The research work in this dissertation focuses on turbulent air jet heat transfer for commercial cooking applications. As a part of this study, convective heat transfer coefficient and its interdependency with various key parameters is analyzed for single nozzle turbulent jet impingement. Air is used as the working fluid impinging on the flat surface. A thorough investigation of velocity and temperature distributions is performed by varying nozzle velocity and height over diameter ratio (H/D). Nusselt number and Turbulent Energy are presented for the impingement surface. It was found that for H/D ratios ranging between 6 and 8, nozzle velocities over 20 m/s provide a large percentage increase in heat transfer. Single nozzle jet impingement is followed by study of turbulent multi-jet impingement. Along with parameters mentioned above, spacing over diameter ratio (S/D) is varied. Convective heat transfer coefficient, average impingement surface temperature and heat transfer rate are calculated over the impingement surface. It was found that higher S/D ratios result in higher local heat transfer coefficient values near stagnation point. However, increased spacing between the neighboring jets results in reduced coverage of the impingement surface lowering the average heat transfer. Lower H/D ratios result in higher heat transfer coefficient peaks. The peaks for all three nozzles are more uniform for H/D ratios between 6 and 8. For a fixed nozzle velocity, heat transfer coefficient values are directly proportional to nozzle diameter. For a fixed H/D and S/D ratio, heat transfer rate and average impingement surface temperature increases as the nozzle velocity increases until it reaches a limiting value. Further increase in nozzle velocity causes drop in heat transfer rate due to ingress of large amounts of cold ambient air in the control volume. The final part of this dissertation focuses on case study of conveyor oven. Lessons learned from analysis of single and multi-jet impingement are implemented in the case study. A systematic approach is used to arrive to an optimal configuration of the oven. As compared to starting configuration, for optimized configuration the improvement in average heat transfer coefficient was 22.7%, improvement in average surface heat flux was 24.7% and improvement in leakage air mass flow rate was 59.1%.

Dust control is a very significant issue in underground coal mining. The benefits of reducing dust levels will be a lesser risk of lung disease to coal miners, improved working conditions and a reduced risk of dust explosions. Coal dust is commonly suppressed by water sprays but suppression efficiency is not high because dust tends to travel in the air flow round the water droplets rather than being captured by them. If water sprays are electrostatically charged, then a significant improvement in dust suppression efficiency may be achieved. Of the three principal droplet charging mechanisms, i.e. corona charging, induction charging and contact charging, corona charging is the most widely used in many industrial fields including dust suppression, However, it requires a high applied voltage, ranging from thousands to more than a hundred thousand volts, depending on the geometry of the charging equipment. Induction charging has been used in agricultural spraying since Law (1978) developed an embedded-electrode induction charging spraying nozzle. This nozzle provides a compact, inexpensively fabricated droplet charger and, reduces design requirements on size and output voltage (of the order of 1000 volts). It also reduces the potential for mechanical damage, misalignment and personnel hazard. In order to evaluate the effectiveness of dust suppression, either the charge on individual droplets or the charge-to-mass ratio of water sprays needs to be known. However, the parameters which control the charge applied to water and the charging rate have been unsolved theoretically for any charging mechanism. The existing theories for the induction-charged and air-atomising a liquid jet have been found to be inadequate. And there is no theory available for corona charging of the droplets produced with a pneumatic nozzle in order to predict the spray charge level or the spray charge-to-mass ratio. In view of this situation, mathematical models have been developed in this thesis for both the corona and induction charging mechanisms. During the development of the theories, it has been assumed that for corona charging, that the jet is disintegrated into droplets and the droplets are then charged; for induction charging, that the jet is first charged and the charged jet is then disintegrated into charged droplets. The Sauter mean diameter of the sprays, D32 , plays an important role in linking the individual droplet charge to the spray charge-to-mass ratio for both charging mechanisms. The developed theories are general models suitable for any liquid with both corona and induction charging. Theoretical calculations for the spray charge-to-mass ratio, individual droplet charge and the ratio of droplet charge to the Rayleigh charge limit have been presented for almost all of the influencing electrical and mechanical parameters such as applied voltage, air flowrate, liquid flowrate, liquid conductivity, liquid dielectric constant, nozzle dimensions, cylindrical electrode dimensions, and fluid parameters, for example, density, viscosity and surface tension. In the calculation for corona charging of droplets, the effect of the droplets on corona current and corona-onset voltage has been assessed for first time. The introduction of the Sauter mean diameter of the sprays, D32 , makes the assessment possible. Theoretical calculations for induction charging of liquid jets have shown that provided liquids have a conductivity value higher than the critical value, s = - 10 4 S/m, then they can be charged satisfactorily by the induction charging method. Among all of the influencing parameters, the electrical and mechanical parameters determine the charging rate and the water spray charge level. The suitability of employing these two charging mechanisms to dust suppression in coal mine has been evaluated based on the spray charge level, safety issues and the simplicity or otherwise of the equipment. The induction charging method was considered to have advantages over its corona charging counterpart, and has been chosen for charging the water sprays in the experiment program. Water has a conductivity of s = - 10 2 S/m, higher than the critical value, s = - 10 4 S/m. Based upon theoretical considerations, it is concluded that water is an appropriate liquid for corona charging, based on its dielectric constant, and for induction charging, based on its conductivity. In order to facilitate the testing of electrostatically charged water spray cloud parameters, a spray charger/collector was designed and constructed by others and a computerised data acquisition system has been employed. According to the theory developed for induction charging, the optimum length of the charging electrode has been analysed based upon the assumption that water jet is first charged and then the charged jet is disintegrated into charged droplets by the high pressure air. An experimental program examined the dependence of spray current upon four parameters: air flowrate, water flowrate, applied voltage and jet diameter. The experiments have shown that the induction-charged air-atomising nozzle used in the experiment is able to impart a significant charge into the water sprays. The spray charge-to-mass ratio calculated based upon the measured spray current demonstrates the same characteristics as predicted by theory: increasing with air flowrate, decreasing with water flowrate, increasing with applied voltage to a peak value then decreasing with further increase in the voltage, and increasing with jet diameter. A successful interpretation of an important phenomenon in the inductioncharged air-atomising a water jet, that spray charge-to-mass ratio and spray current increase with air pressure (or air flowrate) and decrease with increasing water flowrate, has been achieved based on the theories developed in this thesis. This phenomenon occurs because increasing air flowrate and/or decreasing water flowrate leads to a higher velocity of jet flowing through the induction electrode. However, when water flowrate becomes very small, a decrease in spray current with increasing air pressure (or flowrate) may be caused both by jet breakup inside the electrode and by contraction of the jet. In order to verify the theory, a preliminary comparison of experimental data with theoretical predictions employing a constant kic in the air-jet interaction coefficient a which was assumed to be 0.7 has shown a general agreement. However, the value of kic appears to be related to jet diameter, air/water mass ratio and applied voltage. An empirical equation for kic has then been formulated based on the experimental data for the spray charge-to-mass ratio. Finally a comparison of experimental results with theoretical predictions using the formulated kic shows an improved agreement. It is concluded that the induction-charged air-atomising nozzle has a potential application in dust suppression in coal mines, as the voltage required to charge water sprays is only 1000 ~ 1200 volts, and that the theory developed for induction charging of water sprays can be used to guide laboratory investigations and design processes for dust suppression and other industrial applications which might employ the electrostatic charging of liquid sprays.

Research into the fluidic precessing jet, used in industrial burners, has been carried out within the School of Mechanical Engineering at the University of Adelaide for over a decade. The flow field generated by the fluidic precessing jet (FPJ) is extremely complex, and there are many questions yet to be answered about the mechanisms by which precession influences the mixing of the jet and ambient fluid, and hence combustion. Some may be answered by studying a non-reacting precessing jet. The mechanical precessing jet (MPJ) nozzle generates a precessing jet for which the exit conditions are well known, unlike the fluidic precessing jet. The non-reacting flow from this 'mechanical analogue' of the FPJ forms the basis of the current study. The MPJ provides a means of controlling and changing the structure of turbulence in a precessing jet by varying its precessional frequency. The characteristics of the MPJ flow are primarily determined by a Strouhal number of precession, and may be categorised as belonging to either a 'low Strouhal number' or 'high Strouhal number' regime of behaviour. The fundamental aim of studying the mechanical precessing jet flow is to determine the influence of the structure of turbulent motions, and in particular the large scale motions, on jet mixing. The analyses presented in this thesis lead to a better understanding of the underlying mechanisms of precession-enhanced turbulent mixing and combustion. Simultaneously collected phase-averaged velocity and concentration fields of the MPJ flow are presented, and correlations between the fields analysed, for one low and one high Strouhal number. Additionally, because the turbulent flow produced by the MPJ nozzle is unsteady in nature and instantaneous realisations of the flow may differ significantly from the mean flow patterns, planar velocity and concentration measurements which show instantaneous flow structure over the entire field are presented. The phase-averaged velocity and concentration field data have enabled new analytical models of the MPJ trajectory to be developed, and the behaviour of the major flow features, including the stability of the counter-rotating vortex pair, to be studied. The strong entrainment and mixing characteristics of the MPJ flow are also illustrated. The data and analysis strongly suggest that the initial trajectory of the jet is essentially radial, during which the jet experiences axial compression. At larger radius the jet experiences axial stretching. A counter- rotating vortex pair is seen to form approximately two potential core lengths from the jet exit, where the jet appears to bend sharply towards the axis of rotation. These vortices dominate the jet motion in the near field and eventually merge in the transition region of the flow. The inner vortex of the counter-rotating vortex pair mixes at approximately half the rate of the outer vortex, thus delivering a rich fuel mixture to the transition region when the MPJ is used as a burner. This may explain in part earlier observations of highly radiant, fuel-rich flames in the transition region. This study also outlines the development of an experimental technique for the simultaneous measurement of velocity and concentration in a plane. The medium is air, and the technique combines Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF) of acetone vapour in a unique manner. / Thesis (Ph.D.)--School of Mechanical Engineering, 2004.

Droplet formation from a rigid and a vibration nozzle driven by a pulsing pressure is simulated. Droplet formation is simulated by using one-dimensional model. For the case of droplet formation from a vibration nozzle, the nozzle vibration is simulated by large deflection plate vibration equation. Droplet formation from a rigid nozzle is studied simply by setting the nozzle deflection always to be zero. The one-dimensional model is solved by MacCormack method. The large deflection plate vibration equation is solved by mode shape approximation and Runga--Kuta time integration method. Three different effect factors, the driving pressure thrust input effects, the fluid viscosity effects, and the nozzle vibration effects, on droplet formation are studied. The driving pressure thrust input effects and the fluid viscosity effects are studied based on a rigid nozzle. The nozzle vibration effects are studied by comparing the results from a vibration nozzle with the results from a rigid nozzle. Results show: 1) the primary droplet break-off time is constant if the driving pressure magnitude is high, but the primary droplet volume and primary droplet velocity increase slightly as the driving pressure thrust input increase; 2) higher thrust input can possibly result in the occurrence of overturn phenomenon; 3) increasing the fluid viscosity cause the primary droplet break-off later, but the primary droplet volume and the primary droplet velocity does not change significantly by fluid viscosity; 4) the nozzle vibration effect on the primary droplet break-off time and the primary droplet size is small, but the nozzle vibration cause the primary droplet velocity to increase by an amount of the nozzle vibration velocity magnitude; 5) nozzle vibration cause longer liquid thread to form and the total satellite droplet volume to increase significantly which eventually break into multiple satellite droplet. / Graduation date: 2004

The following dissertation describes an investigation of the structural response behaviour of a composite solid rocket motor nozzle subjected to thermal and pressure loading during the motor ignition period, derived on the basis of a multidisciplinary numerical simulation approach. To provide quantitative and qualitative context to the results obtained, comparisons were made to the predicted aerothermostructural response of the nozzle over the entire motor burn period. The study considered two nozzle designs – an exploratory nozzle design used to establish the basic simulation methodology, and a prototype nozzle design that was employed as the primary subject for numerical experimentation work. Both designs were developed according to fundamental solid rocket motor nozzle design principles as non-vectoring nozzles for deployment in medium sized solid rocket booster motors. The designs feature extensive use of spatially reinforced carbon-carbon composites for thermostructural components, complemented by carbon-phenolic composites for thermal insulation and steel for the motor attachment substructures. All numerical simulations were conducted using the ADINA multiphysics finite element analysis code with respect to axisymmetric computational domains. Thermal and structural models were developed to simulate the structural response of the exploratory nozzle design in reference to the instantaneous application of pressure and thermal loading conditions derived from literature. Ignition and burn period response results were obtained for both quasi-static and dynamic analysis regimes. For the case of the prototype nozzle design, a flow model was specifically developed to simulate the flow of the exhaust gas stream within the nozzle, for the provision of transient and steady loading data to the associated thermal and structural models. This arrangement allowed for a more realistic representation of the interaction between the fluid, thermal and structural fields concerned. Results were once again obtained for short and long term scenarios with respect to quasi-static and dynamic interpretations. In addition, the aeroelastic interaction occurring between the nozzle and flow field during motor ignition was examined in detail. The results obtained in the present study provided significant indications with respect to a variety of response characteristics associated with the motor ignition period, including the magnitude and distribution of the displacement and stress responses, the importance of inertial effects in response computations, the stress response contributions made by thermal and pressure loading, the effect of loading condition quality, and the bearing of the rate of ignition on the calculated stress response. Through comparisons between the response behaviour predicted during the motor ignition and burn periods, the significance of considering the ignition period as a qualification and optimisation criterion in the design of characteristically similar solid rocket motor nozzles was established. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2009.

No description available.

Bibliography: leaves 190-212. / xxiii, 240 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis describes a thrust vectoring nozzle (TVN) which produces a jet which may be deflected at angles in excess of 80o from the nozzle axis by fluid dynamic means, while maintaining total thrust efficiency of the order of 50%, or at 50o with an efficiency of the order of 70%. The thrust vectoring by fluid dynamic means is achieved by injecting secondary fluid at the nozzle throat and partially separating the primary jet causing it to deform. / Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1995

Bibliography: leaves 228-262. / xxvi, 262, [xxvii] leaves : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This thesis reports on a fundamental investigation of a precessing jet flow which is analogous to that which emanates from the fluidic nozzle. A 'mechanical nozzle' is used to generate a well-defined PJ flow. / Thesis (Ph.D.)--University of Adelaide, Dept. of Mechanical Engineering, 1997?

The design of supersonic flow paths for scramjet engines and high Mach number shock tunnel nozzles is complicated by high temperature flow effects and multidimensional inviscid/ viscous flow interactions. Due to these complications, design in the past has been enabled by making flow modelling simplifications that detract from the accuracy of the flow analysis. A relatively new approach to designing aerodynamic bodies, which automates design and does not require as many simplifying assumptions to be effective, is the coupling of a computational flow solver to an optimization algorithm. In this study, a new three-dimensional space-marching computational flow solver is developed and coupled to a gradient-search optimization algorithm. This new design tool is then used for the design optimization of an axisymmetric scramjet flow path and two high Mach number shock tunnel nozzles. The flow solver used in the design tool is an explicit, upwind, space-marching, finite-volume solver for integrating the three-dimensional parabolized Navier-Stokes equations. It is developed with an emphasis on simplicity and efficiency. Cross-stream fluxes are calculated using Toro's efficient upwind, linearized, approximate Riemann solver in flow regions of slowly varying data, and an Osher type solver in the remainder of the flow. Vigneron's technique of splitting the streamwise pressure gradient in subsonic regions is used to stabilise the flux calculations. A three-dimensional implementation of an algebraic turbulence model, a finite-rate chemistry model and a thermodynamic equilibrium model are also implemented within the solver. A range of test cases is performed to (1) validate and verify the phenomenological models implemented within the solver, thereby ensuring the simulation results used for design are credible, and (2) demonstrate the speed of the solver. The first application of the new computational design tool is the design of a scramjet flow path, which is optimized for maximum axial thrust at a flight Mach number of 12. The optimization of a scramjet flow path has been examined previously, however, this study differs to others published in that the flow is modelled using a turbulence model and a finite-rate chemical reaction model which add to the fidelity of the simulations. The external shape of the scramjet vehicle is constrained early on in the design process, therefore, the design of the scramjet is restricted to the internal flow path. Because of this constraint, and the large internal surface area of the combustor and the high skin friction iv within the combustor, the net calculated force exerted on the scramjet for both the initial and optimized design is a drag force. The drag force of the initial design, however, is reduced by 60% through optimization. The second application of the design tool is the wall contour of an axisymmetric Mach 7 shock tunnel nozzle, which is computationally optimized for minimum test core flow variation to a level of +/- 0.019 degrees for the flow angularity and +/- 0.26% for the Pitot pressure. The design is verified by constructing a nozzle with the optimized wall contour and conducting experimental Pitot surveys of the nozzle exit flow. The measured standard deviation in core flow Pitot pressure is 1.6%. However, because there is a large amount of experimental noise, it is expected that the actual core flow uniformity may be better than indicated by the raw experimental data. The last application of the computational design tool is a contoured Mach 7 square cross-section shock tunnel nozzle. This is a three-dimensional optimization problem that demonstrates the versatility of the design tool, since the effort required to implement the optimization algorithm is independent of the complexity of the flow-field and flow solver. Optimization results show that the variation in the test core flow properties could only be reduced to a Mach number variation of +/- 7% and flow angle variation of +/- 1.2 degrees ,for a short nozzle suitable for a shock tunnel. The magnitudes of the optimized nozzle exit flow deviations for the short nozzle and two other longer nozzles indicate that generating uniform flow becomes increasingly difficult as the length of square cross-section nozzles is reduced. Overall, the current research shows that coupling a flow solver to an optimization algorithm is an effective and insightful way of designing scramjets and shock tunnel nozzles.

Thesis (Ph. D.)--University of New South Wales, 2000. / Also available (in part) online.