dr. mohammad taeibi

The study of pendent drop behavior as a nonlinear dynamical system has long been the focus of researchers. The vibrational behavior of the pendent drop at resonant frequencies contains useful information for investigating more complex dynamic systems. The oscillatory behavior of pendent drop at resonant frequencies contains useful information for investigating more complex dynamical systems. Dimensionless Bond and capillary numbers are important and effective parameters in the pendent drop behavior. In this work, the effect of dimensionless Bond and capillary numbers on the resonant frequency of the pendent drop is investigated. Two-dimensional multi-relaxation ‎time lattice Boltzmann method (MRT-LBM) was used to simulate the oscillations of the drop using a conservative model for high-density ratio. Using this model, the drop oscillatory characteristics were calculated for different values of Bond and capillary numbers. It was realized that increasing the Bo number from 0.11 to 1.96 causes an increase in natural frequency from 3.278E-4 to 1.88E-3 in an almost linear manner. Also, increasing the capillary number from ‎1.8E-5‎ to ‎7.3E-4‎ causes an increase in natural frequency from 3.278E-4 to 5.700E-4 in a non-linear logarithmic manner.

In this article, an immiscible two-phase flow in two dimensional ordinary and modified T-junction microchannels is numerically studied. To this approach, the Lattice Boltzmann method with Pseudo-Potential model is used. The accuracy of the present model is examined by the Laplace test, drop contact angle, and drop formation in an ordinary T-junction microchannel. The comparison shows that the present results have good agreement with previous numerical and experimental data. The effects of various parameters including Capillary number, flow rate ratio, width ratio, and drop contact angle on the width of the drop and on the distance between drops for ordinary and modified T-junction microchannels are investigated in details. The results reveal that by simple modifications to the ordinary T-junction, smaller drops and lower distances between them are generated in the comparison of ordinary T-junction geometry under the same conditions. On the other hand, this study demonstrates that the multiphase flows in micro-devices are very sensitive to even small changes in the channel geometry. It also indicates that lattice Boltzmann method with Pseudo-Potential model is an effective numerical technique to simulate the generation of drops in microchannels.

At the present research, Film Cooling around a gas turbine blade has been studied numerically via Partially Navier-Stokes Simulation (PANS) approach which is one the most success approaches of Very Large Eddy Simulation (VLES) in turbulence flow. For detail investigation of flow around gas turbine blade (airfoil with film cooled holes on leading edge) has been simulated in three dimensions and inlet temperature and blade surface temperature has been considered: 409.5° C and 297.7° C respectively. Inlet Reynolds number is 8.42 X 105. Inlet flow is fully turbulent and turbulence intensity has been set on 0.052 meanwhile secondary flow effect in up and bottom of blade has been waived. Numerical calculation has been done by Fluent and partially averaged Navier- Stokes equations (PANS) have been applied to fluent by UDF’s. The obtained results from Partially Navier-Stokes Simulation (PANS) method have been compared with existed experimental data and other RANS two-equations models in other researches and it demonstrate that Partially Navier-Stokes Simulation (PANS) approach results has admissible correspondence with experimental data in addition these results are accurate than RANS two- equations models.

Flow hydrodynamic effects and film cooling effectiveness of placing a coolant port (upstream jet) just upstream of the main cooling jet were numerically investigated. The upstream jet was added such that the total cooling cross section (cross sections of the main and upstream jets) remains constant, in comparison to the case of ordinary cooling jet. The finite volume method and the unsteady SIMPLE algorithm on a multiblock non-uniform staggered grid arrangement were applied. The large eddy simulation (LES) approach with the one equation subgrid scale model was used. The jet to cross flow velocity ratio (for both of the main and the upstream jets) is 0.5 and the cross flow Reynolds number (based on the main jet parameters) is equal to 4700. The obtained results showed a significant improvement in the flow control capability and both centerline and span-wise averaged film cooling effectiveness applying the new cooling configuration. Effects of the upstream jet dimensions are also studied here. The obtained results showed that the span-wise width of the upstream jet has more essential influence on the cooling performance than that of its stream-wise width. Moreover, it is demonstrated that the film cooling performance could be enhanced even by applying an upstream jet which its temperature is as same as the cross-flow temperature, i.e. applying a hot upstream jet. Finally, it is shown that presence of the upstream jet decreases the stream-wise component of the velocity near the wall, which decreases the wall shear stress and the skin friction drag coefficient significantly.

In this work, three-dimensional turbulent forced convection flow through a flattened pipe, partially and completely filled with a porous material, was investigated numerically. Here, the effects of permeability and thickness of the porous layer on the rate of heat transfer and pressure drop were investigated. For this purpose, porous material was inserted in two geometrical arrangements: central and boundary. Also, the pipe had constant-temperature condition. The results for central arrangement show that the rate of heat transfer first increases and then decreases with increasing the thickness of the porous layer, while the pressure drop is monotonically increasing. While for the porous medium boundary arrangement, the rate of heat transfer first decreases and then increases with increasing the thickness of the porous layer. Also the maximum of Nusselt number is occurred for the fully porous pipe configuration.