J. M. Simmons

Three-component force balance for flows of millisecond duration

The authors investigate the feasibility of a new type of multiple-component force balance for measurements on models in hypervelocity hows of millisecond duration. The balance extends the concept of the single component stress-wave force balance to measurement of axial force, normal force, and pitching moment. Numerical modeling of the performance of the balance shows that coupled deconvolution techniques can be used to decouple the signals from axial strain measurements in the balance to determine the applied loads. Experiments performed in the T4 free-piston shock tunnel on a sharp cone at incidence indicate that the prototype balance performs satisfactorily, forces being measured to within 11% of their theoretical values, and the location of the line of force being measured to within 2.1% of the theoretical location as a fraction of model chord.

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%.

Jet excitation by an oscillating vane

To achieve rapid mixing between a jet flow and its surrounding medium a v is mounted in the jet downstream of the jet nozzle exit. The vane is oscillated in either pitch or plunge by an appropriate excitation mechanism at a constant frequency. The amplitude of oscillation is typically only a few degrees. The oscillation frequency may be varied to control the entrainment rate.

Shock tunnel measurements of hypervelocity blunted cone drag

Presented here are results obtained from an investigation into the effects of nose bluntness on slender cone drag in the hypervelocity flight regime. The results indicate that, for small cone angles, the drag of a blunt cone is reasonably well predicted by the Newtonian sine-square law modified for blunt bodies. This suggests the absence of any real gas effects on the total drag. The effect of nose bluntness at the smaller bluntness ratios is relatively small. This is encouraging for the design of a hypervelocity space plane or a centerbody for an axisymmetric scramjet where a slightly blunted nose is required to reduce stagnation point heating. 7 refs.

Measurement of Scramjet Thrust in Shock Tunnels

By using results obtained in tests on supersonic combustion of hydrogen in air, the conditions governing model size and operating pressure levels for shock tunnel experiments on models of flight vehicles with scramjet propulsion are established. It is seen that large models are required. The development of the stress wave force balance is then described, and its use as a method of measuring thrust/drag on such models is discussed. Test results on a simple, fully integrated scramjet model, with intakes, combustion chambers, thrust surfaces and exterior surfaces, using a 13% silane 87% hydrogen fuel mixture, showed that a steady state with thrust generation could be achieved within the shock tunnel test time, and the thrust could be measured. Results are presented for a range of stagnation enthalpies, and show that the scramjet model produces net positive thrust at velocities up to 2.4 km/sec.

Force Measurement in Hypervelocity Impulse Facilities

A new technique is described and demonstrated for measuring drag with 100 µs rise time on non-lifting models in free piston shock tunnels. Extensions of the technique to measurement of lift and moment on a body and thrust from a scramjet nozzle are discussed.

A drag measurement technique for free piston shock tunnels

A new technique is described for measuring drag with 100-microsecond rise time on a nonlifting model in a free piston shock tunnel. The technique involves interpretation of the stress waves propagating within the model and its support. A finite element representation and spectral methods are used to obtain a mean square optimal estimate of the time history of the aerodynamic loading. Thus, drag is measured instantaneously and the previous restriction caused by the mechanical time constant of balances is overcome. The effectiveness of the balance is demonstrated by measuring the drag on cones with 5 and 15 deg semi-vertex angles in nominally Mach 5.6 flow with stagnation enthalpies from 2.6 to 33 MJ/kg.

Balances for the Measurement of Multiple Components of Force in Flows of a Millisecond Duration

Paper reports a new balance for the measurement of three components of force — lift, drag and pitching moment — in impulsively started flows which have a duration of about one millisecond. The basics of the design of the balance are presented and results of tests on a 15° semi-angle cone set at incidence in the T4 shock tunnel are compared with predictions. These results indicate that the prototype balance performs well for a 1.9 kg, 220 mm long model. Also presented are results from initial bench tests of another application of the deconvolution force balance to the measurement of thrust produced by a 2D scramjet nozzle.

Developing a stress wave thrust balance for a hypersonic shock tunnel

The development of a thrust balance for the measurement of the net thrust produced in a scramjet nozzle is described. The balance has been designed and tested in the T4 shock tunnel at the University of Queensland. Numerical simulations of the balance and measurements made in the shock tunnel demonstrate that the thrust is correctly recovered when the loading in the nozzle is symmetric, but unexpected pressure asymmetry in some cases prevented successful recovery of the thrust.

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.