Noise Associated With Supersonic Flight

1954 ◽  
Vol 58 (520) ◽  
pp. 239-245
Author(s):  
C. H. E. Warren
Keyword(s):  
Shear Flow ◽  
Boundary Layers ◽  
Inviscid Fluid ◽  
Supersonic Flight ◽  
Pressure Changes

Before discussing the noise associated with supersonic flight, it is pertinent to restate the sources of noise at subsonic speeds.As Lilley has pointed out, noise at subsonic speeds is due to turbulence, such as occurs in jets, wakes, boundary layers, and regions of separation, and to vortices and regions of shear flow. In all these types of flow viscosity plays a predominant part, and therefore at subsonic speeds the noise of an aircraft depends very much upon the viscosity of the fluid: in an inviscid fluid, an aircraft would make no noise, because, at subsonic speeds, the pressure changes induced by its motion would be too gradual to be audible.

The lift force on a spherical body in a rotational flow

1987 ◽  
Vol 183 ◽  
pp. 199-218 ◽  
Author(s):  
T. R. Auton
Keyword(s):  
Shear Flow ◽  
Lift Force ◽  
Spherical Body ◽  
Inviscid Fluid ◽  
Far Field ◽  
Rotational Flow ◽  
Field Calculation ◽  
Sphere Surface ◽  
Secondary Velocity

This paper concerns the flow about a sphere placed in a weak shear flow of an inviscid fluid. The secondary velocity resulting from advection of vorticity by the irrotational component of the flow is computed on the sphere surface, and on the upstream axis. The resulting lift force on the sphere is evaluated, and the result is confirmed by an analytical far-field calculation. The displacement of the stagnation streamline, far upstream of the sphere, is calculated more accurately than in previous papers.

Inviscid Shear Flow Analysis of Corner Eddies Ahead of a Channel Flow Contraction

1985 ◽  
Vol 107 (2) ◽  
pp. 212-217
Author(s):  
R. N. Meroney
Keyword(s):  
Shear Flow ◽  
Velocity Distribution ◽  
Equations Of Motion ◽  
Linear Equations ◽  
Flow Analysis ◽  
Inviscid Fluid ◽  
Flow Vorticity ◽  
Flow Geometry ◽  
Linear Shear ◽  
Linear Equations Of Motion

The steady rotational flow of an inviscid fluid in a two-dimensional channel toward a sink or a contraction is treated. The velocity distribution at upstream infinity is approximated by a linear combination of uniform flow, linear shear flow, and a cosine curve. The combinations were adjusted to simulate flows ranging from laminar to turbulent. Vorticity is assumed conserved on streamlines. The resulting linear equations of motion are solved exactly. The solution show the dependence of the corner eddy separation and reattachment on flow geometry and approach flow vorticity and velocity distribution typified by a shape factor.

A note on shear flow past a sphere

1970 ◽  
Vol 40 (3) ◽  
pp. 543-547 ◽  
Author(s):  
R. R. Cousins
Keyword(s):  
Shear Flow ◽  
Flow Field ◽  
Velocity Distribution ◽  
Numerical Approximation ◽  
Inviscid Fluid ◽  
Integral Expression ◽  
Flow Past ◽  
Upstream Part ◽  
Uniform Stream ◽  
Flow Past A Sphere

Flow of an incompressible inviscid fluid past a sphere is considered, where the flow upstream consists of a slight shear flow superimposed on a uniform stream. Secondary vorticity, produced by deformation of vortex elements as they are carried past the sphere, is determined by a method due to Lighthill (1956b). Components of vorticity are calculated from a drift function for which expressions were previously available only in part of the flow field. For the region in which no expansion is valid an exact integral expression is obtained to replace the rough numerical approximation used by Lighthill (1956b). The velocity distribution over the upstream part of the sphere is determined numerically using a Biot–-Savart law. These results are required for the calibration of certain forms of Pitot tubes.

Boundary-Layer Flows in Rotating Cavities

1989 ◽  
Vol 111 (3) ◽  
pp. 341-348 ◽  
Author(s):  
C. L. Ong ◽  
J. M. Owen
Keyword(s):  
Boundary Layer ◽  
Turbulent Flow ◽  
Boundary Layers ◽  
Reverse Flow ◽  
Source Region ◽  
Linear Equations ◽  
Inviscid Fluid ◽  
Eddy Viscosity Model ◽  
Wide Range ◽  
Radial Outflow

A rotating cylindrical cavity with a radial outflow of fluid provides a simple model of the flow between two corotating air-cooled gas-turbine disks. The flow structure comprises a source region near the axis of rotation, boundary layers on each disk, a sink layer on the peripheral shroud, and an interior core of rotating inviscid fluid between the boundary layers. In the source region, the boundary layers entrain fluid; outside this region, nonentraining Ekman-type layers are formed on the disks. In this paper, the differential boundary-layer equations are solved to predict the velocity distribution inside the entraining and nonentraining boundary layers and in the inviscid core. The equations are discretized using the Keller-box scheme, and the Cebeci–Smith eddy-viscosity model is used for the turbulent-flow case. Special problems associated with reverse flow in the nonentraining Ekman-type layers are successfully overcome. Solutions are obtained, for both laminar and turbulent flow, for the “linear equations” (where nonlinear inertial terms are neglected) and for the full nonlinear equations. These solutions are compared with earlier LDA measurements of the radial and tangential components of velocity made inside a rotating cavity with a radial outflow of air. Good agreement between the computations and the experimental data is achieved for a wide range of flow rates and rotational speeds.

scholarly journals Lubricating Grease Shear Flow and Boundary Layers in a Concentric Cylinder Configuration

2014 ◽  
Vol 57 (6) ◽  
pp. 1106-1115 ◽  
Author(s):  
J. X. Li ◽  
Lars G. Westerberg ◽  
E. Höglund ◽  
P. M. Lugt ◽  
P. Baart
Keyword(s):  
Shear Flow ◽  
Boundary Layers ◽  
Concentric Cylinder ◽  
Lubricating Grease

scholarly journals Inviscid Uniform Shear Flow past a Smooth Concave Body

2014 ◽  
Vol 2014 ◽  
pp. 1-7
Author(s):  
Abdullah Murad
Keyword(s):  
Shear Flow ◽  
Stream Function ◽  
Inviscid Fluid ◽  
Oncoming Flow ◽  
Circular Arc ◽  
River Islands ◽  
Uniform Shear ◽  
Uniform Shear Flow ◽  
Flow Past ◽  
Special Cases

Uniform shear flow of an incompressible inviscid fluid past a two-dimensional smooth concave body is studied; a stream function for resulting flow is obtained. Results for the same flow past a circular cylinder or a circular arc or a kidney-shaped body are presented as special cases of the main result. Also, a stream function for resulting flow around the same body is presented for an oncoming flow which is the combination of a uniform stream and a uniform shear flow. Possible fields of applications of this study include water flows past river islands, the shapes of which deviate from circular or elliptical shape and have a concave region, or past circular arc-shaped river islands and air flows past concave or circular arc-shaped obstacles near the ground.

scholarly journals Acoustic boundary conditions at an impedance lining in inviscid shear flow

2016 ◽  
Vol 796 ◽  
pp. 386-416 ◽  
Author(s):  
Doran Khamis ◽  
Edward James Brambley
Keyword(s):  
Boundary Condition ◽  
Shear Flow ◽  
Boundary Conditions ◽  
Boundary Layers ◽  
Temporal Stability ◽  
Impedance Boundary ◽  
Impedance Boundary Conditions ◽  
Ricatti Equation ◽  
Approximate Boundary Conditions ◽  
Lined Ducts

The accuracy of existing impedance boundary conditions is investigated, and new impedance boundary conditions are derived, for lined ducts with inviscid shear flow. The accuracy of the Ingard–Myers boundary condition is found to be poor. Matched asymptotic expansions are used to derive a boundary condition accurate to second order in the boundary layer thickness, which shows substantially increased accuracy for thin boundary layers when compared with both the Ingard–Myers boundary condition and its recent first-order correction. Closed-form approximate boundary conditions are also derived using a single Runge–Kutta step to solve an impedance Ricatti equation, leading to a boundary condition that performs reasonably even for thicker boundary layers. Surface modes and temporal stability are also investigated.

scholarly journals Oblique instability of a stratified oscillatory boundary layer

2021 ◽  
Vol 933 ◽  
Author(s):  
Jason Yalim ◽  
Bruno D. Welfert ◽  
Juan M. Lopez
Keyword(s):  
Boundary Layer ◽  
Shear Flow ◽  
Boundary Layers ◽  
Oscillation Frequency ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Buoyancy Frequency ◽  
Oblique Waves ◽  
Oscillatory Shear Flow ◽  
Oscillatory Boundary Layer

The instability and dynamics of a vertical oscillatory boundary layer in a container filled with a stratified fluid are addressed. Past experiments have shown that when the boundary oscillation frequency is of the same order as the buoyancy frequency, the system is unstable to a herringbone pattern of oblique waves. Prior studies assuming the basic state to be a unidirectional oscillatory shear flow were unable to account for the oblique waves. By accounting for confinement effects present in the experiments, and the ensuing three-dimensional structure of the basic state, we are able to numerically reproduce the experimental observations, opening the door to fully analysing the impacts of stratification on such boundary layers.

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