Crossflow instability in a hypersonic boundary layer

2016 ◽  
Vol 808 ◽  
pp. 224-244 ◽  
Author(s):  
Stuart A. Craig ◽  
William S. Saric
Keyword(s):  
Boundary Layer ◽  
Frequency Band ◽  
Stationary Wave ◽  
Secondary Instability ◽  
Transition To Turbulence ◽  
Type I ◽  
Angle Of Incidence ◽  
Adiabatic Wall ◽  
Low Speed ◽  
Crossflow Instability

The crossflow instability in a hypersonic, laminar boundary layer is investigated using point measurements inside the boundary layer for the first time. Experiments are performed on a 7° right, circular cone with an adiabatic wall condition at 5.6° angle of incidence in the low-disturbance Mach 6 Quiet Tunnel at Texas A&M University. Measurements are made with a constant-temperature hot-wire anemometer system with a frequency response up to 180 kHz. Stationary crossflow waves are observed to grow and saturate. A travelling wave coexists with the stationary wave and occurs in a frequency band centred around 35 kHz. A type-I secondary instability is also observed in a frequency band centred around 110 kHz. The behaviour of all three modes is largely consistent with their low-speed counterparts prior to saturation of the stationary wave. Afterward, the behaviour remains in partial agreement with the low-speed case. Neither type-II secondary instability nor transition to turbulence are observed in this study.

scholarly journals Three-dimensional organisation of primary and secondary crossflow instability

2016 ◽  
Vol 799 ◽  
pp. 200-245 ◽  
Author(s):  
Jacopo Serpieri ◽  
Marios Kotsonis
Keyword(s):  
Boundary Layer ◽  
Spectral Characteristics ◽  
Three Dimensional ◽  
Low Frequency ◽  
High Energy ◽  
Secondary Instability ◽  
Type I ◽  
Type Iii ◽  
Topological Features ◽  
Crossflow Instability

An experimental investigation of primary and secondary crossflow instability developing in the boundary layer of a $45^{\circ }$ swept wing at a chord Reynolds number of $2.17\times 10^{6}$ is presented. Linear stability theory is applied for preliminary estimation of the flow stability while surface flow visualisation using fluorescent oil is employed to inspect the topological features of the transition region. Hot-wire anemometry is extensively used for the investigation of the developing boundary layer and identification of the statistical and spectral characteristics of the instability modes. Primary stationary, as well as unsteady type-I (z-mode), type-II (y-mode) and type-III modes are detected and quantified. Finally, three-component, three-dimensional measurements of the transitional boundary layer are performed using tomographic particle image velocimetry. This research presents the first application of an optical experimental technique for this type of flow. Among the optical techniques, tomographic velocimetry represents, to date, the most advanced approach allowing the investigation of spatially correlated flow structures in three-dimensional fields. Proper orthogonal decomposition (POD) analysis of the captured flow fields is applied to this goal. The first POD mode features a newly reported structure related to low-frequency oscillatory motion of the stationary vortices along the spanwise direction. The cause of this phenomenon is only conjectured. Its effect on transition is considered negligible but, given the related high energy level, it needs to be accounted for in experimental investigations. Secondary instability mechanisms are captured as well. The type-III mode corresponds to low-frequency primary travelling crossflow waves interacting with the stationary ones. It appears in the inner upwelling region of the stationary crossflow vortices and is characterised by elongated structures approximately aligned with the axis of the stationary waves. The type-I secondary instability consists instead of significantly inclined structures located at the outer upwelling region of the stationary vortices. The much narrower wavelength and higher advection velocity of these structures correlate with the higher-frequency content of this mode. The results of the investigation of both primary and secondary instability from the exploited techniques agree with and complement each other and are in line with existing literature. Finally, they present the first experimental observation of the secondary instability structures under natural flow conditions.

scholarly journals An experiment on the adiabatic compressible turbulent boundary layer in adverse and favourable pressure gradients

1972 ◽  
Vol 51 (4) ◽  
pp. 657-672 ◽  
Author(s):  
J. E. Lewis ◽  
R. L. Gran ◽  
T. Kubota
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradients ◽  
Mean Flow ◽  
Adiabatic Wall ◽  
Flow Measurements ◽  
Low Speed ◽  
Velocity Transformation ◽  
Tunnel Model ◽  
Gradient Parameter

A wind-tunnel model was developed to study the two-dimensional turbulent boundary layer in adverse and favourable pressure gradients with out the effects of streamwise surface curvature. Experiments were performed at Mach 4 with an adiabatic wall, and mean flow measurements within the boundary layer were obtained. The data, when viewed in the velocity transformation suggested by Van Driest, show good general agreement with the composite boundary-layer profile developed for the low-speed turbulent boundary layer. Moreover, the pressure gradient parameter suggested by Alber & Coats was found to correlate the data with low-speed results.

LES Prediction of Wall-Pressure Fluctuations and Noise of a Low-Speed Airfoil

2009 ◽  
Vol 8 (3) ◽  
pp. 177-197 ◽  
Author(s):  
Meng Wang ◽  
Stephane Moreau ◽  
Gianluca Iaccarino ◽  
Michel Roger
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Transition To Turbulence ◽  
Trailing Edge ◽  
Frequency Spectra ◽  
Potential Core ◽  
Low Speed ◽  
Wall Pressure Fluctuations

This paper discusses the prediction of wall-pressure fluctuations and noise of a low-speed flow past a thin cambered airfoil using large-eddy simulation (LES). The results are compared with experimental measurements made in an open-jet anechoic wind-tunnel at Ecole Centrale de Lyon. To account for the effect of the jet on airfoil loading, a Reynolds-averaged Navier-Stokes calculation is first conducted in the full wind-tunnel configuration, and the mean velocities from this calculation are used to define the boundary conditions for the LES in a smaller domain within the potential core of the jet. The LES flow field is characterized by an attached laminar boundary layer on the pressure side of the airfoil and a transitional and turbulent boundary layer on the suction side, in agreement with experimental observations. An analysis of the unsteady surface pressure field shows reasonable agreement with the experiment in terms of frequency spectra and spanwise coherence in the trailing-edge region. In the nose region, characterized by unsteady separation and transition to turbulence, the wall-pressure fluctuations are highly sensitive to small perturbations and thus diffcult to predict or measure with certainty. The LES, in combination with the Ffowcs Williams and Hall solution to the Lighthill equation, also predicts well the radiated trailing-edge noise. A finite-chord correction is derived and applied to the noise prediction, which is shown to improve the overall agreement with the experimental sound spectrum.

Numerical investigation of transition in a boundary layer subjected to favourable and adverse streamwise pressure gradients and elevated free stream turbulence

2015 ◽  
Vol 781 ◽  
pp. 52-86 ◽  
Author(s):  
Joshua R. Brinkerhoff ◽  
Metin I. Yaras
Keyword(s):  
Boundary Layer ◽  
Pressure Gradient ◽  
Free Stream ◽  
Large Strain ◽  
Adverse Pressure Gradient ◽  
Secondary Instability ◽  
Transition To Turbulence ◽  
Pressure Gradients ◽  
Turbulent Spot ◽  
Free Stream Turbulence

Laminar-to-turbulent transition of a boundary layer subjected to streamwise pressure gradients and elevated free stream turbulence is computed through direct numerical simulation. The streamwise pressure distribution and elevated free stream turbulence levels mimic the conditions present on the suction side of highly-cambered airfoils. Longitudinal streamwise streaks form in the laminar boundary layer through the selective inclusion of low-frequency disturbances from the free stream turbulence. The spanwise spacing normalized by local inner variables indicates stabilization of the streaks occurs by the favourable pressure gradient and prevents the development of secondary streak instability modes until downstream of the suction peak. Two distinct processes are found to trigger transition to turbulence in the adverse pressure gradient region of the flow. One involves the development of varicose secondary instability of individual low-speed streaks that results in their breakdown and the formation and growth of discrete turbulent spots. The other involves a rapid amplification of free stream disturbances in the inflectional boundary layer in the adverse pressure gradient region that results in a largely homogeneous breakdown to turbulence across the span. The effect of high-frequency free stream disturbances on the streak secondary instability and on the nonlinear processes within the growing turbulent spot are analysed through the inviscid transport of instantaneous vorticity. The results suggest that free stream turbulence contributes to the growth of the turbulent spot by generating large strain rates that activate vortex-stretching and tilting processes within the spot.

On the laminar–turbulent transition of the rotating-disk flow: the role of absolute instability

2014 ◽  
Vol 745 ◽  
pp. 132-163 ◽  
Author(s):  
Shintaro Imayama ◽  
P. Henrik Alfredsson ◽  
R. J. Lingwood
Keyword(s):  
Boundary Layer ◽  
Rotating Disk ◽  
Reynolds Numbers ◽  
Secondary Instability ◽  
Transition To Turbulence ◽  
Absolute Instability ◽  
Nonlinear Saturation ◽  
Global Mode ◽  
Turbulent Transition ◽  
Laminar Turbulent Transition

AbstractThis paper describes a detailed experimental study using hot-wire anemometry of the laminar–turbulent transition region of a rotating-disk boundary-layer flow without any imposed excitation of the boundary layer. The measured data are separated into stationary and unsteady disturbance fields in order to elaborate on the roles that the stationary and the travelling modes have in the transition process. We show the onset of nonlinearity consistently at Reynolds numbers, $R$, of $\sim $510, i.e. at the onset of Lingwood’s (J. Fluid Mech., vol. 299, 1995, pp. 17–33) local absolute instability, and the growth of stationary vortices saturates at a Reynolds number of $\sim $550. The nonlinear saturation and subsequent turbulent breakdown of individual stationary vortices independently of their amplitudes, which vary azimuthally, seem to be determined by well-defined Reynolds numbers. We identify unstable travelling disturbances in our power spectra, which continue to grow, saturating at around $R=585$, whereupon turbulent breakdown of the boundary layer ensues. The nonlinear saturation amplitude of the total disturbance field is approximately constant for all considered cases, i.e. different rotation rates and edge Reynolds numbers. We also identify a travelling secondary instability. Our results suggest that it is the travelling disturbances that are fundamentally important to the transition to turbulence for a clean disk, rather than the stationary vortices. Here, the results appear to show a primary nonlinear steep-fronted (travelling) global mode at the boundary between the local convectively and absolutely unstable regions, which develops nonlinearly interacting with the stationary vortices and which saturates and is unstable to a secondary instability. This leads to a rapid transition to turbulence outward of the primary front from approximately $R=565$ to 590 and to a fully turbulent boundary layer above 650.

Experiments on localized secondary instability in bypass boundary layer transition

2017 ◽  
Vol 817 ◽  
pp. 217-263 ◽  
Author(s):  
G. Balamurugan ◽  
A. C. Mandal
Keyword(s):  
Boundary Layer ◽  
Shear Layer ◽  
Free Stream ◽  
Secondary Instability ◽  
Boundary Layer Transition ◽  
Convection Velocity ◽  
Layer Transition ◽  
Time Resolved ◽  
Piv Measurements ◽  
Low Speed

An experimental study on localized secondary instability of unsteady streamwise streaks in bypass boundary layer transition under an elevated level of free-stream turbulence has been carried out mainly using the particle image velocimetry (PIV) technique. Simultaneous orthogonal dual-plane PIV measurements were performed for a concurrent examination of the transitional flow features in both wall-normal and spanwise planes. These quantitative and simultaneous visualizations clearly show the wall-normal view of a low-speed streak undergoing sinuous/varicose motion in the spanwise plane. An oscillating shear layer in the wall-normal plane is found to be associated with the sinuous/varicose streak oscillation in the spanwise plane. Further, these measurements indicate that a localized secondary instability wavepacket can originate near the boundary layer edge. The time-resolved PIV measurements in the wall-normal plane clearly show how an instability develops on a lifted-up inclined shear layer and leads to flow breakdown. The estimated wavelength and convection velocity of such instabilities are found to compare well with those calculated from the one-dimensional linear stability analysis of the spatially averaged velocity profiles associated with the lifted-up shear layers. The time-resolved PIV measurements in the spanwise plane also facilitate quantitative visualizations of sinuous and varicose instabilities. These measurements experimentally confirm that a varicose instability at the juncture of an incoming high-speed streak and a downstream low-speed streak can eventually lead to the formation of lambda structures. The estimated convection velocity, wavelength and growth rate of these instabilities are found to be consistent with the numerical results reported in the literature. Moreover, the streak secondary instability is found to be apparent in the velocity contours, while the estimated streak amplitude is approximately 30 % of the free-stream velocity.

EXPERIMENTAL INVESTIGATION OF FLOW RESPONSE TO STATIONARY DISTURBANCE IN ROTATING-DISK FLOW

2019 ◽  
Vol XVI (2) ◽  
pp. 13-22
Author(s):  
Muhammad Ehtisham Siddiqui
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Three Dimensional ◽  
Rotating Disk ◽  
Careful Analysis ◽  
Laboratory Frame ◽  
Transition To Turbulence ◽  
Turbulent Regime ◽  
Mean Velocity ◽  
Layer Flow

Three-dimensional boundary-layer flow is well known for its abrupt and sharp transition from laminar to turbulent regime. The presented study is a first attempt to achieve the target of delaying the natural transition to turbulence. The behaviour of two different shaped and sized stationary disturbances (in the laboratory frame) on the rotating-disk boundary layer flow is investigated. These disturbances are placed at dimensionless radial location (Rf = 340) which lies within the convectively unstable zone over a rotating-disk. Mean velocity profiles were measured using constant-temperature hot-wire anemometry. By careful analysis of experimental data, the instability of these disturbance wakes and its estimated orientation within the boundary-layer were investigated.

Robustness and Transition to Turbulence in Boundary Layer Flows

2001 ◽  
Author(s):  
John C. Doyle
Keyword(s):  
Boundary Layer ◽  
Transition To Turbulence ◽  
Boundary Layer Flows

scholarly journals Shock-induced heating and transition to turbulence in a hypersonic boundary layer

2020 ◽  
Vol 909 ◽  
Author(s):  
Lin Fu ◽  
Michael Karp ◽  
Sanjeeb T. Bose ◽  
Parviz Moin ◽  
Javier Urzay
Keyword(s):  
Boundary Layer ◽  
Transition To Turbulence ◽  
Hypersonic Boundary Layer

Abstract

The effects of Coriolis force and radial stretch on the convective instability characteristics of the Bödewadt flow

2021 ◽  
pp. 095440622110071
Author(s):  
Dip Mukherjee ◽  
Bikash Sahoo
Keyword(s):  
Boundary Layer ◽  
Coriolis Force ◽  
Boundary Layer Flow ◽  
Convective Instability ◽  
Type I ◽  
Similarity Transformations ◽  
Instability Modes ◽  
Neutral Curves ◽  
Lower Disk ◽  
Layer Flow

The Bödewadt boundary-layer flow is induced by the rotation of a viscous fluid rotating with a constant angular velocity over a stationary disk. In this paper, the Bödewadt boundary-layer flow has been studied in the presence of the Coriolis force to observe the effect of radial stretch of the lower disk on the flow. For the first time in the literature, a numerical investigation of the effects of both stretching mechanism and the Coriolis force on the flow behaviour and on the convective instability characteristics of the above flow has been carried out. In this paper, the Kármán similarity transformations have been considered in order to convert the system of PDEs representing the momentum equations of the flow into a system of highly non-linear coupled ODEs and solved numerically to obtain the velocity profiles of the Bödewadt flow. Then, a convective instability analysis has been performed by using the Chebyshev collocation method in order to obtain the neutral curves. From the neutral curves it is observed that radial stretch has a globally stabilising effect on both the inviscid Type-I and the viscous Type-II instability modes. This underlying physical phenomena has been verified by performing an energy analysis of the flow. The results obtained excellently supports the previous works and will be prominently treated as a benchmark for our future studies.

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