Troy N. Eichmann

Carrier transport in PbS nanocrystal conducting polymer composites

In this letter we report the carrier mobilities in an inorganic nanocrystal: conducting polymer composite. The composite material in question (lead sulphide nanocrystals in the conducting polymer poly [2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) was made using a single-pot, surfactant-free synthesis. Mobilties were measured using time of flight techniques. We have found that the inclusion of PbS nanocrystals in MEH-PPV both balances and markedly increases the hole and electron mobilities—the hole mobility is increased by a factor of ∼105 and the electron mobility increased by ∼107 under an applied bias of 5kVcm−1. These results explain why dramatic improvements in electrical conductivity and photovoltaic performance are seen in devices fabricated from these composites.

Experimental expansion tube study of the flow over a toroidal ballute

An experimental investigation of high-enthalpy flow over a toroidal ballute (balloon/parachute) was conducted in an expansion tube facility. The ballute, proposed for use in a number of future aerocapture missions, involves the deployment of a large toroidal-shaped inflatable parachute behind a space vehicle to generate drag on passing through a planetary atmosphere, thus, placing the spacecraft in orbit. A configuration consisting of a spherical spacecraft, followed by a toroid, was tested in a superorbital facility. Measurements at moderate-enthalpy conditions (15-20 MJ/kg) in nitrogen and carbon dioxide showed peak heat transfer rates of around 20 MW/m(2) on the toroid. At higher enthalpies (>50 MJ/kg) in nitrogen, carbon dioxide, and a hydrogen-neon mixture, heat transfer rates above 100 MW/m(2) were observed. Imaging using near-resonant holographic interferometry showed that the flows were steady except when the opening of the toroid was blocked.

Observation of an ablating surface in expansion tunnel flow

The observation of an ablating surface in expansion tunnel flow was reported. A one-dimensional (1-D) semi-infinite analysis was performed using an empirical estimation of the stagnation-point heat flux. A surface temperature change for epoxy of 178 K in 50 μs was calculated, which is sufficient for the epoxy coating to commence ablation during the steady test period. The 10% temperature penetration depth is 6 μm in 50 μs. The luminosity from substantial portions of the model and shock-layer flow was visualized using a Shimadzu HPV1 high-speed charge-coupled device (CCD) video camera recording at 500 kfps with a 1 μs exposure time. The uniform image response over the axisymmetric model implies the shock-layer gas irradiance is high immediately behind the shock and decreases rapidly as the model surface is approached. The measurements showed that use of an epoxy coating results in greatly increased CN and C2 radiation, much greater than when no coating is employed.

Enhanced flow visualization with near-resonant holographic interferometry

Holographic interferometry measurements have been performed on high-speed, high-temperature gas flows with a laser output tuned near a resonant sodium transition. The technique allows the detection and quantification of the sodium concentration in the flow. By controlling the laser detuning and seeded sodium concentration, we performed flow visualization in low-density flows that are not normally detectable with standard interferometry. The technique was also successfully used to estimate the temperature in the boundary layer of the flow over a flat plate.

Simulation of radiating CO2-N2 shock layer experiments at hyperbolic entry conditions

Numerical simulations supporting radiating shock layer experiments with a CO2 – N2 test gas in the X2 free-piston impulse facility are presented. A ueq = 9.7 km/s, 1L = 5.4×10−5 kg/m2 expansion tunnel condition and a u1 = 8.5 km/s, 1 = 2.35×10−4 kg/m3 shock tube condition are investigated. Shock layer simulations with the Euler equations, a two-temperature thermal model and coupled nonequilibrium radiation are compared with radiant intensity and temperature profiles derived from emission spectroscopy measurements of the CN Violet band system. Applying the CO2 – N2 reaction scheme modifications proposed by Lee, Park and Chang1 and omitting translation-electron energy exchange is found to give the closest agreement with calibrated intensity measurements.

Expansion tunnel radiation experiments to support Hayabusa re-entry observations

The Hayabusa sample return capsule is scheduled for re-entry near Woomera, Australia in June 2010 and expansion tube experiments are being performed to support the planned re-entry observation campaign. Initial experiments using a 1/10th scale model of the Hayabusa forebody have been performed in the X2 expansion tunnel facility at The University of Queensland to simulate aerothermal elements of the anticipated re-entry. Experiments have been performed at an effective flight speed of around 9.8 km/s using steel models, and steel models coated with a layer of epoxy to simulate pyrolysis gases associated with heat shield ablation. Spectral emissions from the stagnation region of the capsule have been acquired using a spectrograph system. Two dimensional maps of the luminous emissions from the shock heated flow have also been acquired using a high speed camera. Deduction of flow conditions generated in the X2 expansion tunnel is achieved using quasione-dimensional simulations coupled to an axisymmetric simulation of the flow through the expansion tunnel nozzle. The effects of the ablative epoxy material are observed in the data from both the spectrograph system and the high speed camera. Both systems register strong emissions in the ablative layer, and the strength of the spectral peaks associated with CN emissions are shown to be enhanced by the presence of the epoxy. Further measurement and analysis is required to confidently define the flow conditions produced by the expansion tunnel, and to quantify results from the spectrograph and high speed camera measurements.

Simulation of CO2-N2 Expansion Tunnel Flows for the Study of Radiating Shock Layers

A 25MJ/kg CO2–N2 expansion tunnel condition has been developed for the study of radiating shock layers in the X2 impulse facility at the University of Queensland. A hybrid Lagrangian and Navier–Stokes computational simulation technique is found to give good correlation with experimentally measured shock speeds and pressure traces. The use of a decaying inertial diaphragm model for describing secondary diaphragm rupture is found to predict between 4% and 25% more CO2 recombination over the test time than the widely accepted holding-time model. Inviscid simulations of the hypersonic nozzle expansion process with a two-temperature model indicate the final test gas is in both chemical and thermal nonequilibrium. The obtained freestream conditions are applied to radiatively coupled simulations of a 25mm diameter cylinder in the test flow. Grid independent solutions show good agreement with experimentally measured shock detachment and predict a radiative emission spectrum dominated by the CO Fourth-Postive band system.

Vacuum Ultraviolet Emission Spectroscopy System for Superorbital Re-entries

The following paper outlines the importance of vacuum ultraviolet (VUV) aerothermodynamic heating during re-entry, the current level of uncertainty in the models used to predict radiative heating load, and the challenges associated with reducing this uncertainty. A method has been developed at The Centre for Hypersonics that allows the capture of VUV emission spectra from across and through the surface of a blunt model. Two superorbital conditions were generated to match high-speed points on a re-entry trajectory and validated computationally and experimentally. The proposed system has been constructed and a calibration procedure developed. There have now been over one hundred experiments at superorbital velocities conducted with this system and some sample uncalibrated spectral images are presented.

A simulation technique for radiating shock tube flows

We describe a numerical modelling technique used to simulate the gas flow in the complete X2 facility in non-reflected shock tube mode. The technique uses a one-dimensional model to simulate piston dynamics and diaphragm rupture and couples this to an axisymmetric simulation of the shock tube which captures viscous and finite-rate chemistry effects. This technique is used to simulate a nonequilibrium radiation condition relevant to a Titan atmospheric manoeuvre. The condition is a 7,km/s shock propagating into a N2/CH4 mixture at 80,Pa. The results show that the shock remains relatively planar at the exit of the shock tube such that there should be little difficulty for the optics. In terms of modelling, the finite-rate chemistry gas performs better than the equilibrium gas for these flows with regards to flow property estimates.

Radiometric temperature analysis of the Hayabusa spacecraft re-entry

Hayabusa, an unmanned Japanese spacecraft, was launched to study and collect samples from the surface of the asteroid 25143 Itokawa. In June 2010, the Hayabusa spacecraft completed it’s seven year voyage. The spacecraft and the sample return capsule (SRC) re-entered the Earth’s atmosphere over the central Australian desert at speeds on the order of 12 km/s. This provided a rare opportunity to experimentally investigate the radiative heat transfer from the shock-compressed gases in front of the sample return capsule at true-flight conditions. At these conditions, the total heat transfer to the vehicle has a significant radiative component and this can be estimated by studying the radiation emitted from the shock layer and the hot surface. Such measurements can be compared with numerical simulations of the flow and with results from ground-based testing in shock tunnels and expansion tubes. This in turn leads to a better understanding of the complex thermochemistry occurring within the shock layer and aids in the design of more efficient thermal protection systems for future spacecraft.