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This study aims to investigate effects of sonic jet injection into supersonic cross-flow (JISC) numerically in different dynamic pressure ratio values and free stream Mach numbers.

Large Eddy simulation (LES) with dynamic Smagorinsky model is used as the turbulence approach. The numerical results are compared with the experimental data, and the comparison shows acceptable validation.

According to the results, the dynamic pressure ratio has critical effects on the zone related to barrel shock. Despite free stream Mach number, increasing dynamic pressure ratio leads to expansion of barrel shock zone. Consequently, expanded barrel shock zone would bring about more obstruction effect. In addition, the height of counter-rotating vortex pair increases, and the high-pressure area before jet and low-pressure area after jet will rise. The results show that the position of barrel shock is deviated by increasing free stream Mach number, and the Bow shock zone becomes stronger and close to barrel shock. Moreover, high pressure zone, which is located before the jet, decreases by high free stream Mach number.

In this study, LES with a dynamic Smagorinsky model is used as the turbulence approach. Effects of sonic JISC are investigated numerically in different dynamic pressure ratio values and free stream Mach numbers.

As summary, the following are the contribution of this paper in the field of JISC subjects: several case studies of jet condition have been performed. In all the cases, the flow at the nozzle exit is sonic, and the free stream static pressure is constant. To generate proper grid, a cut cell method is used for domain modelling. Boundary condition effect on the wall pressure distribution around the jet and velocity profiles, especially S shape profiles, is investigated. The results show that the relation between representing the location of Mach disk centre and at transonic regime is a function of second-order polynomial, whereas at supersonic regime, the relationship is modelled as a first-order polynomial. In addition, the numerical results are compared with the experimental data demonstrating acceptable validation.

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.

The data on round jets in still air and in a general stream are analysed to determine the spread of the jet and the decay of the axial velocity distribution. The temperature distributions for heated jets are treated in the same way. Methods of model test technique for jets and jet aircraft are discussed; it is shown that the jet momentum is the most important quality in the representation of hot jets. Illustrations of the effect of jets on neighbouring surfaces, including the Coanda effect, are given, and finally an examination of the effect of jets on aircraft stability is made.

An aircraft powered by a gas‐turbine jet‐propulsion engine, the exhaust gases from which are discharged rearwardly through a jet pipe as a propulsive jet stream for normal forward flight, is provided with a fan mounted with its axis vertical, the fan drawing in air from atmosphere and discharging an air stream downwardly so as to produce an upward component of thrust on the aircraft, and means operable at will for diverting the exhaust gases from the jet pipe to drive the fan. The delta‐wing aircraft shown in FIG. 1 is powered by a gas‐turbine jet‐propulsion engine 3 which discharges exhaust gases as a propulsive jet stream through a jet pipe 5. An intermediate pipe 5a between the engine and the jet pipe is connected with two branch pipes 7 and is provided with a valve (not shown) which allows any desired proportion of the exhaust gases to be diverted into the branch pipes. The aircraft is provided with two fans, one in each wing, which rotate in opposite directions to balance out gyroscopic effects. As shown in FIG. 2, each fan rotor 12 comprises rotor blades 12b, a shroud ring 12c connecting the tips of the rotor blades, and a row of axial flow turbine rotor blades 12dmounted on the outer surface of the shroud ring. Exhaust gases diverted through the hand pipes 7 are supplied to these turbine rotor blades through a turbine inlet volute 13 which has a downwardly facing outlet provided with turbine nozzle vanes 14 co‐operating with the turbine rotor blades 12d. Rows of stator blades 19, 20 are provided above and below the fan rotor blades 12b, and these blades may be adjustable to enable the vertical lift to be varied; the pitch of the fan rotor blades may also be variable. Control of the aircraft may be effected by differential control of the blading of the two fans; alternatively or in addition the turbine nozzle vanes 14 may be adjustable. The inlets and outlets of the fans may communicate with the atmosphere through apertures in the wings which may be opened or closed by pivoted vanes 21, 22 which may be operated differentially to control the aircraft. Alternatively the inlets may be connected to one or more boundary layer suction openings in the surface of the aircraft. Additional fans 23, 24 may be mounted in the wing tips and nose of the aircraft to control the aircraft, these fans being driven by compressed air bled off from the compressor of the engine 3.

This study aims to analyze co-flowing jets (CFJs) with constant velocity ratio (VR) and varying primary nozzle lip thickness (LT) to find a critical LT in CFJs below which mixing enhances and beyond which mixing inhibits.

CFJs were characterized with a constant VR and varying LTs. A single free jet with a diameter equal to that of a primary nozzle of the CFJ was used for characteristic comparison. Numerical simulation is carried out and is validated with the experimental results.

The results show that within a critical limit, the mixing enhanced with an increase in LT. This was signified by a reduction in potential core length (PCL). Beyond this limit, mixing inhibited leading to the elongation of PCL. This limit was controlled by parameters such as LT and constant VR. A new region termed as influential wake zone is identified.

In this study, the VR is maintained constant and bypass ratio (BR) was varied from low value to very high values. Presently, subsonic commercial turbo fan operates under low to ultra-high BR. Hence the present study becomes vital to the current scenario.

To the best of the authors’ knowledge, this is the first effort to find the critical value of LT for a constant VR for compressible co-flow jets. The CFJs with constant VR and varying LT have not been studied in the past. The present study focuses on finding a critical LT below which mixing enhances and above which mixing inhibits.

Solutions of the twin plane jets HF chemical laser flow based on a turbulent kinetic theory, due to a modified Green’s function method, are presented. The calculated results of probability density function (PDF) of various chemical species in velocity space, and mass fraction concentration distributions of various reactants and products in the flow field, are revealed and discussed in this analysis. The transport phenomena of different pumping rate, collisional deactivation rate, and radiative deactivation rate in the interaction between the twin plane jets HF chemical laser show that the properties of species mass fraction concentrations, collisional reaction rate, and radiative incident intensity are the dominant factors. The present study provides the fundamentals for theoretical understanding of twin plane jets HF chemical laser and further application to multiple‐jet HF chemical laser analysis.

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.

The development of novel cooling techniques is needed in order to be able to substantially increase the performance of integrated electronic circuits whose operations are limited by the maximum allowable temperature. Air cooled micro‐channels etched in the silicon substrate have the potential to remove heat directly from the chip. For reasonable pressure drops, the flow in micro‐channels is inherently laminar, so that the heat transfer is not very large. A synthetic jet may be used to improve mixing, thereby considerably increasing heat transfer. This paper seeks to address this issue.

CFD has been used to study the flow and thermal fields in forced convection in a two‐dimensional micro‐channel with an inbuilt synthetic jet actuator. The unsteady Navier‐Stokes and energy equations are solved. The effects of variation of the frequency of the jet at a fixed pressure difference between the ends of the channel and with a fixed jet Reynolds number, have been studied with air as the working fluid. Although the velocities are very low, the compressibility of air has to be taken into account.

The use of a synthetic jet appreciably increases the rate of heat transfer. However, in the frequency range studied, whilst there are significant changes in the details of the flow, due primarily to large phase changes with frequency, there is little effect of the frequency on the overall rate heat transfer. The rates of heat transfer are not sufficiently large for air to be a useful cooling medium for the anticipated very large heat transfer rates in future generations of microchips.

The study is limited to two‐dimensional flows so that the effect of other walls is not considered.

It does not seem likely that air flowing in channels etched in the substrate of integrated circuits can be successfully used to cool future, much more powerful microchips, despite a significant increase in the heat transfer caused by synthetic jet actuators.

CFD is used to determine the thermal performance of air flowing in micro‐channels with and without synthetic jet actuators as a means of cooling microchips. It has been demonstrated that synthetic jets significantly increase the rate of heat transfer in the micro‐channel, but that changing the frequency with the same resulting jet Reynolds number does not have an effect on the overall rate of heat transfer. The significant effect of compressibility on the phase shifts and more importantly on the apparently anomalous heat transfer from the “cold” air to the “hot” wall is also demonstrated.

This study aims to present the numerical study on supersonic jet mixing characteristics of the co-flow jet by varying lip thickness (LT). The LT chosen for the study is 2 mm, 7.75 mm and 15 mm.

The primary nozzle is designed for delivering Mach 2.0 jet, whereas the secondary nozzle is designed for delivering Mach 1.6 jet. The Nozzle pressure ratio chosen for the study is 3 and 5. To study the mixing characteristics of the co-flow jet, total pressure and Mach number measurements were taken along and normal to the jet axis. To validate the numerical results, the numerical total pressure values were also compared with the experimental result and it is proven to have a good agreement.

The results exhibit that, the 2 mm lip is shear dominant. The 7.75 mm and 15 mm lip is wake dominant. The jet interaction along the jet axis was also studied using the contours of total pressure, Mach number, turbulent kinetic energy and density gradient. The radial Mach number contours at the various axial location of the jet was also studied.

The effect of varying LT in exhaust nozzle plays a vital role in supersonic turbofan aircraft.

Supersonic co-flowing jet mixing effectiveness by varying the LT between the primary supersonic nozzle and the secondary supersonic nozzle has not been analyzed in the past.

The paper seeks to perform a detailed numerical study of flow over a generic fan‐wing airfoil and also attempts to modify the geometry for the improvement of the aerodynamic performance.

Advanced computational fluid dynamics (CFD) technique has been employed for evaluation of the aerodynamic performance (e.g. lift/drag ratio) of a model problem. Numerical investigation starts with sensitivity studies to minimize domain size influence and grid dependency, followed by time‐accurate transient calculations. A preliminary re‐design exercise has been performed by analyzing the results of a current design.

CFD predicted lift force agrees fairly well with the measurement data with about 6.55 per cent error, while drag force compares less favourably with about 12.59 per cent error. Both errors are generally acceptable for an engineering application of complex flow problems. Several key flow features observed previously by experiment have also been re‐produced by simulation, notably the eccentric vortex motions in the blade interior and the stream “jet” flow outside the blades near the exit. With the modified geometry, there is a considerable lift/drag ratio improvement of about 29.42 per cent. The possible reasons for such a significant improvement have been discussed.

As it is the first step towards the detailed flow analysis of this type of model, a simpler blade shape rather than “real” one has been used.

The paper provides a very useful source of information and could be used as guidance for further industry practice of unmanned aerial vehicles design.

This paper is valuable for both academic researchers and industry engineers, especially those working in the area of high‐lift wing design. The works presented are original.