Browsing by Subject "Turbulence."
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Item The effect of roughness element thermal conductivity on turbulent convection.(2011-05-12T15:41:42Z) Mart, Steven Robert.; McClain, Stephen Taylor.; Engineering.; Baylor University. Dept. of Mechanical Engineering.Many flows of engineering interest occur over surfaces that exhibit roughness with thermal conductivities much lower than common metals and alloys. This is especially true of in-service gas turbine blades with surface depositions. Depending on the local convection coefficients, low thermal conductivity deposits may create situations where temperature changes along the heights of the elements are important and must be considered in predicting the overall surface convection coefficient. Using four test plates constructed with hexagonal distributions of hemispheres or cones made of either aluminum or ABS plastic, a series of experiments were performed in the Baylor University Subsonic Wind Tunnel to investigate the effects of roughness element thermal conductivities on turbulent convection. Results indicate that the packing density of the elements and the enhancement on the floor of the roughness distribution compete with the roughness element thermal conductivity in determining the overall convection enhancement.Item Experimental and numerical study on flow control using obliquely aligned elements.(2010-06-23T12:33:08Z) Narvaez, Gilberto.; McClain, Stephen Taylor.; Engineering.; Baylor University. Dept. of Mechanical Engineering.The use of micro-electromechanical system devices (MEMS) have been studied extensively in literature for control of flow separation and transitioning to turbulent flow. However, there is limited information about how obliquely aligned roughness elements affect the boundary layer development and induce turbulence. The purpose of this study was to measure the transverse flow and turbulent intensities produced by an array of 0°, 5°, 10°, and 15° obliquely-aligned elliptical control elements in turbulent flow at 2, 5, and 10 m/s on a flat plate. The resulting boundary-layer measurements demonstrate the ability of the control elements to produce tailored secondary flows. Since the test coupon was of finite span, results demonstrate that controlled vortices can also be generated using the arrays. Additionally, CFD simulations were performed and compared to the experimental results using the realizable k-ε turbulence model in ANSYS FLUENT 12.0 with solutions converging to residuals less than 1x10⁻⁶ for flow and turbulence quantities.Item Large eddy simulation of turbulent flow over transverse variations in aerodynamic roughness length.(2014-09-05) Willingham, David, 1989-; Anderson, William C., 1943-; Mechanical Engineering.; Baylor University. Dept. of Mechanical Engineering.A great deal of literature has been published regarding the impact of complex roughness on turbulent flow. However, the topic of transverse variations in surface roughness, has received relatively little attention. In this thesis, large-eddy simulation is used to investigate the effects on turbulent, high Reynolds number flow, caused by periodic step-changes in aerodynamic roughness length, which persist in the streamwise direction. A parametric study is conducted with respect to the ratio of high to low roughness length and the transverse width of high roughness regions. Results show that lateral momentum flux across shear layers, generates secondary flows in the vicinity of transverse transitions in roughness. These secondary flows form boundary layer scale, counter-rotating vortices, which redistribute turbulence and momentum throughout the entire domain and create time-invariant regions of relatively low and high momentum, above low and high surface roughness, respectively.