A Study of the Impact of Wide-Range Roughness Elements on Gortler Instabilities

Sescu, Adrian; Pendyala, Ravi; Haywood, John S.; Visbal, Miguel R.

doi:10.2514/6.2015-0275

Cited by 4 publications

(4 citation statements)

References 36 publications

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“…The focus of this paper is on the effect of small steps on the streamwise elongated streaks that may develop inside a flat-plate boundary layer when the level of freestream disturbances is high, or over a concave surface when the curvature is sufficiently large to allow Görtler vortices to form and grow. Boundary region equations (BRE) are modified using a Prandtl transformation to account for the surface geometry, while the upstream condition are imposed using a periodic array of roughness elements (Goldstein et al, 10,11 Sescu et al [29][30][31] ). The generalized Rayleigh pressure equation is solved to determine the growth rates and the associated modes pertaining the secondary instabilities of a streamwise velocity distribution.…”

Section: Introductionmentioning

confidence: 99%

On the Effect of Small Steps on Pre-transitional Streamwise Elongated Streaks

Sescu

Afsar

Sassanis

2015

45th AIAA Fluid Dynamics Conference

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It is generally agreed that in the process of transition from laminar to turbulent flow in boundary layers at moderately high freestream turbulence, the streamwise elongated streaks play an important role. These streaks may evolve inside boundary layer flows over flat plates or curved surfaces when the amplitudes of freestream disturbances exceed a certain level, or as a result of the imbalance between centrifugal effects and radial pressure gradients, respectively. In this paper, we study the effect of small surface steps on the transient growth associated with streamwise elongated streaks. The question that we aim at answering here is how do such surface imperfections impact the onset of secondary instabilities? These short-scale instabilities are thought to be the precursor to streak breakdown and there continues to remain many unanswered questions about their basic properties. To excite the streaks, we introduce a spanwise periodic distribution of localized surface roughness elements followed by a portion of concave surface in the downstream. Two step configurations of forward and backward facing types, and three 'streak strengths' (quantified by the difference between the maximum and minimum of the high-and low-speed regions, respectively) are considered. We numerically solve the boundary region equations subject to upstream boundary conditions as derived in Goldstein et al. 11,12 The generalized Rayleigh pressure equation is solved as an eigenvalue problem to determine the growth rates associated with the secondary instabilities. It is found that as the height of the step is increased beyond 0.5 of boundary layer displacement thickness, the growth rate reduces at the peak streamwise wavenumber of the instability. It appears that this reduction is greater for forward step configuration for all considered cases of 'streak strengths'.

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Section: Introductionmentioning

confidence: 99%

On the Effect of Small Steps on Pre-transitional Streamwise Elongated Streaks

Sescu

Afsar

Sassanis

2015

45th AIAA Fluid Dynamics Conference

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“…After extensive studies on this subject, especially in incompressible flows, the linear evolution of Görtler vortices have become well known [1][2][3] while receptivity and breakdown mechanisms are far from being completely understood. Görtler vortices can be excited by freestream disturbances [4][5][6] or wall inhomogeneities (e.g., roughness, blowing and suction) [7][8][9]. With controlled inlet forcing, investigators usually obtained a clean flow where Görtler vortices possess only a single dominant wavelength, and almost all the stability analyses have been performed for such flows [10,11].…”

Section: Introductionmentioning

confidence: 99%

“…If the harmonic turns out to be linearly unstable, then the harmonic can grow and form secondary streaks between the primary streaks induced by the primary vortex. Secondary streaks have been reported in both experimental and numerical studies [9,[12][13][14][15], but the corresponding stability characteristics remain unknown until quite recently. [16] have utilized blowing and suction to numerically excite Görtler vortices in a Mach 6.5 concave boundary layer.…”

Section: Introductionmentioning

confidence: 99%

From primary instabilities to secondary instabilities in Görtler vortex flows

Chen

Yuan

et al. 2019

Adv. Aerodyn.

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We have studied the transformation process from primary instabilities to secondary instabilities with direct numerical simulations and stability theories (Spatial Biglobal and plane-marching parabolized stability equations) in detail. First Mack mode and second Mack mode are shown to be able to evolve into the sinuous mode and the varicose mode of secondary instability, respectively. Although the characteristics of second Mack mode eventually lose in the downstream due to the synchronization with the continuous spectrum, second Mack mode is found to be able to trigger a sequence of mode resonations which in turn give birth to highly unstable secondary instabilities. In contrast, first Mack mode does not involve in any mode synchronization. Nevertheless, it can still "jump" to a sinuous mode of secondary instability with a much larger growth rate than that of the first Mack mode. Therefore, secondary instabilities of Görtler vortices are highly receptive to the primary instabilities in the upstream, so that one should consider the primary instability in the upstream and the secondary instability in the downstream as a whole in order to get an accurate prediction of the boundary layer transition.

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“…; SARIC; REED; KERSCHEN, 2002);• Estudos experimentais sobre a transferência de calor com vórticesde Görtler estacionários (MCCORMACK;WELKER;KELLEHER, 1970;MCKEE, 1973;TORII; YANA- GIHARA, 1997;TOE;AJAKH;PEERHOSSAINI, 2002;UMUR;OZALP, 2006);• Estudos teóricos numéricos sobre a transferência de calor com vórtices deGörtler estacionários (LIU;SABRY, 1991;SMITH;HAJ-HARIRI, 1993;LIU;LEE, 1995;LIU, 2008; MALATESTA; SOUZA; LIU, 2013; MALATESTA; ROGENSKI; SOUZA, 2017);• Estudos dos vórtices de Görtler estacionários com gradiente de pressão (RAGAB; NAY-FEH, 1981; GOULPIÉ; KLINGMANN; BOTTARO, 1996; ROGENSKI; SOUZA; FLORYAN, 2016; FERNANDES; MENDONÇA, 2019) • Estudos sobre vórtices de Görtler estacionários em escoamentos compressíveis (MANGA-LAM et al, 1985; HALL; FU, 1989; HALL; MALIK, 1989; MARENSI; RICCO; WU, 2017; VIARO; RICCO, 2019; CHEN; HUANG; LEE, 2019);• Instabilidade secundária(SWEARINGEN;BLACKWELDER, 1987;MALIK, 1995;WHANG;ZHONG, 2001;SHAH, 2004;SESCU et al, 2015;SOUZA, 2017);• Métodos de controle para retardar a transição(MYOSE;BLACKWELDER, 1995; CATHA- LIFAUD;LUCHINI, 2000;LU et al, 2014;AFSAR, 2018); e• Vórtices deGörtler não estacionários (BOIKO et al, 2010b; BOIKO et al, 2010a; IVA- NOV;MISCHENKO, 2012;XU;MARENSI;.…”

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Estudo numérico de escoamento transicional sobre placa côncava com perturbações não estacionárias

Takata¹

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The generation of Görtler vortices is the first stage of the turbulent laminar transition process in a boundary layer flow over a concave surface. These vortices produce distortions both in the velocity profile and in the temperature profile, intensifying the heat transfer rate and the drag coefficient compared to the laminar flow. There are several studies to understand the mechanisms of the formation of Görtler vortices to delay or anticipate their generation to maximize or minimize the effects of these two properties in this type of flow. This work investigates the evolution, structure, and influence of non-stationary disturbances in a boundary layer flow over a concave surface through numerical simulation with high-precision methods. The results show the stationary sub-harmonic mode (0,2) dominates the flow generating the stationary Görtler vortices as the spanwise wavelength and time-frequency increase, otherwise, the fundamental mode (1,1) dominates the flow and generated the unsteady vortices. Non-stationary disturbances delay the appearance of Görtler vortices since the growth rate of the fundamental mode (1,1) decreases when the frequency increases regardless of the transverse wavelength. The heat transfer rate and the drag coefficient for the unsteady vortices are lower than for the steady vortices.

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A Study of the Impact of Wide-Range Roughness Elements on Gortler Instabilities

Cited by 4 publications

References 36 publications

On the Effect of Small Steps on Pre-transitional Streamwise Elongated Streaks

On the Effect of Small Steps on Pre-transitional Streamwise Elongated Streaks

From primary instabilities to secondary instabilities in Görtler vortex flows

Estudo numérico de escoamento transicional sobre placa côncava com perturbações não estacionárias

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