Topic
Flow separation
About: Flow separation is a research topic. Over the lifetime, 16708 publications have been published within this topic receiving 386926 citations.
Papers published on a yearly basis
Papers
More filters
TL;DR: In this article, the authors investigated the relationship between the time-averaged and phaseaveraged flow fields in turbulent backward-facing step flow under the influence of periodic perturbation and found that the change in the mean velocity field due to the organized fluid motion alters the production rate of Reynolds stress.
89 citations
TL;DR: Flow structures in models of the distal end-to-side anastomosis were visualised under steady and pulsatile flow conditions using planar illumination of suspended tracer particles in agreement with the observation that intimal hyperplasia occurs in regions of flow separation at the toe and the heel, and flow stagnation on the floor of the anastOMosis.
89 citations
04 Jan 2011
TL;DR: In this article, a dielectric barrier discharge (DBD) plasma actuator driven by repetitive nanosecond pulses for high Reynolds number aerodynamic flow control is demonstrated at various post-stall angles of attack (α) for Reynolds numbers (Re) and Mach numbers (M) up to 1.15x10 6 and 0.26 respectively.
Abstract: This work continues an ongoing development and use of dielectric barrier discharge (DBD) plasma actuators driven by repetitive nanosecond pulses for high Reynolds number aerodynamic flow control. These actuators are believed to influence the flow via a thermal mechanism which is fundamentally different from the more commonly studied AC-DBD plasmas. Leading edge separation control on an 8-inch chord NACA 0015 airfoil is demonstrated at various post-stall angles of attack (α) for Reynolds numbers (Re) and Mach numbers (M) up to 1.15x10 6 and 0.26 respectively (free stream velocity, U∞ = 93 m/s). The nanosecond pulse driven DBD can extend the stall angle at low Re by functioning as an active trip. At poststall α, the device generates coherent spanwise vortices that transfer momentum from the freestream to the separated region, thus reattaching the flow. This is observed for all Re and M spanning the speed range of the subsonic tunnel used in this work. The actuator is also integrated into a feedback control system with a stagnation-line-sensing hot film on the airfoil pressure side. A simple on/off type controller that operates based on a threshold of the mean value of the power dissipated by the hot film is developed for this system. A preliminary extremum seeking controller is also investigated for dynamically varying Re. Several challenges typically associated with integration of DBD plasma actuators into a feedback control system have been overcome. The most important of these is the demonstration of control authority at realistic takeoff and landing Re and M.
89 citations
TL;DR: In this article, a direct numerical simulation is carried out of the initial stages of development of a mixing layer with a velocity ratio of ten, a fast stream Mach number of 0.6 and equal free-stream temperatures.
Abstract: A direct numerical simulation is carried out of the initial stages of development of a mixing layer with a velocity ratio of ten, a fast stream Mach number of 0.6 and equal free-stream temperatures. The fast stream is a fully developed turbulent boundary layer with a trailing-edge displacement thickness Reynolds number of 2300, while the slow stream is laminar. The computations include a splitter plate with zero thickness. The initial flow development is dominated by the rapid spreading of an internal shear layer formed as the viscous sublayer of the upstream turbulent boundary layer crosses the trailing edge. A tendency towards spanwise-coherent structures is observed very early in the shear layer development, within five displacement thicknesses of the trailing edge, despite such structures not being present in the upstream boundary layer. A numerical search for a global mode in the vicinity of the splitter plate trailing edge found only convective growth of disturbances. Instead, a convective mechanism...
89 citations
TL;DR: In this article, simulations of Mach 5 turbulent flow over a 28-deg compression corner are performed using a hybrid large-eddy/Reynolds-averaged Navier-Stokes method.
Abstract: Simulations of Mach 5 turbulent flow over a 28-deg compression corner are performed using a hybrid large-eddy/ Reynolds-averaged Navier-Stokes method. The model captures the mean-flow structure of the interaction reasonably well, with observed deficiencies relating to an underprediction of the displacement effects of the shock-induced separation region. The computational results provide some support for a recent theory concerning the underlying causes of low-frequency shock-wave oscillation. In the simulations, the sustained presence of a collection of streaks of fluid with lower/higher momentum than the average induces a low-frequency undulation of the separation front. Power spectra obtained at different streamwise stations are in good agreement with experimental results. Downstream of reattachment, the simulations capture a three-dimensional mean-flow structure, dominated by counter-rotating vortices that produce wide variations in the surface skin friction. Predictions of the structure of the reattaching boundary layer agree well with experimental pitot pressure measurements. In comparison with Reynolds-averaged model predictions, the hybrid large-eddy/Reynolds-averaged Navier-Stokes model predicts more amplification of the Reynolds stresses and a broadening of the Reynolds stress distribution within the boundary layer that is probably due to reattachment-shock motion.
89 citations