FLUID MECHANICS AND AERODYNAMICS JOURNAL
Year:2018 | Volume:6 | Issue:2 |Papers Count:6

In this study, a compressive duplex injector was designed, fabricated, and its operational characteristics were investigated. Effects of pressure and viscosity on injector's operational characteristics (i. e., flow rate, discharge coefficient, break-up length, cone angel, spraying spatial distribution, and droplets' mean diameter) were presented as a function of injector's Reynolds and Weber numbers. Water and Mazut were employed as agent fluids due to their high viscosity differences. All experiments were carried out at atmospheric standard conditions. Picturing of spraying area was performed utilizing fast shooting, based on backlighting. The results showed increasing pressure would lead to raise in flow rate. Furthermore, raising Reynolds number leads to initial cone angel increase, then the spraying angel maintains constant as fully developed condition is dominated. The constant spraying angels are observed at Reynolds numbers above 265 and 7. 5×104 for Mazut and water, respectively. Moreover, break-up lengths are decreased at the Weber numbers lower than 50 and 170 for Mazut and water respectively, followed by maintain constant as the flow pattern is developed. The results showed that discharge coefficient depends on Reynolds number and fluid material, in addition to injector's geometry. The discharge coefficient is increased, as the Reynolds numbers raise to 200 and 5×104 for Mazut and water, respectively. The spatial distribution measurements showed significant performance of the injector for creating a hollow cone spray.

In the present study, the rheological behavior of hybrid nanofluid (MgO(65%) – MWCNT(35%)/5w50) has been studied. the viscosity of mentioned nanofluid was measured at 5oC-55oC and 0% – 1% volume fraction range. then the effect of these two parameters on viscosity was studied. Also, the effect of shear rate changes (665. 5 s-1-11997 s-1 ) on viscosity changes was studied. Fitting power law curves on experimental data and achieve R2's with very close to unity was considered as a sign of non-Newtonian behavior of present nanofluid. In order to forecast viscosity quantities as functions of solid volume fraction, temperature, and shear rate, a novel three variable correlation has been proposed (with R2=0. 999). Viscosity reduction of nanofluid in comparison with the base oil in solid volume fractions of 0. 05%, 0. 1%, and 0. 25% is another remarkable result of the present study.

The best way to increase turbine efficiency is increasing the temperature of the incoming air. On the other hand, film cooling is the most efficient tool. In this work triple jet film cooling has been numerically investigated. Cross sections of all jets were rectangular and were inclined normally into hot cross-flow. As far as turbulence modeling, k-ω /SST along with an algebraic non-isotropic turbulence model, as its modification, has been used. In addition, staggered grid and finite volume method with SIMPLE algorithm were implemented. The turbulence model used was shown to be able to predict mean quantities relatively close. Also, it had a much better convergence rate compared with standard k-ω SST model. On the other hand, this model did not predict some of the turbulent quantities (such as turbulent kinetic energy) close enough. Finally, it seems to work better in single-jet film cooling, compared to a triple jet one.

This paper discusses the application of Taguchi method in assessing maximum heat transfer rate for a natural convection with magneto hydrodynamic flow in a semicircle enclosure, embedded with a heat source. The simulations were planned based on Taguchi method with each trial performed under different magnetic field, heat source aspect ratio, and particle volume fraction of nanofluid. Thermal lattice Boltzmann methods was used to simulate flow and thermal fields. Signal-to-noise ratio analysis was carried out in order to determine the effects of process parameters and optimal factor settings. Finally, confirmation tests verified that Taguchi method achieved optimization of heat transfer rate with sufficient accuracy.

Shock waves are presented in hypersonic aircrafts. They increase drag and as a result of additional friction, surface heating increases. In this research, a wind tunnel model; a combination of a 60o slender physical spike, used as cathode and a 60o truncated cone-cylinder, as anode, were experimented in flows with Mach numbers 1. 5, 1. 95, and 2. 45. Plasma was produced in front of the aero-spike model by electrical discharge of 50 HZ, 30 KVDC, and 50 mA. Shadow and plasma glow imaging techniques were used simultaneously for flow and plasma visualization. Shadow imaging, in the afore mentioned Mach numbers, shows that the plasma being discharged behind shock wave, in spite of increasing the magnetic field, has a slight effect on decreasing the intensity of the shock wave. With increasing Mach number, the Shock wave of the truncated conical nose moves downstream and as a result of the plasma discharge taking place below the nose and the constant magnetic field, the wave below the nose is eliminated. The experimental results indicate that at Mach number 2. 45, the shock wave attaches to the truncated nose, thus; the continuous plasma discharge below the spike and in front of the wave eliminates the wave. This is the most important result of this study indicates that aero-spike plasma discharge can remove shock waves and thus reduce drag.

One of the problems in repairing pipelines containing fuels or any other liquid in industrial units or public and residential buildings is impossibility of separating damaged part of the whole path for repair, avoiding waste of fluid. The present design attempts to introduce a method based on use of freezing in pipeline repairs, which, while removing pipe discharge operations locally, recommends it as a superior technique. In this method, by producing cold condition outside the pipe and on both sides of the damaged part, the fluid is frozen in the tube and creates an obstacle in the fluid flow path. The freezing operation is performed by closing a temporary refrigerant coating around the tube. Thus, the damaged part is separated from the rest of the pipeline and is repaired. In this research, the freezing equation was first calculated by numerical solution based on Simpson's integration, and the duration of freezing of the fluid in a tube with different boundary conditions (pipe diameter, type and fluid velocity, etc. ) was calculated. At the end, the results of the numerical methods were compared with the results of the experiment on a device designed for this purpose.