Receptivity coefficients at excitation of cross-flow waves due to scattering of free-stream vortices on surface vibrations

2016 ◽  
Vol 793 ◽  
pp. 162-208 ◽  
Author(s):  
V. I. Borodulin ◽  
A. V. Ivanov ◽  
Y. S. Kachanov ◽  
A. P. Roschektaev
Keyword(s):  
Free Stream ◽  
Cross Flow ◽  
Fourier Space ◽  
Streamwise Direction ◽  
Swept Wing ◽  
Incident Flow ◽  
Model Surface ◽  
Sweep Angle ◽  
Wing Model ◽  
Surface Vibrations

This paper is devoted to an experimental investigation of receptivity of a laminar swept-wing boundary layer due to scattering of free-stream vortices on localized (in the streamwise direction) surface vibrations. The experiments were conducted under completely controlled disturbance conditions by means of a hot-wire anemometer on a model of a swept wing with a sweep angle of 25°. Both the free-stream vortices and the surface vibrations were generated by disturbance sources; their frequency–wavenumber spectra were measured thoroughly. The free-stream vorticity vectors were directed perpendicular to the incident-flow velocity vector and parallel to the swept-wing-model surface. The linearity of the receptivity mechanism under investigation (in a sense that the corresponding receptivity coefficients are independent of the disturbances amplitudes) has been checked carefully. The main goal of this experiment was to estimate the vibration-vortex receptivity coefficients as functions of the disturbance frequency, spanwise wavenumber and vortex offset parameter. This goal has been attained. Being defined in Fourier space, the obtained receptivity coefficients are independent of the specific surface vibration shape and can be used for verification of various receptivity theories.

Receptivity coefficients at excitation of cross-flow waves by free-stream vortices in the presence of surface roughness

2013 ◽  
Vol 716 ◽  
pp. 487-527 ◽  
Author(s):  
V. I. Borodulin ◽  
A. V. Ivanov ◽  
Y. S. Kachanov ◽  
A. P. Roschektaev
Keyword(s):  
Surface Roughness ◽  
Free Stream ◽  
Cross Flow ◽  
Leading Edge ◽  
Vortex Street ◽  
Swept Wing ◽  
Model Surface ◽  
Wing Model ◽  
Roughness Elements ◽  
The Stability

AbstractThe present experimental study is devoted to examination of the vortex receptivity mechanism associated with excitation of unsteady cross-flow (CF) waves due to scattering of unsteady free-stream vortices on localized steady surface non-uniformities (roughness). The measurements are carried out in a low-turbulence wind tunnel by means of a hot-wire anemometer in a boundary layer developing over a $25\textdegree $ swept-wing model. The harmonic-in-time free-stream vortices were excited by a thin vibrating wire located upstream of the experimental-model leading edge and represented a kind of small-amplitude von Kármán vortex street with spanwise orientation of the generated instantaneous vorticity vectors. The controlled roughness elements (the so-called ‘phased roughness’) were placed on the model surface. This roughness had a special shape, which provided excitation of CF-waves having basically some predetermined (required) spanwise wavenumbers. The linearity of the stability and receptivity mechanisms under study was checked accurately by means of variation of both the free-stream-vortex amplitude and the surface roughness height. These experiments were directed to obtaining the amplitudes and phases of the vortex-roughness receptivity coefficients for a number of vortex disturbance frequencies. The vortex street position with respect to the model surface (the vortex offset parameter) was also varied. The receptivity characteristics obtained experimentally in Fourier space are independent of the particular roughness shape, and can be used for validation of receptivity theories.

Free-stream turbulence and the development of cross-flow disturbances

2013 ◽  
Vol 735 ◽  
pp. 347-380 ◽  
Author(s):  
Robert S. Downs ◽  
Edward B. White
Keyword(s):  
Surface Roughness ◽  
Flow Problem ◽  
Free Stream ◽  
Flow Instability ◽  
Cross Flow ◽  
Stream Velocity ◽  
Swept Wing ◽  
Free Stream Turbulence ◽  
Flow Disturbances ◽  
The Cross

AbstractThe cross-flow instability that arises in swept-wing boundary layers has resisted attempts to describe the path from disturbance initiation to transition. Following concerted research efforts, surface roughness and free-stream turbulence have been identified as the leading providers of initial disturbances for cross-flow instability growth. Although a significant body of work examines the role of free-stream turbulence in the cross-flow problem, the data more relevant to the flight environment (turbulence intensities less than 0.07 %) are sparse. A series of recent experiments indicates that variations within this range may affect the initiation or growth of cross-flow instability amplitudes, hindering comparison among results obtained in different disturbance environments. To address this problem, a series of wind tunnel experiments is performed in which the free-stream turbulence intensity is varied between 0.02 % and 0.2 % of free-stream velocity,${U}_{\infty } $. Measurements of the stationary and travelling mode amplitudes are made in the boundary layer of a 1.83 m chord,$45{{}^\circ} $swept-wing model. These results are compared to those of similar experiments at higher turbulence levels to broaden the current knowledge of this portion of the cross-flow problem. It is observed that both free-stream turbulence and surface roughness contribute to the initiation of unsteady disturbances, and that free-stream turbulence affects the development of both stationary and unsteady cross-flow disturbances. For the range tested, enhanced free-stream turbulence advances the transition location except when a subcritically spaced roughness array is employed.

Influence Of Vortex Disturbances On Laminar-Turbulent Transition In Supersonic Boundary Layer On A Swept Wing At M = 2.5

2016 ◽  
Vol 11 (1) ◽  
pp. 16-22
Author(s):  
Andrey Dryasov ◽  
Yuri Yermolaev ◽  
Aleksandr Kosinov ◽  
Nikolay Semionov ◽  
Aleksandr Semionov
Keyword(s):  
Boundary Layer ◽  
Supersonic Boundary Layer ◽  
Free Flow ◽  
Experimental Investigations ◽  
Swept Wing ◽  
Sweep Angle ◽  
Wing Model ◽  
Turbulent Transition ◽  
Different Diameters ◽  
Vortex Disturbances

Experimental investigations of the receptivity of a supersonic boundary layer on a swept wing to the vortex perturbations were made at Mach 2.5. A symmetrical wing model with a 45 sweep angle and a 3-percent-thick circular-arc airfoil was used in experiments. The investigation of the vortex disturbances structure generated by a wire was done. It has been shown that the level of disturbances in the free flow increases with increasing wire diameter. The positions of the laminarturbulent transition at different diameters of wire were determined and data of the disturbances development in the model boundary layer were obtained. It was found that an increase in the intensity of vortex disturbances in the free flow leads to an earlier transition. Receptivity coefficients were determined.

scholarly journals Study on Riblet Drag Reduction Considering the Effect of Sweep Angle

Energies ◽  
2019 ◽  
Vol 12 (17) ◽  
pp. 3386 ◽  
Author(s):  
Yufei Zhang ◽  
Yuhui Yin
Keyword(s):  
Drag Reduction ◽  
Channel Flow ◽  
Flow Direction ◽  
Cross Flow ◽  
Friction Drag ◽  
Swept Wing ◽  
Sweep Angle ◽  
Pressure Drag ◽  
The Cross ◽  
Inclined Angle

This study computationally evaluates the riblet drag reduction effect considering the effect of sweep angle. An implicit large eddy simulation is performed on a channel flow and an infinite swept wing. First, three different inclined angles between the riblets and the flow direction are tested in the channel flow. The results show that with increases in the inclined angle, the friction drag decreases, while the pressure drag increases approximately quadratically. The riblets with a 30° inclined angle increase the total drag of the channel flow. Then, an infinite wing with a 30° swept angle with and without riblets is studied. The riblets demonstrate satisfactory drag reduction efficiency because the cross flow over most parts of the wing is mild. The lift and friction drag follow the relation of the cosine law of a swept wing. Moreover, the cross flow and the turbulence fluctuation are suppressed by the riblets.

Swept-wing boundary-layer receptivity to surface non-uniformities

2002 ◽  
Vol 461 ◽  
pp. 93-126 ◽  
Author(s):  
V. R. GAPONENKO ◽  
A. V. IVANOV ◽  
Y. S. KACHANOV ◽  
J. D. CROUCH
Keyword(s):  
Boundary Layer ◽  
Flow Instability ◽  
Normal Modes ◽  
Cross Flow ◽  
Swept Wing ◽  
Surface Vibration ◽  
Theoretical Approaches ◽  
Surface Vibrations ◽  
Wave Trains ◽  
Good Agreement

The linear receptivity of a swept-wing three-dimensional boundary layer is studied experimentally and theoretically. Cross-flow instability normal modes are excited by means of surface vibration or roughness perturbations. The resulting disturbances are investigated, and the normal modes are linked to the source perturbations. Experiments are performed under controlled disturbance conditions with a time-harmonic source that is localized in the spanwise direction. A localized surface vibration is used to excite wave trains consisting of cross-flow instability waves. Normal oblique modes (harmonic in time and space) are obtained by Fourier decomposition of the wave trains. This provides the spatial variation of the normal modes and, in particular, the initial amplitudes and phases of the modes at the source location. The shape of the surface vibrator is measured and used to determine the complex receptivity coefficients for the normal modes (i.e. for various spanwise wavenumbers, wave propagation angles, and disturbance frequencies – including zero frequency). The experimental receptivity coefficients are independent of the specific shape of the surface non-uniformities and can be directly compared with calculations. The theoretical work is based on a linear approximation to the disturbance source – valid for small forcing amplitudes. Like earlier studies on roughness-induced receptivity, the basic flow is locally assumed to satisfy the parallel-flow approximation. The modal response for the cross-flow instability is determined from the residue associated with the least-stable eigenmode.A detailed quantitative comparison between the experimental and theoretical receptivity characteristics is carried out. Good agreement is found for the roughness–vibrational receptivity coefficients of the swept-wing boundary layer (especially for the most-unstable cross-flow modes) over a range of disturbance frequencies and spanwise wavenumbers. The theory correctly predicts the initial spectra for the travelling and stationary cross-flow instabilities excited by the surface vibrations and surface roughness, respectively. The good agreement between theory and experiment suggests that the linear receptivity theory can be used effectively in engineering methods for transition prediction. The experimental data can also be used for validation of other theoretical approaches to the problem.

Swept-wing boundary-layer receptivity

2012 ◽  
Vol 700 ◽  
pp. 490-501 ◽  
Author(s):  
David Tempelmann ◽  
Ardeshir Hanifi ◽  
Dan S. Henningson
Keyword(s):  
Boundary Layer ◽  
Surface Roughness ◽  
Free Stream ◽  
Stokes Equations ◽  
Cross Flow ◽  
Leading Edge ◽  
Navier Stokes ◽  
Flow Mode ◽  
Swept Wing ◽  
Worst Case

AbstractAdjoint solutions of the linearized incompressible Navier–Stokes equations are presented for a cross-flow-dominated swept-wing boundary layer. For the first time these have been computed in the region upstream of the swept leading edge and may therefore be used to predict receptivity to any disturbances of the incoming free stream as well as to surface roughness. In this paper we present worst-case scenarios, i.e. those external disturbances yielding maximum receptivity amplitudes of a steady cross-flow disturbance. In the free stream, such an ‘optimal’ disturbance takes the form of a streak which, while being convected downstream, penetrates the boundary layer and smoothly turns into a growing cross-flow mode. The ‘worst-case’ surface roughness has a wavy shape and is distributed in the chordwise direction. It is shown that, under such optimal conditions, the boundary layer is more receptive to surface roughness than to incoming free stream disturbances.

scholarly journals Features of the interaction of localized free-stream disturbances with the straight and swept wing boundary layer

2019 ◽  
Vol 1404 ◽  
pp. 012092
Author(s):  
M M Katasonov ◽  
V V Kozlov ◽  
A M Pavlenko ◽  
I A Sadovskii
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Swept Wing
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