Effects of Acoustic and Vortical Disturbances on the Turbulent Boundary Layer at Free-Stream Mach Number 0.5

1977 ◽  
Author(s):  
John A. Benek
Keyword(s):  
Boundary Layer ◽  
Mach Number ◽  
Turbulent Boundary Layer ◽  
Free Stream ◽  
Free Stream Mach Number

Subsonic Flow Over Open Cavities: Part 1 — Analytical Models and Numerical Investigations

2016 ◽  
Author(s):  
Weidong Shao ◽  
Jun Li
Keyword(s):  
Boundary Layer ◽  
Mach Number ◽  
Shear Layer ◽  
Layer Thickness ◽  
Boundary Layer Thickness ◽  
Feedback Loop ◽  
Subsonic Flow ◽  
Free Stream ◽  
Open Cavities ◽  
Free Stream Mach Number

The aeroacoustical oscillation and acoustic field generated by subsonic flow grazing over open cavities has been investigated analytically and numerically. The tone generation mechanism is elucidated with an analytical model based on the coupling between shear layer instabilities and acoustic feedback loop. The near field turbulent flow is obtained using two-dimensional Large Eddy Simulation (LES). A special mesh is used to absorb propagating disturbances and prevent spurious numerical reflections. Comparisons with available experimental data demonstrate good agreement in both the frequency and amplitude of the aeroacoustical oscillation. The physical phenomenon of the noise generated by the feedback loop is discussed. The correlation analysis of primitive variables is also made to clarify the characteristics of wave propagation in space and time. The effects of free-stream Mach number and boundary layer thickness on pressure fluctuations within the cavity and the nature of the noise radiated to the far field are examined in detail. As free-stream Mach number increases velocity fluctuations and mass flux into the cavity increase, but the resonant Strouhal numbers slightly decrease. Both the resonant Strouhal numbers and sound pressure levels decrease with the increase of boundary layer thickness. Results indicate that the instability of the shear layer dominates both the frequency and amplitude of the aeroacoustical oscillation.

Second-order boundary-layer effects in hypersonic flow past axisymmetric blunt bodies

1964 ◽  
Vol 20 (4) ◽  
pp. 593-623 ◽  
Author(s):  
R. T. Davis ◽  
I. Flügge-Lotz
Keyword(s):  
Boundary Layer ◽  
Mach Number ◽  
Free Stream ◽  
Practical Interest ◽  
Second Order ◽  
The Body ◽  
Specific Flow ◽  
Flow Past ◽  
Free Stream Mach Number ◽  
Stability And Accuracy

First- and second-order boundary-layer theory are examined in detail for some specific flow cases of practical interest. These cases are for flows over blunt axisymmetric bodies in hypersonic high-altitude (or low density) flow where second-order boundary-layer quantities may become important. These cases consist of flow over a hyperboloid and a paraboloid both with free-stream Mach number infinity and flow over a sphere at free-stream Mach number 10. The method employed in finding the solutions is an implicit finite-difference scheme. It is found to exhibit both stability and accuracy in the examples computed. The method consists of starting near the stagnation-point of a blunt body and marching downstream along the body surface. Several interesting properties of the boundary layer are pointed out, such as the nature of some second-order boundary-layer quantities far downstream in the flow past a sphere and the effect of strong vorticity interaction on the second-order boundary layer in the flow past a hyperboloid. In several of the flow cases, results are compared with other theories and experiments.

scholarly journals Nonlinear unsteady streaks engendered by the interaction of free-stream vorticity with a compressible boundary layer

2017 ◽  
Vol 817 ◽  
pp. 80-121 ◽  
Author(s):  
Elena Marensi ◽  
Pierre Ricco ◽  
Xuesong Wu
Keyword(s):  
Boundary Layer ◽  
Mach Number ◽  
Wind Tunnel ◽  
Boundary Layers ◽  
Free Stream ◽  
Nonlinear Interactions ◽  
Compressible Boundary Layer ◽  
Displacement Effect ◽  
Free Stream Mach Number ◽  
First Time

The nonlinear response of a compressible boundary layer to unsteady free-stream vortical fluctuations of the convected-gust type is investigated theoretically and numerically. The free-stream Mach number is assumed to be of $O(1)$ and the effects of compressibility, including aerodynamic heating and heat transfer at the wall, are taken into account. Attention is focused on low-frequency perturbations, which induce strong streamwise-elongated components of the boundary-layer disturbances, known as streaks or Klebanoff modes. The amplitude of the disturbances is intense enough for nonlinear interactions to occur within the boundary layer. The generation and nonlinear evolution of the streaks, which acquire an $O(1)$ magnitude, are described on a self-consistent and first-principle basis using the mathematical framework of the nonlinear unsteady compressible boundary-region equations, which are derived herein for the first time. The free-stream flow is studied by including the boundary-layer displacement effect and the solution is matched asymptotically with the boundary-layer flow. The nonlinear interactions inside the boundary layer drive an unsteady two-dimensional flow of acoustic nature in the outer inviscid region through the displacement effect. A close analogy with the flow over a thin oscillating airfoil is exploited to find analytical solutions. This analogy has been widely employed to investigate steady flows over boundary layers, but is considered herein for the first time for unsteady boundary layers. In the subsonic regime the perturbation is felt from the plate in all directions, while at supersonic speeds the disturbance only propagates within the dihedron defined by the Mach line. Numerical computations are performed for carefully chosen parameters that characterize three practical applications: turbomachinery systems, supersonic flight conditions and wind tunnel experiments. The results show that nonlinearity plays a marked stabilizing role on the velocity and temperature streaks, and this is found to be the case for low-disturbance environments such as flight conditions. Increasing the free-stream Mach number inhibits the kinematic fluctuations but enhances the thermal streaks, relative to the free-stream velocity and temperature respectively, and the overall effect of nonlinearity becomes weaker. An abrupt deviation of the nonlinear solution from the linear one is observed in the case pertaining to a supersonic wind tunnel. Large-amplitude thermal streaks and the strong abrupt stabilizing effect of nonlinearity are two new features of supersonic flows. The present study provides an accurate signature of nonlinear streaks in compressible boundary layers, which is indispensable for the secondary instability analysis of unsteady streaky boundary-layer flows.

Effect of Wall Divergence on Sonic Flows in Solid Wall Tunnels

1962 ◽  
Vol 66 (614) ◽  
pp. 125-128
Author(s):  
D. Tirumalesa ◽  
B. Satyanarayana
Keyword(s):  
Boundary Layer ◽  
Mach Number ◽  
Free Stream ◽  
Solid Wall ◽  
Layer Growth ◽  
Wind Tunnels ◽  
Normal Value ◽  
Free Stream Mach Number ◽  
Boundary Layer Growth

The effect of wall divergence (in excess of the normal value given for compensating the Boundary Layer growth on the tunnel walls), on the simulation of Sonic flows in solid wall wind tunnels is presented in this note which is a condensed version of Ref. 1.Recently Spreiter showed that flows with free stream Mach number one can be simulated reasonably well in choked solid tunnels. Berndt and Petersohn showed that the thickening of the boundary layer on the walls of solid wall tunnels reduced the interference considerably. Wall divergence θg in excess of the normal one of about one degree (used for Boundary Layer compensation) may lead to favourable conditions for the thickening of the Boundary Layer and this appeared to be an interesting way of reducing the interference.

Boundary-layer Pitot and hot-wire surveys at a free-stream Mach number of about 20

AIAA Journal ◽  
1971 ◽  
Vol 9 (5) ◽  
pp. 826-834 ◽  
Author(s):  
M. C. FISCHER ◽  
D. V. MADDALON ◽  
L. M. WEINSTEIN ◽  
R. D. WAGNER
Keyword(s):  
Boundary Layer ◽  
Mach Number ◽  
Free Stream ◽  
Hot Wire ◽  
Free Stream Mach Number

On solutions of the compressible laminar boundary-layer equations and their behaviour near separation

1977 ◽  
Vol 80 (2) ◽  
pp. 279-292 ◽  
Author(s):  
T. Davies ◽  
G. Walker
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Mach Number ◽  
Skin Friction ◽  
Laminar Boundary Layer ◽  
Numerical Solutions ◽  
Free Stream ◽  
Suction Velocity ◽  
Boundary Layer Equations ◽  
Free Stream Mach Number

A numerical solution of the two-dimensional compressible laminar boundary-layer equations up to the point of separation is presented. For a particular mainstream velocity distribution it is necessary to specify the surface temperature (or the heat flux across the surface), the suction velocity, the free-stream Mach number and the viscosity-temperature relationship for a solution to be generated. The effect upon the position of separation of a hot or cold wall and of varying the free-stream Mach number is given special emphasis. The variations of the skin friction, heat transfer and various boundary-layer thicknesses for compressible flow past a circular cylinder and for flow with a linearly retarded mainstream were found. The behaviour of the solutions close to separation is investigated. Known functions which model the skin friction and heat transfer are introduced and are used to match the numerical solutions with the Buckmaster (1970) expansions.

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