Concave Surface Boundary Layer Flows in the Presence of Streamwise Vortices

Abstract

Concave surface boundary-layer flows are subjected to centrifugal instability which results in the formation of streamwise counter-rotating vortices. Such boundary layer flows have been experimentally investigated on concave surfaces of 1 m and 2 m radius of curvature. In the experiments, to obtain uniform vortex wavelengths, thin perturbation wires placed upstream and perpendicular to the concave surface leading edge, were used to pre-set the wavelengths. Velocity contours were obtained from hot-wire anemometer velocity measurements. The most amplified vortex wavelengths can be pre-set by the spanwise spacing of the thin wires and the free-stream velocity. The velocity contours on the cross-sectional planes at several streamwise locations show the growth and breakdown of the vortices. Three different vortex growth regions can be identified. The occurrence of a secondary instability mode is also shown as mushroom-like structures as a consequence of the non-linear growth of the streamwise vortices. Wall shear stress measurements on concave surface of 1 m radius of curvature reveal that the spanwise-averaged wall shear stress increases well beyond the flat plate boundary layer values. By pre-setting much larger or much smaller vortex wavelength than the most amplified one, the splitting or merging of the streamwise vortices will respectively occur.

Nonlinear evolution and secondary instability of steady and unsteady Görtler vortices induced by free-stream vortical disturbances

“…No attempt is made here to survey all the literature on Görtler vortex experiments. The reader is referred to Saric (1994) and Winoto, Shah & Mitsudharmadi (2011) for reviews.…”

Görtler Instability and Transition in Compressible Flows

“…Görtler vortices have been studied experimentally mainly in the incompressible regime [14,21,113,123,124] as it is more difficult to carry out boundary-layer experiments at high speeds. Only a few experiments have been conducted on compressible Görtler vortices over simple curved walls, while more effort has been devoted to experimental investigations of Görtler vortices over more complex surfaces that őnd direct applications in engineering problems (refer to table 3).…”

Characterization of counter-rotating streamwise vortices in flat rectangular channel with one-sided wavy wall

“…The fully developed laminar and turbulent flows in a wavy channel have been characterized experimentally as well as numerically with one of the earlier work using flow visualization techniques such as hydrogen bubble and laser Doppler anemometry to look at vortices in water channel with 90 • bend (Winoto and Crane, 1980;Nishimura et al, 1985Nishimura et al, , 1986Nishimura et al, , 1990Floryan, 2002;Bahaidarah et al, 2005;Asai and Floryan, 2006;Aider et al, 2009;Winoto et al, 2011;Tandiono et al, 2013). Flow in a channel over wavy walls can become turbulent due to instability of the shear layer caused by the main flow interacting with a Kelvin-Helmhotz type vortex or a centrifugal instability over concave surface (H.Görtler, 1954;Smith, 1955;Gschwind et al, 1995) which takes the form of counter-rotating streamwise vortices called Görtler vortices with a form of a symmetrical mushroom-like shape over its cross section (Bakchinov et al, 1995;Mitsudharmadi et al, 2004Mitsudharmadi et al, , 2006Tandiono et al, 2009;Winoto et al, 2011;Budiman et al, 2015). There are two regions in the flowfield of these vortices: the so-called upwash region where low velocity fluid is lifted from the surface and the so-called downwash region where higher velocity fluid is pushed back towards the surface resulting in thinner boundary layer and higher shear stress (Winoto et al, 2011).…”

“…Flow in a channel over wavy walls can become turbulent due to instability of the shear layer caused by the main flow interacting with a Kelvin-Helmhotz type vortex or a centrifugal instability over concave surface (H.Görtler, 1954;Smith, 1955;Gschwind et al, 1995) which takes the form of counter-rotating streamwise vortices called Görtler vortices with a form of a symmetrical mushroom-like shape over its cross section (Bakchinov et al, 1995;Mitsudharmadi et al, 2004Mitsudharmadi et al, , 2006Tandiono et al, 2009;Winoto et al, 2011;Budiman et al, 2015). There are two regions in the flowfield of these vortices: the so-called upwash region where low velocity fluid is lifted from the surface and the so-called downwash region where higher velocity fluid is pushed back towards the surface resulting in thinner boundary layer and higher shear stress (Winoto et al, 2011).…”