• Energy Research

AbstractIn the present work, a recently developed in-house 2D CFD code is used to study the effect of gas turbine stator blade roughness on various performance parameters of a two-dimensional blade cascade. The 2D CFD model is based on a high resolution flux difference splitting scheme of Roe (1981). The Reynolds Averaged Navier-Stokes (RANS) equations are closed using the zero-equation turbulence model of Baldwin-Lomax (1978) and two-equation Shear Stress Transport (SST) turbulence model. For the smooth blade, results are compared with experimental data to validate the model. Finally, a correlation between roughness Reynolds number and loss coefficient for both turbulence models is presented and tested for three other roughness heights. The results of 2D turbine blade cascades can be used for one-dimensional models such as mean line analysis or quasi-three-dimensional models e.g. streamline curvature method.

Abstract This paper investigates the forced convection of alumina-water nanofluids within helical tubes, maintaining a constant wall temperature and assuming thermal equilibrium between the nanoparticles and the base fluid. The nanofluid model incorporates the effects of alumina (Al2O3) nanoparticle volume fraction, diameter, and temperature on thermophysical properties. The governing equations are solved using the Forward-Time Central-Space Finite Volume method in conjunction with the simple algorithm. Numerical results are validated against experimental data, demonstrating high accuracy. The study explores the effects of pitch size, curvature ratio, nanoparticle volume fraction, nanoparticle diameter, and Reynolds number on velocity contours, temperature profiles, secondary flow, thermophysical properties, friction coefficient, and heat transfer rate. Additionally, the figure of merit evaluates the impact of these parameters on the thermal performance of the system. The results indicate that an increase in Reynolds number and nanoparticle diameter negatively affects thermal performance, while higher nanoparticle volume fraction, curvature ratio, and pitch size enhance it. Furthermore, incorporating nanoparticles in straight tubes proves to be more advantageous compared to helical tubes. This study tested volumetric ratios of 1%, 2%, and 4%, which resulted in increases in heat transfer coefficients of 21%, 32%, and 43%, respectively, compared to pure water under similar conditions, such as Reynolds number and coil pitch.

Abstract In the current study, forced convective heat transfer of an MHD fully developed laminar nanofluid between two concentric horizontal cylinders is investigated in the presence of a radial magnetic field. In contrast to a conventional no-slip condition at the surfaces, the Navier’s slip condition is considered at the surface to represent the non-equilibrium region near the surfaces. Employing the modified Buongiorno model, the conservative partial differential equations have been collapsed to two-point ordinary boundary value differential equations before being numerically solved. To consider the effects of thermal boundary condition on nanoparticle migration, two distinctive cases including constant heat flux at the outer wall and adiabatic inner wall (Case A) and constant heat flux at the inner wall with adiabatic outer wall (Case B) have been considered. Our results indicate that due to thermophoresis force, the distribution of nanoparticles was denser at the adiabatic wall for the case A which affects the local and the universal fluid flow and heat transfer characteristics. Moreover, inducing a radial magnetic field on the system, heat transfer rate was increased for the case A which had a decreasing effect on the case B. Finally, slip velocity at the walls enhances heat transfer rate for both cases.

The effect of thermal asymmetry on forced convection of alumina/water nanofluid in a parallel-plate microchannel in the presence of heat source/sink is theoretically investigated. Walls are subjected to different heat fluxes, qwt′′ for the top wall and qwb′′ for the bottom wall, and nanoparticles are assumed to have a slip velocity relative to the base fluids induced by Brownian motion and thermophoresis. Because of low-dimensional structures in microchannels, a linear slip condition is considered at the surfaces, which appropriately represents the nonequilibrium region near the interface. Considering hydrodynamically and thermally fully developed flow, the basic partial differential equations including the continuity, momentum, energy, and nanoparticle fraction have been reduced to two-point ordinary boundary value differential equations before they have been solved numerically. It is shown that nanoparticles eject themselves from the heated walls, construct a depleted region, and accumulate in the core ...

AbstractIn this paper, the viscous and inviscid flow fields of a gas turbine blade cascade are investigated. A two-dimensional CFD solver is developed to simulate the flow field through VKI blade cascade. A high resolution flux difference splitting scheme of Roe is applied to discretize the convective part of Navier–Stokes equations. Baldwin Lomax (BL) model is used to account for turbulent effects on the viscous flow field of the blade cascade. For validation of the code, the flow field was solved by Ansys Fluent commercial software. The flow solution was done by third order flux difference splitting scheme of Roe and k–ω turbulence model. The findings show that the high turbulent and the shock creation in the flow field, lead to the same results in viscous and inviscid flows. Also, the results show that the grid and solver’s focus must be on the precise prediction of the shock effects, when the shock is occurred in the domain.