Interaction between the normal shock wave and the turbulent boundary layer in a supersonic nozzle becomes complex with an increase of a Mach number just before the shock wave. When the shock wave is strong enough to separate the boundary layer, the shock wave is bifurcated, and the 2nd and 3rd shock waves are formed downstream of the shock wave. The effect of a series of shock waves thus formed, called shock train, is considered to be similar to the effect of one normal shock wave, and the shock train is called pseudo-shock wave. There are many researches on the configura- tion of the shock wave. However, so far, very few researches have been done on the asymmetric characteristics of the leading shock wave in supersonic nozzles. In the present study, the effect of nozzle geometry on asymmetric shock wave in supersonic nozzles has been investigated experimentally.
A 3D, multi-physics, transient state model was developed to simulate various nozzle geometry changes using the CFD solver Fluent, and takes into account buoyancy forces, convection and radiation. The model geometry was constructed in Gambit to replicate the experimental setup. The nozzle was centrally positioned, 10 mm above a 250 x 500 x 8 mm plate (width x length x depth), in a volume of fluid 600 x 1000 x 200 mm, encapsulating the nozzle and plate in order to model all flow development of interest. A simplification of the welding arc was assumed which involved a 12 mm diameter hemisphere being positioned adjacent to the plate surface, directly beneath the welding nozzle, as shown in Figure 1. The density of the mesh was increased in the area between the nozzle outlet and the plate surface, as this was the main area of interest.
The present study aims to build upon previous research which showed that a circumferential restriction around the nozzle exit has the ability to considerably improve the shielding gas columns resistance to the detrimental effects of cross draughts. As a result, this study aims to further refine the nozzle geometry in order to further reduce the shielding gas consumption by investigating the effects that the internal nozzle geometry has on the shielding gas flow characteristics i.e. through the addition of a double helix insert, a restricted end plate and an internal plate. A CFD model, validated through extensive experimental trials was used to determine the susceptibility of each different nozzle design to side draughts when using various shielding gas flow rates.
32 Read more
A numerical study is presented on the effects of various nozzle geometries and operating conditions on the performance of a Pulse Detonation Engine (PDE). An unsteady numerical simulation model, which is second order accurate in space and first order accurate in time, using an automated Java based computational fluid dynamics (CFD) software is presented. One- and two-dimensional transient CFD models were employed in a systematic manner to study the propulsive performance characteristics of the PDE under different operating conditions. Preliminary studies of the effects of nozzle geometry on the performance characteristics of a generic PDE are presented. The results indicate that an expanding nozzle, capable of adapting with the cycle time and the ambient pressure, is very suitable for optimizing the PDE performance. Addition of a straight, diverging or converging nozzle improves the performance. However, it is observed that there is an optimum value of the exit area of a divergent nozzle for performance improvement. At low ambient pressure addition of a nozzle increases the specific impulse of the PDE tube. It is also seen that a diverging nozzle is more effective than a converging-diverging nozzle at low ambient pressure. The study indicates that increased volume of the reacting fuel mixture has a negative effect on the PDE performance. The results show that a 25% reduction of the reacting fuel mixture leads to approximately 18% increase in the value of the specific impulse.
Flow of gases through a converging-diverging nozzle is one of the benchmark problems used for modeling compressible flow using computational fluid dynamics algorithms. In a converging nozzle, the highest speed that a fluid can be accelerated to is sonic speed, which occurs at the exit. The converging-diverging nozzle is used to accelerate the fluid to supersonic speeds depending on the average exit pressure to the total stagnation pressure. There is a possibility of creating shock waves in the flow-field. The flow out from a converging-diverging nozzle often has strong gradients of pressure, temperature, density, and speed in radial and axial direction. Ratios of pressure, density and temperature can be related to the stagnation temperature, pressure and density at a given Mach number as seen in equations 1 – 3. and ratio across section area to cross section area at throat a given Mach number as seen in equation 4, and relation between the speed of the sound and the temperature as seen in equation 5, and the relation between gas velocity and sound speed as seen in equation 6.
12 Read more
An issue that is commonly encountered in the stripping section is the fouling of the stripper sheds. Wet agglomerates of coke particles may stick to the surface of the sheds, and reduce the area through which the fluidization gas can pass through. This can lead to poor coke circulation and reduced fluidization velocity throughout the reaction zone. Bi et al. (2004) discuss a V-shape stripper shed geometry that can be used to reduced stripper fouling and improve contact between the fluidization gas and descending coke particles. Sanchez et al. (2013) investigated the configuration of V-shape stripper sheds as well as the fraction of cross sectional area covered by the sheds in the stripper zone of a pilot scale cold model Fluid Coker. A grid-like mesh configuration was found to be advantageous for the prevention of liquid flow through the sheds, as well as the prevention of vapors reaching the stripper level inside the reactor. As well, it was found that using the current stripper shed configuration, the fraction of open area within the stripper section should be around 60-70% to reduce loss of valuable liquids to the burner.
150 Read more
Tetrahedral elements are adapted to the regions where the hexahedral scheme is not suitable and will result in a higher skewness. This ensures a higher grid quality and more accurate results. The no-slip condition was used for the nozzle wall because the gas velocity near the wall zone is much low. In this study, the heat transfer process between the gas and the wall was not considered, and thus a fixed heat flux (heat transfer rate) of zero was enforced at the wall. The gas used was ideal, compressible and continuous. A coupled implicit method was used to solve the flow field and the result of that in a steady state was obtained. The standard K–e turbulence model was utilized.
Experimental investigation were carried out on a single cylinder four stroke direct injection diesel engine operated in duel fuel mode using rice bran oil methyl ester (ROME) and coconut shell derived producer gas. ROME is used as a pilot injected fuel which ignites the producer gas and air mixture when subjected to higher compression ratio. In order to study the effect of nozzle geometry on the performance of dual fuel engine an effort has been made to enhance the performance of a dual fuel engine utilizing different nozzle orifice. In this present work injector nozzle (3, 4 and 5 hole injector nozzle, each having 0.2, 0.25 and 0.3 mm hole diameter and injection pressure (varied from 210 to 240 bar in steps of 10 bar) was optimized. The HC, CO and smoke emission was less with the use of 4 hole injector compared to three and five hole injectors used for fuel injection.
The heat transfer and pressure drop characteristics of both submerged and free- surface liquid jet arrays with modified inlet and/or outlet geometries have been investigated for a range of volumetric flow rates for a fixed number of 1.0 mm jets. With regards to heat transfer, the submerged jets exceeded the performance of their free jet counterparts. Generally, the presence of an inlet modification alone was observed to lead to decreases in pressure drop, whilst the addition of an outlet modification had an adverse effect. For free-surface jets, the addition of outlet modifications had a positive effect on heat transfer. It was found that for both free-surface and confined-submerged conditions, those nozzle configurations that caused enhancements in the heat transfer coefficient generally had a more significant improvement on the overall performance than those that caused pressure drop reductions. An exception to this was the contoured inlet nozzle configuration which, under confined-submerged conditions, was one of the highest performing jets primarily due to its ability to significantly reduce the pressure drop. From an electronics packaging standpoint, where power consumption may need to be minimized whilst achieving a given design heat transfer coefficient, the confined- submerged nozzles with contoured inlet or inlet/outlet are the suggested nozzle configurations.
46 Read more
In order to obtain more efficient and reliable hypersonic propulsion system , mixing of two high speed streams in a short mixing duct of short residence time is a basic requirement. Samitha et al.  experimentally and numerically studied the mixing performance of three lobed clover nozzle with rectangular cavity of different aspect ratios and compare with that of conventional conical nozzle with cavity in coaxial supersonic streams of Mach number 2 and 1. Samitha et al.  were conducted experimental study on supersonic mixing using three lobed nozzle. The result showed a complete mixing of the streams with marginal loss in stagnation pressure loss within a short mixing length. Three lobbed clover nozzle is introduced to add passive mixing. Studies towards this direction  showed that a clover nozzle, which is a class of radially lobbed nozzle, provides better pressure recovery compared to normal lobbed nozzle. Deepu et al.  numerically studied that shock induced vortex generation enhance mixing and reaction. It is found that the shock reflections are responsible for blocking the development of jets and thereby creating the low velocity region cavity.
The simulations were performed for a two-dimensional axi-symmetric geometry in order to reduce the computation time and memory requirements. Unsteady incompressible Reynolds- Averaged Navier-Stokes (RANS) equations for turbulent flow inside the nozzle were solved using the CFD package from Fluent Inc. The Re-Normalized Group (RNG) κ-ε turbulence model was used, as it showed the best degree of convergence (detailed description of RNG κ-ε is available in the literature and will not be repeated here (See appendix A)). The convergence criteria for these simulations are defined in terms of the “residuals”. The residuals provide a measure of the degree to which each of the conservation equations is satisfied throughout the flow field. The residual for each flow variable gives a measure of the error magnitude in the solution in iteration. A simulation is considered to be at the state of convergence when residuals show at least three orders of magnitude reduction along with no significant change in the flow properties upon considering additional iterations.
211 Read more
The aim of the current paper is to link nozzle geometry, and its effects on spray characteristics, with combustion characteristics in the chamber of IC engine. The combustion and formation in a diesel engine is governed mainly by spray formation and mixing. Important parameters governing these are droplet size, distribution concentration and injection velocity. Smaller orifices are believed to give smaller droplet size, even with reduce injection pressure, which leads to better fuel atomization, faster evaporation and better mixing. For this purpose, three 6-hole sac nozzles, with different orifices degree of concavity, have been used. The analysis of all the results allows linking nozzle geometry, spray behavior and combustion development. In particular, CH-radicals have shown to appear together with vapor spray, both temporally and in their location, being directly related to nozzle characteristics.
465 They showed the result, for a nozzle with sharp-edge inlet with l/d ratio of 1, (Re=29,485), the maximum point Nusselt number is 155,which occurs at H/D=4. With countered inlet, Nu=125 at H/D=8. Popiel et al. shows the similar results, the heat transfer rate with countered nozzle is 25% less than the sharp edged orifice at H/D=4 with Re=20,000. Gundappa et al. also shows the similar comparison between orifice jet and and the jet from pipe (l/D=10). The axial velocity decay more slowly in case of jet from pipe which led to the higher values of Nusselt number at all radial position with H/D=7.8. K.jambunathan et al. suggests that the nozzle geometry affects the velocity profile at the nozzle exit which affects the toroidal vortices formed near the jet circumference and the turbulent layer generated in the shear layer. The turbulent intensity would affects the mixing of the jet with ambient air and so the rate of velocity decay which also affects the heat transfer rate.
10 Read more
cylindrical shape with 5 holes nozzle geometry reduced NOx emissions up to 45% and slightly reduced BTE of the engine was observed as compared to a standard shape . The diesel engine with pongamia oil methyl ester B40 blend reported higher BTE in baseline shape, but reduced emissions in TCC shape . The engine performance of diesel engine remains same but emissions were reduced by modification of combustion shape . The diesel engine operated with TRCC shape reported better BTE, minimum SFC and reduced pollutants at retarded fuel IT . The HOME -producer operated diesel engine performed better BTE and reduced pollutants for TRCC shape, higher IOP and 4 holes nozzle injector . The diesel engine powered with 20% of JOME fuel found higher efficiency and lower pollutants for TCC shape . The diesel engine found higher BTE and reduced harmful pollutants for TRCC shape, 200 bar IOP and 25 o BTDC . The experimental results in diesel engine found that fuel IT of 27° BTDC, IOP of 240 bars, 5 holes nozzle geometry and TRCC shape are most favorable for better BTE with nominal emissions (36).
13 Read more
Abrasive waterjet (AWJ) machining process utilized increasingly in industrial applications. It is a non-traditional machining process and involves complex mechanics. The main problem of AWSJ machining process is nozzle wear during the process. The wear of nozzle depends on various parameters such as water jet characteristics, abrasive size and nozzle geometry, etc. Also the inlet pressure of the abrasive water suspension has significant influence on the erosion characteristics of the inside surface in the nozzle. The uncontrolled nozzle wear can affect the effectiveness and surface finish obtained through the AWSJ machining process. The wear rate of the nozzle can be minimized by controlling these parameters. This paper discusses a review on nozzle wear in abrasive water jet machining. In machine tools industry is very important to reduce the costs when are using the lubricant and coolant fluids to increase the productivity. It was been performed a simulation of the fluid flow through a nozzle, that nozzle type is commonly used for pressure cooling of the machined area. In these types of nozzles can be made a mixture of two types of fluids, such as air and water, to increase machined productivity and decrease the quantity of lubricant used for cooling systems.
Fig.15 Velocity distribution plot at Mach no-2 Above all the plots are describing the velocity distribution of C-D nozzle for various Mach number and different turbulence model. All the distribution was quite similar to each other with different Mach number. The differences are very small. It reveals that, not much relation between Mach number and turbulence model. Variation was found between various turbulence models at same Mach number. K-epsilon and K- omega were had similar distribution except small deviation at tail of C-D nozzle. But Spalart allmaras model had immense digression form other two models. It might of large turbulence at tail section of C-D nozzle
without regulator is usually used for low required mass flow such as monopropellant thruster. Turbo-pumps are used for high thrust level and mass flow such as bipropellant propulsion systems. Constant thrust level is usually required in conceptual design phase. Constant thrust level needs constant feeding pressure thus; regulator is used to keep the propellant tank pressure near the desire values. Feeding subsystem consists of feed line (tubes and ducting), regulator, valves, gas tank and pressurizer gas. Some of these components can be vanished in conceptual phase because of same effect in various concepts. Most part of feeding subsystem mass (changing by concepts) connected to the gas tank and pressurizer gas. Propellant tank volume and feeding pressure specify the feeding subsystem geometry and mass. Required radius of gas tank is derived by equation (5). Complete modeling of the pressurized feeding subsystem can be found in .
In Model 1, with a nozzle-nozzle distance (S/d) of 0.5, and a nozzle-plate distance (H/d) of 0.5, the contours of the predicted static temperature for a k-ε model in Model 1, which displayed the contours of the total temperature, were described in Figures 9-10. Figure 9 presents the thermal distribution of a hot plate, wherein the Nu was high in the centre of the plate surface and decreased gradually away from the plate centre. A high-temperature region was noted on the surface of the plate where a strong recirculation air flow was noted that resulted from twin jets under high velocity. Other models, presented in the other figures, showed similar results. This model showed a Heat Transfer Coefficient (h) of 57.97 (W/m 2 ·K).
20 Read more
see section 3.3.4, operated at the same injection pressure. Water was caused to flow through the perspex tube at a velocity of 1.43 m.min-1 - identical to the velocity at which the water flowed past the injection nozzles in the bloom caster model system. Pictures were taken of the views of the tip area of the stainless tube with the aid of the micro-flash. Two arrangements were used for taking pictures. The first arrangement, as shown in figure 3.19, provided a general view of the nozzle tip area, pictures being taken directly using a standard camera lens. The second arrangement, as shown in figure 3.20, provided a close-up view, in which the pictures were taken through a microscope. The value of the magnification factor was not important in either arrangement, since the particle size could be measured by reference to the known outer diameter of the stainless tube. The particle diameters were measured by projecting negatives obtained using the standard camera lens onto a screen and making direct measurements.
378 Read more
A novel idea of reducing turbine rotor friction losses through adding riblets to the rotor hub was explored thoroughly. Computational Fluid Dynamics (CFD) has been used to study the effects of those features at design point conditions of the MGT. Riblets with different height and spacing have been examined to determine the riblet geometry where the maximum drag reduction is achieved. To improve the predictability of performance of the turbomachinery components of the MGT over the operating envelope, a prediction methodology was developed during this research which used a combination of CFD and empirical correlations to account for losses that are not included in the CFD model. It was found that riblets reduce the cross-stream motion of the low momentum fluid flow near the hub surface of the rotor passage, and separate the streamwise vortex from interaction with the hub surface. The maximum drag reduction was found to occur with riblets of a relative height of 2.5% with respect to the rotor inlet blade height.
191 Read more