Numerical Simulation of Film Cooling Effectiveness in a Rotating Blade

The film-cooling performance in a low-speed rotor blade of a 1-1/2 turbine stage has been examined using LES approach. Two rows of film holes were positioned on the rotor blade surface, one on the pressure surface and the other one the suction surface, with axial locations of 24.2% and 22.6% of the chord length, respectively. Each row has three cylindrical film-cooling holes with a diameter (D) of 4 mm and a tangential injection angle of 28o on the pressure side and 36o on the suction side. The Reynolds number, based on the mainstream velocity of the turbine outlet and axial length of the turbine, was fixed at Re=1.92×105, the coolant-to-mainstream density ratio (DR) was about 2.0, and the speed of the rotor blade was taken to be 1800 rpm. Several blowing ratios (BR) in the range of 1.0–5.0 were investigated. The effects of blowing ratio, rotation, and curved surfaces were analysed to investigate the effects of the stator–rotor interaction on the film-cooling characteristics. The commercial CFD code STAR-CCM+ was used to run the simulations using the WALE subgrid-scale model for modelling the turbulence. The solutions were obtained by solving the incompressible, 3D Navier–Stokes equations under the rotating coordinates system with the energy equation, and the pressure–velocity coupling was achieved by using the well-known SIMPLE algorithm. The results show that on the pressure side, the film coverage and film-cooling effectiveness increase with increasing BR. A lower BR results in stronger film deflection. The film injection with higher BR produces better film attachment. The film deflects centripetally due to the effect of rotation. On the suction side, the trend of film coverage and film-cooling effectiveness is parabola as the blowing ratio rising and a centripetal deflection of the film is observed. The deflection of the film path could be amplified by decreasing the BR.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016

Performance Improvement of a Counter-Flowing Double-Pipe Heat Exchanger Partially Filled with a Metal Foam and Rotating Coaxially

In order to enhance the amount of heat transported in a double-pipe heat exchanger, a compound enhancement is proposed herein incorporating both active and passive methods. The first one is through introducing secondary flows in the vicinity of the conducting surface using metal foam guiding vanes, which are fixed obliquely and rotating coaxially to trap fluid particles while rotation and then force them to flow over the conducting surface. The other is via covering the conducting surface between the two pipes with a metal foam layer to improve the heat conductance across it. This proposal is examined numerically by studying the three-dimensional, steady, incompressible, and laminar convective fluid flow in a counter-flow double-pipe heat exchanger partially filled with high porosity metal foam and rotating in a coaxial-mode. In regards to the influence of rotation, both the centrifugal buoyancy and Coriolis forces are considered in the current study. The generalised model is used to mathematically simulate the momentum equations in the porous regions employing the Boussinesq approximation for the density variation. Moreover, thermal dispersion has been taken into account with considering that fluid and solid phases are in a local thermal non-equilibrium. Computations are performed for a range of design parameters influencing the performance achieved such as the operating conditions and the configuration of the guiding vanes utilised. The results are presented by means of the heat exchanger effectiveness, pressure drop, and the overall system performance. The current proposal has proved its potential to enhance the heat transported considerably with saving significant amount of the pumping power required compared to the corresponding heat exchangers, which are fully filled with metal foam. Also, the data obtained reveal an obvious impact of the design parameters inspected on both the heat exchanged and the pressure loss; and hence, the overall performance obtained. Although the heat exchanger effectiveness can be improved considerably by manipulating the design factors, care must be taken to avoid unjustified expenses resulted from potential augmentation in pressure drop.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016