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Numerical simulations of the fluid flow around a small rotating vertical axis wind turbine are performed using a time accurate Reynolds Averaged Navier Stokes (RANS) solver. A moving mesh technique is applied for the simulation of the rotating wind turbine. The RANS equations are then formulated in ALE. All computations are performed assuming 2D incompressible fully turbulent flow. Turbulence is modelled by the SST k/ω model of Menter.Blade forces and torque are obtained from the solution of the RANS equations by integrating the pressure and shear stress over the blade surface. The expected wind turbine output is determined at given rotational speeds. The resulting power coefficients are compared to that obtained by applying a multiple stream tube theory.

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In this work the instability of the Taylor-Couette flow for Newtonian and non-Newtonian fluids (dilatant and pseudoplastic fluids) is investigated for cases of finite aspect ratios. The study is conducted numerically using the lattice Boltzmann method (LBM). In many industrial applications, the apparatuses and installations drift away from the idealized case of an annulus of infinite length, and thus the end caps effect can no longer be ignored. The inner cylinder is rotating while the outer one and the end walls are maintained at rest. The lattice two-dimensional nine-velocity (D2Q9) Boltzmann model developed from the Bhatnagar-Gross-Krook approximation is used to obtain the flow field for fluids obeying the power-law model. The combined effects of the Reynolds number, the radius ratio, and the power-law index n on the flow characteristics are analyzed for an annular space of finite aspect ratio. Two flow modes are obtained: a primary Couette flow (CF) mode and a secondary Taylor vortex flow (TVF) mode. The flow structures so obtained are different from one mode to another. The critical Reynolds number Re(c) for the passage from the primary to the secondary mode exhibits the lowest value for the pseudoplastic fluids and the highest value for the dilatant fluids. The findings are useful for studies of the swirling flow of non-Newtonians fluids in axisymmetric geometries using LBM. The flow changes from the CF to TVF and its structure switches from the two-cells to four-cells regime for both Newtonian and dilatant fluids. Contrariwise for pseudoplastic fluids, the flow exhibits 2-4-2 structure passing from two-cells to four cells and switches again to the two-cells configuration. Furthermore, the critical Reynolds number presents a monotonic increase with the power-law index n of the non-Newtonian fluid, and as the radius ratio grows, the transition flow regimes tend to appear for higher critical Reynolds numbers.

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a b s t r a c tThe problem of unsteady natural convection heat transfer in a vertical, open ended, porous cylinder heated laterally with a sinusoidal time variation of the temperature has been investigated numerically. The model considered is the classical Darcian flow coupled with the energy equation. In the case of constant wall temperature, two types of chimney flows take place, with and without fluid recirculation. The present problem depends on the filtration Rayleigh number (Ra), the aspect ratio (A) and the inletoutlet conditions (Bi). For low dimensionless temperature amplitudes (XA < 0.5) in the sinusoidal time variation, the resulting heat transfer is found to be globally equivalent to the case of constant wall temperature. The observed relative difference between sinusoidal and constant wall temperature is less than 5%. This difference decreases as the Ra is reduced.