VKI Longshot Research Articles

Aerodynamic characterization of space debris in the VKI Longshot hypersonic tunnel using a free-flight measurement technique

Hypersonic experiments are performed in the VKI Longshot wind tunnel on hemispherical and annular geometries representative of space debris, aiming at determining their lift, drag and pitching moment coefficients. A free-flight technique is used for this purpose where the model is automatically released in the hypersonic flow and safely recovered by the end of the experiment. A schlieren flow visualization technique coupled with a high-speed camera follows the motion of the object as it is exposed to the high-velocity flow. The instantaneous attitude of the free-flying model and its trajectory are determined from image analysis techniques. Correction terms are included to account for the gravity and for the relative motion of the object within the flow. Experimental results are compared with both numerics and theory.

An overview of HyFIE Technical Research Project: cross-testing in main European hypersonic wind tunnels on EXPERT body

HyFIE project aimed at improving the measurement techniques in hypersonic wind tunnels and comparing the experimental data provided by four major European facilities: DLR HEG and H2K, ONERA F4 and VKI Longshot. A common geometry of EXPERT body was chosen and four different models were used. A large amount of experimental data was collected and compared with the results of numerical simulations. Collapsing all the measured values showed a good agreement between the different facilities, as well as between experimental and computed data.

Free-stream static pressure measurements in the Longshot hypersonic wind tunnel and sensitivity analysis

The performance of fast-response slender static pressure probes is evaluated in the short-duration, cold-gas, VKI Longshot hypersonic wind tunnel. Free-stream Mach numbers range between 9.5 and 12, and unit Reynolds numbers are within 3–10 × 106/m. Absolute pressure sensors are fitted within the probes, and an inexpensive calibration method, suited to low static pressure environments (200–1000 Pa), is described. Transfer functions relating the probe measurements pw to the free-stream static pressure p∞ are established for the Longshot flow conditions based on numerical simulations. The pressure ratios pw/p∞ are found to be close to unity for both laminar and turbulent boundary layers. Weak viscous effects characterized by small viscous interaction parameters \({\bar{\chi }} 16.5 by installing multiple pressure sensors in a single probe. The effect of pressure orifice geometry is also evaluated experimentally and found to be negligible for either straight or chamfered holes, 0.6–1 mm in diameter. No sensitivity to probe angle of attack could be evidenced for α < 0.33°. Pressure measurements are compared to theoretical predictions assuming an isentropic nozzle flow expansion. Significant deviations from this ideal case and the Mach 14 contoured nozzle design are uncovered. Validation of the static pressure measurements is obtained by comparing shock wave locations on Schlieren photographs to numerical predictions using free-stream properties derived from the static pressure probes. While these results apply to the Longshot wind tunnel, the present methodology and sensitivity analysis can guide similar investigations for other hypersonic test facilities.

Hypersonic testing in the VKI longshot free- piston tunnel

This paper presents an evaluation of the performance and hypersonic testing capabilities of the Longshot high Reynolds number nitrogen tunnel. Longshot differs from a conventional gun tunnel in that a heavy piston is used to compress the nitrogen test gas, which is then trapped in a reservoir at the end of the barrel at peak pressure and temperature by the closing of a system of check valves as the piston rebounds. Nozzle supply conditions up to 60,000 psi and 2350°K have been obtained using nitrogen driver gas at pressures up to 15,000 psi. The piston cycle performance is satisfactorily predicted when the thermodynamic behaviour of real nitrogen is taken into account. Experimental data obtained at M = 15 to 18.6 on laminar heat transfer and pressure interaction on a flat plate, flow condensation, stagnation-point heating, laminar incipient separation, and free-flight static stability of cones are found to agree well with predictions.

Dense gas phenomena in a free-piston hypersonic wind tunnel

A theoretical and experimental study has been made of dense gas effects in the VKI Longshot M = 15-27 high Reynolds number tunnel. Longshot differs from a conventional gun tunnel in that the nitrogen test gas compressed by a heavy piston is trapped in a reservoir at the end of the barrel at peak pressure and temperature (typically 30,000 psi at 2150 °K) by the closing of a system of check valves as the piston rebounds. The supply conditions decay gradually during the 25 msec running time as the gas flows through the nozzle from the finite reservoir volume. Theoretical analyses, which account for real gas effects due to intermolecular forces and vibrational excitation, are presented for the free-piston cycle, the decay of reservoir conditions, and the flow through the hypersonic nozzle. Experimental data are found to agree well with predictions.