Physics of unsteady blunt-fin-induced shock wave/turbulent boundary layer interactions

Abstract

Fluctuating wall-pressure measurements have been made on the centreline upstream of a blunt fin in a Mach 5 turbulent boundary layer. By examining the ensemble-averaged wall-pressure distributions for different separation shock foot positions, it has been shown that local fluctuating wall-pressure measurements are due to a distinct pressure distribution, [weierp ]i, which undergoes a stretching and flattening effect as its upstream boundary translates aperiodically between the upstream-influence and separation lines. The locations of the maxima and minima in the wall-pressure standard deviation can be accurately predicted using this distribution, providing quantitative confirmation of the model. This model also explains the observed cross-correlations and ensemble-average measurements within the interaction. Using the [weierp ]i model, wall-pressure signals from under the separated flow region were used to reproduce the position–time history of the separation shock foot. The unsteady behaviour of the primary horseshoe vortex and its relation to the unsteady separation shock is also described. The practical implications are that it may be possible to predict some of the unsteady aspects of the flowfield using mean wall-pressure distributions obtained from either computations or experiments; also, to minimize the fluctuating loads caused by the unsteadiness, flow control methods should focus on reducing the magnitude of the [weierp ]i gradient (∂[weierp ]i/∂x).

Space and time organisation of a shock wave/turbulent boundary layer interaction

“…A decrease of the frequency scale appear when the shock is stronger. We can notice an analogous evolution for the compression ramp case [2]. For comparison we can define a Strouhal number S L = f L/U ∞ , based on the interaction length L and on the external upstream velocity U ∞ .…”

“…Reference is made to recent experimental, computational and analytical work on this question. On the experimental side, results have already been obtained in this field by Doerffer and Dallmann [7], Thomas et al [21], Brusniak and Dolling [2] for example. Most of the classical references can be found in Smits and Dussauge [20] and in recent reviews by Dolling [8] and Lee [17], and also by Delery [5].…”

A scaling analysis for turbulent shock-wave/boundary-layer interactions

“…The most commonly considered interactions concern those with a turbulent boundary layer, although laminar or transitional interactions have also been investigated in the literature. Cases under consideration cover a large range of geometric configurations, including normal shock interactions (Atkin & Squire 1992;Bruce & Babinsky 2008;Bur et al 2008), blunt fin interactions (Brusniak & Dolling 1994;Ünalmis & Dolling 1996;Bueno 2006), over-expanded nozzles (Frey & Hagemann 1998, 2000Bourgoing & Reijasse 2005), compression ramp interactions (Thomke & Roshko 1969;Spaid & The characteristic length L used in the Strouhal number represents the effects of the presence of the boundary layer in comparison to a purely inviscid flow (see the scheme in figure 1). It is defined as the observed upstream shift of the shock wave C S due to the thickening of the boundary layer, subject to the imposed pressure jump (or equivalently the angle of deviation of the flow).…”

Experimental Investigation of Upstream Boundary Layer Acceleration on Unsteadiness of Shock-Induced Separation

“…[1][2][3][4][5][6][7][8][9][10][11] Erengil and Dolling's 9 studies of separation shock foot unsteadiness showed a correlation between the wall pressure fluctuations beneath the incoming boundary layer and the shock foot velocity, from which it was inferred that the small-scale motion of the shock is caused by its response to the convection of turbulent fluctuations through the interaction. Their work also demonstrated that the large-scale motion is a result of the shock's displacement due to the expansion and contraction of the separation bubble.…”