Resonant interaction of wave packets in a boundary layer

1989 ◽  
Vol 23 (6) ◽  
pp. 857-861 ◽  
Author(s):  
M. B. Zel'man ◽  
B. V. Smorodskii
Keyword(s):  
Boundary Layer ◽  
Wave Packets ◽  
Resonant Interaction

Global three-dimensional optimal disturbances in the Blasius boundary-layer flow using time-steppers

2010 ◽  
Vol 650 ◽  
pp. 181-214 ◽  
Author(s):  
ANTONIOS MONOKROUSOS ◽  
ESPEN ÅKERVIK ◽  
LUCA BRANDT ◽  
DAN S. HENNINGSON
Keyword(s):  
Boundary Layer ◽  
Boundary Layer Flow ◽  
Wave Packets ◽  
Three Dimensional ◽  
Computational Domain ◽  
Initial Condition ◽  
Oblique Wave ◽  
Layer Flow ◽  
Optimal Disturbances ◽  
Matrix Free

The global linear stability of the flat-plate boundary-layer flow to three-dimensional disturbances is studied by means of an optimization technique. We consider both the optimal initial condition leading to the largest growth at finite times and the optimal time-periodic forcing leading to the largest asymptotic response. Both optimization problems are solved using a Lagrange multiplier technique, where the objective function is the kinetic energy of the flow perturbations and the constraints involve the linearized Navier–Stokes equations. The approach proposed here is particularly suited to examine convectively unstable flows, where single global eigenmodes of the system do not capture the downstream growth of the disturbances. In addition, the use of matrix-free methods enables us to extend the present framework to any geometrical configuration. The optimal initial condition for spanwise wavelengths of the order of the boundary-layer thickness are finite-length streamwise vortices exploiting the lift-up mechanism to create streaks. For long spanwise wavelengths, it is the Orr mechanism combined with the amplification of oblique wave packets that is responsible for the disturbance growth. This mechanism is dominant for the long computational domain and thus for the relatively high Reynolds number considered here. Three-dimensional localized optimal initial conditions are also computed and the corresponding wave packets examined. For short optimization times, the optimal disturbances consist of streaky structures propagating and elongating in the downstream direction without significant spreading in the lateral direction. For long optimization times, we find the optimal disturbances with the largest energy amplification. These are wave packets of Tollmien–Schlichting waves with low streamwise propagation speed and faster spreading in the spanwise direction. The pseudo-spectrum of the system for real frequencies is also computed with matrix-free methods. The spatial structure of the optimal forcing is similar to that of the optimal initial condition, and the largest response to forcing is also associated with the Orr/oblique wave mechanism, however less so than in the case of the optimal initial condition. The lift-up mechanism is most efficient at zero frequency and degrades slowly for increasing frequencies. The response to localized upstream forcing is also discussed.

Excitation Of Localized Wave Packet In 3d Supersonic Boundary Layer

2017 ◽  
Vol 12 (1) ◽  
pp. 57-65
Author(s):  
Alex Yatskih ◽  
Marina Rumenskikh ◽  
Yuri Yermolaev ◽  
Aleksandr Kosinov ◽  
Nikolay Semionov ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Wave Packet ◽  
Wave Packets ◽  
Leading Edge ◽  
Supersonic Boundary Layer ◽  
Swept Wing ◽  
Sweep Angle ◽  
Asymmetric Shape ◽  
Pulse Electric ◽  
Pulse Electric Discharge

The results of experimental study of excitation of localized in time and space controlled disturbances (wave packets) in a supersonic swept-wing boundary layer are presented. The experiments were performed at Mach number M = 2 on the model of wing with a lenticular profile and a 40 degrees sweep angle of the leading edge at zero angle of attack. Wave packets were generated by a pulse electric discharge on the surface of the model. A structure of controlled wave packet was studied. It was found that the wave packet has an asymmetric shape. Comparison with the case of twodimensional boundary layer was done.

Three-wave resonant interaction involving unstable wave packets

2003 ◽  
Vol 48 (8) ◽  
pp. 441-446
Author(s):  
S. Yu. Annenkov ◽  
N. N. Romanova
Keyword(s):  
Wave Packets ◽  
Resonant Interaction ◽  
Unstable Wave

Excitation of internal waves in a stably-stratified atmosphere with considerable wind-shear

1968 ◽  
Vol 32 (1) ◽  
pp. 145-171 ◽  
Author(s):  
A. A. Townsend
Keyword(s):  
Boundary Layer ◽  
Internal Waves ◽  
Wind Shear ◽  
Wave Packets ◽  
Normal Modes ◽  
Wave Number ◽  
Spectral Energy ◽  
Air Turbulence ◽  
Wave Numbers ◽  
Horizontal Wave

The rate of generation of internal waves by a thin turbulent boundary layer was calculated in a previous paper for a stably-stratified atmosphere with no significant wind-shear outside the boundary layer by considering the excitation of normal modes of wave propagation. By using the concept of wave-packets propagating upwards from the boundary layer, the effects of wind-shear can be included. Conditions for the validity of the approximation are given. In general, the spectral distribution of wave-energy at a particular height takes large values in two bands of horizontal wave-number, one band deriving from wave-packets undergoing internal reflexion near that height and the other from wave-packets of very small local frequency that accumulate there. The ‘reflexion’ wave-numbers are dominant if the wind increases with height and the ‘accumulation’ wave-numbers if the wind initially decreases with height. The spectral energy distributions and intensities of the wave-motion are discussed in more detail for an atmosphere of uniform stability and unidirectional wind-shear. The accumulation process may lead to instability or overturning of the waves, and estimates are made of the probable scale and intensity of the ‘clear-air’ turbulence produced. An interesting point is that the rate of energy loss from the boundary layer by radiation of internal waves turns out to be comparable with the rate of production in the outer nine-tenths of the layer, both for atmospheric boundary layers and for the surface layer of the ocean. It seems likely that radiation limits the layer thickness to some extent.

Evolution of wave packets in supersonic flat-plate boundary layer

2015 ◽  
Vol 22 (1) ◽  
pp. 17-27 ◽  
Author(s):  
A. A. Yatskikh ◽  
Yu. G. Ermolaev ◽  
A. D. Kosinov ◽  
N. V. Semionov
Keyword(s):  
Boundary Layer ◽  
Flat Plate ◽  
Wave Packets ◽  
Plate Boundary ◽  
Flat Plate Boundary Layer

Development of the Wave Packets-Forerunners at the Straight Wing Boundary Layer

2012 ◽  
Vol 7 (1) ◽  
pp. 28-37
Author(s):  
Mikhail Katasonov ◽  
Pavel Мotyrev ◽  
Dmitriy Sboev ◽  
Viktor Kozlov ◽  
Quentin Evers
Keyword(s):  
Boundary Layer ◽  
Flow Velocity ◽  
Wave Packets ◽  
Drastic Change ◽  
Local Velocity ◽  
Single Wire ◽  
Localized Structures ◽  
Velocity Gradients ◽  
Flow Pressure ◽  
Straight Wing

This work is devoted to the study of wave packets (forerunners) formed in straight wing boundary layers in the regions preceding a drastic change in the flow velocity inside the boundary layer, near the fronts of streaks. The investigations were carried out in the subsonic low turbulence wind tunnel. Measurements of the flow fields were carried out using a single-wire probe of a constant-temperature hot-wire anemometer. It was shown that the localized structures, which modeled artificially from incoming flow, generate streaks in a boundary layer. The wave packets (forerunners) are appears in the regions preceding a drastic change of flow velocity inside the boundary layer at the streaks fronts. The characteristics of the forerunners, affected by the external-flow pressure gradient, intensity of streak, and local velocity gradients near the front of the streak were investigated

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