Zaib Ali

Multiblock Structured Mesh Generation for Turbomachinery Flows

Multiblock structured meshes offer better computational efficiency than the unstructured meshes which, on the other hand, are more flexible for complex geometries. The multiblock structured meshing could be more useful if the partitioning of the domain can be performed automatically. In this paper, we consider various automated blocking approaches for some turbomachinery zones. We then assess these methods by employing adjoint based error estimation which shows that medial axis based methods perform better than the other approaches like Cartesian fitting. A hybrid approach is also demonstrated for the cases where the existing automatic blocking techniques might not be useful. New blocking templates can also be generated using the techniques applied in the work presented here.

Advances of turbomachinery design optimization

© 2015 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. Automatic design methods are changing the approach to and processes involved in gas turbine design. These methods can be used on a global scale to explore design space, on a local scale as tools in the specialized design of engine components, or as supporting methods in the optimization of existing design methods. For these purposes, optimization methods may be deployed as the primary design tool or hybridized with other automatic design methods to find new ways to explore the design space. In this paper, three novel examples are presented to demonstrate each of these ways of designing via automation. In the first study, a state-of-the-art inverse design method is used to design a compressor stage. The calculation achieves multiple design targets of streamwise loading distribution, stage pressure ratio, and stage exit ow angle, all radially varying, in addition to massflow. These targets can be distributed across two operating points without compromising the ability to satisfy them. For the first time, a genetic algorithm is wrapped around this inverse design code to form a hybrid automatic design method which is used to optimize for improved aerodynamic efficiency and stall margin, and demonstrate the potential for useful hybridization of automatic techniques in turbomachinery design. In the second study, a very large-scale eddy simulation is used to simulate the ows around the cutback trailing edges of high-pressure turbine blades. For a given external blade design and mainstream ow, a genetic algorithm was used to control the progress of the optimization, aimed at improving the layout of the internal structures within the blade. The genetic algorithm was run for ten generations, by which time, the parameter of fitness-an idealised measure of film cooling performance-was found to have improved significantly over the initial precursor generation. The third study shows the adjoint based improvement of multi-block structured meshes for CFD in several engine parts. The form of the block structure used for complex domains considerably affects the quality of the mesh, which necessarily has a significant knock-on effect on the quality of CFD design. It is normally unclear which blocking would yield the optimal mesh for a specific geometry. Here, the adjoint methods typically employed in design optimization can be used to decide on the mesh block structure. As well as showing the above examples, the paper finally explores some future aspects of design optimization and in particular how eddy-resolving simulations might be used in design optimization in say the next 10 years.

Automatic grid adaptation for unstructured finite volumes

An automatic grid refinement method is presented for the simulation of ship flows. It provides directional refinement of unstructured grids and derefinement of refined grids for unsteady simulation, it is fully parallel and includes automatic dynamic load balancing. Different refinement criteria are implemented. Results are presented that confirm the increased accuracy of solutions obtained on refined grids. Refinement around the water surface proves to be very effective for the simulation of strong breaking waves. A pressure gradient criterion is shown to detect the main features of a ship flow and to be able to generate effective fine grids in their entirety.

Optimal multi-block mesh generation for CFD

ABSTRACT An assessment of various automatic block topology generation techniques for creating structured meshes has been performed in the first part of the paper. The objective is to find out optimal blocking methods for generating meshes suitable for flow simulations. The comparison has been carried out using an adjoint-based error analysis of the meshes generated by these block topologies. Different objective functions and numerical schemes have been used for this assessment. It is found that, in general, the medial axis-based approaches provide optimal blocking and yields better accuracy in computing the functional of interest. This is because the medial axis-based methods produce meshes which have better flow alignment specially in case of internal flows. In the second part of the paper, the adjoint-based error indicator has been used to adapt the block topology in the regions of large error.

Adaptive Grid Refinement for Hydrodynamic Flow Simulation

Abstract An automatic grid refinement method is presented for the simulation of ship flows. It provides directional refinement of unstructured grids, is fully parallel, and includes automatic dynamic load balancing. Results confirm the increased accuracy of solutions obtained on refined grids: wave fields are captured more accurately and in greater detail, hull vorticity generation can be detected and resolved automatically. The combination of the refinement method with free ship motion is demonstrated.