Experimental analysis of the vorticity and turbulent flow dynamics of a pitching airfoil at realistic flight (helicopter) conditions

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Title: Experimental analysis of the vorticity and turbulent flow dynamics of a pitching airfoil at realistic flight (helicopter) conditions
Author: Sahoo, Dipankar
Abstract: Improved basic understanding , predictability , and controllability of vortex -dominated and unsteady aerodynamic flows are important in enhancement of the performance of next generation helicopters . The primary objective of this research project was improved understanding of the fundamental vorticity and turbulent flow physics for a dynamically stalling airfoil at realistic helicopter flight conditions . An experimental program was performed on a large -scale (C = 0 .45 m ) dynamically pitching NACA 0012 wing operating in the Texas A &M University large -scale wind tunnel . High -resolution particle image velocimetry data were acquired on the first 10 -15 % of the wing . Six test cases were examined including the unsteady (k >0 ) and steady (k=0 ) conditions . The relevant mechanical , shear and turbulent time -scales were all of comparable magnitude , which indicated that the flow was in a state of mechanical non -equilibrium , and the expected flow separation and reattachment hystersis was observed . Analyses of the databases provided new insights into the leading -edge Reynolds stress structure and the turbulent transport processes . Both of which were previously uncharacterized . During the upstroke motion of the wing , a bubble structure formed in the leading -edge Reynolds shear stress . The size of the bubble increased with increasing angle -of -attack before being diffused into a shear layer at full separation . The turbulent transport analyses indicated that the axial stress production was positive , where the transverse production was negative . This implied that axial turbulent stresses were being produced from the axial component of the mean flow . A significant portion of the energy was transferred to the transverse stress through the pressure -strain redistribution , and then back to the transverse mean flow through the negative transverse production . An opposite trend was observed further downstream of this region .
URI: http : / /hdl .handle .net /1969 .1 /85893
Date: 2008-10-10

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Experimental analysis of the vorticity and turbulent flow dynamics of a pitching airfoil at realistic flight (helicopter) conditions. Available electronically from http : / /hdl .handle .net /1969 .1 /85893 .

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