Flow separation

About: Flow separation is a research topic. Over the lifetime, 16708 publications have been published within this topic receiving 386926 citations.

Energy injection in closed turbulent flows: Stirring through boundary layers versus inertial stirring

Abstract: The mean rates of energy injection and energy dissipation in steady regimes of turbulence are measured in two types of flow confined in closed cells. The first flow is generated by counterrotating stirrers and the second is a Couette-Taylor flow. In these two experiments the solid surfaces that set the fluid into motion are at first smooth, so that everywhere the velocity of the stirrers is locally parallel to its surface. In all such cases the mean rate of energy dissipation does not satisfy the scaling expected from Kolmogorov theory. When blades perpendicular to the motion are added to the stirring surfaces the Kolmogorov scaling is observed in all the large range of Reynolds numbers (10,Re,10) investigated. However, with either smooth or rough stirring the measurements of the pressure fluctuations exhibit no Reynolds number dependence. This demonstrates that, though the smooth stirrers are less efficient in setting the fluid into motion, their efficiency is independent of the Reynolds number so that the Kolmogorov scaling characterizes, in all cases, the dissipation in the bulk of the fluid. The difference in the global behaviors corresponds to a different balance between the role of the different regions of the flow. With smooth stirrers the dissipation in the bulk is weaker than the Reynoldsnumber-dependent dissipation in the boundary layers. With rough ~or inertial! stirrers the dissipation in the bulk dominates, hence the Kolmogorovian global behavior. @S1063-651X~97!11606-3#

Unsteady flow past an airfoil pitching at a constant rate

Abstract: The unsteady flow past a NACA 0012 airfoil that is undertaking a constant-rate pitching up motion is investigated experimentally by the PIDV technique in a water towing tank. The Reynolds number is 5000, based upon the airfoil's chord and the free-stream velocity. The airfoil is pitching impulsively from 0 to 30 deg. with a dimensionless pitch rate alpha of 0.131. Instantaneous velocity and associated vorticity data have been acquired over the entire flow field. The primary vortex dominates the flow behavior after it separates from the leading edge of the airfoil. Complete stall emerges after this vortex detaches from the airfoil and triggers the shedding of a counter-rotating vortex near the trailing edge. A parallel computational study using the discrete vortex, random walk approximation has also been conducted. In general, the computational results agree very well with the experiment.

Resistance Coefficients for Accelerated and Decelerated Flows Through Smooth Tubes and Orifices

Abstract: : This paper summarizes the results of investigations in the M, I, T. Unsteady Flow Water Tunnel of accelerated and decelerated flow through uniform conduits and orifices in conduits. In the uniform conduit shear and turbulence is generated through boundary layer friction and is essentially uniform along the duct. The orifices cause separation and jet formation with accompanying high shear and turbulence which varies along the duct as the jet diffuses and the turbulence is dissipated.

Surface pressure fluctuations in a separating turbulent boundary layer

Abstract: A novel, microphone-employing technique for the measurement of pressure fluctuations through pinhole apertures in the flow surface is used in the present study of separating boundary layer pressure fluctuation spectra and wavespeeds. The rms of the surface pressure fluctuation increases monotonically through the adverse-pressure gradient attached flow region and the detached flow zone. A correlation of the detached flow data is given which is derived from velocity and length scales of the separated flow. The celerity of the surface pressure fluctuations for the attached flow increases with frequency to a maximum, and the streamwise coherence decreases drastically after the begining of flow reversal.