Hypersonic boundary-layer transition in the presence of wind-tunnel noise.

Stainback, P. C.

doi:10.2514/3.6541

Cited by 27 publications

(5 citation statements)

References 6 publications

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“…In general, such facility-produced acoustic noise results in a significantly lower transition Reynolds number in laboratory experiments than that in flight conditions (Schneider 2001). Therefore, prior to possible applications of laboratory data to flight situations, systematic corrections have to be carried out by extrapolating empirical correlations between the transition Reynolds number and relevant parameters characterizing the acoustic disturbances (Stainback 1971). This imperative demand has been the main reason why the majority of experiments have focused on acoustic disturbances while few have considered vortical disturbances.…”

Section: Bypass Transition In Compressible Boundary Layersmentioning

confidence: 99%

Response of a compressible laminar boundary layer to free-stream vortical disturbances

Riccó

2007

J. Fluid Mech.

112

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As a first step towards understanding the role of free-stream turbulence in laminar–turbulent transition, we calculate the fluctuations induced by free-stream vortical disturbances in a compressible laminar boundary layer. As with the incompressible case investigated by Leibet al. (J. Fluid Mech. vol. 380, 1999, p. 169), attention is focused on components with long streamwise wavelength. The boundary-layer response is governed by the linearized unsteady boundary-region equations in the typical streamwise region where the local boundary-layer thickness δ* iscomparable with the spanwise length scale Λ of the disturbances. The compressible boundary-region equations are solved numerically for a single Fourier component to obtain the boundary-layer signature. The root-mean-square of the velocity and mass-flux fluctuations induced by a continuous spectrum of free-stream disturbances are computed by an appropriate superposition of the individual Fourier components.Low-frequency vortical disturbances penetrate into the boundary layer to form slowly modulating streamwise-elongated velocity streaks. In the compressible regime, vortical disturbances are found to induce substantial temperature fluctuations so that ‘thermalstreaks’ also form. They may have a significant effect on the secondary instability. The calculations indicate that for a vortical disturbance with a relatively large Λ, the induced boundary-layer fluctuation ultimately evolves into an amplifying wave. This is due to a receptivity mechanism, in which a vortical disturbance first excites a decaying quasi-three-dimensional Lam–Rott eigensolution. The latter then undergoes wavelength shortening to generate a spanwise pressure gradient, which eventually converts the Lam–Rott mode into an exponentially growing mode. The latter is recognized to bea highly oblique Tollmien–Schlichting wave. A parametric study suggests that this receptivity mechanism could be significant when the free-stream Mach number is larger than 0.8.

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Section: Bypass Transition In Compressible Boundary Layersmentioning

confidence: 99%

Response of a compressible laminar boundary layer to free-stream vortical disturbances

Riccó

2007

J. Fluid Mech.

112

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“…From a practical point of view, the fluctuating pressure on aerodynamic surfaces of flight vehicles plays an important role in vibrational loading and often leads to damaging effects as fatigue and flutter (Willmarth 1975;Blake 1986;Bull 1996). The freestream pressure fluctuations radiated from the turbulent boundary layer on the nozzle wall in a conventional hypersonic wind tunnel is largely responsible for the genesis of tunnel background disturbances (commonly referred to as tunnel noise) (Laufer 1964;Stainback 1971;Pate 1978). Such facility disturbances significantly impact laminar-turbulent transition behavior of the test article, leading to an earlier onset of transition relative to that in a flight environment or in a quiet tunnel (Schneider 2001).…”

Section: Introductionmentioning

confidence: 99%

Pressure fluctuations induced by a hypersonic turbulent boundary layer

2016

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Direct numerical simulations (DNS) are used to examine the pressure fluctuations generated by a spatially developed Mach 5.86 turbulent boundary layer. The unsteady pressure field is analysed at multiple wall-normal locations, including those at the wall, within the boundary layer (including inner layer, the log layer, and the outer layer), and in the free stream. The statistical and structural variations of pressure fluctuations as a function of wall-normal distance are highlighted. Computational predictions for mean-velocity profiles and surface pressure spectrum are in good agreement with experimental measurements, providing a first ever comparison of this type at hypersonic Mach numbers. The simulation shows that the dominant frequency of boundary-layer-induced pressure fluctuations shifts to lower frequencies as the location of interest moves away from the wall. The pressure wave propagates with a speed nearly equal to the local mean velocity within the boundary layer (except in the immediate vicinity of the wall) while the propagation speed deviates from Taylor’s hypothesis in the free stream. Compared with the surface pressure fluctuations, which are primarily vortical, the acoustic pressure fluctuations in the free stream exhibit a significantly lower dominant frequency, a greater spatial extent, and a smaller bulk propagation speed. The free-stream pressure structures are found to have similar Lagrangian time and spatial scales as the acoustic sources near the wall. As the Mach number increases, the free-stream acoustic fluctuations exhibit increased radiation intensity, enhanced energy content at high frequencies, shallower orientation of wave fronts with respect to the flow direction, and larger propagation velocity.

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“…Early work suggested that pressure fluctuations measured on the surface of a sharp cone under a laminar boundary layer were equal to the freestream pressure fluctuations. [16][17][18][19] Stainback et al 17 conducted experiments that suggested that the freestream tunnel noise was not attenuated through the cone shock. This meant that the acoustic disturbances in the tunnel freestream entered the model laminar boundary layer and remained constant.…”

Section: Introductionmentioning

confidence: 99%

Hypersonic Wind-Tunnel Measurements of Boundary-Layer Pressure Fluctuations

Casper

2009

39th AIAA Fluid Dynamics Conference

107

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During atmospheric reentry, hypersonic vehicles are subjected to high levels of boundarylayer pressure fluctuations. To improve understanding and prediction of these fluctuations, measurements of surface pressure fluctuations on a 7 • sharp cone were conducted in Sandia's Hypersonic Wind Tunnel under noisy flow and in Purdue University's Boeing/AFOSR Mach-6 Quiet Tunnel under noisy and quiet flow. Fluctuations under laminar boundary layers reflected tunnel noise levels. Laminar boundary-layer measurements under quiet flow were an order of magnitude lower than under noisy flow. Transition on the model only occurred under noisy flow, and fluctuations peaked during transition. The transition location, marked by the peak, was predicted using tunnel noise parameters (Pate's correlation). Turbulent boundary-layer fluctuations were lower than transitional fluctuations and also reflected tunnel noise levels. Measurements of second-mode waves showed the waves started to grow under a laminar boundary layer, saturated, and then broke down near the peak in transitional pressure fluctuations. Nomenclature δ * boundary-layer displacement thickness φ cone azimuthal angle τ w nozzle wall shear stress c tunnel test section circumference c aerodynamic-noise-transition correlation size parameter c 1 test section circumference of a 0.305 × 0.305 m tunnel C F II mean turbulent skin-friction coefficient calculated using method of Van-Driest II M freestream Mach number M e Mach number at boundary-layer edge

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Hypersonic boundary-layer transition in the presence of wind-tunnel noise.

Cited by 27 publications

References 6 publications

Response of a compressible laminar boundary layer to free-stream vortical disturbances

Response of a compressible laminar boundary layer to free-stream vortical disturbances

Pressure fluctuations induced by a hypersonic turbulent boundary layer

Hypersonic Wind-Tunnel Measurements of Boundary-Layer Pressure Fluctuations

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