Oblique Jet Research Articles

Study on Side-Jet Injection Near a Duct Entry With Various Injection Angles

Turbulent flowfields resulting from an oblique jet injecting from a rectangular side-inlet duct into a rectangular main duct with an aspect ratio 3.75 without a forced crossflow are presented in terms of laser-Doppler velocimetry measurements. The main focuses are the effects of the side-jet angle (θ) and side-jet flow rate (Qs) on the mass entrainment upstream of side-jet port and the flowfield in the rectangular duct. The side-inlet angles investigated were 30, 45, and 60 deg and Reynolds numbers based on the air density, rectangular duct height and bulk mean velocity were in the range of 7.1 × 103 to 3.6 × 104 corresponding to Qs values of 1 × 103 to 5 × 103 L/min. The present study suggests the presence of a critical side-injection angle θc (30 ≤ θc ≤ 45 deg) above which a recirculation zone appears in the rectangular duct, whereas below which the recirculation zone is absent. For the more tangential angle (θ = 30 deg), almost as much fluid is entrained into the main duct as was injected from the side jet. The mean flow field in the rectangular duct is found to be a weak function of the Reynolds-number for the range of Qs investigated. In addition, a simple linear correlation between the mass entrainment upstream of the side-jet port and side-injection angle is obtained. Complementary flow visualizations and numerical computations with an algebraic Reynolds stress model were also performed. The discrepancies between measured and computed results are documented.

Oblique and Vertical Jet Dispersion in Channels

The generalized laws of degradation and spreading of the boundaries of a submerged round jet discharging under oblique and vertical impingements into a channel have been investigated and derived. The laser Doppler anemometry (LDA) technique was adapted for measurement of mean velocities without any interference in the flow, and was utilized for the investigation of the complex three-dimensional circulating flow that was experienced in the channel. In the experiments, the inclination of the jet was varied from 45° to 90° to the bed of the channel, while differing ratios of channel width and depth to jet diameter were studied for various Froude numbers of the flow. The experimental results have been analyzed and compared with Glauret's theory for a radial wall jet as a first approximation neglecting gravity forces when small compared with turbulent forces. The research provides practical information for determining an efficient form of stilling basin for high velocity discharge from pipe outlets.

Mixing and Penetration Studies of Sonic Jets in a Mach 2 Freestream

A comparison of the penetration and mixing characteristics of three transverse/oblique injector configurations is presented. The three geometries studied include circular transverse, circular oblique, and elliptical transverse injectors, and the crossflow is at Mach 2. Planar Mie scattering images of three near-field flow planes produced substantial information about the flowfield created by each injector. In addition to global flowfield characteristics, the Mie scattering images provided transverse and lateral penetrations for each injector. Instantaneous and time-averaged information concerning the structural organization of the flowfields was obtained. Results demonstrate increasing jet penetration in the transverse direction with increasing jet-to-freestream momentum flux ratio. Penetration of the oblique jet is appreciably less in the near-field compared to the two transverse jets due to the reduced component of momentum in the transverse direction. The transverse elliptic jet appears to spread more quickly in the lateral direction than the other two jets, suggesting that some type of axis-switchin g phenomenon occurs. Large-scale structures at the interface between the jet and freestream fluids are shown for the two transversely oriented jets, while small-scale eddies are prominent in the oblique jet flowfield. Near-field mixing appears dominated by these eddies and the counter-rotating structures that develop in the streamwise direction.

Spreading flow of a plane laminar jet over a horizontal plate

An approximate theory of film flow produced by an oblique jet incident on a surface is proposed that enables one to describe both velocity profiles and the properties of the hydraulic jump. The distribution over the surface of the coefficient of mass or heat transfer is estimated in the approximation of a thin, diffusional boundary layer.

Effects of a hypervelocity jet on a layered target

We present a new approach to the numerical simulations of jet target interactions. We represent the jet by sources of mass, momentum and energy moving with a prescribed velocity. This velocity is related to local flow parameters through the incompressible theory of jet penetration. A Lagrangian, 2-dimensional elastic plastic code is used to model the flow in the target. The interaction between the jet and the target is obtained by appropriate deposition of the jet material with its momentum and energy in the computational mesh of the target. To prevent large grid distortions the grid is continuously rezoned. For normal jet impingement the calculations are carried out with axial symmetry. Oblique incidence is treated approximately considering a “sheet jet” and a two dimensional plane strain flow. Results for normal and 45° oblique jet impacts on a 25.4mm thick homogeneous armor plate are presented. The computed and experimental distributions of behind-the-armor debris are compared. An additional case of a 45° oblique jet penetration into a multi-layered plate is carried out. The flow in the target and its influence on the penetration process is discussed.

Mean Flow Characteristics for the Oblique Impingement of an Axlisymmetric Jet

The oblique impingement of an axisymmetric jet has been investigated. A summary of the data and the analytical interpretations of the dominant mechanisms which influence the flow are reported. The major characteristics of the shallow angle oblique jet impingement flow field are: (1) minimal dynamic spreading as revealed by the surface pressure field, (2) pronounced kinematic spreading as revealed by the jet flow velocity field, (3) a pronounced upstream shift of the stagnation point from the maximum pressure point, (4) the production of streamwise vorticity by the impingement process.

A discussion on deformation of solids by the impact of liquids, and its relation to rain damage in aircraft and missiles, to blade erosion in steam turbines, and to cavitation erosion - Oblique impact of a jet on a plane surface

The dynamics of the region where a jet, striking a plane surface obliquely, is transformed into a thin sheet will be discussed. The maximum (stagnation) pressure is the same for all angles of incidence but the area over which the high pressure acts is much reduced as the angle of incidence, 0 , becomes small. The main transformation from a jet to a sheet is due to a pressure of order sin 2 0 x the jet cross section. The pressure is due to the destruction of the component of velocity normal to the impact surface, but since pressure acts equally in all directions it imparts lateral velocity to streams which are not in the plane of symmetry. Each element of the stream can be regarded as passing through a small region where an impulsive body force changes its direction without changing its velocity, and some properties of this impulse will be described. One case will be given where the transformations from a jet to a thin flat sheet can be described completely and the calculated distribution of pressure in the region where it occurs compared with experimental measurements. Though a jet cannot produce a pressure greater than the stagnation pressure as a steady state, it seems theoretically possible to attain a much higher pressure for a short time when a very oblique jet is moved sideways.