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Tuesday, July 21, 2020 | History

2 edition of Influence of free-stream disturbances on boundary-layer transition found in the catalog.

Influence of free-stream disturbances on boundary-layer transition

Bill Harvey

Influence of free-stream disturbances on boundary-layer transition

by Bill Harvey

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  • 33 Currently reading

Published by National Aeronautics and Space Administration, Scientific and Technical Information Office, for sale by the National Technical Information Office in [Washington], Springfield, Va .
Written in English

    Subjects:
  • Boundary layer.,
  • Noise.,
  • Turbulence.

  • Edition Notes

    StatementWilliam D. Harvey.
    SeriesNASA technical memorandum -- 78635.
    ContributionsUnited States. National Aeronautics and Space Administration. Scientific and Technical Information Office.
    The Physical Object
    Pagination30 p. :
    Number of Pages30
    ID Numbers
    Open LibraryOL17118307M

    In engineering applications, the presence of free-stream disturbances promotes early breakdown to turbulence, and transition is said to “bypass” the classical Tollmien-Schlichting route. Numerical simulations of bypass transition reveal that high-frequency disturbances from the free stream are expelled by the boundary-layer shear –. To acquire insight into the role of free-stream turbulence on laminar-turbulent transition, the interaction between a boundary layer and an array of single-wavenumber vortices convected at the mean free-stream velocity is studied analytically and numerically. For small amplitudes, the effect of a spectrum can be obtained by superposition. The flow field is taken to be the sum of .

    x t = xt (Pa, us, p xk, k, Ma, free-stream disturbances) (1) in which x is transition position and p~, us, p6, M8 are as usual the density, t , viscosity, and Mach number at the outer edge of the boundary layer. k is the size of the roughness element and xk is the distance to the trip from the cone apex. influence of external disturbances on the boundary layer. Boundary layer flow with large initial disturbances, or equivalently high FST, requires less amplification to reach an amplitude that initiates transition, thus also has a lower. If the assumption that FST is the main operating condition effect, an.

    Measurements from heated boundary layers along a concave-curved test wall subject to high (initially 8 percent) free-stream turbulence intensity and strong (K = (ν/U ∞ 2) dU ∞ /dx) as high as 9 × 10 −6) acceleration are presented and ions for the experiments were chosen to roughly simulate those present on the downstream half of the pressure side of a gas . findings on influence of intense free stream (FST) turbulence on boundary layer transition. Experimental investigation was conducted in TsAGI T wind tunnel (WT). The distributions of intermittency over straight and swept wings models were used to specify the start and the end of transition zone.


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Influence of free-stream disturbances on boundary-layer transition by Bill Harvey Download PDF EPUB FB2

Influence of free-stream disturbances on boundary-layer transition. Washington: National Aeronautics and Space Administration, Scientific and Technical Information Office ; Springfield, Va.: for sale by the National Technical Information Service, (OCoLC) Material Type: Government publication, National government publication.

The study of transition under hypersonic conditions has increasingly become an attractive research topic. Hypersonic boundary layer transitions at low disturbance levels are caused by various flow instabilities, among which the first mode and the second mode are the most basic and important.

This is the companion volume on the effects of artificial disturbance on the transition process of a boundary layer over a flat plate. The artificial disturbance with the frequency in the range of second-mode instability is introduced into the boundary layer by glowing discharge on the surface of the plate.

Considerable experimental evidence exists which shows that free stream disturbances (the ratio of root-mean-square pressure fluctuations to mean values) in conventional wind tunnels increase with increasing Mach number at low supersonic to moderate hypersonic speeds.

In addition to local conditions, the free stream disturbance level influences transition behavior on simple Cited by: The initial stage of the natural transition process is known as the Receptivity phase and consists of the transformation of environmental disturbances – both acoustic (sound) and vortical (turbulence) – into small perturbations within the boundary layer.

The mechanisms by which these disturbances arise are varied and include freestream. When both free-stream fluctuations and wall roughness act on the boundary layer at the same time, transition is dominated by steady crossflow waves unless the incoming turbulence intensity is larger than about % for roughness amplitudes of about one tenth of the boundary-layer displacement thickness.

Abstract. We investigate the influence of free-stream turbulent vortical disturbances on a compressible laminar boundary layer by solving the unsteady linear boundary region equations for the velocity and temperature fluctuations. These equations describe the evolution of the perturbations when the boundary layer thickness becomes of the order of the transverse free-stream.

Local boundary-layer receptivity to a convected free-stream disturbance - Volume - A. DIETZ. The Influence of Wake Passing Frequency and Elevated Free Stream Turbulence Intensity on Transition in Low Response of a compressible laminar boundary layer to free-stream vortical disturbances.

Journal of Fluid Mechanics, Vol.Issue. This book is organized into two main topics—boundary layer control for low drag, and shock-induced separation and its prevention by design and boundary layer control.

It specifically discusses the nature of transition, effect of two-dimensional and isolated roughness on laminar flow, and progress in the design of low drag aerofoils. The present measurement campaign on the free-stream turbulence induced boundary layer transition scenario has provided a unique set of experimental data.

This new set of data has the potential to enhance the understanding of the effect of the free-stream turbulence characteristic length scales on the transition location and not only the.

Investigations of influence of Free Stream Turbulence and Acoustic Disturbances on the Laminar-Turbulent Transition on LV6 Airfoil and Swept Wing Models Conference Paper January with 7 Reads.

To acquire insight into the role of free-stream turbulence on laminar-turbulent transition, the interaction between a boundary layer and an array of single-wavenumber vortices convected at the mean free-stream velocity is studied analytically and numerically.

For small amplitudes, the effect of a spectrum can be obtained by superposition. Transition to the turbulent flow mode in the boundary layer of a flat plate for different free-stream turbulence scales Fluid Dynamics, Vol.

7, No. 3 Hypersonic boundary-layer transition in the presence of wind-tunnel noise. The influence of suction on step-induced boundary-layer transition has been experimentally investigated in the Cryogenic Ludwieg-Tube Goettingen at large chord Reynolds numbers (up to 16 10 6), Mach numbers from to and various streamwise pressure gradients by means of temperature-sensitive e imperfections, implemented as.

The nonlocalized receptivity of Falkner-Skan boundary layers is analyzed. An acoustic disturbance in the free stream interacts with a surface-generated disturbance to excite the natural boundary-layer instabilities. Results for the streamwise evolution of disturbances are presented along with receptivity amplitudes.

The influence of increasing of free-stream turbulence level on transition location was determined. The comparison is made of the results obtained with the boundary layer transition data for the straight wing with the same airfoil at similar external condition.

It was shown that at high and stationary disturbances (longitudinally-oriented. The laminar-turbulent transition has significant influence on determining the the free stream.

These disturbances may transfer energy to the boundary layer and an important role in the transition boundary layer, such as turbulence intensity of free stream, streamline curvature, flow pressure gradient, etc.

The influence of suction on step-induced boundary-layer transition has been experimentally investigated in the Cryogenic Ludwieg-Tube Goettingen at large.

An experimental study on the transition of a flat plate boundary layer was conducted in the large wind tunnel of the chair of fluid dynamics (LSTM) in Erlangen, Germany.

Although this is not an especially designed transition tunnel it was possible to maintain a stable laminar regime up to Re x =4x10^6, one of the highest transition Reynolds numbers achieved in a flat plate boundary layer. outer boundary layer and delay bypass transition.

The streaks which precede transition onset were weaker in amplitude than in the single-fluid configuration, and the stabilizing influence of the film step is the receptivity of the boundary layer to free-stream disturbances. Influence of measured freestream disturbances on hypersonic boundary-layer transition.

Free stream disturbances influence on hypersonic boundary layer transition Reynolds number in heated and unheated flow.Influence of glow discharge on evolution of disturbance in a hypersonic boundary layer: The effect of second mode Physics of Fluids, Vol.

32, No. 7 Experimental investigation of boundary layer transition over a delta wing at Mach number 6.This thesis provides insight into the origin of steady vortical free-stream disturbances, creation of streaks, and their influence on boundary layer transition.

Computational results are co-validated with published experimental observations of steady streaks, generated by the wake of .