Experimental investigation of liquid jet injection into Mach 6 hypersonic crossflow

The injection of a liquid jet into a crossing Mach 6 air flow is investigated. Experiments were conducted on a sharp leading edge flat plate with flush mounted injectors. Water jets were introduced through different nozzle shapes at relevant jet-to-air momentum–flux ratios. Sufficient temporal resolution to capture small scale effects was obtained by high-speed recording, while directional illumination allowed variation in field of view. Shock pattern and flow topology were visualized by Schlieren-technique. Correlations are proposed on relating water jet penetration height and lateral extension with the injection ratio and orifice diameter for circular injector jets. Penetration height and lateral extension are compared for different injector shapes at relevant jet-to-air momentum–flux ratios showing that penetration height and lateral extension decrease and increase, respectively, with injector’s aspect ratio. Probability density function analysis has shown that the mixing of the jet with the crossflow is completed at a distance of x/d _j  ~ 40, independent of the momentum–flux ratio. Mean velocity profiles related with the liquid jet have been extracted by means of an ensemble correlation PIV algorithm. Finally, frequency analyses of the jet breakup and fluctuating shock pattern are performed using a Fast Fourier algorithm and characteristic Strouhal numbers of St = 0.18 for the liquid jet breakup and of St = 0.011 for the separation shock fluctuation are obtained.     

Dynamic characteristics of pulsed supersonic fuel sprays

This paper describes the dynamic characteristics of pulsed, supersonic liquid fuel sprays or jets injected into ambient air. Simple, single hole nozzles were employed with the nozzle sac geometries being varied. Different fuel types, diesel fuel, bio-diesel, kerosene, and gasoline were used to determine the effects of fuel properties on the spray characteristics. A vertical two-stage light gas gun was employed as a projectile launcher to provide a high velocity impact to produce the liquid jet. The injection pressure was around 0.88–1.24 GPa in all cases. The pulsed, supersonic fuel sprays were visualized by using a high-speed video camera and shadowgraph method. The spray tip penetration and velocity attenuation and other characteristics were examined and are described here. An instantaneous spray tip velocity of 1,542 m/s (Mach number 4.52) was obtained. However, this spray tip velocity can be sustained for only a very short period (a few microseconds). It then attenuates very quickly. The phenomenon of multiple high frequency spray pulses generated by a single shot impact and the changed in the angle of the shock structure during the spray flight, which had already been observed in previous studies, is again noted. Multiple shock waves from the conical nozzle spray were also clearly captured.      

Droplet size and velocity characteristics of water-air impinging jet atomizer

A water-air impinging jets atomizer is investigated in this study, which consists of flow visualization using high speed photography and mean droplet size and velocity distribution measurements of the spray using Phase Doppler Anemometry (PDA). Topological structures and break up details of the generated spray in the far and near fields are presented with and without air jet and for an impinging angle of 90°. Spray angle increases with the water jet velocity, air flow rate and impinging angle. PDA results indicate that droplet size is smallest in the spray center, with minimum value of Sauter mean diameter (SMD) of 50 µm at the air flow rate of Q_m = 13.50 g/min. SMD of droplets increases towards the spray outer region gradually to about 120 µm. The mean droplet velocity component W along the air-jet axis is highest in the spray center and decreases gradually with increasing distance from the spray center. SMD normalized by the air nozzle diameter is found firstly to decrease with gas-to-liquid mass ratio (GLR) and air-to-liquid momentum ratio (ALMR) and then remain almost constant. Its increasing with aerodynamic Weber number indicates an exponential variation. The study sheds light on the performance of water-air impinging jets atomizers providing useful information for future CFD simulation works.     

Effects of the jet-to-crossflow momentum ratio on a sonic jet into a supersonic crossflow

Numerical investigation of a transverse sonic jet injected into a supersonic crossflow was carried out using large-eddy simulation for a free-stream Mach number M = 1.6 and a Reynolds number Re = 1.38 × 10⁵ based on the jet diameter. Effects of the jet-to-crossflow momentum ratio on various fundamental mechanisms dictating the intricate flow phenomena, including flow structures, turbulent characters and frequency behaviors, have been studied. The complex flow structures and the relevant flow features are discussed to exhibit the evolution of shock structures, vortical structures and jet shear layers. The strength of the bow shock increases and the sizes of the barrel shock and Mach disk also increase with increasing momentum ratio. Turbulent characters are clarified to be closely related to the flow structures. The jet penetration increases with the increase of the momentum ratio. Moreover, the dominant frequencies of the flow structures are obtained using spectral analysis. The results obtained in this letter provide physical insight in understanding the mechanisms relevant to this complex flow.     

Visual observations of supersonic transverse jets

We present experimental results on penetration of round sonic and supersonic jets normal to a supersonic cross flow. It is found that penetration is strongly dependent on momentum ratio, weakly dependent on free-stream Mach number, and practically independent of jet Mach number, pressure ratio, and density ratio. The overall scaling of penetration is not very different from that established for subsonic jets. The flow is very unsteady, with propagating pressure waves seen emanating from the orifice of helium jets.     

Experimental study on the condensation of supersonic steam jet submerged in quiescent subcooled water: Steam plume shape and heat transfer

The condensation of supersonic steam jet submerged in the quiescent subcooled water was investigated experimentally. The results indicated that the shape of steam plume was controlled by the steam exit pressure and water temperature. Six different shapes of steam plume were observed under the present test conditions. Their distribution as a function of the steam exit pressures and water temperatures was given. As the steam mass velocity and water temperature increase, the measured maximum expansion ratio and dimensionless penetration length of steam plume were in the ranges of 1.08–1.95 and 3.05–13.15, respectively. The average heat transfer coefficient of supersonic steam jet condensation was found to be in the range of 0.63–3.44 MW/m²K. An analytical model of steam plume was found and the correlations to predict the maximum expansion ratio, dimensionless penetration length and average heat transfer coefficient were also investigated.     

Experimental and numerical analysis of spray-atomization characteristics of biodiesel fuel in various fuel and ambient temperatures conditions

The purpose of this work is to reveal the effects of fuel temperatures and ambient gas conditions on the spray-atomization behavior of soybean oil methyl ester (SME) fuel. The spray-atomization behavior was analyzed through spray parameters such as the axial distance from the nozzle tip, local and overall Sauter mean diameter (SMD). These parameters were obtained from a spray visualization system and a droplet measuring system. In addition, the experimental results were compared with the numerical results calculated by the KIVA-3V code. It was revealed that the increase of the fuel temperature (from 300 K to 360 K) little affects the spray liquid tip penetration. The increase of the ambient gas temperature (from 300 K to 450 K) caused a increase in the spray liquid tip penetration. Also, biodiesel fuel evaporation actively occurred due to the increase in the fuel temperature and the ambient gas temperature. Of special significance was that the highest vapor fuel mass concentration was observed at the center region of the spray axis. In the results of the microscopic characteristics, the detected local droplet size at the axial direction and overall droplet size at the axial and radial direction in a control volume increased when the fuel temperature increased. This is believed to be due to an increase in the number of small droplets that quickly evaporated. In addition, the increased fuel temperature caused the decrease of the number of droplets and the increase of the vapor fuel mass. The mean axial velocity of droplets decreased with increasing fuel temperature.     

Hydrodynamic shock tube for quick transportation of spray with large flow rate

 This paper reports an experimental study of generating water spray with large flow rate by means of hydrodynamic shock tubes. A water column was put in the low-pressure section of the shock tube and high-pressure helium gas was added into the high-pressure section. When the diaphragm separating the gas and the water was ruptured by the high-pressure gas, the water column was driven downwards to discharge from the tube exit to form a jet/spray. Two kinds of rupture methods, namely quasi-static and dynamic processes, were tested. Flow visualizations confirmed that the gas/liquid contact surface and the generated jet/spray were quite unstable. Received: 8 December 2000 / Accepted: 20 July 2001     

Flowfield characteristics of a transverse jet into supersonic flow with pseudo-shock wave

We performed an experimental investigation of the flowfield of a transverse jet into supersonic flow with a pseudo-shock wave (PSW). In this study, we injected compressed air as the injectant, simulating hydrocarbon fuel. A back pressure control valve generated PSW into Mach 2.5 supersonic flow and controlled its position. The positions of PSW were set at nondimensional distance from the injector by the duct height (x/H) of ?1.0, ?2.5, and ?4.0. Particle image velocimetry (PIV) gave us the velocity of the flowfield. Mie scattering of oil mist only with the jet was used to measure the spread of the injectant. Furthermore, gas sampling measurements at the exit of the test section were carried out to determine the injectant mole fraction distributions. Gas sampling data qualitatively matched the intensity of Mie scattering. PIV measurements indicated that far-upstream PSW decelerated the flow speed of the main stream and developed the boundary layer on the wall of the test section. The flow speed deceleration at the corner of the test section was remarkable. The PSW produced nonuniformity in the main stream and reduced the momentum flux of the main stream in front of the injector. The blowing ratio, defined as the square root of the momentum flux ratio, of the jet and the main stream considering the effect of the boundary layer thickness was shown to be a useful parameter to explain the jet behavior.     

Transient positively and negatively buoyant turbulent round jets

 The transient character of the jet issuing from an upward nozzle centered at the bottom of a vertical cylindrical tank into bulk liquid of a different density was measured using flow visualization and PIV for varying densimetric Froude numbers by varying the jet Reynolds numbers and the ratios of fluid densities. Positively buoyant jets penetrate to the free surface, driven by both momentum and buoyancy in the upward direction. The lighter jet fluid stratifies in a layer above the bulk liquid. Upon starting, a negatively buoyant jet has three stages. First the jet penetrates to its maximum height in the tank. Then the jet penetration decreases due to the downward backflow of heavier fluid surrounding the jet, which reduces the jet’s upward momentum. Finally the jet penetration height fluctuates around a mean value about 70% the maximum height of penetration. For small negative Froude numbers, the flow is fountain-like. The downward flow turns radially outward as it reaches the bottom of the tank and eventually an annular recirculation zone forms at the bottom of the tank with vortical motion opposite the vorticity of the jet. For large negative Froude numbers, the spreading of the jet extends far enough so the annular downward flow is along the walls of the tank resulting in a large annular recirculation zone. The penetration depth, h, and time, t, scale with buoyancy flux, F, and the jet momentum flux, M, as hM ^-3/4∣F∣^1/2 and t∣F∣/M to collapse the transient jet penetration height data onto a single curve over a wide range of Froude numbers for either positively or negatively buoyant jets. Received: 8 June 1998/Accepted: 3 February 1999     

Axisymmetric impingement of a hot jet on a flat plate: equilibrium flow analysis of high-temperature air

The flow structure of an underexpanded supersonic jet with high reservoir temperature impinging on a flat plate has been numerically investigated using a Total Variation Diminishing (TVD) scheme. When the temperature of the flow field is high enough to cause chemical reaction, the specific heat ratio,, is no longer equal to 1.4, nor constant. This explains the difference found in the literature between the flow properties of the calorically perfect gas and that of the chemically reacting flow. Under the equilibrium flow assumption the effect of high temperature gas on the impinging jet has been taken into account in the present paper by using specific heat ratio and speed of sound given by correlation polynomials of thermodynamic variables. The limiting case of cold jet calculation in the present numerical results agreed well with the existing experimental data. For the equilibrium jet with high reservoir temperature,T _o=1000K, qualitative support of the present result has been provided by means of the approximation theory.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Low-density jets beyond a sonic nozzle at large pressure drops

The gas-dynamical structure of jets of a low-density diatomic gas beyond a sonic nozzle at large pressure drops under conditions of a transition from continuous medium processes to rarefied gas processes is examined on the basis of experimental data obtained in low-density gas-dynamical tubes using electron-beam diagnostics and the Pitot tube method. Isomorphism is shown in the density distribution and total pressure in all cross sections of the jet with respect to pressures at a constant value of the complex R_L=R_*/N^1/2(R_* is the Reynolds number in the critical cross section of the nozzle, and N is the ratio of the Pitot pressure and the pressure in the discharge chamber). It is shown on the basis of a comparison of local Reynolds numbers for all zones of the jet that this is an analog complex. The experimental data on the variation in the jet structure are presented as a function of the number R_L in the range of 5–600. For R_L> 100 the flow in the jet can be considered as continuous; for R_L< 5–10 the flow corresponds to a scattering process; the range of 5–10< R_L< 100 corresponds to a transitional state. Ranges of isomorphism of the jet with respect to R_* and N are indicated. Based on the results of the measurements, it is shown that the flow behind a Mach disk for R_L> 200 remains subsonic on the axis to a distance of several lengths of the primary cycle. A transition to supersonic velocity on the jet axis can occur with a decrease in the numbers R_L owing to ejection acceleration by the supersonic ring-shaped compressed layer.This word is apparently interchangeable with self-similarity-Translator.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 64–73, March–April, 1973.     

Interaction of a transverse gas jet with supersonic flow in a dihedral

The results of an experimental investigation of supersonic flow at the Mach number M₁=3 past a transverse gas jet flowing from an orifice in the edge of a dihedral with a linear angle of 90° are presented. The Mach number of the jet was varied from 1 to 3, and the ratio of the total pressure in the jet to the free stream pressure from 90 to 760. Visualization of the flow near the faces of the dihedral revealed the existence of internal lines of flow convergence and divergence in the region of three-dimensional separated flow, which indicates the presence of complex vortex structures. The dependence of the dimensions of the separated flow zone and the characteristic pressures in it on the jet parameters is explored.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, pp. 161–165, November–December, 1994.     

Spray Penetration in a Turbulent Flow

Analytical expressions for mass concentration of liquid fuel in a spray are derived taking into account the effects of gas turbulence, and assuming that the influence of droplets on gas is small (intitial stage of spray development). Beyond a certain distance the spray is expected to be fully dispersed. This distance is identified with the maximum spray penetration. Then the influence of turbulence on the spray stopping distance is discussed and the rms spray penetration is computed from a trajectory (Lagrangian) approach. Finally, the problem of spray penetration is investigated in a homogeneous two-phase flow regime taking into account the dispersion of spray away from its axis. It is predicted that for realistic values of spray parameters the spray penetration at large distances from the nozzle is expected to be proportional to t ^2/3 (in the case when this dispersion is not taken into account this distance is proportional to t ^1/2). The t ^2/3 law is supported by experimental observations for a high pressure injector. This revised version was published online in July 2006 with corrections to the Cover Date.     

Some features of spray breakup in effervescent atomizers

The near orifice spray breakup at low GLR (gas to liquid ratio by mass) values in an effervescent atomizer is studied experimentally using water as a simulant and air as atomizing gas. From the visualizations, the near orifice spray structures are classified into three modes: discrete bubble explosions, continuous bubble explosions and annular conical spray. The breakup of the spray is quantified in terms of the mean bubble bursting distance from the orifice. The parametric study indicates that the mean bubble bursting distance mainly depends on airflow rate, jet diameter and mixture velocity. It is also observed that the jet diameter has a dominant effect on the bubble bursting distance when compared to mixture velocity at a given airflow rate. The mean bubble bursting distance is shown to be governed by a nondimensional two-phase flow number consisting of all the aforementioned parameters. The location of bubble bursting is found to be highly unsteady spatially, which is influenced by flow dynamics inside the injector. It is proposed that this unsteadiness in jet breakup length is a consequence of varying degree of bubble expansion caused due to the intermittent occurrence of single phase and two-phase flow inside the orifice.     

Study of material agglomeration during nozzle injection of multiviscosity liquid into a fluidized bed reactor by the electric conductance method

Fluidized bed agglomeration is an important and challenging problem for thermal cracking in fluid cokers. A low coker temperature can be problematic because the bitumen is injected into the fluidized bed with a different viscosity, resulting in formation of agglomerates of varying sizes, which slows the cracking reactions. In the present study, the bed material agglomeration process during nozzle injection of multiviscosity liquid was investigated in a fluidized bed operated at different mass ratios of the atomization gas to the liquid jets (GLR = 1%–3.5%) and gas velocities (3.9U_mf and 5.9U_mf) based on a conductance method using a water–sand system to simulate the hot bitumen–coke system at room temperature. During the tests of liquid-jet dispersion throughout the bed, different agglomeration stages are observed at both gas velocities. The critical amount of tert-butanol in the liquid jets that could lead to severe agglomeration of the bed materials (poor fluidization) at GLR = 1% is about 10 wt% at the low fluidizing gas velocity (3.9U_mf) and 18 wt% at the high gas velocity (5.9U_mf). This study provides a new approach for on-line monitoring of bed agglomeration during liquid injection to guarantee perfect contact between the atomized liquid and the bed particles.     

Effect of Nozzle Exit Turbulence on the Column Trajectory and Breakup Location of a Transverse Liquid Jet in a Gaseous Flow

This study examines the effect of fully developed turbulent flow at the exit of nozzle/injector on the trajectory and column breakup location of a liquid jet injected transverly into a gaseous crossflow. Liquid jet trajectory and column breakup for different nozzle geometries at different velocities of liquid jet and crossflow are analytically and experimentally Investigated. Shadowgraph imaging technique is used to determine the jet trajectory and breakup location of a transverse liquid jet in a uniform airflow. Particle image velocimetry (PIV) is used to measure the near-field velocity profile of a liquid jet discgarged into a quiescent atmosphere. The experimental results show a higher penetration and breakup height for the liquid jet ensuing from a nozzle with a smaller length to diameter ratio. This is due to the surface irregularities of the liquid column of a turbulent jet, which breaks up and consequently follows the cross airflow sooner. In order to capture the effect of turbulence, the analytical trajectory correlation developed in our previous studies is modified to account for the discharge coefficient of a nozzle. The discharge coefficient is estimated indirectly by comparing the liquid column trajectory predicted by the modified analytical correlation with that determined experimentally. The indirectly determined discharge coefficient is then used in the analytical correlation for predicting the breakup height of a transverse liquid jet. The results predicted using this approach are in good agreement with the experimental data of the present study at standard temperature and pressure (STP) test conditions.     

Dynamics of turbulent air-flow in droplet driven sprays

This paper presents a study of the fundamental mechanics of droplet and gas motion in sprays. Only vertical sprays are considered and our theoretical analysis identifies two main flow zones, corresponding to where the droplet velocity is much greater than or of the same order as the induced air velocity. Analytical asymptotic results for the induced air velocity for small and large downstream distances confirmed a full numerical calculation and also agreed with experimental results. The second half of the paper deals with some of the most important aspects of spray jets in a cross flow. We find that the ratio of the cross-wind speed to the induced air jet speedU ₀/V _j is a crucial factor for specifying the dynamical behaviour. We present results for an axi-symmetric spray in uniform cross flow for bothweak andstrong cross-winds.     

The analysis of silica suspensions atomization

The paper contains the results of experimental investigation of air–water and air–silica suspension atomization process in effervescent nozzles with internal mixing obtained by the use of the digital microphotography method. In experiments the different aqueous solutions of silica Aerosil 300 of different concentration have been used. The suspensions containing up to 0.04 (kg solid particles/kg solution) have Newtonian rheological properties. The observations were carried out at liquid flow rates changed from 0.0014 to 0.011 (kg/s) and gas flow rates from 0.00015 to 0.0065 (kg/s). It corresponded to gas to liquid mass ratios (GLR) values from 0.014 to 0.46. The analysis of photos shows that the droplets which have been formed during the liquid atomization have very different sizes. The differences between characteristics of effervescent atomization for water and suspensions used have not been observed. The present study confirmed the previous reports which suggested that the small particles added to solution do not change spray characteristics. The experimental results show that C_D and SMD are non-linear functions of GLR. Their values are decreasing rapidly as GLR is increased from zero to around 0.07 and thereafter decreasing at a slower rate with further increase in GLR. In the same point (GLR = 0.07) the value of α is maximal. The first regime is characteristic for bubbly flow. The second is typical of annular flow regime. Boundary between bubbly and annular flow regime is observed at GLR = 0.07 for investigated systems. The correlations for C_D and Sauter mean diameter were proposed. The results may be used for example to verify numerical models or comparisons with respect to similar atomization processes.