Design and Characterization of a Hypervelocity Expansion Tube Facility

We report on the design and characterization of a 152 mm diameter expansion tube capable of accessing a range of high enthalpy test conditions with Mach numbers up to 7.1 for aerodynamic studies. Expansion tubes have the potential to offer a wide range of test flow conditions as gas acceleration is achieved through interaction with an unsteady expansion wave rather than expansion through a fixed area ratio nozzle. However, the range of test flow conditions is in practice limited by a number of considerations such as short test time and large amplitude flow disturbances. We present a generalized design strategy for small-scale expansion tubes. As a starting point, ideal gas dynamic calculations for optimal facility design to maximize test time at a given Mach number test condition are presented, together with a correction for the expansion head reflection through a non-simple region. A compilation of practical limitations that have been identified for expansion tube facilities such as diaphragm rupture and flow disturbance minimization is then used to map out a functional design parameter space. Experimentally, a range of test conditions have been verified through pitot pressure measurements and analysis of schlieren images of flow over simple geometries. To date there has been good agreement between theoretical and experimental results

A 2022 τ\tau-Herculid meteor cluster from an airborne experiment: automated detection, characterization, and consequences for meteoroids

Context. The existence of meteor clusters has long since been a subject of speculation and so far only seven events have been reported, among which two involve less than five meteors, and three were seen during the Leonid storms. Aims. The 1995 outburst of Comet 73P/Schwassmann-Wachmann was predicted to result in a meteor shower in May 2022. We detected the shower, proved this to be the result of this outburst, and detected another meteor cluster during the same observation mission. Methods. The {\tau}-Herculids meteor shower outburst on 31 May 2022 was continuously monitored for 4 hours during an airborne campaign. The video data were analyzed using a recently developed computer-vision processing chain for meteor real-time detection. Results. We report and characterize the detection of a meteor cluster involving 38 fragments, detected at 06:48 UT for a total duration of 11.3 s. The derived cumulative size frequency distribution index is relatively shallow: s = 3.1. Our open-source computer-vision processing chain (named FMDT) detects 100% of the meteors that a human eye is able to detect in the video. Classical automated motion detection assuming a static camera was not suitable for the stabilized camera setup because of residual motion. Conclusions. From all reported meteor clusters, we crudely estimate their occurrence to be less than one per million observed meteors. Low heliocentric distance enhances the probability of such meteoroid self-disruption in the interplanetary space.Comment: 6 pqges, 5 figure

Shock tunnel studies of scramjet phenomena, supplement 7

Reports by the staff of the University of Queensland on various research studies related to the advancement of scramjet technology are presented. These reports document the tests conducted in the reflected shock tunnel T4 and supporting research facilities that have been used to study the injection, mixing, and combustion of hydrogen fuel in generic scramjets at flow conditions typical of hypersonic flight. In addition, topics include the development of instrumentation and measurement technology, such as combustor wall shear and stream composition in pulse facilities, and numerical studies and analyses of the scramjet combustor process and the test facility operation. This research activity is Supplement 7 under NASA Grant NAGW-674

A pulsed LED system for schlieren flow visualisation

Schlieren flow visualisation can be performed using light emitting diodes (LEDs) operated with a strong pulse of current (typically a few amps can be passed through the LED for a number of microseconds). Commercial systems are available to produce such pulses, but they are prohibitively expensive. This report provides details of a low cost pulsed current circuit which can be used to drive LEDs in flow visualisation systems. The aim of this work is to improve the accessibility of schlieren and shadowgraph flow visualisation in laboratories with significant financial constraints. The LED drive circuit provides a 12 A (maximum) current pulse with a selectable duration of between about 1.5 and 38 microseconds. The optical performance of two LEDs operated with the high current pulses produced by this circuit is also discussed. A sample of the visualisation results obtained with a hot air jet is also presented to demonstrate the success of the schlieren system

Investigation into thin layer drying rates and equilibrium moisture content of abattoir paunch waste

The work reported in this article was conducted to determine thin layer drying rates and equilibrium moisture contents of abattoir paunch waste. The equilibrium moisture content of paunch varied from 7.14% to 13.12% for drying in air between 35 and 55C, and at 40e80% relative humidity. A predictive equilibrium moisture content equation based on the Chung-Pfost model was developed with the constants A found to be 586.72, B (27.461), and C (28.913) with a standard error of ±0.0035. These values were comparable to the published values for wheat and barley. The thin layer drying constant, k, varied from 0.00023 to 0.0029 min-n with an average time exponent, n, value of 1.42 for air temperatures in the range of 35-55C. The variation in drying rates demonstrated a significant sensitivity to humidity

Hypersonic transitional shock-wave-boundary-layer interaction on a flat plate

This work presents an experimental and numerical study of hypersonic transitional shock-wave-boundary-layer interaction, wherein transition occurs between separation and reattachment in the detached shear layer. Experiments were conducted in a free-piston compression-heated Ludwieg tube that provided a Mach 5.8 flow at a freestream Reynolds number of 7x106 m-1. A shock generator deflected the flow by 10 degrees, resulting in an oblique shock impinging on a flat plate. The shock triggered transition in the boundary layer and the formation of Gortler-like vortices downstream of reattachment. Heat flux and pressure distributions on the plate were measured globally using infrared thermography and pressure-sensitive paint. Oil film visualization was employed to evaluate the boundary-layer reattachment. Numerical results consist of Reynolds-averaged Navier-Stokes and fully laminar steady-state three-dimensional simulations. Shock-induced transition is considered to be the cause of the overshoot in peak pressure and peak heating of approximately 15%, in agreement with previous studies. Gortler instability, triggered by the concave nature of the bubble at separation, is identified as the main mechanism leading to boundary-layer transition, resulting in heat-flux variations of less than 30%. By comparing numerical results against thermographic values it is possible to delineate the extent of transition. Within this region, the disturbance amplification factor was estimated to be approximately between 6 and 10, in reasonable agreement with other relevant numerical and experimental data

Pulsed operation of high-power light emitting diodes for imaging flow velocimetry

High-powered light emitting diodes (LED) are investigated for possible uses as light sources in flow diagnostics, in particular, as an alternative to laser-based illumination in particle imaging flow velocimetry in side-scatter imaging arrangements. Recent developments in solid state illumination resulted in mass-produced LEDs that provide average radiant power in excess of 10 W. By operating these LEDs with short duration, pulsed currents that are considerably beyond their continuous current damage threshold, light pulses can be generated that are sufficient to illuminate and image micron-sized particles in flow velocimetry. Time-resolved PIV measurements in water at a framing rate of 2 kHz are presented. The feasibility of LED-based PIV measurements in air is also demonstrated

Lava flow hazard at Mount Etna (Italy): new data from a GIS-based study

Invasion of inhabited areas and destruction of human property by lava flows represents the greatest volcanic hazard at Mount Etna (Italy) in the short term, based on the character of the historically documented eruptions of the volcano. Virtually all eruptions of Etna produce lava flows, which are more likely to cause damage when emitted from flank vents. Since 1600, more than sixty eruptions have occurred on the flanks of Etna. About half of these caused damage to, or destruction of, human property, dwellings and infrastructures, and at least two destroyed entire population centers. We present a quantitative analysis and evaluation of a new database containing numerical volcanological parameters of each post-1600 eruption, which allows us to quantify the hazard from future eruptions and to create a preliminary hazard zonation map divided into six zones. A total area of nearly 1400 km2 is considered vulnerable, which is home to >900,000 people. The greatest hazard is from voluminous and/or low-altitude flank eruptions, which during the historical period have occurred at irregular intervals of 120-400 years, the most recent in 1669. In the future, eruptions at higher elevations will occur much more frequently, at intervals of a few months to several decades, and many will cause damage in relatively limited areas. A recent increase in the intensity and frequency of eruptions indicate that the Etna volcanic system is presently more dynamic than during the past 330 years, and low-altitude flank eruptions have to be considered a realistic possibility for the near future

Testing of Ultra Fast Response, Durable Co-axial Thermocouples for High Enthalpy Impulse Facilities

Fast response heat flux gauges relying on the semi-infinite heat conduction principle have commonly been used to study heat flux in impulse test facilities such as expansion tubes and reflected shock tunnels. For studying the very harsh environments experienced at the stagnation point of entry vehicles, generally metallic gauges such as thermocouples are required to survive the heat loads which may be above ten megawatts per metre squared at peak heating in flight and can be upwards of a hundred megawatts per metre squared in heavily scaled impulse facility testing, which can be challenging for even the toughest heat flux gauges. This paper reports on the design and testing of a new, extremely durable, fast response co-axial thermocouple which was designed at the University of Southern Queensland and has been subjected to over a hundred experiments in the very harsh conditions experienced over a small stagnation point heat flux probe in a free piston driven expansion tube at the University of Queensland. No degradation in the performance of the thermocouple was seen over the more than a hundred experiments and it was shown to maintain its ability to respond to changes in the flow in a matter of microseconds over the whole campaign. Little to no maintenance was required between experiments, even though the thermocouple’s surface temperature had often risen by hundreds of Kelvin by the end of the post-experiment flow. As previous co-axial thermocouples which have been used in these expansion tubes in the past have only survived several experiments before their performance begins to degrade, this is a very positive result