TY - JOUR

T1 - Helical structure of longitudinal vortices embedded in turbulent wall-bounded flow

AU - Velte, Clara Marika

AU - Hansen, Martin Otto Laver

AU - Okulov, Valery

PY - 2009

Y1 - 2009

N2 - Embedded vortices in turbulent wall-bounded flow over a flat plate, generated by a passive rectangular vane-type vortex generator with variable angle \beta to the incoming
flow in a low-Reynolds number flow (Re = 2600 based on the inlet grid mesh size L = 0:039 m and free stream velocity U_{\infty} = 1.0 ms^{-1}) have been studied with respect to helical symmetry. The studies were carried out in a low-speed closed-circuit wind tunnel utilizing Stereoscopic Particle Image Velocimetry (SPIV). The vortices have been shown to possess helical symmetry, allowing the flow to be described in a simple fashion. Iso-contour maps of axial vorticity revealed a dominant primary vortex and a weaker secondary one for 20^{\circ} \leq \beta \leq 40^{\circ}. For angles outside of this range, the helical symmetry was impaired due to the emergence of additional flow effects. A model describing the flow has been utilized, showing strong concurrence with the measurements, even though the model is decoupled from external flow processes that could perturb the helical symmetry. The pitch, vortex core size, circulation and the advection velocity of the vortex all vary linearly with the device angle \beta. This is important for flow control, since one thereby can determine the axial velocity induced by the helical vortex as well as the swirl redistributing the axial velocity component for a given device angle \beta. This also simplifies theoretical studies, e.g. to understand and predict the stability of the vortex and to model the flow numerically.

AB - Embedded vortices in turbulent wall-bounded flow over a flat plate, generated by a passive rectangular vane-type vortex generator with variable angle \beta to the incoming
flow in a low-Reynolds number flow (Re = 2600 based on the inlet grid mesh size L = 0:039 m and free stream velocity U_{\infty} = 1.0 ms^{-1}) have been studied with respect to helical symmetry. The studies were carried out in a low-speed closed-circuit wind tunnel utilizing Stereoscopic Particle Image Velocimetry (SPIV). The vortices have been shown to possess helical symmetry, allowing the flow to be described in a simple fashion. Iso-contour maps of axial vorticity revealed a dominant primary vortex and a weaker secondary one for 20^{\circ} \leq \beta \leq 40^{\circ}. For angles outside of this range, the helical symmetry was impaired due to the emergence of additional flow effects. A model describing the flow has been utilized, showing strong concurrence with the measurements, even though the model is decoupled from external flow processes that could perturb the helical symmetry. The pitch, vortex core size, circulation and the advection velocity of the vortex all vary linearly with the device angle \beta. This is important for flow control, since one thereby can determine the axial velocity induced by the helical vortex as well as the swirl redistributing the axial velocity component for a given device angle \beta. This also simplifies theoretical studies, e.g. to understand and predict the stability of the vortex and to model the flow numerically.

U2 - 10.1017/S0022112008004588

DO - 10.1017/S0022112008004588

M3 - Journal article

SN - 0022-1120

VL - 619

SP - 167

EP - 177

JO - Journal of Fluid Mechanics

JF - Journal of Fluid Mechanics

ER -