Advancing the Multi-Solver Paradigm for Overset CFD Toward Heterogeneous Architectures

Abstract

A multi-solver, overset, computational fluid dynamics framework is developed

for efficient, large-scale simulation of rotorcraft problems. Two primary features

distinguish the developed framework from the current state of the art. First, the

framework is designed for heterogeneous compute architectures, making use of both

traditional codes run on the Central Processing Unit (CPU) as well as codes run on

the Graphics Processing Unit (GPU). Second, a framework-level implementation of

the Generalized Minimal Residual linear solver is used to consider all meshes from

all solvers in a single linear system. The developed GPU flow solver and framework

are validated against conventional implementations, achieving a 5.35× speedup for

a single GPU compared to 24 CPU cores. Similarly, the overset linear solver is

compared to traditional techniques, demonstrating the same convergence order can

be achieved using as few as half the number of iterations.

Applications of the developed methods are organized into two chapters. First,

the heterogeneous, overset framework is applied to a notional helicopter configuration

based on the ROBIN wind tunnel experiments. A tail rotor and hub are added

to create a challenging case representative of a realistic, full-rotorcraft simulation.

Interactional aerodynamics between the different components are reviewed in detail.

The second application chapter focuses on performance of the overset linear solver

for unsteady applications. The GPU solver is used along with an unstructured code

to simulate laminar flow over a sphere as well as laminar coaxial rotors designed for a

Mars helicopter. In all results, the overset linear solver out-performs the traditional,

de-coupled approach. Conclusions drawn from both the full-rotorcraft and overset

linear solver simulations can have a significant impact on improving modeling of

complex rotorcraft aerodynamics.