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Under‐ and over‐expanded jet flows are calculated for the Euler equations. The solution procedure is based on the two‐stage Runge‐Kutta time‐stepping scheme. The studies of the flow field structure in diffusers, free jets and impinging jets have been investigated for a range of jet‐to‐stream total pressure ratios and for different exit Mach numbers. The resulting flows show a complex shock‐shear expansion structure with Mach discs. Numerical results are compared with available experimental data and with previously published data. An oscillating phenomenon was observed in the case of free jets operating at sonic exit Mach number and in another case of impingement of under‐expanded jets on a flat plate.

AN analysis of the mechanism of jet drag is given by Stratford, it being suggested that jet drag is zero if the density velocity products of the free‐stream and jet are equal, among other conditions. Under certain conditions Stratford concludes that ‘negative’ jet drag (i.e. thrust augmentation) is possible.

This paper aims to describe the numerical simulation of a three‐dimensional turbulent free jet issuing from a sharp‐edged equilateral triangular orifice into still air.

The numerical simulation was carried out by solving the governing three‐dimensional Reynolds‐averaged Navier‐Stokes equations. Several two‐equation eddy‐viscosity models (i.e. the standard k‐ε, renormalization group (RNG) k‐ε, realizable k‐ε, shear‐stress transport (SST) k‐ω), as well as the Reynolds stress models (i.e. the standard RSM and the SSG) were tested to simulate the flowfield. The numerical predictions were compared with experimental data in order to assess the capability and limitations of the various turbulent models examined in this work. Findings –The vena contracta effect was predicted by all the tested models. Among the eddy‐viscosity models only the realizable k‐ε model showed good agreement of the near‐field jet decay. None of the eddy‐viscosity models was capable of predicting the profiles of the jet turbulence intensities. The RSMs, especially the standard RSM, were able to produce much better predictions of the features of the jet in comparison with the eddy‐viscosity models. The standard RSM predictions were found to agree reasonably well with the experimental data.

The conclusion, that among the tested RANS turbulence closure models, the RSM appeared the only one capable of reproducing reasonably well the experimental data concerns only the jet flow case examined here. Also, the average computational time for a single run was quite long, i.e. 340 h, but it is believed that parallel computing will reduce it considerably.

The numerical results reported in this paper provide a comparison between several RANS turbulence closure models for simulating a turbulent free jet issuing from an equilateral triangular nozzle.

This study aims to investigate the effect of slanted perforation diameter in tabs for the control of Mach 1.4 underexpanded supersonic jet flow characteristics.

Numerical investigation was carried out for NPR 5 to analyze the effect of slanted perforation diameter in tabs to control the Mach 1.4 jet. Four sets of tabs with slanted circular perforation geometries (Φ_p = 1, 1.5, 2 and 2.5 mm) were considered in this study. The inclination angle of 20° (α_P) with reference to the jet axis was maintained constant for all the four tabs considered.

Determined value indicates there is a 68%, 71%, 73% and 75% drop in supersonic core for the Φ_p = 1, 1.5, 2.0 and 2.5 mm, respectively. The results show that the tabs with 2.5 mm perforation diameter were found to be efficient in reducing the supersonic jet core in comparison with other tab cases. The reduction in supersonic core length is due to the extent of miniscule vortices exuviating from slanted small and large diameter perforation in the tabs.

The concept of slanted perforation can be applied in scramjet combustion, which finds its best application in hypersonic vehicles and in noise suppression in fighter aircraft.

Slanted perforation and circular shapes with different diameters have not been studied in the supersonic regime. Examining the effect of circular diameter in slanted perforation is an innovation in this research paper.

The purpose of the present study is to investigate the flow and turbulence characteristics of a turbulent wall jet flowing over a surface inclined with the horizontal and to investigate the effect of variation of the angle of inclination of the wall on the flow structure of the wall jet.

The high Reynolds number two-equation κ− model with standard wall function is used as the turbulence model. The Reynolds number considered for the present study is 10,000. The Reynolds averaged Navier-Stokes (RANS) equations are used for predicting the turbulent flow. A staggered differencing technique employing both contravariant and Cartesian components of velocity has been applied. Results for distribution of wall static pressure and skin friction, decay of maximum streamwise velocity, streamwise variation of integral momentum and energy flux have been compared for the cases of α=0°, 5°, and 10°.

Flow field has been represented in terms of streamwise and lateral velocity contours, static pressure contour, vorticity contour and streamwise velocity and static pressure profiles at different locations along the oblique offset plate. Distribution of Reynolds stresses in terms of spanwise, lateral and turbulent shear stresses, and turbulent kinetic energy and its dissipation rate have been presented to describe the turbulent characteristics. Similarity of streamwise velocity and the velocity parallel to the oblique wall has been observed in the developed region of the wall jet flow. A decaying trend is observed in the variation of total integral momentum flux in the developed region of the wall jet which becomes more evident with increase in oblique angle. Developed flow region has indicated trend of similarity in profiles of streamwise velocity as well as velocity component parallel to the oblique wall. A depression in wall static pressure has been observed near the nozzle exit when the wall is inclined and the depression increases with increase in inclination. Effect of variation of oblique angles on skin friction coefficient has indicated that it decreases with increase in oblique angle. Growth of the outer and inner shear layers and spread of the jet shows linear variation with distance along the oblique wall. Decay of maximum streamwise velocity is found to be unaffected by variation in oblique angle except in the far downstream region. The streamwise variation of spanwise integral energy shows increase in oblique angle and decreases the magnitude of energy flux through the domain. In the developed flow region, streamwise variation of centreline turbulent intensities shows increased values with increase in oblique angle, while turbulence intensities along the jet centreline in the region X<12 remain unaffected by change in oblique angles. Normalized turbulent kinetic energy distribution highlights the difference in turbulence characteristics between the wall jet and reattached offset jet flow. Near wall velocity distribution shows that the inner region of boundary layer of the developed oblique wall jet follows a logarithmic profile, but it shows some difference from the standard logarithmic curve of turbulent boundary layers which can be attributed to an increase in skin friction coefficient and a decrease in thickness of the wall attached layer.

The study presents an in-depth investigation of the interaction between the jet and the inclined wall. It is shown that due to the Coanda effect, the jet follows the nearby wall. The findings will be useful in the study of combined flow of wall jet and offset jet and dual offset jet on oblique surfaces leading to a better design of some mechanical jet flow devices.

The research in this paper helps to understand the difference between the Eulerian method and the Lagrangian method in describing the performance of Pelton turbine buckets, so as to improve the design level and design efficiency of the runner.

This paper used DualSPHysics to calculate the unsteady flow of the Pelton turbine runner bucket and compared it with the mesh-based method to explore the difference between mesh-based and particle-based methods in torque curves, jet flow patterns and pressure characteristics.

It is noted that the particle-based method is challenging to compare with the mesh-based method concerning accuracy. In addition to better describing the free water film, the particle method also captures many droplets near the water film, but it cannot well describe the negative pressure region on the bucket back and the resulting jet interference after cutting off the jet. Compared with the mesh-based method, the pressure measurement points obtained by the particle-based method generally have shorter periods and violent fluctuations, and the pressure value of some points is underestimated.

This paper helped to calculate the unsteady characteristics of the Pelton turbine by Fluent, CFX and DualSPHysics; exploration jet flow pattern differences between the mesh and meshfree methods; prediction of the flow interference between the bucket back and the jet and the pressure curve of SPH usually has a shorter period and violent fluctuations.

This study aims to study the interaction effects between a rectangular supersonic jet with a flat wall computationally using wall length as a parameter. The purpose of this study is to investigate the effect of change in wall length on supersonic core length (SCL) reduction, jet deflection and jet decay behavior.

The design Mach number and aspect ratio at the rectangular exit were 1.8 and 2, respectively. To study the wall length effects on jet-wall interactions, wall length (L_w) was varied as 0.5D_h, 1D_h, 2D_h, 4D_h and 8D_h, where D_h was the hydraulic diameter of the nozzle exit. The flat wall with the matching width of the rectangular exit section of a supersonic nozzle was placed at the nozzle exit such that the supersonic jet grazed past the wall. The studies were carried out at over-expansion [nozzle pressure ratio (NPR) = 4], near optimum expansion (NPR = 6) and under-expansion (NPR = 8) levels.

Results indicated that significant reduction in wall-bounded SCL was noticed in the range of 0.5D_h  ≤  L_w ≤ 1D_h for both over-expansion and under-expansion conditions. At L_w ≥ 4D_h, SCL got enhanced at NPR = 4 and 6 but had a negligible effect at NPR = 8.

Thrust vector control, noise reduction and easy take-off for high-speed aircraft.

The effect of change in flat wall length on interaction characteristics of a rectangular supersonic jet was not studied before in terms of SCL reduction and jet decay behavior.

A radial offset jet has the flow characteristics of a radial jet and an offset jet, which are encountered in many engineering applications. The purpose of this paper is to study the dynamics and mass transfer characteristics of the radial offset jet with an offset ratio 6, 8 and 12.

Three turbulence models, namely the SST k-? model, detached eddy simulation model, and improved delayed detached eddy simulation (IDDES), were applied to the radial offset jet with an offset ratio eight and their results were compared with experimental results. The contrasting results, such as the distributions of mean and turbulent velocity and pressure, show that the IDDES model was the best model in simulating the radial offset jet. The results of the IDDES were analyzed, including the Reynolds stress, turbulent kinetic energy, triple-velocity correlations, vertical structure and the tracer concentration distribution.

In the axisymmetric plane, Reynolds stresses increase to reach a maximum at the location where the jet central line starts to be bent rapidly, and then decrease with increasing distance in the radial direction. The shear layer vortices, which arise from the Kelvin-Helmholtz instability near the jet exit, become larger scale results in the entrainment and vortex pairing, and breakdown when the jet approaches the wall. Near the wall, the vortex swirling direction is different at both front and back of attachment point. In the wall-jet region, the concentration distributions present self-similarity while it keeps constant below the jet in the recirculation region.

The radial offset jet with other offset ratio and exit angle is not considered in this paper and should be investigated.

The results obtained in this paper will provide guidance for studying similar flow and a better understanding of the radial offset jet.

The purpose of this paper is to describe a procedure to simulate impact-driven liquid jets by computational fluid dynamics (CFD). The proposed CFD model is used to investigate nozzle flow behavior under ultra-high injection pressure and jet velocities generated by the impact driven method (IDM).

A CFD technique was employed to simulate the jet generation process. The injection process was simulated by using a two-phase flow mixture model, while the projectile motion was modeled the moving mesh technique. CFD results were compared with experimental results from jets generated by the IDM.

The paper provides a procedure to simulate impact-driven liquid jets by CFD. The validation shows reasonable agreement to previous experimental results. The pressure fluctuations inside the nozzle cavity strongly affect the liquid jet formation. The average jet velocity and the injection pressure depends mainly on the impact momentum and the volume of liquid in the nozzle, while the nozzle flow behavior (pressure fluctuation) depends mainly on the liquid volume and the impact velocity.

Results may slightly deviate from the actual phenomena due to two assumptions which are the liquid compressibility depends only on the rate of change of pressure respected to the liquid volume and the super cavitation process in the generation process is not taken into account.

Results from this study will be useful for further designs of the nozzle and impact conditions for applications of jet cutting, jet penetration, needle free injection, or any related areas.

This study presents the first success of employing a commercial code with additional user defined function to calculate the complex phenomena in the nozzle flow and jet injection generated by the IDM.

The purpose of this paper is to evaluate the synthetic jet actuator design's performance based on piezoelectric diaphragms that can be appropriately used for flow separation control.

Design the synthetic jet actuators by means of estimating the several parameters and non‐dimensional parameters. Understanding the relationship and coupling effects of these parameters on the actuator to produce exit air jet required. Experiments were conducted to measure the exit air jet velocity using a hot‐wire anemometry and determine the good operational frequencies and voltages of the actuators for different cavity volume.

The performance of synthetic jet actuator is not consistent to a particular given frequency and it depends on design configurations. Each actuator will give a very good speed for a certain frequency. The results show that the exit air jet velocity increases would be better if the cavity volume is reduced and if the input voltage is increased to certain limits.

The limit of input voltage for the actuators that can be achieved for good jet speed is 2V of about 205V output voltage for each frequency. The jet speed obtained is sufficient enough to control the separation for an aircraft which has a small wing chord and low speed. Therefore, more studies are needed to optimize the sizes of an orifice and cavity, and the selection of piezoelectric diaphragm.

The study helps in establishing a flow control device for controlling flow separation, especially on airfoils.

Design the synthetic jet actuators based on piezoelectric diaphragm for applications of flow separation control.