Finite element modelling of a three-component force balance for hypersonic flows

Measurement of aerodynamic forces on a model craft exposed to hypervelocity flow in a shock tunnel must be performed during the period of steady flow which may be less than a millisecond. Measurement of drag has previously been achieved in this time frame at The University of Queensland, by deconvolution of strain signals measured in a sting attached to the model craft. This procedure has been extended to include measurement of lift and pitching moment. Finite element modelling has played a major role in the design of the device used to achieve this. Limitations of finite element predictions of strain signals are discussed, as is the applicability of two- and three-dimensional models in the design process. Finite element modelling has enabled questions to be answered that cannot easily be investigated experimentally: in particular, establishing what strain signals can be successfully processed to recover the input loading and what physical configurations produce acceptable strain signals. As well, the sensitivity of the procedure to the time history of loading, the distribution of loading and the flexibility of the model is studied. The chosen configuration for lift measurement involves mounting the craft to the sting by means of symmetrical triangulated bars, in which the axial strains are measured. Experimental tests on this support arrangement are compared to the finite element simulations.