Study of transition phenomena in a straight channel with 40 to 1 aspect ration with and without imposed pulsations Part two: Reynolds number surveys

Abstract

A channel with rectangular cross-section, 40 to 1 aspect ratio (height is0.0127 m) and 4.27 m test section length (336 channel lengths) is used to study the effects of imposed pulsations on laminar, transitional, and turbulent flow phenomena. Periodic velocity variations are produced in the test section using a single rotating vane located in the flow downstream of the test section. Survey data for Y/d of 0.50, 0.85, and 0.90 show how normalized average velocity and turbulence intensity data vary with Reynolds number for Reynolds numbers from 1100 to 3400 at Stokes numbers of 4.08 and 5.79 and Strouhal numbers from 0.033 to 0.121. These conditions are produced from pulsations imposed at 1 Hz and 2 Hz to show how transition develops both with and without imposed pulsations. Intermittency variations increase from near zero to one as Reynolds number changes from 1450- to 2100 for Y/d = 0.90, 0.85, and 0.50. Time-averaged magnitudes of the internalized longitudinal turbulence intensity increase significantly as RE changes from 1450 to 3100 at Y/d - 0.90. A maxima is reached near Re 2400. Afterwards these data show a decrease and level off in the turbulent region. At Y/d - 0.85, the same trend in normalized longitudinal turbulence intensity appears with a maxima appearing near re = 2300. For the enter of the channel (Y/d = 0.50), the maxima appears near Re = 2000. The normalized longitudinal turbulence intensity level in the turbulent region increase with Y/d. Of particular interest are conditions where the normalized longitudinal turbulence intensity is greater near the center of the channel than near the walls. This occurs for Reynolds numbers of 1500 to 2500. Spectra show evidence of intermittency and drastic increases in fluctuating energy starting at Re =1500 and continuing to Re = 1700.