Sonic Jet Research Articles

Thermal effects of a sonic jet fire impingement on a pipe

Although the effects of jet fires are often limited to rather short distances, if their flames impinge on a pipe or a vessel collapse can occur in very short times. In such cases, the heat flux on the affected equipment is very high and wall temperature can increase very rapidly. This can happen in parallel pipelines, if a release occurs and impinges on another one. Nevertheless, jet fire impingement has been scarcely studied. In this communication the results obtained from an experimental set-up are presented. Sonic jet fires impinged on a pipe containing stagnant air or water. The temperatures of the flames impinging on it were measured for the worst case (flame front-bright zone), as well as the evolution with time of the pipe wall temperature at different locations. Initial temperature increases up to around twenty °C/s were registered for the air inside, with maximum values of up to 600 °C reached in 2.5 min, and 800 °C in approximately 9 min. In the case of pipe containing water, in the zone of the wall in contact with the liquid the heating rates were much lower, the maximum temperature reached being up to approximately 150 °C. From the temperatures of the jet flames and of the pipe, the heat fluxes reaching the pipe and the corresponding heat transfer coefficients were obtained. The results obtained emphasized that safe distances are essential in pipelines, together with fire proofing and other safety measures.

Experimental investigation on mixing characteristics of high speed co-flow jets by using tabbed chevron nozzle

Abstract The present study investigates the effect of chevron with tab (Tabbed chevron) fixed at the exit of the co-flowing primary nozzle on the mixing characteristics in subsonic and sonic jets. The experiment was conducted for the jet Mach number 0.6 and 0.8. The centerline Mach number decay was calculated for all these jet Mach numbers for the co-flow baseline nozzle, nozzle with chevrons and tabbed chevron (primary flow) nozzle respectively. It was found that tabbed chevron was effective in reducing the potential core length by 88.23% as compared to the chevron nozzle with baseline nozzle. The radial profile also shows that the mixing enhancement by tabbed chevron is better than chevron nozzle.

Experimental investigation on mixing characteristics of high speed co-flow jets by using tabbed chevron nozzle

Abstract The present study investigates the effect of chevron with tab (Tabbed chevron) fixed at the exit of the co-flowing primary nozzle on the mixing characteristics in subsonic and sonic jets. The experiment was conducted for the jet Mach number 0.6 and 0.8. The centerline Mach number decay was calculated for all these jet Mach numbers for the co-flow baseline nozzle, nozzle with chevrons and tabbed chevron (primary flow) nozzle respectively. It was found that tabbed chevron was effective in reducing the potential core length by 88.23% as compared to the chevron nozzle with baseline nozzle. The radial profile also shows that the mixing enhancement by tabbed chevron is better than chevron nozzle.

Investigation of an optimal pulsed jet mixing and combustion in supersonic crossflow

The enhanced mixing and combustion mechanism of pulsed sonic jet with optimal frequency in supersonic crossflow with a 10° ramp has been investigated using Large Eddy Simulation (LES). The results show that the energetic structures from the barrel shock and shear vortex are further enlarged at the phase of 1/4T0 periodically due to the swing forward and backward effect of the bow shock. There coexists clockwise and counter-clockwise rotating shear layer vortex structures in the pulsed jet, while only counter-clockwise rotating shear layer vortex structure is found in the steady case. The mixing process and the flame distribution are significantly affected by these structures of different scales. The reflected shock waves in the transverse jet in supersonic crossflow have strong coupling effects with the heat release rate. The pulsed jet is also found to improve the non-premixed dominant heat release rate, but not the premixed one. The mechanism of enhanced mixing and combustion efficiency relevant to the optimal frequency of 50 kHz is studied with Power Spectral Density (PSD) and wavelet analysis, and it is interesting to notice that the optimal pulsed jet frequency has strong coupling effects with the bow shock swing back and forward frequency, the jet shear layer and barrel shock frequencies (i.e., 50 kHz). However, for the non-pulsed steady case, the bow shock characteristic frequency is found to be 40 kHz, which suggests the optimal pulsed jet frequency can be 40 kHz. In order to further validate it, Unsteady Reynolds Averaged Navier Stokes (URANS) simulations have been performed with the pulsed jet frequency of 40 kHz. It is optimising to see that the mixing and combustion efficiency are further improved.

Speckle beam-oriented schlieren technique

An advanced background-oriented schlieren (BOS) method, named as the speckle beam-oriented schlieren technique, was newly developed to measure the distribution of refraction angles in transparent media. A speckle pattern is generated by passing a coherent laser beam through a holographic diffuser, a pinhole, and a lens, generating a collimated background image that is projected directly onto the image sensors. Since the intensity of the background image is maintained at a high level, this method is, in principle, useful for diagnosing fast and/or low signal-to-noise phenomena, such as high-temperature gasses with radiation emission. Moreover, by splitting the background beam into two imaging paths with different focal lengths, the refraction angles can be measured for a schlieren object with uncertain location, and the depth position of the refraction angles can be resolved. This technique was demonstrated by measuring the refraction angle and the depth position distribution in a sonic jet with different injected locations.

Study on underexpanded sonic jets from square convergent nozzles

Study on underexpanded sonic jets from square convergent nozzles

Experimental investigation of sonic transverse jets in Mach 5 crossflow

An experimental investigation of sonic transverse jets in Mach 5 cross flow over a flat plate with a sharp leading edge was carried out. Jet to free stream momentum flux ratio, J, was varied from 1.16 to 5.30. Schlieren visualisation provided information regarding mean flow features such as Mach disc height, h, separation length, xsep as well as inherent unsteadiness. Steady wall pressure measurements diagnosed the interaction region between the jet and the incoming cross flow developing on the flat plate. To assess the jet penetration characteristics and trajectories, two-component Particle Image Velocimetry (PIV) measurements were carried out at the centreplane of the flat plate. Raw PIV image analysis was used to specify jet penetration boundaries. Ensemble-averaged streamwise and transverse velocity contours revealed the mean flow structures. The barrel shocks and the Mach disc forming the jet boundary can be easily seen and were visualised/quantified using PIV measurement technique. Maximum turbulence occurred above the Mach disc due to the presence of the shear layer and at the intersection of the windward side of the barrel shock and bow shock.

Effect of downstream sinusoidal wall on mixing performance of hydrogen multi-jets at supersonic flow: Numerical study

Fuel mixing and penetration are known as substantial factor for advance of current scramjet engine. In this article, mixing and distribution of multi hydrogen jets are investigated under the impacts of downstream sinusoidal wall. This research tries to estimate the fuel jet interactions through the deflection of flow by downstream wavy wall. To perform our investigations, computational fluid dynamic with SST turbulence model is employed to simulate sonic multi hydrogen cross jets at supersonic air stream (M=4). The influences of fuel jet gaps and downstream wavy profile are comprehensively studied to disclose the importance of downstream on the fuel distribution and mixing region. Our results indicate that the fuel distribution in the downstream is substantially limited by increasing the frequency of downstream wavy wall. It is also noticed that the fuel concentration is decreased by increasing the jet space on the symmetry plane.

Numerical study of a sonic jet in a supersonic crossflow over a flat plate

A sonic circular injector discharging into a Mach 1.6 freestream over a flat plate with a jet to crossflow momentum flux ratio of 1.73 is investigated numerically using a three-dimensional Reynolds-averaged Navier–Stokes equation. Menter’s shear stress transport k–ω turbulence model is employed to understand the complex flow features associated with jet–freestream interaction. The validation of the numerical solution is achieved by comparing the velocity and flat plate surface pressure measurements from the experiments, and the numerical solution shows good agreement with the experimental data. The present work emphasizes the flow field studies that include the identification of shocks, recirculation zones, and vortex structures. The Omega (Ω) vortex visualization method is employed for identifying the vortex structures. Comparison with high Mach number freestream conditions (M∞ = 2 and 4) shows that the vortex structures remain the same, irrespective of the freestream Mach number. A close analysis of the jet near-field shows several new vortex structures, including a secondary surface trailing vortex. The formation of each of these vortices lacks clarity to date. Considering the complex three-dimensional nature of the flow field, an attempt has been made to trace the formation of the vortex structures associated with a jet in supersonic crossflow.

Influence of the relative momentum flux ratio on the mixing of hydrogen jets in an M=4 crossflow

The paper presents the results of numerical simulation of the 3D flows in a plane channel with the abrupt expansion. Sonic hydrogen jets are supplied from two circle orifices located opposite each other on the channel walls before the backward-facing step. The numerical simulations are carried out under the conditions of experiments performed at the hot-shot wind tunnel IT-302M ITAM SB RAS for the following flow parameters: Mach number at the entrance of the channel M = 3.84, the total temperature T0 = 1715 K, and the total pressure P0 = 6.5 MPa. Calculations were performed with a change in the jet supply pressure from 0.4 to 3.6 MPa, which ensures the variation in the jet-to-crossflow momentum flux ratio in the range of J = 0.7 ÷ 6. Mathematical modeling was performed in ANSYS Fluent based on the Reynolds-Averaged Navier-Stokes equations supplemented by the k-ω SST turbulence model. A comparison of the calculated and experimental data on the flow structure, as well as the static pressure distributions on the walls, indicates a satisfactory agreement. The calculated results made it possible to obtain a clearer understanding of the 3D flow structure in the channel and reveal the influence of the injection pressure on the level of mixing.

Experimental study of near-wall underexpanded jet impingement on a flat plate using temperature-insensitive semi-transparent pressure-sensitive paint

The aim of this study is to experimentally investigate the pressure field of underexpanded sonic jet impingement with a short nozzle–plate distance (L/Dn) and a large impingement angle (θ). The measurement of surface pressure is difficult using traditional non-transparent PSP due to optical obstruction. Here, a novel pressure-sensitive paint (PSP) with a high degree of transparency was used, which enabled back illumination and back imaging to resolve the issue of optical obstruction. The temperature sensitivity of the PSP was also greatly reduced using the self-assembled monolayer (SAM) technique, which reduced the effect of temperature variation on the impingement plate, as demonstrated via comparison with pressure tap data. With this technique, the effects of the nozzle–plate distance (L/Dn = 1, 2, and 3), impingement angle (θ = 90°, 60°, and 30°), and pressure ratio (PR = 1.2 and 1.5) on the pressure-field characteristics were evaluated in detail, with a focus on the fine flow structures near the impingement point. The surface pressure distribution in the wall jet region was found to be significantly influenced by the nozzle–plate distance, which could be related to variation in the flow field, based on a physical model of the sonic line. The obtained PSP results with a high spatial resolution revealed interesting flow physics that improve our understanding of high-speed near-wall jet impingement.

Secondary fuel jet strategies on mixing enhancement performance of rocket-based combined cycle engine

The mixed augmentation performance between secondary fuel jet and uneven supersonic inflow is a significant evaluation index of the rocket-based combined cycle engine. In this study, the effects of the secondary fuel jet on the flow field structure and mixing enhancement performance are discussed by changing both the secondary fuel jet angle and spacing of multiple rows of jet holes. The three-dimensional coupled implicit Reynolds averaged Navier-Stokes equations, SST k-ω turbulence model, and eddy dissipation concept (EDC) reaction model were adopted to evaluate the flow field structure with a sonic hydrogen jet. It is indicated that the 135° fuel jet has the largest penetration depth value, followed by the 90° fuel jet, whereas the 45° fuel jet has the smallest penetration depth value. However, the 45° fuel jet possesses the best mixing performance, it easily induces a pair of downstream counter-rotating vortex, and the oblique torque is further generated to aggravate the tearing ability to the jet. The three jet holes induce a stronger shock wave and form a larger barrier under the 90° jet. Additionally, when the spacing between the multiple rows of jet holes reduces, penetration depth is easily created. Further, when the spacing of the three rows of jet holes is larger, the fluctuation of the mixing coefficient increases.

Ignition and flame stabilization characteristics in an ethylene-fueled scramjet combustor

Successful ignition process is the prerequisite for achieving stable combustion in a scramjet combustor coupled with a cavity. A single pulse laser is adopted to ignite the fuel/air mixture that is generated by a sonic ethylene jet injection into heated Mach 2.92 crossflows. In order to reveal the complicated combustion regime, large eddy simulations are performed to reproduce the unsteady reactive process observed in the experiments, from an initial ignition kernel to the cavity-stabilized flame. From qualitative comparisons, the predicted results show reasonably good agreement with experimental observations. After ignition, the flow dynamics drive the flame kernel to the leading edge of the cavity. Herein, a flame base is established, and provides hot intermediate products and high temperature to continually ignite the fresh combustible mixture downstream. Finally, a partially-premixed flame is stabilized in the cavity. Due to a shorter flow residence time, the intensity of chemical reactions becomes weak in the downstream region of cavity. In comparison with no-reactive flows, the chemical heat released during the reactions induces high temperature, and the jet wakes penetrate a deep height into the mainstream. A thorough understanding of unsteady flame regime is propitious to instruct the design and optimization of combustor.

Quantitative Flow Visualization of Slightly Underexpanded Microjets by Mach\u2013Zehnder Interferometers

The Mach–Zehnder interferometer with the finite fringe setting is applied for a shock-containing microjet issued from an axisymmetric convergent nozzle with an inner diameter of 1.0 mm at the exit. Experiments are performed at a nozzle pressure ratio of 3.0 to produce a slightly underexpanded sonic jet where the Reynolds number, based upon the diameter and flow properties at the nozzle exit, is 4.45 times 10^4. The reconstruction of the jet density field is performed using the Abel inversion method under the assumption of an axisymmetric flow as well as the Fourier transform method for the phase shift analyses of interferograms. The three-dimensional density field of a shock-containing microjet can be captured with a spatial resolution of 4 upmum, and the near-field shock structure inside the jet plume is shown in the density contour plot at the cross-section including the jet centerline. In addition, the density field of the microjet is illustrated with various techniques, including representation such as the vertical-knife-edge schlieren, the horizontal-knife-edge schlieren, the bright-field schlieren, and the shadowgraphy. In addition to experiments, the Reynolds averaged Navier–Stokes (RANS) simulation with the SST k–omega turbulence model is carried out to model the microjets, and a quantitative comparison with the experiments is performed. The jet centerline density profile obtained by the present experiment is quantitatively compared with those from the previous Mach–Zehnder interferometer, the background oriented schlieren, as well as the RANS simulation.

Mixing Characteristics and Enhancement of Sonic Elliptic Jets from a Twin Elliptic Orifice

The knowledge of jet mixing and its enhancement of elliptic jet are important in a propulsion system of aircraft, rocket, and missile’s system design for advancement of combustion via fuel-air mixture increment, lowering the jet noise and reduction of the plume infrared (IR) signature. The jet issuing from a twin elliptic orifice is non-uniform in shape that promotes the faster mixing and it influences by orifice exit conditions, so knowledge of absence of boundary layer and jet mixing characteristics is important. Hence, an experimental work helps to study the jet mixing for a twin elliptic orifice of aspect ratio two at nozzle pressure ratios of one, two, and three. The proximity between the orifices kept as one to 3mm in steps of one. The experimental readings were taken using pitot probe. The results revealed that jet mixing is faster and effective when the proximity between the orifices is closer to each other than the faraway distances at measured nozzle pressure ratios. Difference in orifice jet core exerted a noticeable influence at high proximity levels of nozzle pressure ratio of three and four for elliptic orifice.

Control of mach 2 jet using sonic coflow

An experimental investigation was done to understand the effect of sonic coflow jet on the core length of Mach 2 jet at different levels of expansion. The sonic jet surrounding the primary Mach 2 jet was produced using a sonic nozzle, whereas a convergent-divergent nozzle was used for Mach 2 jet. The annular gap between the sonic and supersonic nozzles was 1mm. For a fixed main jet NPR, the NPR of the sonic jet was varied from 4 to 6 (in steps of 1), which correspond to underexpanded levels of the sonic jet. The NPR of Mach 2 jet was varied from 4 to 6, which correspond to overexpanded states of Mach 2 jet. Without sonic coflow, the core length of Mach 2 jet was found to increase with the increase of NPR which was quantified using shadowgraph visualization. For all the main jet NPRs, the increase in coflow NPR resulted in the increase of core length. For each NPR of Mach 2 jet, the core length increases with the increase of coflow NPR. The maximum core length for NPRs 4 to 6 was at coflow NPR of 6 and minimum was at coflow NPR 4. The sonic coflow was found to retard the mixing of Mach 2 jet at all the pressure ratios, but it resulted in weakening the strength of waves present in the core of Mach 2 jet.

Control of sonic jets by fluidic injection

The present experimental study aims at investigating the effect of fluidic injection by means of air tabs on the core of circular and square sonic jets issuing from orifice at different levels of underexpansion. The experiments were conducted by varying the injection pressure ratio (IPR) from 3 to 5 for a fixed nozzle pressure ratio (NPR) 3, 4 or 5. Shadowgraph visualization was used to quantify core length of jet with and without fluidic injection. The injection in both circular and square sonic jets resulted in reduction of core length at all the NPRs. For each NPR, the maximum and minimum core length reductions occurred at IPRs 5 and 3, respectively, showing that the mixing promotion in circular or noncircular sonic jets is influenced by momentum of the injected jet. Among the NPRs, the reduction in core length was maximum at NPR 3 and minimum at NPR 5 for both circular and square jets at all the IPRs. The injection caused a highest reduction in the core of square jet than the circular jet all NPRs except NPR 5. A highest reduction of about 50% was achieved at NPR 3 and IPR 5 for square jet.

Passive control of coaxial jet with supersonic primary jet and sonic secondary jet

The mixing enhancement of a coaxial jet with a Mach 1.4 primary jet and sonic secondary jet, at different convective Mach numbers, is presented in this study. Rectangular tabs of aspect ratios (AR = h/w, where h and w are the tab height and width, respectively) 2.0 and 0.75 were employed to manipulate the primary and secondary jets, respectively. The primary jet (C0) and coaxial jet without control or manipulation (C1) are studied in order to decouple the effects of rectangular tabs on jet mixing. Four different tab configurations were studied, viz., tabs placed in the primary jet (C2), tabs placed in the secondary jet (C3), and tabs placed in both primary and secondary jets with the relative orientation between them of 0° (C4) and 90° (C5), to document the effect of tabs on mixing. The supersonic core length Lc* of the manipulated jet was used as a measure to quantify the mixing performance of the manipulated jet. The secondary flow reduces the growth rate of the primary shear layer and elongates the supersonic core length. This study reveals that the manipulated jet emulates the characteristic of a non-circular jet. Primary tabs are highly effective in reducing the supersonic core length of the coaxial jet than secondary tabs, and hence, the jet mixing increases. Two different flow categories of the manipulated jet have been identified. The physical reason behind the observed jet mixing and flow categories have been presented based on arguments related to changes in the flow field and shock structure.

Flame shapes and thermal fluxes for an extensive range of horizontal jet flames

The prediction of the flame-geometry descriptors and thermal fluxes of jet flames may contributes to the provision of effective fire protection measures in industry plants. Previous works were mainly devoted to assess the related-hazardous effects of vertical jet fires, while horizontal ones were barely investigated. This paper collects a vast database of horizontal sonic and subsonic jet fire experiments involving multiple gas fuels and release conditions. Based on the experimental results, state-of-the-art correlations are developed to describe the flame shapes and thermal fluxes for extensive ranges of jet flames horizontally released.

Turbulent boundary layer subjected to a sonic transverse jet in a supersonic flow

Particle Image Velocimetry (PIV) technology, oil flow visualization and Nanoparticle-based Planar Laser Scattering (NPLS) technology are used to investigate the turbulent boundary layer (BL) of a sonic jet injected into a supersonic flow at Ma=2.95. Instantaneous and averaged NPLS images display detailed structures of the bow shock, the horseshoe vortex, separation zones and the collision shock. Root Mean Square (RMS) values of flow quantities calculated from NPLS images and PIV data reveal that turbulent fluctuations are suppressed downstream of the horseshoe separation zone in the jet lateral region and a 33%-35% reduction of the density fluctuation magnitude across the boundary layer is observed, while it is enhanced in the jet wake by 34%-50%. Further away from the wall, the influences of the λ shock system, the expansion process, and the reflected shock on turbulence intensity and velocities of the crossflow BL is weakened. A three-dimensional schematic diagram of the interaction between the sonic jet and the turbulent BL is presented, explaining the formation of the turbulence decay zone in the jet lateral region.