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This paper describes a study concerning the numerical simulation of a sonic helium jet through a transverse nozzle in a flat plate exhausting normally into a supersonic air flow. Three‐dimensional Reynolds‐averaged Navier—Stokes equations coupled with the modified Baldwin‐Lomax algebraic turbulence model and relevant species equations are solved by using a finite‐volume upwind scheme. In this approach, Roe’s flux function, explicit multi‐stage integration and multi‐block procedure are applied to achieve the steady state solution efficiently. The Roe’s flux function is modified to suit the simulation of helium‐air mixing. The comparison between two‐dimensional calculated results with experimental data of surface pressure shows good agreement. The results of three‐dimensional computations for square, circular and rectangular jets are presented, and the essential flow features including induced shocks, upstream separations, and downstream primary and secondary vortices are adequately simulated.

The literature on jets is extensive but scattered. A concise guide is needed, and this paper attempts (at the risk of over‐simplification) to summarise some of the available information, both theoretical and experimental (some of it obtained in the Department of Mechanical Engineering) on those jet properties which are important in engineering — velocity profile and decay, spread, entrainment and static pressure.

Turbulent mixing of two co‐axial jets having a low annular to core area ratio is enhanced by employing a chute mixer, directing part of the annular stream at 10° towards the core region. Aims to present results from measurements of time‐averaged and fluctuating components of velocity under cold flow conditions.

Experiments were conducted at a bypass ratio of 0.47 which is a typical value for low bypass turbofan engines. Contours of time‐averaged velocity and streamwise and transverse turbulence intensities were obtained by making detailed measurements close to the chutes. Distributions of time‐averaged velocity and turbulence intensity were obtained at different axial locations downstream of the chute mixer. Total and static pressure measurements were also performed.

The high velocity annular stream was found to quickly diffuse after entering through the chutes and mix with the core stream due to high turbulence generation. A strong transverse turbulence component enhanced the mixing of the streams. With the aid of the chute mixer, nearly complete mixing is achieved over a length of 5 duct radii. A higher total pressure loss of about 1.38 percent is the penalty paid for the enhanced mixing.

Provides results from experiments into the process of turbulent mixing of co‐axial jets.

A device for steering an aircraft having a jet propulsion nozzle is characterized by a tubular member 4 having a longitudinal slot 2, mounted at the nozzle outlet and rotable relatively thereto about its axis, the latter being perpendicular to the nozzle axis, the slot opening into the jet at an angle depending on the position of member 4, the latter being connected to a source of gas under pressure. In the embodiment of FIG. 1, a rectangular section nozzle 1 is provided with a curved smooth extension 3 along one of its longer sides, and has on its opposite side a cylinder 4, provided with a slot 2, rotatable in a part cylindrical housing 5 secured to the nozzle. A servo‐operated toothed rack may rotate a pinion fast to the cylinder. The interior of the cylinder is connected through a valve to a source of pressure, e.g. the compressor or combustion chambers of a turbo‐jet unit, so that a transverse jet of variable direction issues from slot 2. Variation of the direction of the transverse jet varies the direction of the main jet to control the aircraft, In a modification, the housing 5 comprises a wide slot, and a wide slot is provided in the cylinder 2, so that rotation thereof causes the slots more or less to overlap, controlling the quantity of flow in the directing jet. In this case the valve in the pressure supply line, which may be of the simple full on or full off type, may be omitted.

This paper aims to experimentally study the external flow characteristic of an isolated two-dimensional synthetic jet actuator undergoing diaphragm resonance.

The resonance frequency of the diaphragm (40 Hz) depends on the excitation mechanism in the actuator, whereas it is independent of cavity geometry, excitation waveform and excitation voltage. The velocity response of the synthetic jet is influenced by excitation voltage rather than excitation waveform. Thus, this investigation selected four different voltages (5, 10, 15 and 20 V) under the same sine waveform as experiment parameters.

The velocity field along the downstream direction is classified into five regions, which can be obtained by hot-wire measurement. The first region refers to an area in which flow moves from within the cavity to the exit of orifice through the oscillation of the diaphragm, but prior to the formation of the vortex of a synthetic jet. In this region, two characteristic frequencies exist at 20 and 40 Hz in the flow field. The second region refers to the area in which the vortices of a synthetic jet fully develop following their initial formation. In this region, the characteristic frequencies at 20 and 40 Hz still occur in the flow field. The third region refers to the area in which both fully developed vortices continue traveling downstream. It is difficult to obtain the characteristic frequency in this flow field, because the mean center velocities (ū) decay downstream and are proportional to (x/w)^−1/2 for the four excitation voltages. The fourth region reveals variations in both vortices as they merge into a single vortex. The mean center velocities (ū) are approximately proportional to (x/w)⁰ in this region for the four excitation voltages. A fifth region deals with variations in the vortex of a synthetic jet after both vortices merge into one, in which the mean center velocities (ū) are approximately proportional to (x/w)⁻¹ in this region for the four excitation voltages (x/w is the dimensionless streamwise distance).

Although the flow characteristics of synthetic jets had reported for flow control in some literatures, variations of flow structure for synthetic jets are still not studied under the excitation of diaphragm resonance. This paper showed some novel results that our velocity response results obtained by hot-wire measurement along the downstream direction compared with flow visualization resulted in the classification of five regions under the excitation of diaphragm resonance. In the future, it makes valuable contributions for experimental findings to provide researchers with further development of flow control.

This study aims to numerically investigate the flow features and mixing/combustion efficiencies in a turbulent reacting jet in cross-flow by a hybrid Eulerian-Lagrangian methodology.

A high-order hybrid solver is employed where, the velocity field is obtained by solving the Eulerian filtered compressible transport equations while the species are simulated by using the filtered mass density function (FMDF) method.

The main features of a reacting JICF flame are reproduced by the large-eddy simulation (LES)/FMDF method. The computed mean and root-mean-square values of velocity and mean temperature field are in good agreement with experimental data. Reacting JICF’s with different momentum ratios are considered. The jet penetrates deeper for higher momentum ratios. Mixing and combustion efficiency are improved by increasing the momentum ratio.

The authors investigate the flow and combustion characteristics in subsonic reacting JICFs for which very limited studies are reported in the literature.

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.

These abstracts of British Patent Specifications are condensed, by permission, from the official specifications. Copies of the full specifications are obtainable from the Patent Office, 25 Southampton Buildings, W.C.2, price 2s. 8d. each.

Maintaining the turbine blade’s temperature within the safety limit is challenging in high-pressure turbines. This paper aims to numerically present the conjugate heat transfer analysis of a novel approach to mini-channel embedded film-cooled flat plate.

Numerical simulations were performed at a steady state using SST k – ω turbulence model. Impingement and film cooling are classical approaches generally adopted for turbine blade analysis. The existing film cooling techniques were compared with the proposed design, where a mini-channel was constructed inside the solid plate. The impact of the blowing ratio (M), Biot number (Bi) and temperature ratio (TR) on overall cooling performance was also studied.

Overall cooling effectiveness was always shown to be higher for mini-channel embedded film-cooled plates. The effectiveness increases with increasing the blowing ratio from M = 0.3 to 0.7, then decreases with increasing blowing ratio (M = 1 and 1.4) due to lift-off conditions. The mini-channel embedded plate resulted in an approximately 21% increase in area-weighted average overall effectiveness at a blowing ratio of 0.7 and Bi = 1.605. The lower uniform temperature was also found for all blowing ratios at a low Biot number, where conduction heat transfer significantly impacts total cooling effectiveness.

To the best of the authors’ knowledge, this study presents a novel approach to improve the cooling performances of a film-cooled flat plate with better cooling uniformity by using embedded mini-channels. Despite the widespread application of microchannels and mini-channels in thermal and fluid flow analysis, the application of mini-channels for blade cooling is not explored in detail.

The purpose of this paper is to analyze the effect of pressure fluctuations on the combustion efficiency of the hydrogen fuel injected into the supersonic oxidizing cross flow. The pressure fluctuations are imposed on inlet air flow and also on the fuel flow stream. Two different situations are considered: the combustion chamber once without and again with the inlet standing oblique shock wave.

The pressure fluctuations are imposed on inlet air flow and also on the fuel flow stream. Two different situations are considered: the combustion chamber once without and again with the inlet standing oblique shock wave. The unsteady turbulent reacting flow solver is developed to simulate the supersonic flow field in the combustion chamber with detail chemical kinetics, to predict the time-variation of the combustion efficiency due to the imposed pressure fluctuations.

The results show that the response of the reacting flow field depends on both the frequency of fluctuations and the existence of the inlet shock wave. In addition, the inlet standing shock wave has some attenuating role, but the reacting flow shows an amplifying role on imposed oscillations which is also augmented by imposing anti-phase fluctuations on both inlet and fuel flow streams.

This study is performed to analyze the instabilities in the supersonic combustion which has not been considered before in this manner.