GLTRS--Glenn
TITLE AND SUBTITLE:
A Study of Dean Vortex Development and Structure in a Curved Rectangular Channel With Aspect Ratio of 40 at Dean Numbers up to 430

AUTHOR(S):
Phillip M. Ligrani

REPORT DATE:
July 1994

FUNDING NUMBERS:
WU-505-62-0K
1L162211A47A

PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES):
Naval Postgraduate School
Department of Mechanical Engineering
Monterey, California 94943-5000

PERFORMING ORGANIZATION REPORT NUMBER:
E-8918

SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES):
Vehicle Propulsion Directorate
U.S. Army Research Laboratory
Cleveland, Ohio 44135-3191
and
NASA Lewis Research Center
Cleveland, Ohio 44135-3191

REPORT TYPE AND DATES COVERED:
Final Contractor Report

SPONSORING/MONITORING AGENCY REPORT NUMBER:
NASA CR-4607
ARL-CR-144

SUPPLEMENTARY NOTES:
Project Manager, Kestutis C. Civinskas, Propulsion Systems Division, NASA Lewis Research Center, organization code 2760, (216) 433-5890.

ABSTRACT:
Flow in a curved channel with mild curvature, an aspect ratio of 40 to 1, and an inner to outer radius ratio of 0.979 is studied at Dean numbers De ranging from 35 to 430. For positions from the start of curvature ranging from 85 to 145 degrees, the sequence of transition events begins with curved channel Poiseuille flow at De < 40-64. As the Dean number increases, observations show initial development of Dean vortex pairs, followed by symmetric vortex pairs which, when viewed in spanwise/radial planes, cover the entire channel height (De=90-100). At De from 40 to 125-130, the vortex pairs often develop intermittent waviness in the form of vortex undulations. Splitting and merging of vortex pairs is also observed over the same experimental conditions as well as at higher De. When Dean numbers range from 130 to 185-200, the undulating wavy mode is replaced by a twisting mode with higher amplitudes of oscillation and shorter wavelengths. The twisting wavy mode results in the development of regions where turbulence intensity is locally augmented at Dean numbers from 150 to 185-200, principally in the upwash regions between the two individual vortices which make up each vortex pair. These turbulent regions eventually increase in intensity and spatial extent as the Dean number increases further, until individual regions merge together so that the entire cross section of the channel contains chaotic turbulent motions. When Dean numbers then reach 400-435, spectra of velocity fluctuations then evidence fully turbulent flow.

SUBJECT TERMS:
Curved channel; Concave and convex curvature; Dean vortex pairs; Twisting and
undulating vortices

NUMBER OF PAGES:
237

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