Supersonic Impinging Jets Research Articles

1110 ワイヤの挿入による超音速衝突噴流の自励振動の抑制(流体工学I)

1110 ワイヤの挿入による超音速衝突噴流の自励振動の抑制(流体工学I)

SPONTANEOUS NONEQUILIBRIUM CONDENSATION IN SUPERSONIC JETS IMPINGING ON CAVITY

Spontaneous condensation of moist air in supersonic jets is of considerable interest in a variety of natural and industrial processes. During impingement of supersonic moist air jets, the nonequilibrium homogeneous condensation can be experienced at the region between downstream of nozzle exit and an obstacle. The subsequent release of latent heat thus results in a deceleration of the flow and a rise in pressure, known traditionally as the condensation shock; likely have strong effect on the flow features. The present paper reported of the effect of spontaneous nonequilibrium homogeneous condensation of moist air on the aerodynamic and oscillatory flow features of supersonic jets impinging on cavity. A total variation diminishing (TVD) scheme was used to solve the time dependent Favre averaged Navier–Stokes equations, and the droplet growth equation of liquid phase production for simulating the condensing jets. Both qualitative and quantitative validations of the numerical model were accomplished, and the results showed a good agreement between the computed results and experimental data. Predicted flow and oscillatory features of jets were presented.

Ultra-high-speed 3D astigmatic particle tracking velocimetry: application to particle-laden supersonic impinging jets

The paper demonstrates ultra-high-speed three-component, three-dimensional (3C3D) velocity measurements of micron-sized particles suspended in a supersonic impinging jet flow. Understanding the dynamics of individual particles in such flows is important for the design of particle impactors for drug delivery or cold gas dynamic spray processing. The underexpanded jet flow is produced via a converging nozzle, and micron-sized particles (d p = 110 μm) are introduced into the gas flow. The supersonic jet impinges onto a flat surface, and the particle impact velocity and particle impact angle are studied for a range of flow conditions and impingement distances. The imaging system consists of an ultra-high-speed digital camera (Shimadzu HPV-1) capable of recording rates of up to 1 Mfps. Astigmatism particle tracking velocimetry (APTV) is used to measure the 3D particle position (Cierpka et al., Meas Sci Technol 21(045401):13, 2010) by coding the particle depth location in the 2D images by adding a cylindrical lens to the high-speed imaging system. Based on the reconstructed 3D particle positions, the particle trajectories are obtained via a higher-order tracking scheme that takes advantage of the high temporal resolution to increase robustness and accuracy of the measurement. It is shown that the particle velocity and impingement angle are affected by the gas flow in a manner depending on the nozzle pressure ratio and stand-off distance where higher pressure ratios and stand-off distances lead to higher impact velocities and larger impact angles.

Supersonic Jet Impingement on a Cylinder and Characterization of the Resulting Deflected Jets

The interaction between a mildly underexpanded supersonic jet and a single cylinder was studied experimentally at laboratory scale by using the schlieren technique coupled with high-speed photography and pitot pressure measurements. This study was motivated by the need to optimize sootblowing operation in kraft recovery boilers. The effects of the transverse distance between the jet and cylinder centerlines (eccentricity), nozzle–cylinder distance, and cylinder size on jet–cylinder interaction were determined. Results show that upon impingement on a cylinder, a supersonic jet deflects at an angle and creates a weaker supersonic jet that we refer to as a “secondary” jet. The angle and strength of the deflected or secondary jet depend on the eccentricity between the primary jet and cylinder centerlines. When a jet impinges on a cylinder of diameter comparable to that of the jet or smaller, secondary jets form not only when the cylinder is placed close to the nozzle (in the stronger portion of the jet) but also when the cylinder is placed far away (in the jet's weaker portion; up to 20–24 nozzle exit diameters in the present study). Changing the eccentricity slightly results in a significant change in the secondary jet characteristics. For a cylinder much larger than the jet, secondary jets do not form at zero eccentricity (head-on impingement); the eccentricity at which they begin to form increases with the cylinder size. A study of the secondary jets shows that they spread out much more than the primary jet and are sheet- or fan-like with an oblong, oval cross section. The centerline pitot pressure of the secondary jets remains as high as the primary jet for a considerable distance from the tube only during weak interaction between the primary jet and the cylinder (i.e., during strongly eccentric/off-centerd impingement). As the interaction between the primary jet and the cylinder intensifies at lower eccentricities, the maximum centerline pitot pressure of the secondary jet decreases, and the pitot pressure decreases more quickly with distance from the tube.

Computational study on the behaviours of supersonic jets and their impingement onto molten liquid free surface in BOF steelmaking

A mathematical model is proposed to study the impingement of multiple supersonic jets onto the free surface of the liquid bath containing molten slag and metal in a steelmaking converter by means of volume of fluid (VOF) approach. The applicability of the proposed model is verified by the good agreement with measured and calculated results. The model is then used to study the jet hydrodynamic behaviours such as jet profile, impact force, penetration depth and impact area, as well as time-dependent evolution of cavity, with respect to temperature, operating pressure and lance height. The results show that the temperature effect on total impact force is negligible but significant for penetration depth and impact area. A semi-empirical correlation is used to describe penetration depth under the steelmaking condition of high temperature. It is also shown that the proposed model can reproduce the splashing phenomenon on the bath surface.On propose un modèle mathématique pour étudier l’impact de jets supersoniques multiples à la surface libre du bain liquide contenant de la scorie et du métal fondus dans un convertisseur de production d’acier, au moyen de l’approche du Volume de Fluide (VOF). On vérifie l’applicabilité du modèle proposé par l’agrément entre les résultats calculés et les résultats mesurés. On utilise ensuite le modèle pour étudier les comportements hydrodynamiques du jet, comme le profil du jet, la force de choc, la profondeur de pénétration et la superficie de l’impact, ainsi que l’évolution de la cavité en fonction du temps par rapport à la température, à la pression d’opération et à la hauteur de la lance. Les résultats montrent que l’effet de la température sur la force totale de choc est négligeable mais qu’il est important pour la profondeur de pénétration et pour la superficie de l’impact. On utilise une corrélation semi-empirique pour décrire la profondeur de pénétration pour la production d’acier à température élevée. On montre également que le modèle proposé peut reproduire le phénomène d’éclaboussement à la surface du bain.

Large eddy simulation and Reynolds-averaged Navier-Stokes calculations of supersonic impinging jets at varying nozzle-to-wall distances and impinging angles

This paper utilises two different computational methods to investigate the characteristics of a supersonic impinging jet at non-dimensionalised nozzle-to-wall distances (Zn/D) of 1.5 and 2.5 with the impinging angles from 0° to 45°. The static Smagorinsky subgrid-scale model was chosen for the LES and the two equation k–∊ turbulence model for the RANS. Computational parameters applied in the simulations emulated the experimental setup conducted by Risborg (2008). From the results obtained, both methodologies were able to predict the location of the first shock cell fairly accurately when compared to the steady-state shadowgraph images of Risborg (2008). However, the intensities of the shocks were significantly different between the two numerical methods, with the RANS underestimating the value of the density gradients at the shocks. The pressure distribution near the impinging plate have been investigated and found to differ between the RANS and the LES for small impinging angles (0° and 10°) when Zn/D=1.5. In addition, the RANS data was not able to capture the recirculation zone for Zn/D=1.5 and 0°. The instantaneous velocity fluctuations and temperature contours of the LES were also plotted to visualise the shear layer instability and also the chaotic nature of the supersonic jet. For Zn/D=2.5 and 0°, the jet experiences high velocity fluctuations as the configuration causes the axially flapping instability. Overall, there are discrepancies between the RANS and LES but both are able to capture the key averaged flow features of the supersonic impinging jets.

Flow characteristics of hypersonic inlets with different cowl-lip blunting methods

Under hypersonic flight conditions, the sharp cowl-lip leading edges have to be blunted because of the severe aerodynamic heating. This paper proposes four cowl-lip blunting methods and studies the corresponding flow characteristics and performances of the generic hypersonic inlets by numerical simulation under the design conditions of a flight Mach number of 6 and an altitude of 26 km. The results show that the local shock interference patterns in the vicinity of the blunted cowl-lips have a substantial influence on the flow characteristics of the hypersonic inlets even though the blunting radius is very small, which contribute to a pronounced degradation of the inlet performance. The Equal Length blunting Manner (ELM) is the most optimal in that a nearly even reflection of the ramp shock produces an approximately straight and weak cowl reflection shock. The minimal total pressure loss, the lowest cowl drag, maximum mass-capture and the minimal aeroheating are achieved for the hypersonic inlet. For the other blunting manners, the ramp shock cannot reflect evenly and produces more curved cowl reflection shock. The Type V shock interference pattern occurs for the Cross Section Cutting blunting Manner (CSCM) and the strongest cowl reflection shock gives rise to the largest flow loss and drag. The cowl-lip blunted by the other two blunting manners is subjected to the shock interference pattern that transits with an increase in the blunting radius. Accordingly, the peak heat flux does not fall monotonously with the blunting radius increasing. Moreover, the cowl-lip surface suffers from severe aerothermal load when the shear layer or the supersonic jet impinges on the wall.

On the Assessment of Compressibility Effects of Two-Equation Turbulence Models for Supersonic Transition Flow with Flow Separation

An assessment of two-equation turbulence models, the low Reynolds k-<TEX>${\varepsilon}$</TEX> and k-<TEX>${\omega}$</TEX> SST models, with the compressibility corrections proposed by Sarkar and Wilcox, has been performed. The compressibility models are evaluated by investigating transonic or supersonic flows, including the arc-bump, transonic diffuser, supersonic jet impingement, and unsteady supersonic diffuser. A unified implicit finite volume scheme, consisting of mass, momentum, and energy conservation equations, is used, and the results are compared with experimental data. The model accuracy is found to depend strongly on the flow separation behavior. An MPI (Message Passing Interface) parallel computing scheme is implemented.

함정 수직발사대 화염처리장치 형상에 따른 유동특성 연구

The gas management system for a vertical launching system must be safely managed within a ship. The plenum and uptake are capable of containing and surviving a full-burning restrained firing without loss of gas management integrity. To secure the safety, the pressure characteristics with a supersonic under-expanded jet on a gas management system are numerically investigated using computational fluid dynamics. The results of present analysis and the preliminary design of the gas management system are described in this paper.Keywords : Gas Management System(화염처리장치), Vertical Launching System(수직발사대), Supersonic Impinging Jet(초음속 충돌 제트)

Homogeneous Condensation in Supersonic Impinging Jets onto Cylindrical Cavity

Over half a century researchers have engaged themselves in doing research on supersonic impinging jets for their fundamental fluid dynamic perspectives as well as their huge practical applications. In a variety of engineering applications steam or moist air is used as working gas. Rapid expansion of steam or moist air leads to an occurrence of non-equilibrium homogeneous condensation at the region between downstream of nozzle exit and an obstacle. Surrounding gas is heated due to the release of latent heat of condensation, and may affect the jet flow features. The present numerical work deals with the effect of condensation on the aerodynamic and oscillatory flow features of supersonic impinging jets onto a cylindrical cavity. A TVD scheme is used to solve the RANS equations and droplet growth equations for simulating condensation in the jet flowfield. The numerical code is validated through comparison with experimental results. Predicted flow and oscillatory properties of jets are presented.

Interaction between Underexpanded Supersonic Jet and Obstacle

When an underexpanded supersonic jet impinges on an obstacle, a self-induced flow oscillation occurs. This oscillation depends on the pressure ratio in the flowfield, the position of an obstacle and is related to the noise problems of aeronautical and other industrial engineering. The characteristic and the mechanism of self-induced flow oscillation, therefore, have to be understood to control the various noise problems. The characteristics of the oscillatory flowfield and the mechanism of an oscillation have to be studied further to control the oscillation. This paper aims to clarify the effect of the pressure ratio and the obstacle position on the mechanism of self-induced flow oscillation by the numerical analysis and the experiment, when the underexpanded supersonic jet impinges on the cylindrical body. From the result of this study, it is clear that occurrence of self-induced flow oscillation depends on the pressure balance in the flowfield.

Numerical Simulation of Supersonic Jet Impingement on Inclined Plate

Supersonic jet impinging on an inclined plate is explored numerically by solving Reynolds Averaged Navier Stokes (RANS) equations using a commercial solver. The numerical uncertainty is quantified by grid convergence index parameter analysis. Simulations capture crisply all the essential features of the flow field including jet boundary, jet shock, upper tail shock, front and behind plate shocks. Good agreement between computational and experimental results for different plate angles forms the basis of further analysis. Four different two equations turbulence models predict similar jet structures. Effect of plate angles, pressure ratio, nozzle-plate distance on impinged jet structures are evaluated from numerical results. It has been observed that with increase in the plate angle, the maximum pressure zone in the plate changed from crescent shape to round shape. Well resolved RANS simulations are capable of capturing finer details of supersonic impinging jets on inclined plate. Defence Science Journal, 2013, 63(4), pp.355 -362 , DOI:http://dx.doi.org/10.14429/dsj.63.2545

Role of coherent structures in supersonic impinging jets

This paper describes the results of a study examining the flow field and acoustic characteristics of a Mach 1.5 ideally expanded supersonic jet impinging on a flat surface and its control using steady microjets. Emphasis is placed on two conditions of nozzle to plate distances (h/d), of which one corresponds to where the microjet based active flow control is very effective in reducing flow unsteadiness and near-field acoustics and the other has minimal effectiveness. Measurements include unsteady pressures, nearfield acoustics using microphone and particle image velocimetry. The nearfield noise and unsteady pressure spectra at both h/d show discrete high amplitude impinging tones, which in one case (h/d = 4) are significantly reduced with control but in the other case (h/d = 4.5) remain unaffected. The particle image velocimetry measurements, both time-averaged and phase-averaged, were used to better understand the basic characteristics of the impinging jet flow field especially the role of coherent vortical structures in the noise generation and control. The results show that the flow field corresponding to the case of least control effectiveness comprise well defined, coherent, and symmetrical vortical structures and may require higher levels of microjet pressure supply for noise suppression when compared to the flow field more responsive to control (h/d = 4) which shows less organized, competing (symmetrical and helical) instabilities.

Simulation of Tonal Noise Generation by Supersonic Impinging Jets

Large-eddy simulations are performed using high-fidelity numerical schemes developed for turbulence simulations and computational aeroacoustics to study near-ideally expanded and tone-producing supersonic jets vertically impinging on a large flat plate. The simulations compute the complex interaction of the supersonic jet with the flat impingement plane and directly provide the noise generated by this interaction. Two jet-operating temperatures, which correspond to isothermal and heated conditions, are considered in the simulations. The simulation results from both cases are examined to investigate the intense tonal noise generation arising from the jet impingement. The comparisons between the simulation results and the corresponding experimental measurements generally show a reasonable agreement and provide credibility to the quality of the simulation predictions. The simulations reveal important details about the problem of interest, which are not observable from the experiments. A dynamic mode decomposition is performed to identify the dynamically important modes of the supersonic impinging-jet flowfield for the simulated conditions. The most dominant mode of the flowfield is found to possess a temporal frequency that corresponds to the fundamental impingement tone frequency. Coherent nearly axisymmetric structures in the flowfield are also identified, which are generated at the fundamental impingement tone frequency.

Characteristic and mechanism of pressure fluctuation caused by self-induced oscillation of supersonic impinging jet

When the underexpanded supersonic jet impinges on the obstacle, it is well known that the self-induced flow oscillation occurs. This oscillation depends on the pressure ratio in the flowfield, the position of an obstacle and is related with the noise problems of aeronautical and other industrial engineering. The characteristic and the mechanism of self-induced flow oscillation, have to be clarified to control various noise problems. But, it seems that the characteristics of the oscillated flowfield and the mechanism of an oscillation have to be more cleared to control the oscillation. This paper aims to clarify the effect of the pressure ratio and the obstacle position and the mechanism of self-induced flow oscillation by numerical analysis and experiment, when the underexpanded supersonic jet impinges on the cylindrical body. From the result of this study, it is clear that occurrence of the self-induced flow oscillation depends on the pressure balance in the flowfield.

Effect of Non-Equilibrium Condensation in Shear Layer on Supersonic Impinging Jets

Abstract Impinging jet on a solid surface can be found in various engineering applications. In the flow fields, the characteristics of impinging jet are generally found to become complex extremely. In various industrial jet technologies such as jet burner, steam turbine and so on, condensable gas is often used as working gas. In these cases, the non-equilibrium condensation may occur at the region between nozzle exit and an object. On the other hand, in reality, there is a variety of engineering applications for discharge of the dry air into the atmosphere with moisture. In this case, non-equilibrium condensation may occur in the shear layer and affect the jet structure or energy loss in the flow field. However, the feature of non-equilibrium condensing flow in the jet shear layer are not investigated so far satisfactorily. In the present study, the effect of local occurrence of non-equilibrium condensation in shear layer on the characteristics of an under-expanded supersonic impinging jet was investigated numerically. As a result, non-equilibrium condensation occurred in shear layer and increased the displacement thickness on flat plate.

Analysis of Acoustic-Fields Generated by a Supersonic Jet Impinging on Flat and Curved Inclined Plates

Analysis of Acoustic-Fields Generated by a Supersonic Jet Impinging on Flat and Curved Inclined Plates

1303 自励振動する超音速不足膨張衝突噴流中の衝撃波の振幅と周波数解析

1303 自励振動する超音速不足膨張衝突噴流中の衝撃波の振幅と周波数解析

The visualization of the acoustic feedback loop in impinging underexpanded supersonic jet flows using ultra-high frame rate schlieren

The use of modern ultra-high speed cameras to acquire time-resolved schlieren image sequences of supersonic jet impingement is presented. The use of these cameras, with framerates of up to 1 million frames per second, allows for the first time-resolved visualizations of the impinging jet acoustic feedback loop. The role of upstream travelling acoustic waves in generating perturbations in the jet shear layer at the nozzle exit is also directly observed for the first time. The arrival of the acoustic wave at the nozzle lip generates a sinusoidal variation in density gradient that persists until a distance of $$\frac{x}{d}=0.3$$ . A structure that rapidly evolves into a large-scale vortex ring forms at the trailing edge of this initial instability, first observed at approximately $$\frac{x}{d}=0.25$$ .

Conical separation zone formation at impingement of supersonic jet on obstacle under cold spraying

Impingement of supersonic jet upon substrate surface, in front of which conical separation zone is created artificially with the aid of a spike or particle under conditions typical of cold spraying on geometric and dynamic parameters, is considered. Numerical simulation is carried out. Simulation results are in qualitative agreement with experimental observation data. Preliminary analysis of obtained pattern of supersonic jet impingement shows that in local ring area, creation of more favorable conditions for cold spraying of fine particles sized 1 micron or less is possible comparing to typical conditions.