FLUID MECHANICS AND AERODYNAMICS JOURNAL
Year:2019 | Volume:7 | Issue:2 |Papers Count:6

Comprehensive analysis of coolant thermal behavior in regenerative cooling channels is one of the main steps in optimum design of launch vehicles. In methane-based propulsion systems, thermal analysis of methane coolant is important to predict the thermodynamic properties which depend on local temperature and pressure. Methane may experience a state change from subcritical to supercritical and heat transfer deterioration due to the high temperature gradients in the proximity of the walls, high Reynolds numbers, and three-dimensional flow structures in cooling channels. In the present study, a computational fluid dynamics solver was developed, which is able to simulate the convective heat transfer of supercritical methane coolant flow inside rectangular cooling channels. The solver was validated using reliable experimental data. The coefficients of current Nusselt number correlations were improved using minimization of relative root mean square error. Additionally, the entrance-region effects on heat transfer coefficient were simulated. The accuracy of the proposed relations was studied at different operating conditions. The proposed modified Nusselt correlations have errors less than 10% at outlet pressures higher than 8 MPa and heat transfer rates lower than 13 kW.

The purpose of this study is to numerically investigate the heat and mass transfer of magnetic nanoparticles inside a 3D capillary with non-Newtonian blood flow, Under the influence of external non-uniform magnetic field. For this purpose, the governing equations including continuity, momentum, energy, Maxwell, and concentration were coupled and solved by COMSOL, a finite element based software. Blood is assumed as non-Newtonian fluid with Carreau viscosity model and the vessel wall is assumed to be rigid. the results indicate that the concentration of magnetic nanoparticles in the upper wall of the vessel at long times reaches a constant value. This accumulation affects the blood flow temperature. Magnetic field strength, magnetic susceptibility, and concentration of nanoparticles are directly related to the temperature of the bloodstream at the location of particles accumulation. By increasing the size of nanoparticles and inlet velocity, the blood flow temperature decreases so that in sizes above 70 nm, the thermal effect of particles becomes very low. Also, the non-Newtonian blood assumption has significant effect on the results.

In film cooling, coolant air is injected over the surface to provide a protective cool film against the high temperature gases. Film-cooling performance is largely influenced by the jet hole shape. And thus optimizing the hole shape configuration is necessary to achieve better cooling performance. The present study investigated the cooling effectiveness of the novel incomplete cylindrical jet hole (pea jet hole) experimentally, using an infrared thermography method. Steady state heat transfer experiments were performed at free stream Reynolds number, based on jet hole diameter of 10, 000, over a flat plate. Measurements were carried out at four blowing ratios (M=ρ jetVjet/ρ ∞ V∞ ) of 0. 4, 0. 5, 0. 7, and 0. 8. Out results show that the novel pea jet hole has an optimum blowing ratio of 0. 7 and at the same blowing ratio, in comparison to the cylindrical jet hole, the cooling effectiveness of the new geometry is higher. Another words applying the same amount of injected fluid, the coolout fluid is distributed more uniformly over the surface.

Nowadays, improving the aerodynamic performance of supersonic flying vehicles in order to reduce drag forces and increase in heat transfer coefficient is an interesting matter for researchers. Many of the supersonic vehicles use blunt nose to reduce heat generations, while these noses cause higher drag forces. Equipping the nose with spikes is a technique to reduce the drag of blunt noses. Spikes also increase their heat transfer rate. The accuracy and the validity of RANS based numerical simulations of turbulent flow over these bodies depend directly on the capabilities of the turbulence models used. This paper presents numerical simulation of supersonic flow over a blunt nose equipped with a spike, using four different turbulence models, namely: one-equation turbulence model of Spalart-Almaras and two-equation turbulence models of k-ε , k-ω and k-ω-SST. We wanted to find the appropriate turbulence model for this type of flows. Air flow Mach number and angle of attack were considered 6 and zero, respectively. The axi-symmetric, compressible and steady RANS equations are solved numerically. In spite of initial expectations, comparison of numerical results with experimental data showed that Spalart-Almamras has more consistency with experiment.

In this research, the effects of Ag-nanoparticles, volume fraction on the hydrodynamic and thermal behaviors of convective flow in a three-dimensional duct with abrupt contraction are studied. The abrupt contraction is created by an inclined forward facing step. The blocked-off method is used to simulate the inclined surfaces of the step. The set of non-dimensional governing equations, consisting continuity, momentum, and energy were solved numerically by CFD techniques and SIMPLE algorithm. To investigate the influences of nanoparticle´ s volume fraction, distributions of temperature, velocity, friction coefficient, Nusselt number, and mean bulk temperature were presented graphically. Our numerical results show that the Ag-nanoparticles volume fraction has significant effects on thermal and hydrodynamical behaviors of the flow.

In the present study, an intelligent computational grid is introduced which adapts itself to the body displacements in the computational domain by regular and systematic changes of the nodes. Configuration of the introduced grid is based on defining separate zones around the body for rotational and translational motions. Therefore, the ordinary problems in available moving grids which try to keep the nodes stable, such as: reduction of the grid quality, the need for regenerating the grid overally or locally, interpolation, or data transfer between different parts of grid are decreased to a great extent. Defining a three-dimensional moving-grid and the lack of limitations on the size of rotation or translation of body are also amongst the advantages of this method. Then, changes made following the body rotation/translation and reformation of the grid through changes in its connection for a rectangular wing with NACA0012 airfoil was shown. Finally, to validate the correct performance of the introduced moving-grid method, the three-dimensional unsteady form of the Euler equations was solved. Several test cases were solved and the results were compared with reliable experimental and numerical. Results, showing relatively close agreements