Showing papers by "H. Bijl published in 2012"

Analysis of biplane flapping flight with tail

Abstract: Numerical simulations have been performed to examine the interference effects between an upstream flapping biplane airfoil arrangement and a downstream stationary tail at a Reynolds number of 1000, which is around the regime of small flapping micro aerial vehicles. The objective is to investigate the effect of the relative distance and angle of attack between the airfoils and its tail on the overall propulsive efficiency, thrust and lift. An immersed boundary method Navier-Stokes solver is used for the simulation. Results show that overall efficiency and average thrust per airfoil can be increased up to 17% and 126% respectively when the top and bottom airfoils come into contact during flapping. When placing the tail at a strategic position, the overall configuration generates much higher lift, although at the expense of decreased efficiency and thrust. Increasing the angle of attack of the tail also helps to increase the lift. Analysis of the vorticity plots reveals the interaction between the vortices and the airfoils and the reason behind the high thrust and lift. The results obtained from this study can be used to optimize the performance of small flapping MAVs.

A Computational Study on the Aerodynamic Influence of a Propeller on an MAV by Unstructured Overset Grid Technique and Low Mach Number Preconditioning

Abstract: The influence of a propeller on the aerodynamic performance of an MAV is investigated using an unstructured overset grid technique. The flow regime of a fixed-wing MAV powered by a propeller contains both incompressible regions due to the low flight speed, as well as compressible flow areas near the propeller-tip region. In order to simulate all speed flow efficiently, a dual-time preconditioning method is employed in the present study. The methodology in this paper is verified as providing a reliable numerical simulation tool for all flow regimes, in the additional presence of moving boundaries, which is treated with an overset grid approach.

Higher order implicit time integration schemes to solve incompressible navier-stokes on co-located grids using consistent unsteady rhie-chow

Abstract: Noting that time-accurate computations of the unsteady incompressible Navier-Stokes (INS) equations can be computationally expensive, a family of higher order implicit multi-stage time integration schemes (namely ESDIRK) is used for advancing the solution to the unsteady INS in time. The higher order time integration schemes have the potential to decrease the computational cost of obtaining engineering levels of accuracy relative to the traditionally used 2nd order implicit schemes. The finite volume method is used for spatial discretization, and co-located arrangement of the primitive variables is considered. Furthermore, an iterated PISO algorithm is used to solve the incompressible Navier-Stokes equations. By using a temporally consistent Rhie-Chow interpolation, higher order temporal accuracy in solving the INS equations on co-located grids is achieved. For a two-dimensional lid driven cavity test case, the temporal convergence of the solution is investigated, with the third and fourth order ESDIRK schemes for time integration. The results demonstrate the temporal consistency and temporal order preservation of the algorithm.

On the stability of loose and strong partitioned algorithms for thermal coupling of domains using higher order implicit time integation schemes

Abstract: Thermal interaction of fluids and solids, or conjugate heat transfer (CHT), is encountered in many engineering applications. Since time-accurate computations of such coupled problems can be computationally expensive, we consider loosely-coupled and strongly- coupled solution algorithms in which higher order multi-stage Runge-Kutta schemes are employed for time integration. The higher order time integration schemes have the potential to improve the computational efficiency at arriving at a certain accuracy relative to the traditionally used 1st and 2nd order implicit schemes. The spatial coupling between the subdomains is realized using Dirichlet-Neumann interface conditions and the coupled domains are solved in a sequential manner at each stage (Block Gauss-Seidel). In this paper, the stability of two partitioned algorithms is analyzed by considering a one dimensional model problem. The model problem consists of two thermally coupled domains where the governing equation within each subdomain is unsteady linear heat conduction. In the loosely-coupled approach, a family of multi-stage IMEX schemes is used for time integration. By observing similarities between the second stage of the IMEX schemes and the ? scheme with ? = 0.5 (Crank-Nicolson), the stability of the partitioned algorithm in which the Crank-Nicolson scheme is used for time integration is first analyzed by applying the stability theory of Godunov-Ryabenkii. The stability of the IMEX schemes is next investigated by numerically solving the model problem and comparing the results to the conclusions of the stability analysis for the Crank-Nicolson scheme. Due to partly explicit nature of the IMEX schemes, the loosely-coupled algorithm becomes unstable for sufficiently large Fourier numbers (similar to the Crank-Nicolson scheme). When the ratio of the thermal effusivities of the coupled domains is much smaller than unity, time step restriction due to stability is sufficiently weak that computations can be performed with reasonably large Fourier numbers. Furthermore, the results show better stability properties of the IMEX schemes compared to the Crank-Nicolson scheme. In the strongly-coupled approach, the stability and rate of convergence of performing (Gauss-Seidel) subiterations at each stage of the higher order implicit ESDIRK time integration schemes are analyzed. From the stability analysis, an expression for the rate of convergence of the iterations (?) is obtained. For cases where ? ? 1, subiterations will convergence rapidly. However, when ? ? 1, the convergence rate of the iterations is slow. The results obtained by solving the model problem numerically are in line with the performed analytical stability analysis.