Lift, Drag and Thrust Measurement in a Hypersonic Impulse Facility

This paper reports the extension of the stress wave force balance to the measurement of forces on models which are non-axisymmetric or which have non-axisymmetric load distributions. Recent results are presented which demonstrate the performance of the stress wave force balance for drag measurement, for three-component force measurement and preliminary results for thrust measurement on a two-dimensional scramjet nozzle. In all cases, the balances respond within a few hundred microseconds

Wall effects on sound propagation in tubes

Numerical solutions have been obtained for the exact equations describing the propagation of periodic axisymmetric waves in a rigid cylindrical tube. Results were obtained for air over a range of conditions corresponding to shear wave numbers (s = R √ρ{variant}ω/μ) from 0·2 to 5000 and reduced frequencies (k = ωR/a) from 0·01 to 6. For conciseness and convenient application, the results for the attenuation and phase shift coefficients are given in the form of simple polynomials for the ranges 5 ≤ s ≤ 5000 and 0·01 ≤ k ≤ 6. This range covers virtually all values of tube diameter and sound frequency likely to be met in practical situations that are consistent with a continuum gas model

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

Mechanical and Space Engineering, a degree for undergraduates

Australia is a country which makes significant use of space based services and technology, but is dependent primarily on overseas suppliers. This paper discusses a new degree offered at The University of Queensland, aimed at preparing graduates for the integration of space related activities into the Engineering workplace. The degree is based on the current Mechanical Engineering degree offered at the University, and contains extra material relevant to pursuing Engineering practice in space. The structure of the degree is such that a mixture of stand alone space subjects are offered, along with space related ‘add ons’ whereby a traditional Mechanical subject is interpreted in a space related context. The basic premise which lead to the new degree is that if a substantial space engineering Industry is to develop in Australia, then it must do so from the existing Industrial base, and Engineers with the appropriate background will be required. Mechanical Engineering being an important discipline to space based projects, it is sensible, and educationally efficient, to use it as a structure for a space engineering degree. The paper details the structure of the course, discusses the methodology behind its formulation and its perceived role in Australia’s future

Experiments on supersonic combustion ramjet propulsion in a shock tunnel

Measurements have been made of the propulsive effect of supersonic combustion ramjets incorporated into a simple axisymmetric model in a free piston shock tunnel. The nominal Mach number was 6, and the stagnation enthalpy varied from 2.8 to 8.5 MJ kg-1. A mixture of 13% silane and 87% hydrogen was used as fuel, and experiments were conducted at equivalence ratios up to approximately 0.8. The measurements involved the axial force on the model, and were made using a stress wave force balance, which is a recently developed technique for measuring forces in shock tunnels. A net thrust was experienced up to a stagnation enthalpy of 3.7 MJ kg-1, but as the stagnation enthalpy increased, an increasing net drag was recorded. Pitot and static pressure measurements showed that the combustion was supersonic. The results were found to compare satisfactorily with predictions based on established theoretical models, used with some simplifying approximations. The rapid reduction of net thrust with increasing stagnation enthalpy was seen to arise from increasing precombustion temperature, showing the need to control this variable if thrust performance was to be maintained over a range of stagnation enthalpies. Both the inviscid and viscous drag were seen to be relatively insensitive to stagnation enthalpy, with the combustion chambers making a particularly significant contribution to drag. The maximum fuel specific impulse achieved in the experiments was only 175 s, but the theory indicates that there is considerable scope for improvement on this through aerodynamic design

Drag measurements at Mach 5 using a stress wave force balance

The stress wave force balance, which has been used for measurements of drag on short models in hypersonic impulse facilities, is investigated here for its suitability for drag measurements on a longer, axisymmetric model. The sensitivity of the balance to loading distribution is investigated and results are reported for experiments on a 5° semi-angle cone, 425 mm in length and of 1.71 kg mass. Experimental drag measurements are shown to be in good agreement with theoretical levels. An investigation into the period over which the stress wave force balance can be used is addressed and, for the present model, the balance is shown to be suitable for measurements in flows of durations of one to several milliseconds with an estimated accuracy of ±10%