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Flow separation
About: Flow separation is a research topic. Over the lifetime, 16708 publications have been published within this topic receiving 386926 citations.
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TL;DR: In this article, the authors applied scanning PIV to a laminar separation bubble to investigate the spanwise structure and dynamics of the roll-up of vortices within the bubble, showing the quasi-periodic development of large vortex-rolls at the downstream end of the separation bubble, which have a convex structure and an extension of 10-20% chord length in the span-wise direction.
Abstract: Scanning PIV is applied to a laminar separation bubble to investigate the spanwise structure and dynamics of the roll-up of vortices within the bubble. The laminar flow separation with turbulent reattachment is studied on the suction side of an airfoil SD7003 at Reynolds numbers of 20,000–60,000. The flow is recorded with a CMOS high-speed camera in successive light-sheet planes over a time span of 1–2 s to resolve the temporal evolution of the flow in the different planes. The results show the quasi-periodic development of large vortex-rolls at the downstream end of the separation bubble, which have a convex structure and an extension of 10–20% chord length in the spanwise direction. These vortices possess an irregular spanwise pattern. The evolution process of an exemplary vortex structure is shown in detail starting from small disturbances within the separation bubble transforming into a compact vortex at the downstream end of the separation bubble. As the vortex grows in size and strength it reaches a critical state that leads to an abrupt burst of the vortex with a large ejection of fluid into the mean flow.
147 citations
TL;DR: Some of the basic principles of vortex dynamics arc are reviewed in this paper and applied to calculating and understanding various kinds of turbulent flows, such as cyclonic and e.g. vortex arcs.
Abstract: Some of the basic principles of vortex dynamics arc reviewed in this paper and applied to calculating and understanding various kinds of turbulent flows. After setting out the basic equations and b...
146 citations
TL;DR: In this paper, the authors defined the Reynolds number based on distance from leading edge (or chord) and freestream velocity, which is a measure of the amount of fluid being injected or withdrawn through a wall.
Abstract: Nomenclature CD = drag coefficient ( = 2D/pUlc) Cf = local skin-friction coefficient ( = 2rw/pUl) CL = lift coefficient ( = 2L/pU^c) Cq = suction coefficient ( = I vw I / UQ) c = airfoil's chord D = drag force per unit span L = lift force per unit span P = instantaneous hydrostatic pressure PO = pressure outside boundary layer P = mean pressure R = wall's radius of curvature /?6* = displacement thickness Reynolds number (= Uod*/v) RO = momentum thickness Reynolds number ( = U0de/v) Re = Reynolds number based on distance from leading edge (or chord) and freestream velocity T = instantaneous temperature T = mean temperature J7, = instantaneous velocity component Uj = mean velocity component U0 = velocity outside the boundary layer t/oo = freestream velocity HI = fluctuating velocity component u* = friction velocity ( = Vr^/p) vw = normal velocity of fluid injected or withdrawn through the wall X-, = Cartesian coordinates x = streamwise distance from leading edge y = normal distance from the wall y = normal distance in wall units ( = yu*/v) Z = spanwise coordinate a. = angle of attack 6 = boundary-layer thickness 60 = momentum thickness 6* = displacement thickness /x = dynamic coefficient of viscosity v = kinematic viscosity v/u * = viscous length scale (wall unit) p = density — p~uv = tangential Reynolds stress T.W = shear stress at the wall ( = pu *) [AJo = instantaneous spanwise vorticity at the wall _ [fijo = rnean spanwise vorticity at the wall (= — [dU/dy]Q)
146 citations
TL;DR: In this paper, experimental data describing the transonic, turbulent, separated flow generated by an axisymmetric flow model was presented, which consisted of a circular-arc bump affixed to a straight, circular cylinder aligned with the flow direction.
Abstract: Experimental data describing the transonic, turbulent, separated flow generated by an axisymmetric flow model are presented. The model consisted of a circular-arc bump affixed to a straight, circular cylinder aligned with the flow direction. Measurements of the mean velocity, turbulence intensity, and Reynolds shear-stress profiles were made in the separated flow. These data revealed dramatic changes in the shear-stress levels as the flow passed through the interaction to reattachment. Behavior of the turbulence reaction to the imposed pressure gradients was examined in terms of the mixing length and the excursions of the turbulence from equilibrium.
146 citations
TL;DR: In this paper, the effect of vertical shaft height on natural ventilation in urban road tunnel fires was investigated, and two special phenomena, plug-holing and turbulent boundary-layer separation were observed, both of which will influence the impact of smoke exhaust.
146 citations