Marching distance functions for smooth control of hyperbolic grids

The smooth control of hyperbolic grids is achieved by using marching distance functions. The marching distance can be expressed as a function of grid control. The derivative expressions of the linearized hyperbolic equations are approximated by second order central differences

Aerodynamic optimization of turbomachinery cascades using Euler/boundary-layer coupled genetic algorithms

A new methodology is developed to find the optimal aerodynamic performance of a turbine cascade. A boundary-layer coupled Euler algorithm and a genetic algorithm are linked within an automated optimization loop. The multiparameter objective function is based on the blade loading. For a given inlet Mach number and baseline cascade geometry, the flow inlet and exit angles, the blade thickness and the solidity are optimized by a robust genetic algorithm. First, the Sanz subcritical turbine cascade is selected as the baseline cascade and is used for How solver validation. Second, the baseline cascade parameters are modified to yield the maximum tangential blade force. Finally, the effects of different crossover techniques, random number seeds, and population sizes on the performance of the genetic algorithm are studied. It is shown that the maximum blade loading is achieved for a higher flow turning, a wider pitch, and a thicker cascade

Tilt duct vertical takeoff and landing uninhabited aerial vehicle concept design study

A new autonomously controlled tilt-duct vertical takeoff and landing uninhabited aerial vehicle concept is proposed. This design combines the vertical flight capability of a helicopter and forward flight performance of a fixed-wing conventional aircraft. The two main engines and propellers are located inside the tilting ducts attached to the wing tips. There is a third engine-propeller combination located inside the all fuselage for pitch and yaw control during hover and transition. The advantages and disadvantages of the ducted propellers are discussed. A conceptual design study is performed including airfoil and geometry selection, initial sizing calculations, estimation of stability and control parameters, etc. Drawings of the aircraft in hover, transition and forward flight modes are presented

3-DIMENSIONAL APPLICATION OF THE JOHNSON-KING TURBULENCE MODEL FOR A BOUNDARY-LAYER DIRECT METHOD

The Johnson-King turbulence model [1; AIAA Paper 84-0175 (1984)] as extended to three-dimensional flows was evaluated using a finite-difference boundary-layer direct method. Calculations were compared against the experimental data of the well-known van den Berg-Elsenaar [2; Report NLR-TR-72092U (1972)] incompressible flow over an infinite swept-wing, as well as with some other boundary-layer methods. The Johnson-King turbulence model, which includes the non-equilibrium effects in a developing turbulent boundary layer, was found to significantly improve the predictive quality of a direct boundary-layer method. The improvement was especially visible in the computations with increased three-dimensionality of the mean flow, larger integral parameters and decreasing eddy-viscosity and shear-stress magnitudes in the streamwise direction; all in better agreement with the experiment than simple mixing-length-based methods

Exergy balance of a general system with variation of environmental conditions and some applications

An exergy balance of a system helps to identify causes of losses. Establishing an exergy balance necessitates correction terms if environmental conditions change over the time period under consideration or the system is moving with respect to the environment. Applications show that these effects are considerable in some cases. On the other hand an exergy balance is also a means for checking a computational procedure. (C) 2002 Published by Elsevier Science Ltd

Cell-vertex based parallel and adaptive explicit 3D flow solution on unstructured grids

A parallel adaptive Euler flow solution algorithm is developed for 3D applications on distributed memory computers. Significant contribution of this research is the development and implementation of a parallel grid adaptation scheme together with an explicit cell vertex-based finite volume 3D flow solver on unstructured tetrahedral grids. Parallel adaptation of grids is based on grid-regeneration philosophy by using an existing serial grid generation program. Then, a general partitioner repartitions the grid. An adaptive sensor value, which is a measure to refine or coarsen grids, is calculated considering the pressure gradients in all partitioned blocks of grids. The parallel performance of the present study was tested. Parallel computations were performed on Unix workstations and a Linux cluster using MPI communication library. The present results show that overall adaptation scheme developed in this study is applicable to any pair of a flow solver and grid generator with affordable cost. It is also proved that parallel adaptation is necessary for accurate and efficient flow solutions