Flow Characteristics Of Jet Research Articles

Numerical Investigations of Flow and Heat Transfer Characteristics Between Turbulent Double Jet Impingement and a Moving Plate

The analysis of fluid flow and heat transfer characteristics of double turbulent jet flow impinging on a stationary and moving plate has been numerically studied. Unsteady-state two-dimensional incompressible turbulent forced convection flow is considered for present analysis. Turbulence is modelled by the Reynolds-averaged Navier–Stokes (RANS) equation with the k − ε model and enhanced wall treatment. The governing equations are solved using a finite volume based commercial solver. The results for the effect of single jet and double jet, jet Reynolds number, plate velocity, location, and center spacing between the two jets on flow and heat transfer characteristics are reported. The results show that the enhancement of heat transfer is 32.70% for the double jet compared with the single jet impingement on a stationary plate. As significant enhancement of heat transfer is observed with an increase in the second jet Reynolds number and plate velocity. The results show that the size and shape of the recirculation zones between jets are greatly altered with respect to spacing between the jets to the plate and the center distance between the jets. The results show that the enhancement of heat transfer is 37.3% for moving plate velocity due to a decrease in the spacing between the jets and the plate from 6 to 4. Results show that the local peak Nusselt number is influenced by the plate velocity. These results are validated by experimental and numerical results available in the literature.

Experimental investigation on thermal and flow characteristics of synthetic jet with multiple-orifice of different shapes

The impingement heat transfer characteristics of a multiple-orifice synthetic jet of circular, oval and diamond orifice shapes are investigated experimentally at different Stokes number, normalized axial distance and pitch ratio. In this study, particle image velocimetry (PIV) based measurements are also undertaken to better understand the underlying flow characteristics of multiple-orifice synthetic jet and to support the associated heat transfer data. The average Nusselt number (Nuavg) obtained with multiple-orifice synthetic jet is up to 75% higher than a single orifice synthetic jet using the same input power to synthetic jet actuator. For larger pitch ratio (R > 1.25), the maximum value of Nuavg is observed to be reduced and obtained closer to heated surface. Multiple-orifice configurations with diamond shape exhibited better thermal performance as compared to other shapes examined in the study. The multiple-orifice configurations with one and two satellite orifices demonstrated two local peaks in Nuavg and are observed only with smaller values of pitch ratio. The location of these local peaks illustrated very little or no dependence on Stokes number (S). Configurations with no center orifice exhibited significantly lower heat transfer as compared to the configurations with center orifice as well as the case with single center orifice. The secondary maxima in Nuavg are entirely missing in the configurations with no center orifice. The PIV data reveals interactions between the adjacent synthetic jets in multiple-orifice case to form a combined synthetic jet with better mixing characteristics as compared to a single orifice synthetic jet and therefore the former exhibits higher heat transfer rate. The PIV data further illustrated the individual behavior of synthetic jets resulting from satellite orifices in multiple-orifice configurations with no center orifice. In addition to heat and flow characteristics of multiple-orifice synthetic jet, the heat transfer correlations are also developed from the experimental data for different orifice shapes. The study of multiple-orifice synthetic jet presented here is expected to be useful in designing the cooling modules for electronic devices.

Time-resolved particle image velocimetry measurements of a single impinging jet in the upper plenum of a scaled facility of high temperature gas-cooled reactors

In this study, the flow characteristics of a single isothermal jet discharging into the upper plenum of a 1/16th scaled facility of high temperature gas-cooled reactors was experimentally investigated. Time-resolved particle image velocimetry (TR-PIV) measurements were performed in the central plane of the jet flow and the upper plenum for various jet Reynolds numbers ranging from 3, 413 to 12, 819. From the acquired TR-PIV velocity snapshots, statistical characteristics of the jet flows such as the mean velocity, root-mean-square fluctuating velocity, and Reynolds stress were computed and presented. Furthermore, two-point velocity cross-correlations, spectral analysis, and squared coherent functions were performed on the TR-PIV velocity vector fields. The estimated integral length scales were found to linearly increase downstream and along the jet shear layers in the axial direction, while the squared coherent functions remained close to unity for small spatial separations and lower frequencies up to 50 Hz for points at y/Dj=1 and 2.

Quantitative visualization of the three-dimensional flow structures of a sweeping jet

The flow characteristics of a sweeping jet ejecting from a typical feedback channel fluidic oscillator were investigated using time-resolved particle image velocimetry. The three-dimensional flow structure of the jet was examined through the instantaneous and averaged velocity fields measured at the streamwise center plane and cross-sectional planes of the jet for a range of Reynolds numbers (8000, 12,000, 16,000, 20,000, and 24,000). As the Reynolds number increases, the frequency of the sweeping jet linearly increases from 0.7 to 2 Hz. However, the switching time of the jet flow direction from one side to the other is very short compared to the sweeping period. As a result, the ensemble-averaged flow patterns of the sweeping jet at the streamwise center plane look like twin jets issued from a V-shaped nozzle, regardless of the Reynolds number. The rapidly switching jet contains a counter-rotating vortex at the cross-sectional plane of the jet near the nozzle, similar to a cross-flow jet. The coherent vortex structures are rapidly destroyed and become random when the jet moves downstream.

Heat transfer of a sweeping jet impinging at narrow spacings

Sweeping jet, featuring with temporally continuous and spatially oscillating flow, has attracted a large amount of attention. In the present study, the heat transfer and flow characteristics of a sweeping jet impinging at narrow spacings were investigated. Effects of Reynolds number (i.e., Re = 5000, 10,000, 15,000) and jet-to-wall spacing (i.e., H/D = 0.5, 1.0, 2.0, 3.0) on heat transfer were quantified extensively by using the TSP technique. A high-resolution Particle Image Velocimetry (PIV) system was applied to correlate the heat transfer results with the flow fields pertinent to jet impingements. The heat transfer of sweeping jet was found to increase as the Reynolds number increased and as the jet-to-wall spacings decreased. At Re = 5000 and 10,000, compared to the circular jet, the sweeping jet demonstrated a lower heat transfer in the near-nozzle regions (i.e., x/D < 4) but slightly higher performance in the far regions. At Re = 15,000, however, it exhibited an improved performance across the domain at H/D = 0.5 and 1.0, with a maximum of 40% enhancement around the stagnation region. In general, the sweeping jet could provide superior performance to the circular jet at high Reynolds number and narrow spacing.

Effect of Offset Ratio on Fluid Flow Characteristics of Two-dimensional Offset Jet

Effect of Offset Ratio on Fluid Flow Characteristics of Two-dimensional Offset Jet

Flow Characteristics of a Rectangular Jet with Delta Tabs

Flow Characteristics of a Rectangular Jet with Delta Tabs

Flow and heat transfer characteristics of multi-armed impinging jet using DNS

Flow and heat transfer characteristics of multi-armed impinging jet using DNS

Flow and heat transfer characteristics of multi-armed impinging jet using DNS

Flow and heat transfer characteristics of multi-armed impinging jet using DNS

Analysis of the flow characteristics of the high-pressure supercritical carbon dioxide jet

The supercritical carbon dioxide (SC-CO2) jet has a wide application prospect for rock breaking and jet fracturing in the development of the unconventional shale energy, due to its special physicochemical properties. To investigate its jet flow characteristics, the high-speed photography is used in experiments and the simulations through a compressible numerical model are carried out. It is shown that the jet flow field can be divided into three typical regions, the mixing layer possesses the same characteristics as a gas/gas turbulent mixing layer, with the divergent angles evidently smaller than those of the incompressible jets. The predicted results by the numerical model are in a good agreement with those of the experimentations. Through the dimensionless analysis, the potential core shows a length of about 9d and an increasing trend with the increase of the inlet pressure while the decay rate shows a decreasing trend, and the radial profiles consistent well with the “Ue - η” normalized method. In addition, a significant temperature drop of the SC-CO2 is observed between the nozzle inlet and the exit. A simple and convenient semi-empirical equation for calculating this temperature variation is deduced. Finally, the flow characteristics suggest that the SC-CO2 jet should be treated as a compressible jet.

Experimental study on jet flow characteristics of fire water monitor

Fire water monitor is an important part of a sprinkler system. In this study, the jet flow characteristics of the external jet of the fire water monitor are studied. The water jet system is used to launch the water jet experiment under six pressures. A high-speed camera is used to obtain the water jet images. The feature extraction of water jet is obtained based on image processing technology, and it is used to study the jet diffusion angle and bundling of the fire water monitor under different pressures. The results of this study show that the jet pressure is an important parameter, which has a great influence on the cluster and surface characteristics of the jet. The fire water monitor has a limited range of pressure. When the pressure is constant, the jet distance determines the size of the air acting on water column, so the cluster and surface characteristics of the water column have changed obviously with the jet distance.

Heat transfer enhancement of a heated cylinder with synthetic jet impingement from multiple orifices

This study proposed and investigated a method to enhance the heat transfer performance of a heated cylinder with synthetic jet impingement from multiple orifices. A synthetic jet has a flow with alternately changing orientations at its exit and eventually generates a periodic flow in constant orientation in the area far from the exit. First, the flow characteristics of synthetic jets generated from the multiple orifices on a piccolo tube were investigated in detail with a hot-wire anemometer. Next, the heat transfer of a heated cylinder was enhanced with multiple synthetic jets. The Nusselt number of the heated cylinder was calculated using the temperature variation of the cylinder with time. The heat transfer rate enhanced with multiple synthetic jets was 2–3 times higher than that without jets. The results also showed that the heat transfer rate with upward-oriented jets from the piccolo tube located below the heated cylinder was higher than that with downward-oriented jets from the tube located above the cylinder. We also compared synthetic jets to continuous jets generated with a high-pressure air source. The results showed that the effects of the synthetic jets were valid at greater distances than those of the continuous jets.

Reynolds number effect on flow characteristics of surface single and twin jets

ABSTRACTTurbulent characteristics of single and twin jets interacting with a free surface were investigated using a particle image velocimetry system. The exit Reynolds numbers were varied from 2300 to 11,900 at an offset height of two nozzle widths from the free surface. Galilean decomposition showed, irrespective of the Reynolds number, the free surface weakens the instantaneous spanwise vorticity. The jet attachment point to the free surface was located and found to be sensitive at lower Reynolds number. Scaling parameter for the surface velocity defect and turbulence intensities were explored for the single and twin jets. The mixing characteristics of the jets were investigated using maximum velocity decay rate, spread rate and entrainment coefficient, and results showed that the shear layer away from the free surface developed downstream like a free jet. One-dimensional profiles of mean velocity and Reynolds stresses were independent of Reynolds number except in the location of the attachment point.

CFD Analysis of Twin Turbulent Impinging Round Jets at Different Impingement Angles

Round jets impinging at multiple impingement angles were considered for this study to gain better understanding of the parameters affecting resultant jet growth and velocity distribution. Work done by the authors previously on single jet has helped to establish that the SST (Shear Stress Transport) k-ω model is the ideal turbulence model for predicting flow characteristics of jets exiting a fully developed pipe at low Reynolds number. Hence, for the study of impinging jets, SST k-ω turbulence model was used to study the velocity and jet growth characteristics. Based on the mesh obtained from the grid sensitivity study, jets impinging at 30, 45 and 60 degrees at Reynolds number of 7500 were numerically analyzed. It was observed that the profile of the resultant jet closely matched with the prediction of elliptical profile predicted by past researchers. In addition, it was seen that higher jet growth was predicted in the case of jets impinging at a higher impingement angle.

Comparative study of flow characteristics of a single offset jet and a turbulent dual jet

The present paper consists of a numerical investigation of dynamic and thermal characteristics of the flow field resulting from the interaction of dual-jet consisting of a wall jet and an offset jet and comparison with a single turbulent offset jet. The effects of velocity and offset ratios between two jets in the near field region have been simulated numerically using two-dimensional steady RANS equations. The simulation is carried out through the resolution of the different governing Navier–Stokes’ equations by means of the finite volume method. Two different closure models were tested: the standard k–e model and the Reynolds stress model (RSM) second order model. A non-uniform mesh system tightened close to the emitting nozzle and both the vertical and horizontal walls is also adopted. The confrontation of the numerical results with experimental data from literature shows satisfying agreement with the RSM model in the description of the handled flow; that’s why we adopted it for the rest of the paper. Once the model validated, a detailed discussion has been provided on the mean velocities, pressure field, Reynolds stress, and kinetic energy. The merge point, the combined point and the impact point have also been obtained and compared with other results. A similarity profile has been obtained in the downstream direction for different offset and velocity ratios.

Augmentation of Heat Transfer and Investigation of Fluid Flow Characteristics of an Impinging Air Jet on to a Flat Plate

The current work deals with the study on heat transfer augmentation and investigation of fluid flow characteristics of an impinging air jet on a flat plate. Convective heat transfer of an impinging air jet is known to yield high heat transfer coefficients. Experimentation was performed to study the effects of the nozzle diameter (D), geometric center height (H), temperature measuring distance (x), Reynolds number ( $${\textit{Re}}_{\mathrm{D}}$$ ), velocity (v), local, stagnation and average Nusselt numbers ( $${\textit{Nu}}_{\mathrm{L}}$$ , $${\textit{Nu}}_{\mathrm{s}}$$ , and $${\textit{Nu}}_{\mathrm{avg}}$$ respectively) on the heat transfer distribution. The local distribution of heat transfer coefficients on the impinging flat plate was calculated. Average heat transfer distributions were compared for different velocity flow fields. Simultaneously, velocity and heat flux measurements were performed at various points on the impingement surface to explore the temporal nature of the convective heat transfer. $${\textit{Nu}}_{\mathrm{L}}$$ and $${\textit{Nu}}_{\mathrm{avg}}$$ on the impinged surface for different nozzle configurations were studied under constant wall temperature conditions, as a function of the $${\textit{Re}}_{\mathrm{D}}$$ (192.61–1661.26), D (0.5–3 mm), x (0–80 mm), and v (6.4 and 9.2 m/s). It was observed that at low nozzle to impingement surface ratio, the heat transfer distribution exhibited a peak at the center, which varied with $${\textit{Re}}_{\mathrm{D}}$$ , x and H. It was also witnessed that the fluctuations in the velocity normal to the impingement surface had a more significant influence on the heat transfer than fluctuations along and parallel to the impingement surface.

Axisymmetric jet impingement on a dimpled surface: Effect of impingement location on flow field characteristics

Few studies have investigated the flow characteristics of jets impinging on dimpled surfaces that may increase or decrease their heat transfer capabilities. Here, particle image velocimetry (PIV) measurements have been performed on a round jet (diameter D) impinging on a surface having large spherical dimples (opening size d), D/d = 0.83. In particular, the effect of jet impingement location on the flow field was investigated. Impingement of the jet centered on the “dimple” as well as on the flat surface between the dimples (“isthmus”), was compared to impingement on a smooth surface. Measurements were performed at three Reynolds numbers, ⟨Re⟩ = 1,352, 6,268 and 12,342 at a stand-off distance of 4.8D. Results showed that the flow field in the developing wall jet strongly changed for “isthmus” impingement while for “dimple” and “smooth” impingement it was similar. However, outer-layer self-similarity was not attained in the developing wall jet. Furthermore, secondary vortex generation as a result of primary vortex impingement, was the same for “smooth” and “dimple” impingement while for “isthmus” impingement, secondary vortices were created through the generation of an unsteady separation bubble.

Orifice Jet Control Using Sub-Flows Issuing from Circular and Non-Circular Openings

Nozzle shapes offer the possibility of a passive control technique to provide high mixing and heat transfer rates. Thus, a number of investigations have been carried out to elucidate the influence of nozzle configuration including noncircular orifices on the flow and heat transfer characteristics. This paper demonstrates the effects of sub-flows issuing from different shaped openings on main orifice air jet flow characteristics. Mean velocity measurements by a constant temperature hot-wire anemometer are carried out at a Reynolds number of Re = 2.2 × 104 to investigate the flow characteristics of orifice jets with sub-flows. The effects of the opening shape on the main orifice flow are also demonstrated by flow visualization. It is shown that the potential core lengths and mixing characteristics with ambient fluids of orifice jet flows can be controlled by the sub-flows.

Верификация результатов численного моделирования и экспериментальных данных влияния кавитации на гидродинамические характеристики струйного потока

Верификация результатов численного моделирования и экспериментальных данных влияния кавитации на гидродинамические характеристики струйного потока

Analysis and reconstruction of waterjet characteristics in double-side wall confinement

Water jet flow characteristics in double-side wall confined space is investigated, two-dimensional particle image velocimetry is performed on confined plane and unconfined plane, and using Proper orthogonal decomposition to perform dimensionality analysis, extract large-scale coherent structure and reconstruct flow field. Results illustrate that velocity and vorticity fluctuation distribution, mainly reflected in low-order modes, is seriously affected on account of a symmetrical double-wall existence; Reconstruction instantaneous velocity field by the first m modes saving 70% of turbulent kinetic energy, indicating that reconstructed velocity fluctuation fields can truly reflect original fields.