Supersonic Gaseous Jet Research Articles

Analysis of the unsteady flow characteristics of underwater supersonic gaseous jets

To examine the unsteady flow characteristics of underwater supersonic gaseous jets under different jet expansion conditions, a sophisticated numerical model is created. This model accurately predicts the intricate multiphase flow by considering the compressibility of the jet gas and energy exchange, which is then rigorously validated against experimental data. The development process of underwater supersonic gaseous jets displays notably unsteady features in terms of jet morphology, flow structure, and various flow field parameters when compared to atmospheric conditions. The unsteady phenomena, such as necking, breaking, bulging, and back-attack, are observed alongside significant pressure pulsations. These unsteady phenomena occur at a considerable distance from the nozzle exit under under-expanded conditions, while pressure pulsations do not impact the internal gas flow within the nozzle. However, under full-expanded and over-expanded conditions, unsteady phenomena near the nozzle exit lead to oscillatory pressure, causing shock waves to propagate inside the nozzle. This results in a notable increase in internal pressure pulsation and mass flow rate within the nozzle, ultimately affecting engine performance significantly.

Numerical Simulation of Underwater Supersonic Gaseous Jets of Underwater Vehicle with Porous Media Layer

Numerical Simulation of Underwater Supersonic Gaseous Jets of Underwater Vehicle with Porous Media Layer

Numerical study on the influence of nozzle divergence half angle on thrust oscillation characteristic of underwater jet power

Underwater rocket propulsion is increasingly used in advanced marine vehicles that may be subject to supersonic gaseous jets while submerged. This work investigates the influence of supersonic nozzle divergence on the multi-flow field evolution process and the thrust oscillation characteristics by multiple numerical simulations using a VOF multiphase flow model. Four nozzle divergence half angles are taken into consideration. The analysis indicates that the thrust rises sharply at nozzle closure opens, then rapidly decreases and follows another rise. The thrust oscillates at high frequencies. As a result, increase of the nozzle divergence half angle leads to the size decrease of flow bubbles but does not affect the changing trends of the thrust. Increase of the nozzle divergence half angle leads to a reduction of the frequency of the thrust oscillations.

Experimental investigation on flow structure and pressure characteristics of submerged high-speed gaseous jets under co-flow conditions

High-speed gaseous jets are commonly found in deep-water propulsion systems. The submerged high-speed gaseous jet becomes turbulent due to the density difference between the gas and liquid phases. In experimental studies, the interaction between the gaseous jet and the liquid has not been well characterized under co-flow conditions. In this paper, the effects of co-flow velocity, Fr, and jet pressure ratio, p0/p∞, on the flow structure of the gaseous jet and pressure on the nozzle outlet cross-section were experimentally studied. It has been observed that the increase of Fr makes the nozzle outlet cross-section gradually wrap up with transparent bubbles under subsonic gaseous jets. However, the transparent bubbles will be broken entirely under supersonic gaseous jets, and the gaseous jet will intermittently expand into bubbles downstream away from the nozzle outlet cross-section. The flow mechanism of the underwater gas jet at larger Fr seems to be different from that at smaller Fr and still water. Keeping Fr constant, the dimensionless streamwise length of the jet, Ls/LQ, increases as a power law with p0/p∞. Fr further promotes the penetration of the jet downstream under the fixed p0/p∞. In addition, the pressure on the nozzle outlet cross-section is seriously affected by p0/p∞ and Fr. The increase of Fr will seriously weaken the intensity and frequency of pressure oscillations on the nozzle outlet cross-section. This finding can provide theoretical support for the design and control of jet-propelled vehicles.

Flow structures of over-expanded supersonic gaseous jets for deep-water propulsion

Supersonic gaseous jets with large ambient pressure are typically found in deep-water propulsion systems. The interactions between gas and water are turbulent, and the plume exhibits unstable bubbly interfaces. This work employed both experimental and numerical methods to obtain the flow structures of over-expanded gaseous jets driven by different pressure ratios in water. Direct measurements of the interfacial behaviour of submerged gaseous jets with pressurised water, were performed using high-speed digital photography. Numerical simulations were also conducted to characterise flow structures by the interplay of inertia and buoyancy forces. It was found that the interface of injection into water showed continuous fluctuations and strong mixing in the conical regions. The intermittent expansion-necking characteristics just beyond the nozzle exit, induced the pressure oscillation of the flow field near the wall, localised liquid water attack of the exit wall, and aggravated the over-expansion of nozzle working conditions. These periodic phenomena were attributed to Kelvin-Helmholtz (K–H) instabilities, driven by the large gradients of velocity and density in the shearing layers. The oscillation characteristics were assessed at different ambient pressures, providing theoretical support for the design of engineering devices working over a wide range of water depths.

Experimental study on submerged supersonic gaseous jet induced tail cavity

Multiphase jets and cavitation problems are inevitable for high-speed underwater vehicles propelled by jet engines. Unlike being injected into stagnant water, the gaseous jet behind a underwater vehicle is usually conjugated with a tail cavity. The pulsation and collapse of such cavities can seriously affect the vehicle performance. In this study, the shape character, forming mechanism and control conditions for the supersonic gaseous jet induced tail cavity at the wake of a revolution body are experimentally investigated in a water tunnel. The induced cavity is ventilated only by a convergent-divergent nozzle with a designed Mach number of 2.45. The form of the cavity is recorded through two high-speed cameras both horizontally and vertically under different Froude numbers and ventilation rates. The time averaged form is thus obtained through digital image processing to eliminate the transient characteristics of the cavity. The experiment is conducted with the Froude number ranging from 3.2 to 16.2, and the ventilation rate 0 to 0.5. Due to the high density and velocity ratio between water and gas, the structure of such flow is usually very complicated. Many novel phenomena of the jet-cavity interaction are observed. With increasing stagnation pressure of the central jet, the induced cavities evolves form foamy, intact, partially break, to pulsating foamy closure type. The foamy and intact tail cavities share the same profile and characteristics that of a supercavity. And the pulsating foamy closure type was never observed before in a traditional supercavitating flow. The outline of the pulsating foamy cavity is the same as the foamy cavity's, indicating that they have the similar forming mechanism. A comparison with the jet-cavity interaction model is made and the following conclusions are obtained:the real ventilation rate, which corresponds to the re-entrant jet gas blocked by the cavity boundary, is the key factor in controlling the cavity form. When the gaseous jet is completely blocked by the water-gas interface, an intact or foamy cavity will be formed. A partially break cavity appears only when some fraction of the jet is blocked and this is when some of the strongest interactions between jet and cavity occurs. When little gas was blocked by the interface, a pulsating foamy cavity forms. With the structure of gaseous jet considered, the transition of the induced cavity closure between different types is in favour of the prediction from Paryshev's model of cavity closure to a central jet. The variation of the cavity form, thus the interaction strength between jet and cavity, coincides with the real ventilation rate estimated through the theoretical model.

ナトリウム-水反応および圧縮性混相流数値解析コードSERAPHIMの高度化 : 高度不足膨張噴流に対する解析手法の適用性検証(<特集>第14回動力・エネルギー技術シンポジウム)

SERAPHIM is a computer program for the simulation of the compressible multiphase flow involving the sodium-water chemical reaction under a tube failure accident in a steam generator of sodium cooled fast reactors. In this study, the numerical analysis of the highly underexpanded air jets into the air or into the water was performed as a part of validation of the SERAPHIM program. The multi-fluid model, the second-order TVD scheme and the HSMAC method considering a compressibility were used in this analysis. Combining these numerical methods makes it possible to calculate the multiphase flow including supersonic gaseous jets. In the case of the air jet into the air, the calculated pressure, the shape of the jet and the location of a Mach disk agreed with the existing experimental results. The effect of the difference scheme and the mesh resolution on the prediction accuracy was clarified through these analyses. The behavior of the air jet into the water was also reproduced successfully by the proposed numerical method.

Numerical study of the interaction of a supersonic gaseous jet with a planar target

Various regimes of interaction of an axisymmetric supersonic underexpanded jet of a gas with both a finite and an infinite planar target are studied numcrically. The model of an idcal perfect gas and one variant of Godunov's highly accurate scheme are used. The calculated and experimental frequency spectra of pressure oscillations in the center of the target are compared: their good agreement is obscrved.

Upwind adaptive finite element investigations of the two‐dimensional reactive interaction of supersonic gaseous jets

AbstractWe describe an upwind finite element method aimed at numerically simulating the two‐dimensional transonic flow of a reactive gaseous mixture. The method uses in particular a triangular finite element mesh, with an adaptive procedure based on mesh refinement by triangle division, and an upwind non‐oscillatory scheme based on an approximate Riemann solver for the evaluation of the convective terms for all species. Results concerning the reactive interaction of two supersonic gaseous jets are presented.

Shocks, interfaces, and patterns in supersonic jets

Supersonic gaseous jets exhibit coherent nonlinear dynamic structures. We use a supercomputer to obtain solutions to the equations of two-dimensional inviscid hydrodynamics, representing both axisymmetric and planar jets boring their way through a uniform medium. We use color images to display these high resolution computations. Several basic morphologies of interfaces and shock structures arise which we discuss in simple terms. The global structure of the two-parameter solution space is analyzed. A number of the basic structures, which appear in the supercomputer simulations, seem to occur in both terrestrial and astrophysical supersonic jets.