میریوسف هاشمی

Due to the very high importance of gas turbine in electricity production and also its increasing development in the electricity industry, one of the most important methods to increase the efficiency of gas turbine blades is to add thermal barrier coating to their outer surface. These coatings improve the cooling of gas turbine blades, but they also have disadvantages such as roughness of their surface cause to the separation of the hot fluid flow around the turbine blades. The rough surfaces of thermal barrier coatings should be used optimally and purposefully. In this research, using commercial software of Fluent, this type of coating has been investigated and analyzed in order to find the most optimal possible mode for its use. The influence of surface parameters such as roughness, thickness and material of thermal barrier coatings have been investigated. The most optimal state for the mentioned parameters are: 0.1 mm, 0.38 mm and 2.7 W/m.K respectively.

In this study, the effects of nozzle angle variations on vertical axis on nozzles plane has been investigated. Cooling and heating are one of the most important industrial processes that are widely used in industry, for this reason multiple impinging jets have been considered to study by many researchers due to their efficiency and high heat transfer. Simulations has been carried out using SST k-omega turbulence model. First, the cooling by elliptical nozzles are investigated to show increasing their efficiency compare to circular nozzles. Then the arrangement and orientation of the nozzles have been investigated. The obtained results showed that the nozzles angle variation, in some cases can lead to increase in the thermal flux. The modeling results showed that when the diameter ratio are equal to 10 and 4, the change in angle of nozzles had a negative effect on the heat transfer value, While in the diameter ratio of 3, changing the angle of the nozzles increased the heat transfer by about 3.71%. Also, numerical studies showed that changing the angle has little effect on creating heat transfer uniformity.

In the present work, the numerical investigation of a wind turbine airfoil with suction flow control is initially performed to find the relative improvement in its erodynamic efficiency. Consequently the study of turbine performance is accomplished using 2D simulation results as extending the flow control to wind turbine blades. The latter is incorporated via definition of new input data file in Q-blade code including complete set of section aerodynamic coefficients for both with and without suction control against variety of angles of attack and velocities. The benchmark turbine in this study is NREL 5 MW. It is shown that using suction in 1/3 of chord length would lead in better enhancement. Simulation of the airflow with and without suction control has been presented in three different locations in the chord-wise direction (26%C, 33.5%C and 50%C) and for several intensities or suction speed ratios (0.022, 0.045, 0.11, and 0.155). The turbulence model is transitional 4-equation SST model. The aerodynamic improvement in section is dominant and this method could tolerate stall behavior. Wind turbine power and thrust coefficients were analyzed via Q-blade versus tip speed ratio and flow control parameter. The range of tip speed ratio studied here is 3.5 to 15. The results depicted that applying suction in certain part of the blades could increase output power at low tip speed ratio. Applying suction at 33.5% of chord length improves the average power coefficient by 4.1%.

In this paper the governing equation for incompressible flow with heat transfer are solved numerically using artificial compressibility method. The finite volume method was used to solve the governing equation with Jameson’s method on triangular unstructured grid. In order to stabilize the solution a blend of the second and fourth differences of conserved variable used in order to prevent the oscillations. An implicit method with second order accuracy was used to time integration. In order to solve the obtained equation at each time step an artificial time step and the forth order explicit runge-kutta has been used. In order to ensure the accuracy of obtained results independent of the grid size the obtained results has been compared with the standard test cases in the literature and indicated a good agreement. Comparison of results indicated that the method used in the numerical solution of incompressible flow has a desirable accuracy and convergence rate.

In this paper, a meshless approach utilizing least-squares error technique and Taylor series was used to numerically solve an inviscid hypersonic flow. Second and fourth order derivatives were used as artificial dissipation terms to stabilize the solution and prevent unwanted oscillations especially around the vicinity of shockwave. In this study, chemical reactions caused by increased temperature were assumed to be in equilibrium condition and derived graphs were used to estimate the specific heat ratio. We used an explicit four-stage Runge–Kutta method for temporal discretization of governing equations, and used local time-stepping and residual smoothing techniques to accelerate the convergence process. The results obtained from meshless approach were compared with those obtained from finite-volume method with identical point distribution, and this comparison showed that using meshless approach provides better convergence and lower computation time. Result also showed that replacing ideal gas model with real gas model and applying the hot gas effects lead to precise identification of shockwave’s location, and provides a more accurate prediction of temperature and pressure distribution behind the shockwave.