Three-Dimensional Supersonic Jet Behavior in BOF Multijet Lance With Modified Tip Geometry

The main results of a numerical study of the effect of the angle of the rim of a nozzle on the shape of the jet boundary and of the free shock and on the distribution of parameters in a three-dimensional underexpanded jet are presented. A noncentered second-order difference scheme is used to solve the gasdynamic equations for an inviscid perfect gas. Conditions are established for which the three-dimensional jet is observed to coincide partially in the radial planes and the corresponding planes of axisymmetric jets.

Numerical investigations were made of the propagation, in a supersonic wake, of uncalculated jets, flowing out of nozzles of square and rectangular cross section, and of lumped jets, made up of from two to nine individual jets; the special characteristics of their flow were investigated in the initial, transitional, and main sections. Specifically, for lumped jets, the possibility of replacing them by a single axisymmetric jet, equivalent in mass-flow rate, is discussed. To calculate a three-dimensional unexpanded supersonic jet, flowing out into a wake, in [1] it was proposed to use a numerical method for solving a simplified system of Navier-Stokes equations for steady-state flow, and numerical investigations were made of the three-dimensional interaction of four jets in a supersonic wake, at small distances from the outlet cross section of the nozzle, i.e., mainly in the initial sections of the jets, where the mixing layers along the boundaries of the jets are still not closed. Here the method of [1] is used to study the special characteristics of three-dimensional viscous jets at large distances from the outlet cross section of the nozzle in the region of the main section, where the mixing layers have come together and a single three-dimensional jet has been formed. The system of equations, the boundary conditions, the numerical method, the system of coordinates, and the nomenclature used are the same as in [1].

A three-dimensional turbulent jet discharging from a round nozzle along a flat plate has been studied experimentally. Measurements of the three components of mean and fluctuating velocities and the wall shear stress were obtained with a hot wire in various cross-stream planes. The estimation of the Reynolds stress balance was made with the help of the experimental results, and the role of the Reynolds stress to the jet diffusion was discussed. These results suggest that the jet behavior is explained well with the Reynolds stress distribution and that the pressure-strain correlation in the Reynolds stress balance is fairly approximated by the LRR's turbulence model.

Cooling of turbine blades is often achieved with cold discrete jets introduced at the wall. In this paper, a new method for computation of a wall boundary layer with discrete jet interactions is presented. The jets are assumed to be arranged in rows and the flow is assumed locally periodic in the row direction. The conservation equations are spatially averaged between two jet orifices. The resulting equations look like two-dimensional boundary layer equations, but with three-dimensional jet source terms. The numerical method solves the boundary layer equations with a Keller box method. A strong interaction with inviscid flow is also introduced in order to avoid numerical difficulty in the jet region. Three-dimensional jet conservation equations are solved with an integral method, under the boundary layer influence. A coupling of the two methods is performed. Comparisons with low speed experimental data are presented, particularly near the jet orifices. It is shown that the agreement between the results of computation and the experiments depends on the jet behaviour very near to the jet exit.

Cooling of turbine blades is often achieved with cold discrete jets introduced at the wall. In this paper, a new method for computation of a wall boundary layer with discrete jet interactions is presented. The jets are assumed to be arranged in rows and the flow is assumed locally periodic in the row direction. The conservation equations are spatially averaged between two jet orifices. The resulting equations look like two-dimensional boundary layer equations, but with three-dimensional jet source terms. The numerical method solves the boundary layer equations with a Keller box method. A strong interaction with inviscid flow is also introduced in order to avoid numerical difficulty in the jet region. Three-dimensional jet conservation equations are solved with an integral method, under the boundary layer influence. A coupling of the two methods is performed. Comparisons with low-speed experimental data are presented, particularly near the jet orifices. It is shown that the agreement between the results of computation and the experiments depends on the jet behavior very near the jet exit.

Analysis of conditional statistics of a supersonic jet flame in heated coflow via direct numerical simulation

The problem of three-dimensional mode jet screech tones radiated by an imperfectly expanded supersonic cold jet is studied computationally using the general purpose CFD code ANSYS FLUENT, version 12. Pressure-based coupled solver formulation with the secondorder bounded central-upwind spatial discretization and second-order implicit time marching scheme is applied to obtain a quasi-periodic transient solution. The numerical model reproduces physics of the jet screech tone feedback loop generation mechanism driven by interaction of large scale turbulent structures with jet shock cells. Propagation of flapping and helical mode disturbances along the jet column is recovered in the simulation. The acoustic near-field is resolved to accurately propagate screech tone waves to microphone monitors defined on the nozzle lip. Calculated screech tone frequencies and sound pressure levels are compared with experimental data, and favorable near-field agreement is found.

Three-dimensional jet mixing problems are addressed by means of two parabolized Navier-Stokes models. The first of these analyzes supersonic, overexpanded or underexpanded nonaxisymmetric jets, and yields results that exhibit complex, three-dimensional interactions. The second model uses the same numerical framework as the first, and analyzes rectangular jets by means of a pressure-split formulation. Square and rectangular mixing jet problems that highlight this model's capabilities and exhibit the distortion of the nearfield jet contours associated with the streamwise vortices generated by two corner regions are presented.

The overexpanded supersonic jet, formed under the overexpanded condition at the nozzle exit, is very important for industrial devices, the same way as an underexpanded jet. It has been reported, in a recent study, that hysteresis phenomena for the shock reflection type in a three-dimensional supersonic jet occur under the quasi-steady flow. Several papers have described the hysteresis phenomena for underexpanded supersonic jet. However, the characteristics and mechanism of the hysteresis should be discussed more clearly to understand this phenomenon. The purpose of this study is to clear the characteristic of the hysteresis phenomena for the reflection type of shock wave at the overexpanded axisymmetric jet using the TVD method.

A theory of the behavior of three-dimensional peripheral jet ground effect machines (OEM's) in pitch and roll is presented. The physical basis of the theory is the satisfaction of continuity of mass flow through the cushion of high-pressure air supporting the craft, and generated by the peripheral jets. Detailed calculations have been carried out for a rectangular craft with a length-to-breadth ratio of two. Comparisons with experimental data are encouraging, although none of the experimental craft were of identical geometry. The assumptions on which the theory is based are discussed, and a need is shown for fundamental experimental work on the behavior of jets.

A theory of the pitching characteristics is presented for three-dimensional peripheral jet ground effect machines which are equipped with a compartment partition along the pitch axis. The analysis is separated into two parts, i. e. the longitudinal static stability and the dynamic pitching motion. In both cases, the behaviors of jet are quantitatively treated as the underfed and overfed operation. At the static pitch condition, the cushion pressures in the falling downward and rising upward compartments are first discussed, and, applying those results, the simple expression of the static moment about the pitch axis is derived. Furthermore, utilizing the quasi-static principle, a second order nonlinear differential equation is obtained as the equation of pitching motion. Detailed calculations have been carried out for a circular model GEM, and the comparisons with experimental data are encouraging.

High-pressure water jet technology is widely used in hot-rolling billet descaling process. Impact force and behavior of jets play a vital role on effect of water jet billet descaling. The parameters of nozzles and jet determine the characteristics of jetting. Some of these parameters, however, can only be obtained through experimentation. The mechanism of high-pressure water jet billet descaling was analyzed in this paper. The factors affecting billet descaling were also discussed. Furthermore, theoretical formula accounting for water jet impact force was derived from the discussion. An indoor test set-up investigating impact properties of water jet descaling nozzles was established. Virtual instrument Lab VIEW was combined with mathematics software MATLAB to develop a measuring system of the test set-up. The real-time test of descaling nozzles parameters can be achieved through the system. The measuring system included three modules: pressure-flow curve, three-dimensional platform movement track and jet impact force measurement. Various parameters of the nozzles and jet can be obtained by means of the modules. Experimental results were compared with theoretical ones and observations were made regarding the variation of parameters. Results showed that variation of the parameters yielded by experiments agreed well with theoretical prediction. Variation of each parameter was visually depicted. The impact force and behavior of the jet were accurately measured. It contributes to descaling nozzle design improvement and descaling system structure optimization.

An experimental and computational fluid dynamics study is reported of supersonic jets issuing from a high-aspect-ratio rectangular convergent–divergent nozzle with and without a scarfed exit. Schlieren visualization and laser Doppler anemometry measurements captured near-field aerodynamic development of an unheated jet at overexpanded, design, and underexpanded conditions. Reynolds-averaged Navier–Stokes computational fluid dynamics predictions using an eddy viscosity closure (Spalart–Allmaras model) for clean and scarfed geometries were compared with measurements to examine the ability to capture nozzle scarfing effects. The measured plume shape for a scarfed nozzle was strongly affected at overexpanded conditions (a distorted four-lobe shape was observed), whereas a rectangular shape was retained for underexpanded flow although plume bifurcation occurred. The development of the plume shape and the mixing rate was a consequence of the strong vortices that occur with rectangular nozzles, with extra vortices introduced by scarfing. The nozzle exit static pressure changed dramatically when scarfing was added, influencing plume secondary flows and near-field development. The main features of scarfed jet development were predicted qualitatively correctly; the four-lobe overexpanded shape was reproduced but the strength of pressure-driven secondary velocities was overpredicted. The experimental data provided represent a challenging validation test case for computational fluid dynamics studies of three-dimensional supersonic jet plumes with scarfed interaction effects.

Underwater supersonic gas jet flows are sophisticated physical phenomena that widely exist in underwater propulsion, such as underwater rocket, high-speed torpedo, and water-piercing missile launcher (WPML). The present study aims to explore the characteristics of underwater supersonic jets. This research carries out two-dimensional and three-dimensional underwater jet experiments and establishes an improved spherical bubble model to study the transient and steady-state characteristics of the underwater supersonic jet. The simulation results show that the entrainment strength and anti-interference ability are the main factors affecting the transient characteristics of underwater supersonic jets. The experimental results show that the jet angle increases with increasing pressure and the increased rate of the jet angle decreases with increasing pressure. The jet pulsation exists in the entire experimental pressure range from 0.4 MPa to 6.5 MPa. The frequency of back-attack increases first and then decreases with increasing pressure in the chamber. The frequency peak appears at 0.8 MPa, which is 5.96 Hz.

The new intermolecular collision scheme is developed to obtain an excellent result even if cells are lengthened in the DSMC calculation. In the new scheme, the velocity of one molecule of a collision pair is modified before and after a conventional collision calculation, assuming that velocity distributions in all flowfield are in local equilibrium with some temperature and flow velocity. The new collision scheme is applied to an one-dimensional normal shock wave, a two-dimensional vortex in a square cavity, an axisymmetric supersonic free jet, and a three-dimensional supersonic jet, respectively, and its effect is confirmed.