Flow Characteristics Of Jet Research Articles

K-1320 同軸噴流に及ぼす外側・内側噴流加振の影響(S15-6 噴流構造とその制御)(S15 噴流・はく離流れの計測と制御)

K-1320 同軸噴流に及ぼす外側・内側噴流加振の影響(S15-6 噴流構造とその制御)(S15 噴流・はく離流れの計測と制御)

Velocity Field Measurements of a Vertical Turbulent Buoyant Jet Using a PIV Technique

The flow characteristics of a turbulent buoyant jet were experimentally investigated using a single-frame PIV system. The Reynolds number based on the nozzle exit velocity and nozzle diameter was about Re=510. The instantaneous velocity fields in the streamwise plane passing the jet axis were measured in the near field X/D does not affect a significant influence to the flow structure in the near field, but the total entrainment rate is increased slightly. The entrainment rate shows a linear variation with the streamwise distance in the region after X/D=5.0.

Study of the Flow Characteristics of Supersonic Coaxial Jets

Supersonic coaxial jets are investigated numerically by using the axisymmetric, Wavier-Stokes equations which are solved using a fully implicit finite volume method. Three different kinds of coaxial nozzles are employed to understand the flow physics involved in the supersonic coaxial jets. Two convergent-divergent supersonic nozzles are designed to have the same Mach number 2.0, and used to compare the coaxial jet flows with those discharging from one constant-area nozzle. The impingement angle of the annular jets are varied. The primary pressure ratio is changed in the range from 2.0 to 10.0 and the assistant jet ratio from 1.0 to 3.0. The results obtained show that the fluctuations of the total pressure and Mach number along the jet axis are much higher in the constant-area nozzle than those in the convergent-divergent nozzles, and the constant-area nozzle lead to higher total pressure losses, compared with the convergent-divergent nozzles. The assistant jets from the annular nozzle affect the coaxial jet flows within the distance less than about ten times the nozzle throat diameter, but beyond it the coaxial jet is conical with self-similar velocity profiles. Increasing both the primary jet pressure ratio and the assistant jet pressure ratio produces a longer coaxial jet core.

504 環状吸込流を付加した円形自由噴流の流動特性に及ぼす吹出し管径の影響(流体工学 : 噴流)

504 環状吸込流を付加した円形自由噴流の流動特性に及ぼす吹出し管径の影響(流体工学 : 噴流)

Flow Mechanism of a Submerged Jet Impinging on a Free Interface.

We report time-dependent flow characteristics of a turbulent water jet impinging vertically upward upon a water-air interface. Mexican-hat wavelet transform was applied to the time-dependent velocity fluctuations obtained in the region near to the air-water interface in order to analyze spatiotemporal turbulent structure at different time scales. The further understanding of the physical meanings of the wavelet transforms was tried by the analysis using logarithmic expectation and information entropy of information theory. The near-interface turbulent structure is constituted not only by the impingement of the large-scale structure of the approaching turbulent jet but also by the time-dependent deformation of the surface bump. Time-series images of the surface bump visualized by an argon laser sheet technique showed some periodical regulation of the surface bump coming from the large-scale structure of the impinging jet

LASER DIAGNOSTICS OF TRANSVERSE TURBULENT JETS

Experiments were conducted in a low-speed wind tunnel to understand the influence of nozzle geometry on the flow characteristics of incompressible air jets injected normal to a freestream. Jets issuing from circular and noncircular nozzles, with exit Reynolds numbers in the range 4500-9200 and velocity ratios from 3.8 to 7.7 are investigated. Measurements, in the zone of established flow, were carried out by laser light sheet flow visualization coupled with image processing, and laser Doppler anemometer techniques. Results show that, with increasing aspect ratio of the nozzles, the jet penetration increases ans carries stronger bound vortex pairs compared with the circular case. The deflected circular and square jets exhibit similar flow characteristics.

C203 衝突噴流の時・空間温度および流動特性(オーガナイズドセッション6 : 自由噴流,衝突噴流およびはく離を伴う熱・物質移動)

C203 衝突噴流の時・空間温度および流動特性(オーガナイズドセッション6 : 自由噴流,衝突噴流およびはく離を伴う熱・物質移動)

Simulation of a Round Jet and a Plume in a Regional Atmospheric Model

The mean flow characteristics of a turbulent round jet and a plume are simulated in a high-resolution regional atmospheric model. The model used for the study is the Advanced Regional Prediction System (ARPS). It is observed that the predicted flow characteristics are very sensitive to the turbulence closure scheme used. Among the three closure options in ARPS, namely, the constant eddy viscosity scheme, the Smagorinsky diagnostic closure, and the 1.5-order total kinetic energy scheme, the constant eddy viscosity scheme predicts the jet characteristics in better agreement with experiments. For the plume, all three schemes are unsatisfactory. It is shown that a modification of the constant eddy viscosity scheme incorporating a length-scale variation as suggested by theory predicts plume characteristics in good agreement with experiments. The simulations are carried out at one fixed grid-box size and flow inlet conditions; extending the present simulation results to other cases is discussed.

PIV measurements of the flow and turbulent characteristics of a round jet in crossflow

The instantaneous and ensemble averaged flow characteristics of a round jet issuing normally into a crossflow was studied using a flow visualization technique and Particle Image Velocimetry measurements. Experiments were performed at a jet-to-crossflow velocity ratio, 3.3 and two Reynolds numbers, 1,050 and 2,100, based on crossflow velocity and jet diameter. Instantaneous laser tomographic images of the vertical center plane of the crossflow jet show that there exists very different natures in the flow structures of the near field jet due to Reynolds number effect even though the velocity ratio is same. It is found that the shear layer becomes much thicker when the Reynolds number is 2,100 because of the strong entrainment of the inviscid fluid by turbulent interaction between the jet and crossflow. The mean and second order statistics are calculated by ensemble averaging over 1,000 realizations of instantaneous velocity fields. The detail characteristics of mean flow field, streamwise and vertical rms velocity fluctuations, and Reynolds shear stress distributions are presented. The new PIV results are compared with those from previous experimental and LES studies.

Measurements of impinging jet flow and heat transfer on a semi-circular concave surface

An experimental study of fluid flow and heat transfer has been carried out for jet impingement cooling on a semi-circular concave surface. The distributions of mean velocity and velocity fluctuation on the concave surface have been measured in free, impinging and wall jet flow regions by using a Laser Doppler Anemometer. Local Nusselt numbers have also been measured. Variations of jet Reynolds numbers, the spacing between the nozzle and the target and the distance from the stagnation point in the circumferential direction have been considered. Emphasis has been placed on measuring turbulent jet flow characteristics including impinging and evolving wall jets and interpreting heat transfer data, particularly, the occurrence and its location of secondary peak in connection with data of measured mean velocity and velocity fluctuations on the concave surface.

PIV Measurements of Flow and Turbulence Characteristics of Round Jet in Crossflow

The instantaneous and ensemble averaged flow characteristics of a round jet issuing normally into a crossflow was studied using a flow visualization technique and Particle Image Velocimetry measurements. Experiments were performed at a jet-to-crossflow velocity ratio, 3.3, and two Reynolds numbers, 1050 and 2100, based on crossflow velocity and jet diameter. Instantaneous laser tomographic images of the vertical center plane of the crossflow jet showed that there exist very different natures in the flow structures of the near field jet even though the velocity ratio is the same. It was found that the shear layer becomes much thicker when the Reynolds number is 2100 due to the strong entrainment of the inviscid fluid by turbulent interaction between the jet and crossflow. The mean and second order statistics were calculated by ensemble averaging over 1000 realizations of instantaneous velocity fields. The detail characteristics of mean flow field, stream wise and vertical r.m.s. velocity fluctuations, and Reynolds shear stress distributions were presented. The new PlV results were compared with those from previous experimental and LES studies.

623 同軸噴流の噴流特性に及ぼす外側・内側噴流加振の影響

623 同軸噴流の噴流特性に及ぼす外側・内側噴流加振の影響

Flow Characteristics, Enhancement and Control of Fluctuation of Resonance Jet.

The enhancement of fluctuation of jet is very important in order to improve the mixing or diffusion properties with the surroundings. There are many ideas about this, and the use of resonance jet will be also one of them. But the details of the flow characteristics of resonance jet has not been made clear. In this paper the flow characteristics, such as resonance frequency, mean and fluctuating velocity profiles, spread of the jet and others, of the resonance turbulent jet and their control by changing the volume, length, of resonance room are made clear experimentally. As a result, the fluctuation and the decay of center line velocity of resonance jet are very large compared with conventional jet and others are made clear.

Flow Analysis on Near Field of Elliptic Jet Using a Single-Frame PIV

Flow characteristics of turbulent elliptic jets were experimentally investigated using a single-frame PIV system. A sharp-edged elliptic nozzle with aspect ratio(AR) of 2 was tested and the experimental results were compared with those of circular jet having the same equivalent diameter(). The Reynolds number based on the nozzle exit velocity and nozzle equivalent diameter was about . The spreading rate along the major and minor axis are different remarkably. The jet half width along the major axis decreases at first and then increases with going downstream. But along the minor axis the jet width increases steadily. The elliptic jet of AR=2 has one switching points at within the near field. Turbulence properties are also found to be significantly different along the major and minor axis planes.

Modelling of Laminar Plasma Jet Impinging on a Flatplate with Approximate Box Relaxation Method

Approximate Box Relaxation method was used to simulate a plasma jet flow impinging on a flatplate at atmospheric pressure, to achieve a better understanding of the characteristics of plasma jet in materials surface treating. The flow fields under different conditions were simulated and analyzed. The distributions of temperature, velocity and pressure were obtained by modelling. Computed results indicate that this numerical method is suitable for simulation of the flow characteristics of plasma jet, and is helpful for understanding of the mechanism of the plasma-material processing.

Experimental and numerical analysis of circular pulse jets

Unsteady circular jets are treated experimentally and numerically. The time evolution of circular pulse jets is investigated systematically for a wide range of jet strength, with the focus on the jet evolution, in particular the formation processes of Mach disks in the middle stage and of shock-cell structures in the later stage. It is shown that unsteady second shocks are realized for all sonic underexpanded jets and they either breed conical shocks for lower pressure ratios or truncated cones (Mach disk and reflected shock) for higher pressure ratios. The vortex ring produced near the nozzle lip plays an important role in the formation of the shock-cell structure. In particular, interactions between the vortex ring and the Mach disk connected with a strong second shock affect remarkably the formation process of the first shock cell. Different formation processes of the first cell structure are found. It is also made clear that the Kelvin–Helmholtz instability along slip surfaces originating from the triple point at the outer edge of the Mach disk is responsible for the generation of large second vortices which entrain the first vortex. This results in strong mixing between the primary jet and surrounding gas for higher pressure ratios. Numerical simulations with a TVD-scheme for the Euler equations are also performed and the numerical results are compared with the experimental ones to understand and predict the flow characteristics of the pulse jets.

310 環状吸込流を付加した円形自由噴流の流動特性

The effects of the jet velocity on the flow characteristics of the circular free jet added the annular suction flow were examined, provided that the velocity ratio of the suction velocity to the jet velocity is the same. The two-dimensional flow field was measured by PIV, and the pass frequency of vortices was analyzed by FFT analyzer using a hot wire. As a result, it was found that the time mean velocity and turbulent statistical values of the flow field in the vicinity of the exit of the pipe are approximately the same in all cases of the jet velocity. Therefore, it was clarified that the velocity ratio is one of parameter that dominates the diffusion phenomenon. It was found that the pass frequency of the vortices is observed clearly in the velocity ratio more than 0.84. As the Strouhal number shows almost a fixed value in all cases of the jet velocity, similarity of the unsteady flow was also confirmed.

Measurements of a confined jet

In this paper we study the flow characteristics of an air jet issuing from a rectangular nozzle of aspect ratio 6.0 into a confined chamber. Hot-wire measurements of mean and root mean square velocities were made in the mixing layers and interaction region of the jet, at two Reynolds numbers. The results showed that the mean velocity profiles achieved approximate self-preservation almost immediately after the end of potential core. However, the self-similarity of root mean square velocity profiles was established only after a distance of 12 nozzle widths downstream of the nozzle exit. The decay rate of the confined jet was found to be almost three times less than that of square and circular free jets but was greater than that of plane free jets by 10–30% with laminar initial conditions and similar Reynolds number (<8000). The spreading rate of the confined jet was found to be quite similar to that of the plane free jets but higher than the circular and square free jets. It is deduced from the results obtained that although the confined jet is three-dimensional flow in nature, the decay rate of the confined jet follows more closely to that of a two-dimensional type of flow rather than that for a three-dimensional flow.

Flow Characteristics of Splined Tipped Circular Jets

Flow Characteristics of Splined Tipped Circular Jets

Flow Characteristics and Their Control of Particle Larden Gas-Solid Two-Phase Annular Jet.

Annular jet has a larger contact area with the ambient than that of a round jet when the flow rate is same, and also the flow charcteristics can be controlled by coaxial round jet. The authors made clear already the mean and the fluctuating flow characteristics of annular air jet and their control by coaxial round air jet. In this paper the flow characteristics of gas-solid two-phase annular jet and their control using coaxial round air jet are discussed by the numerical and experimental analyses. The numerical analysis was carried out using k-ε turbulent model and two-way method in order to take accout the effects of dispersed phase (fine solid particles) on continuous phase (air). The turbulent charceteristics were evaluated by random simulation.