Inviscid Jet Research Articles

The mechanics of wave formation in impact welding

If two metal plates are brought together at a sufficiently high relative velocity, a jet may form which removes much of the surface impurities, and a strong bond occurs. The purpose of this paper is to decribe the formation of a wave interface, and to suggest why a bond often occurs without the appearance of such waves. It is assumed that for sufficiently high values of the shear strain rate, above about 107 sec-1, the metals act as inviscid fluids; a model of a two-dimensional, incompressible, inviscid jet impinging on a plane boundary is considered, and the wave formation is thought to be due to a Helmholtz instability. Below this critical strain rate, the metals act as viscid fluids, and the viscosity acts to remove the instability.

Determination of the base pressure during axisymmetric supersonic jet outflow into a channel

The outflow of an axisymmetric jet into a cylindrical channel of arbitrarily large cross-sectional area is considered. A method is proposed for analysis of the base pressure in the separation zone bounded by the inviscid jet boundary, the channel wall, and the step. New experimental results about the base pressure during jet outflow into a large-diameter channel are presented.

Plane jet flows from slowly varying nozzles

The solution to the steady problem of an inviscid jet emerging from a symmetric nozzle of slowly varying profile is sought as an asymptotic series in the wall slope. The expansion of the solution in the region near the nozzle lip is singular at infinity, so that a matched expansion technique is evolved to solve the problem. To the order to which the solution is obtained in the present paper, the jet contraction ratio is shown to be the same as that from a nozzle formed by two inclined planes with inclination angle the same as the exit slope of the nozzle. Composite expansions are formed and used to check the consistency of expansion and matching procedures.

Turbulent boundary layer shape after a corner expansion

The expansion of a boundary layer about a corner is of primary importance to a near wake flow field. Experimental evidence shows that turbulent boundary layers separate precisely at the corner and methods are available for predicting such an expansion. Inviscid calculations using rotational characteristics have been successfully used. However, one of the simplest techniques of treating the expansion of a boundary layer is the method of isentropic streamtubes. Calculations with such a method may be easily programmed for digital computers or quickly done on an electronic calculator. In this note, results obtained from the simpler streamtube method are compared with results from the more complex rotational characteristic calculations.The streamtube method assumes that the flow field is isoenergetic, the stagnation pressure is constant along a streamline, and the flow is uni-directional before and after expansion. Obviously, the boundary layer is assumed to expand without interacting with the adjacent supersonic flow. The coordinate system used is shown in Fig. 1. Y is the coordinate normal to the attached flow direction, and W is the coordinate normal to the inviscid jet boundary streamline. The individual streamlines are located in the expanded profile by applying conservation of mass to the streamtubes.

Instability of a two-dimensional compressible jet

A linearized analysis of the two-dimensional double vortex sheet model of a jet shows that inviscid jet instabilities occur over a wide range of frequencies at all jet Mach numbers. No particular frequency for maximum growth rate exists unless finite shear layer thickness effects are considered. It is suggested that the model describes the essential characteristics of a real jet disturbed by long wavelength perturbations. The idea is advanced that the jet flow constitutes a broad band amplifier of high gain. Disturbances can grow rapidly to a size when nonlinear effects bring about significant interaction with the mean flow. By seeding the jet with disturbances of a type that are highly amplified it is argued that gross features of the flow may be affected and that the jet may be rendered less noisy at high Mach number. It is argued that some of these ideas are supported by the observation that a supersonic jet diffuses at an unusually rapid rate when subject to the oscillatory condition known as ‘screech’.

Electrohydrodynamic instability of a cylindrical viscous jet

The electrohydrodynamic instability to small axisymmetrical surface wave disturbances of a circular, cylindrical, electrically conducting, viscous jet, which is projected along the axis of a circular conducting cylinder, is considered for the cases when the charges or potentials remain unaltered. The discussion given is applicable for arbitrary viscosities and it is shown that points of transition from stable to unstable modes of oscillation, or vice versa, are the same as for the inviscid jet.

Spatial Instability of the Inviscid Jet and Wake

The stability of the plane inviscid jet and wake is investigated for possible growth in the downstream spatial direction. The combined stability problem in space and time is also explored and numerical results are presented for growth factors and phase velocities.

A one-dimensional treatment of inviscid jet or duct flow

Approximate equations involving one space dimension are derived for variablearea jet or duct flow. At a given cross section, the radial velocity and the sound speed are represented by distributions satisfying necessary boundary conditions for continuity and momentum. By integrating the full equations of inviscid motion over the cross section, quasi-one-dimensional equations with time and axial distance as independent variables are obtained. The equations for duct flow are the same as the characteristic equations from a purely one-dimensional treatment, but with an additional term. The equations for jet flow are also in characteristic form. Sample solutions for four steady jet flows are compared with available results from experiment and with the method of characteristics; agreement is satisfactory. Possible extensions of the technique employed are discussed.

The instability of inviscid jets and wakes in compressible fluid

The instability of inviscid jets and wakes in compressible fluid

Unsteady two-dimensional flows with free boundaries - II. The incompressible inviscid jet

The paper considers the flow which results when a slit of finite width is suddenly opened in a large container and a jet of fluid issues into free space. The early stages of the motion are discussed by expanding in powers of time. It is suggested that the jet boundary may be M-shaped initially. The shape of the jet after large but finite time is calculated by the general theory of part I to have a kink at the nose. However, by expanding in powers of the distance across the jet, the true radius of curvature of the nose has been evaluated. A realistic shape of the jet is sketched in figure 3.