Flow Characteristics Of Jet Research Articles

Performance of an atmospheric plasma torch with various inlet angles

Atmospheric plasma torch has many useful characteristics such as high current, high temperature and highly intensive radiation power. The performance of non-transferred plasma torch is significantly dependent on jet flow characteristics out of nozzle. Also, the compulsory swirl is being produced to gain the shape that can concentrate the plasma to the center of gas flow. In this study, the thermal flow characteristics of non-transferred plasma torch are investigated under atmospheric conditions. Numerical analyses are carried out with various inlet angles considering the swirl strength. In order to solve the governing equations, we have used a commercial code, CFD-ACE+ with FVM and SIMPLER algorithm. Furthermore, the size of flame is also experimentally investigated with various gas species.

Two-Phase Flow Characteristics of Hot Water Discharged from a Thin Nozzle (2nd Report, Flow Characteristics of Self-Evaporating Two-Phase Free Jet)

The flow characteristics of an air-water two-phase jet and an evaporating steam water two-phase jet were investigated experimentally. The air-water two-phase jet has larger radius and denser droplets region near its center with the water-air flow ratio, and has similarity in velocity distributions. The evaporating steam-water two-phase jet has four types of flow patterns depending on the quality at the nozzle exit. The jet radiuses are larger and the axial decreasing rates of dynamic pressure in the center of jet are smaller in order of air single-phase jet, air-water two-phase jet, and steam-water two-phase jet.

Study on Structure of Pseudo-Shock Waves in Asymmetric Under-Expanded Jet (Steady Characteristics of a Single Jet)

The purpose of this study is to clarify the structure of pseudo-shock waves in under-expanded jet issuing from asymmetric nozzle with an oblique outlet. In particular, the steady characteristics of a single jet flow were studied. The flow was visualized by the shadowgraph method and the mean pitot pressures were measured. It was clarified that the asymmetric under-expanded jet was deflected by the stagnation pressure. As a result, it was found that the structure of pseudo-shock wave was affected considerably by the stagnation pressure in an air chamber and the outlet angle of nozzle, and consequently the structure of the pseudo-shock waves were different from the axisymmetric under-expanded jet.

矩形ノズルによる斜め衝突噴流の伝熱と流動特性(オーガナイズドセッション8 伝熱促進)

矩形ノズルによる斜め衝突噴流の伝熱と流動特性(オーガナイズドセッション8 伝熱促進)

Heat transfer from a laminar impinging: jet of a power law fluid

Results of a computational fluid dynamic simulation of the flow and heat transfer characteristics of a single axis-symmetric semi-confined laminar jet impinging normally on a plane wall are presented for purely viscous power law fluids. Effects of Reynolds number, jet exit velocity and nozzle-to-impingement target spacing are presented for several CMC (carboxymethyl cellulose) solutions in water which behave as power law fluids

Experimental study on flow characteristics of a sleeved jet into a main crossflow

AbstractExperiments were carried out on the hydraulic mechanism of the thermal shock caused by cold jet injection at a T‐junction with thermal sleeve in the reactor cooling system using digital particle imaging velocimetry (DPIV) technique to measure the flow in the main duct and in the annular space of the sleeve tube. The flow and vorticity characteristics were investigated at jet‐to‐crossflow velocity ratios of 0.5 to 4. There was a stream of discharge from the annular space at the rear part of the sleeve near the jet exit, which resulted in decreasing the influence of the jet on the downstream wall. The intensive vorticity in the near wake mainly originated from the shear layer vorticity of the jet and the annular discharge stream. The intensive vorticity soon broke down and dissipated, and further developed into the counterrotating vortex pair in the far wake. The flow in the annulus was closely dependent on R, and thermal protection of the sleeve would become evident at higher R. © 2003 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(1): 24–31, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10131

Experimental Investigation of Three Types of Clean Room Diffusers using Particle Image Velocimetry and Laser Doppler Velocimetry Techniques

The main purpose of this paper is to evaluate the main fluid mechanics parameters in the exit region of three different terminal systems commonly used for controlled environments such as clean rooms or operating theatres. Three different types of diffuser were tested i.e. a diffuser grid, a square ceiling diffuser and a swirling radial discharge diffuser. The paper presents results obtained experimentally which were carried out in order to study the flow characteristics of isothermal jets issuing from such devices. The study has been performed for four different air flow rates for each type of terminal tested. To characterise the flow with confidence and obtain high spatial resolution, a Particle Image Velocimetry technique and a Laser Doppler Velocimetry technique were used. For each case investigated, the results were plotted as velocity profile, velocity magnitude, turbulence intensity and vorticity. The study displays the particular behaviour of the flow generated by each terminal. Vorticity regions and turbulence spots were also detected and carefully localised for the investigated configurations.

Instantaneous energy separation in a free jet. Part I. Flow measurement and visualization

“Energy separation” is the re-distribution of the total energy in a fluid flow without external work or heat, and has potential to heat or cool a fluid without using a conventional heating or cooling system. However, currently obtainable heating and/or cooling effects are not big enough for practical applications. It is required to understand the mechanism of energy separation and investigate its enhancement methods. In the present study which consists of two parts, energy separation in a free jet is investigated with instantaneous velocity and total temperature measurements. As a method to enhance energy separation, acoustic excitation with various frequencies is examined. In this first part, an experimental study is performed to investigate the motion of the coherent vortical structure and its response to acoustic excitation in free jets whose Reynolds numbers are 8000 and 120,000. For the low Reynolds number jet, spectral analysis of instantaneous velocity and flow visualization by a schlieren system are performed to characterize the motion of the large scale coherent vortical structure. The frequency of dominant fluctuation, which represents the vortex passing frequency at a given axial location, is around Sr D ≈0.65 at z/ D=1 and moves to Sr D ≈0.4 at z/ D=4. When acoustic excitation is applied, the coherent structure develops more rapidly than in the absence of excitation regardless of the excitation frequency, but very regular and strong vortex pairing is observed only when acoustic excitation with Sr ex=0.9. The flow characteristics of the high Reynolds number jet are also investigated with spectral analysis. The result shows that the velocity fluctuation level is generally elevated, but the frequency of dominant fluctuation is still within 0.4⩽ Sr D ⩽0.6. The response to acoustic excitation is also very similar to the low Reynolds number jet.

Effect of Nozzle Geometry on the Flow Characteristics of Hydroentangling Jets

Cone-capillary nozzles with varying cone angles from 10° to 120° and a capillary diameter of 120μ are experimentally investigated for their application in the hydroen tanglement process. Cone-up and cone-down configurations in a range of water pressures of 30-120 bar are tested. The effects of the cone angle on flow parameters such as discharge and velocity coefficients and intact length are studied. Flow visualization techniques are used to recognize the flow regimes and characteristics and to inspect and compare the intact length and appearance of the jets. Cone-down nozzles with more consistent flow properties, lower discharges, and higher velocity coefficients are more suitable for the hydroentanglement process. Single-cone nozzles without capillaries and with varying cone angles are also tested. The flow properties of the jets from the single-cone nozzles are compared with the cone-capillary nozzles of the same cone angle to study the effect of the capillary section. The effect of the interaction of adjacent nozzles on the flow from multi-hole nozzles is studied, and the characteristics of the jets from the multi-hole nozzles are compared with the single-hole nozzles.

Three-Dimensional Investigation of a Laminar Impinging Square Jet Interaction With Cross-Flow

The flow and heat transfer characteristics of an impinging laminar square jet through cross-flow have been investigated numerically by using the three-dimensional Navier-Stokes and energy equations in steady state. The simulations have been carried out for jet to cross-flow velocity ratios between 0.5 and 10 and for nozzle exit to plate distances between 1D and 6D, where D is the jet width. The complex nature of the flow field featuring a horseshoe vortex has been investigated. The calculated results show that the flow structure is strongly affected by the jet-to-plate distance. In addition, for jet-to-plate spacing of one jet width and for jet to cross-flow velocity ratios less than 2.5 an additional peak occurs at about three-dimensional downstream of the jet impingement point. For high jet to cross-flow ratios two horseshoe vortices form around the jet in the case of small jet-to-plate spacings.

Three-Dimensional Heat Transfer of a Confined Circular Impinging Jet With Buoyancy Effects

This paper describes the heat transfer and flow characteristics of a single circular laminar impinging jet including buoyancy force in a comparatively narrow space with a confined wall. Temperature distribution and velocity vectors in the space were obtained numerically by solving three-dimensional governing equations for the Reynolds number Re=umD/ν=400-2000 and the dimensionless space, H=h/D=0.25-1.0. After impingement, heat transfer behavior on the impingement surface is divided into a forced convection region, a mixed convection region, and a natural convection region in the radial direction. The local heat flux corresponding to these three regions was visualized using a thermosensitive liquid crystal. Moreover, with the increase in Reynolds number, Re, and dimensionless space, H, the recirculation flow on the impingement surface moves downstream and its volume increases correspondingly. The Nusselt number averaged from r=0 to the minimum point of peripherally averaged Nusselt number, Num, was evaluated as a function of Re and H.

Flow and Heat Transfer Characteristics of Circular Impinging Jet Accompanying Annular Suction Flow (Reduction of Suction Flow Rate by Excess Length of Suction Pipe)

As one of the methods for reducing the suction flow rate in order to satisfy the operating condition as one blower, it was proposed to mount the excess length of the suction pipe from the injection pipe. The experiments were carried out to clarify the effects of various excess length of the suction pipe on the flow and heat transfer characteristics of a circular impinging jet accompanying an annular suction flow. As a result, it is found that the higher Nusselt number is obtained at the smaller suction flow rate adding the excess length of the suction pipe. Considering the power loss based on the pressure loss in the suction pipe, it is shown that the optimum excess length of the suction pipe is obtained as a half of the inner diameter of the injection pipe at given experimental conditions. In addition, the counter flow which seems to be an important factor increasing of the fluctuating velocity is observed inside of the suction pipe using Particle Image Velocimetry (PIV).

211 高温円形噴流の流れ場, 温度場の特性とその制御

211 高温円形噴流の流れ場, 温度場の特性とその制御

305 環状吸込流を付加した円形衝突噴流の流動特性 : 管径比および張出し長さの最適寸法

305 環状吸込流を付加した円形衝突噴流の流動特性 : 管径比および張出し長さの最適寸法

408 環状吸込流を付加した円形衝突噴流の流動特性 : 吹出し管助走長さの影響

408 環状吸込流を付加した円形衝突噴流の流動特性 : 吹出し管助走長さの影響

Effects of acoustic excitation positions on heat transfer and flow in axisymmetric impinging jet: main jet excitation and shear layer excitation

An experimental study is conducted to investigate the flow and heat transfer characteristics of an impinging jet with acoustic excitations. Two different acoustic excitation methods based on the locations of the actuator are tested and compared: one is a main jet excitation and the other is a shear layer excitation. Effects of excitation level on the heat transfer and flow characteristics are also investigated. Local Nusselt number distributions are measured on the impingement surface and velocity and turbulence intensity distributions are also measured. The forcing Strouhal numbers (excitation frequency, St) are 1.2, 2.4, 3.0 and 4.0 and the excitation level varies from 80 to 100 dB. When the vortex pairing is promoted by the excitation St of 1.2 with the main jet excitation, low heat transfer rates are obtained at the large nozzle-to-plate distances. For the excitation St of 2.4 with the main jet excitation, high heat transfer rates are obtained at the large gap distances due to the extended potential core length. The main jet excitation method shows similar heat and flow characteristics to the shear layer excitation although the basic flow schemes and the location of the forcing actuator are different. The effects of the acoustic excitation to the jet increase as the excitation level increases. Therefore, the excitation frequency and the excitation level are both important factors in the acoustic excitation.

High-speed jet flows over spillway aerators

The characteristics of high-speed air-entrained jet flow over a spillway aerator were investigated using experimental data. Three different ramp designs (as well as the case of no ramp) were tested in a channel where the bed slope was adjusted to 0, 0.17, and 0.57, respectively. The effects of aerator geometry and flow condition on the air-entrainment process within the water jet and on the pressure fluctuations in the impact region are the main focus of the investigation. An extensive data analysis was performed for data obtained from this study and from a similar laboratory study conducted by another investigator. Experimental relations were derived for nondimensional parameters of jet length, aerator cavity subpressure number, and aeration rates through the lower and upper nappes of the water jet. Scale effects for lower nappe aeration and aerator cavity subpressure number were considered and a good correlation was determined with prototype aerator measurements of Emborcaçao, Foz do Areia, and Keban dams for lower nappe aeration and Guri Dam for aerator cavity subpressure numbers. An aerator without a ramp may be subjected to excessive pressure fluctuations at the impact region due to insufficient air entrainment. Key words: air entrainment, aerator, scale effect, jet length, cavity subpressure.

축대칭 회전분사류의 초기 유동특성

축대칭 회전분사류의 초기 유동특성

Effect of Pulsations on Flow and Heat Transfer Characteristics of an Impinging Jet

Experiments are carried out to investigate the effect of pulsations on the flow and heat transfer characteristics of an axisymmetric impinging jet on a flat plate heated by using a gold coated aim. Vertex motion in the impinging jet is visualized using a fog generator, and a thermochromatic liquid crystal (TLC) technique is used to measure the time averaged local temperature distributions on the impingement plate. In addition, the quantitative data for mean velocity and turbulence intensity are obtained employing hot-wire anemometer. Parameters such as pulsating frequency (f = 0, 10 and 20 Hz) and the nozzle-to-palate spacing (H/D = 2, 10) are considered at the jet Reynolds number of 20,000. Consequently, the significant changes of flow structure and local Nusselt number distribution due to pulsations are observed. In the case of H/D = 2, the enhanced heat transfer coefficient exceeding 30 % is observed at the stagnation point. At the high H/D, heat transfer rate increases with pulsation frequency.

Heat transfer and flow structures in axisymmetric impinging jet controlled by vortex pairing

An experimental study is conducted to investigate the flow and heat transfer characteristics of an impinging jet controlled by vortex pairing. Two kinds of vortex control methods of secondary shear flow and acoustic excitation are applied. Local Nusselt numbers are measured on the impingement surface. Flow visualization, measurements of velocity and turbulence intensity and FFT analysis are used to understand the flow structures. The velocity ratio is changed from 0.45 to 1.75 for the shear flow control and the tested Strouhal number (excitation frequency, St D) is 1.2, 2.4, 3.0 and 4.0 for the acoustic excitation. Enhancement or reduction in heat transfer is obtained by the control of vortex pairing due to the change of flow structures. When the vortex pairing is promoted by the secondary counter-flowing (suction flow) and St D=1.2, low heat transfer rates are obtained at large nozzle-to-plate distances. Conversely, the jet flow has an extended potential core length with the secondary co-flowing (blowing flow) and St D=2.4 and 3.0. Thus high heat transfer rates are obtained at large gap distances.