suction and turbulence within the boundary layer aids this facility's goal of matching flow parameters nondimensionally as experienced on actual turbine blades in the hot section of gas turbine engines. Serving as a new benchmark for this lab, future turbine blade cooling schemes can be tested in nondimensionally matched conditions. While these future experiments will employ advanced nonintrusive measurement techniques, the author utilizes this precursor investigation for conceptual understanding of flow field conditions and the influence of parameters such as suction and turbulence on the boundary layer.

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