September / October 2011

# Pointwise Aids Hypersonic CFD at the University of Queensland

Professor Russell Boyce
DSTO Chair for Hypersonics
School of Mechanical and Mining Engineering
The University of Queensland

The University of Queensland participates in the Pointwise Teaching Partnership program. During 2010, Pointwise was used for our undergraduate thesis courses and a senior elective course in hypersonics and rarefied gas dynamics. It also was used for the UQ Occupational Trainee program, in which undergraduate students, typically from German and French universities, spend several months undertaking projects toward their home university degree requirements.

Two examples of the computational fluid dynamics (CFD) simulations enabled with Pointwise and Gridgen are described below. Both apply to the field of hypersonics and utilize the commercial CFD solver, CFD++ from Metacomp Technologies.

Alex Grainger undertook an undergraduate thesis in the area of hypersonic inlet starting. The flowpath of interest is a blunt-leading-edge axisymmetric Busemann inlet with high contraction ratio.

Figure 1 shows the hybrid mesh, in the vicinity of the leading edge, generated by Mr. Grainger using Pointwise. The black line represents a conical diaphragm that is initially set as a wall boundary condition to establish a shock layer upstream of the inlet and stagnant conditions inside the inlet. After removal of that boundary condition, representing rupture of the diaphragm, transient flow simulations allow the dynamic starting process of the inlet to be studied.

Figure 1: Hybrid mesh, generated using Pointwise, near the leading edge of a hypersonic inlet.

Figures 2 and 3 show the end result, which is critically dependent on the initial pressure inside the inlet. The incoming flow is travelling at Mach 8. For the inlet and diaphragm angle considered here, an unstarted inlet results if that pressure is 65 percent of the freestream static pressure, whereas the inlet starts at 60 percent of the freestream static pressure for this configuration.

Figure 2: Unstarted inlet with pi = 0.65 p

Figure 3: Started inlet with pi = 0.60 p

Philippe Lorrain undertook the UQ Occupational Trainee program as part of his mechanical engineering degree from the Aachen Technical University (RWTH Aachen), Germany. His project was in the area of supersonic fin/body interactions, specifically the 3D flowfield around a strut injector in a simple rectangular scramjet combustion chamber.

Figure 4 shows the Gridgen-generated 3.5 million cell structured computational mesh, in which fluid flows from left to right. The upper surface is a wall, as are the surfaces in and out of the page, and the lower surface upstream of the injector is a symmetry boundary condition. Figure 5 shows skin friction lines on the side wall and injector surface and pressure contours in the symmetry plane upstream of the injector, illustrating the complex flow patterns associated with fin/body interactions.

Figure 4: Structured mesh for a scramjet strut injector, generated using Gridgen

Figure 5: Skin friction lines and pressure contours showing the strut/wall interaction

All students who have had the opportunity to use Gridgen or Pointwise and perform CFD simulations at UQ have been able to create for themselves (and sometimes for the community) new knowledge about high speed flows, and the educational impact of this has been very positive. For example, Mr. Grainger and Mr. Lorrain now have moved into postgraduate degree programs in hypersonics at UQ, and continue to use this meshing software. Pointwise and Gridgen have been and will continue to be important tools in University of Queensland undergraduate teaching.