Spent Gas Handling for Expansion Tubes

Expansion tubes perform an important role in hypersonic flight research by providing a ground-based testing facility in which scale models can be tested at simulated flight conditions. High enthalpy and high velocity flow conditions are generated via an unsteady expansion process which accelerates test gas to hypersonic conditions. Unfortunately, due to the high velocities and low densities created by this expansion process, test times are shortened and very thick boundary layers develop, reducing the useable core flow. This restricts the size of the models that can be tested, as well as the ability to obtain sufficient or accurate experimental data.Previous studies have shown that a nozzle could be added to an expansion tube to not only expand the core flow diameter but also increase the test time. This included the successful implementation of a nozzle on the University of Queensland's X2 expansion tube [31]. In this thesis, a full-capture, contoured, shock-free nozzle has been designed for the X3 expansion tube. The X3 nozzle contour was scaled from the X2 nozzle contour and was originally 3.0075m long.CFD modelling of the X3 expansion tube with the nozzle attached was completed using a hybrid method coupling a one-dimensional and axisymmetric simulation in order to predict the flow conditions produced by the nozzle. Code package L1d [16] was utilised for the onedimensional analysis and MB_CNS [14], for the axisymmetric analysis. The core flow diameter was increased from 150mm to approximately 250mm and the test time increased by 70% to 1ms; confirming that the addition of a nozzle to the X3 expansion tube will expand the core flow and increase the test time. The nozzle was also examined in relation to its potential to be truncated and maintain its core flow diameter and test time. It was determined that the nozzle could be truncated to a length of 2.5m with no observed loss to the core flow size and test time achieved.The X3 nozzle is under construction. A fibre-wound composite construction technique is being utilised. This construction method was previously used by Jacobs in the fabrication of a nozzle for the T4 reflected shock tunnel [18] at the University of Queensland, although, has not been used for expansion tube nozzles. This technique has proved effective in providing a low-weight, reduced cost alternative to metals.The mandrel for the fibre-winding process was fabricated from high-density polyurethane foam in order to overcome issues of weight and surface instability experienced with other materials. This material had not been previously used for this application and proved very successful in this providing a rigid and stable surface that was suitable for machining as well as winding over.On installation of the nozzle on the facility, the testing of larger, more accurate models is possible. Test times will also be longer than previously observed, enabling the collection of more data, further improving the capacity to effectively model hypersonic flight conditions with this facility. This will benefit future ground based hypersonic flight research to beconducted in the X3 expansion tube facility. Overall, the work completed in this thesis has furthered the development of the X3 expansion tube and provided a foundation for greatly expanding the capabilities of this facility.

In this study an expansion tube is used to generate an experiment to study and evaluate the concept of magnetohydrodynamic aerobraking for planetary entry spacecraft. An expansion tube can theoretically generate the required hypersonic flowfield within which ionisation is confined to the shock layer; this is an important characteristic of the true flight case which previous experiments with arcjets have failed to achieve. The first part of this paper explores the operating envelope for The University of Queensland’s X2 expansion tube facility, to identify flow conditions which should produce a significant interaction between the shock layer and an applied magnetic field. Argon test gas was selected for initial experiments due to its simple chemistry and low ionisation enthalpy, and equilibrium chemistry was used to compute the expected properties of the shock layer around a blunt body model. A candidate flow condition was identified for further analysis with finite rate reacting argon CFD, which indicated that relatively short shock layer length scales for the X2 expansion tube would limit the degree of argon ionisation that was generated, however, sufficient ionisation was still expected. Three sphere models were tested: a steel ball, a plain magnet, and a magnet coated with an electrically insulating ceramic paint. It was found that shock stand-off is unchanged between the steel ball and the plain magnet, but increases by approximately 10% for the coated magnet. Spectroscopy revealed that radiance along the stagnation streamline for some, but not all, of the relevant argon wavelengths approximately doubles when a magnet is used, either coated or uncoated. This increase in radiance does not appear to be associated with changes to shock stand-off. Further work is now required to explain the observed phenomena, and also to address some key experimental challenges, which include accurate measurement of shock stand-off and reducing the significant shot-to-shot variability observed for the coated magnet experiments.

Testing of the first heatshield of the Fire II reentry vehicle was performed in the X1 superorbital expansion tube at The University of Queensland. The test model was a 1:28 scale replica of the flight vehicle, and incorporated three thermocouples: stagnation and two radial. A trajectory point towards the end of the first experimental testing period, at a total flight time of 1639.5s, an altitude of 61.5Km and velocity 11.1km/s was simulated in the expansion tube. Stagnation point heat transfer was obtained using a fast response coaxial type E thermocouple. In the current analysis the convective and radiative heating components were treated independently, where the convective component was scaled with the length scale and the absolute value of the radiative heat transfer was held constant. From this, the overall contribution of the radiative heat transfer to the total heat rate is decreased in the expansion tubes from an 18% contribution in flight to less than 1%, whereas the convective component was increased by a factor of 28. This results in the convective heat transfer being the major mode of heat transfer in the experimental models. From the Fay and Riddell empirical convective heat transfer correlation it was shown that the parameter Ch√Re should remain constant between the flight and experimental tests provided ρL scaling is maintained. Results from the current study show good agreement with the convective heating component of the flight vehicle and the Ch√Re values are in agreement to within 20% of the flight results. The results obtained in this study give a strong indication that the relative radiative heat transfer contribution in the expansion tube tests is less than that in flight, supporting the analysis that the absolute value remains constant with ρL scaling.

This paper describes a rarefied hypervelocity test facility producing gas speeds greater than 7 km/s. The X1 expansion tube at The University of Queensland has been used to produce nitrogen flows at 8.9 and 9.5 km/s with test flow durations of 50 and 40 μs respectively. Rarefied flow is indicated by values of the freestream breakdown parameter >0.1 (Cheng’s rarefaction parameter <10) and freestream Knudsen numbers up to 0.038, based on a model size of 9 mm. To achieve this, the test gas is expanded from the end of the acceleration tube into a dump tank. Nominal conditions in the expansion are derived from CFD predictions. Measured bar gauge (Pitot) pressures show that the flow is radially uniform when the Pitot pressure has decreased by a factor ten. The measured bar gauge pressures are an increasing fraction of the expected Pitot pressure as the rarefaction parameters increase.

Future space missions, such as return from Mars, will require entry speeds of the order of . These harsh conditions are dominated by radiative heat flux and have large modeling uncertainties related to radiative coupling, such as precursor radiation and ablation radiation coupling. These conditions have also never been tested in a flight scenario and have limited ground testing data available. This study investigates the feasibility of generating these conditions in the X2 expansion tube at the University of Queensland so that these flows can be tested over scaled test models for the study of shock relaxation, heat flux, shock standoff, or ablation. This paper presents a theoretical performance map of the X2 facility for the generation of these conditions before it presents some of the unique issues that may be encountered when generating and investigating them. Some preliminary experimental data are then presented, showing that these 15 km/s equivalent flight speed test conditions can be generated in X2 within the current performance limits of the facility.

Availability of reflected shock tunnels capable of testing large-scale models and producing long-duration test flows is currently limited. The X3R free-piston reflected shock tunnel is in the final stages of development as an alternate operating mode of the pre-existing X3 expansion tube at The University of Queensland. A set of analytical and numerical procedures have been developed to aid in optimization of new operating conditions. This paper summarizes the condition development process and provides details of three candidate Mach 7 operating conditions theoretically capable of generating at least 10 ms of test time for full-scale scramjet engine testing. The facility’s atypical geometry, arising from its original design as an expansion tube, and the required compromises made during condition development are discussed.

Establishment of steady flows in areas of separation is of critical importance when experimentally studying hypersonic flows. The University of Queensland has two large scale expansion tube test facilities (X2, X3) capable of generating flow speeds up to 15km/s. In this paper flow establishment in X2 is examined for a flat plate and a rearward-facing step model and the results compared to those for existing flow establishment theories. It is found that separated flows can be successfully established in an expansion tube, with the results agreeing well with empirical relationships.

Electrorheological fluids have numerous potential applications in vibration dampers, brakes, valves, clutches, exercise equipment, etc. The flows in such applications are complex three-dimensional flows. Most models that have been developed to describe the flows of electrorheological fluids are one-dimensional models. Here, we discuss the behavior of two fully three-dimensional models for electrorheological fluids. The models are such that they reduce, in the case of simple shear flows with the intensity of the electric field perpendicular to the streamlines, to the same constitutive relation, but they would not be identical in more complicated three-dimensional settings. In order to show the difference between the two models, we study the flow of these fluids between eccentrically placed rotating cylinders kept at different potentials, in the setting that corresponds to technologically relevant problem of flow of electrorheological fluid in journal bearing. Even though the two models have quite a different constitutive structure, due to the assumed forms for the velocity and pressure fields, the models lead to the same velocity field but to different pressure fields. This finding illustrates the need for considering the flows of fluids described by three-dimensional constitutive models in complex geometries, and not restricting ourselves to flows of fluids described by one-dimensional models or simple shear flows of fluids characterized by three-dimensional models.

This paper explores the operating envelope for the University of Queensland’s free-piston driven X2 expansion tube to determine if flow conditions can be produced that generate a significant magnetohydrodynamic interaction. Numerical calculations are presented to demonstrate the existence of viable operating conditions to study magnetohydrodynamics. Argon is selected as the test gas due to its simple chemistry and low ionization enthalpy. A candidate flow condition is selected for detailed analysis and experimental validation. Finite-rate reacting argon numerical simulations indicate that relatively short shock-layer length scales for the models tested in X2 limit the degree of argon ionization that is generated. However, a strong interaction remains available, and use of a larger facility can fully mitigate this issue. It is shown that expansion tubes are capable of generating the required flowfield for these experiments, and important considerations for design of suitable test flows are identified.

The University of Queensland (UQ) is currently developing high Mach number, high total pressure scramjet flow conditions in its X2 and X3 expansion tube facilities. These conditions involve shock-processing a high-density air test gas followed by its unsteady expansion into a low-pressure acceleration tube. This relatively slow shock-processing requires the driver to supply high pressure gas for a significantly greater duration than normally required for superorbital flow conditions. One technique to extend the duration is to operate a tuned free-piston driver. For X2, this involves the use of a very light piston at high speeds so that, following diaphragm rupture, the piston displacement substitutes for vented driver gas, thus maintaining driver pressure much longer. However, this presents challenges in terms of higher piston loading and also safely stopping the piston. This article discusses the tuned driver concept, the design of a very lightweight but highly stressed piston, and details the successful development of a new set of tuned free-piston driver conditions for X2.

As mining develops into a more sophisticated and technological industry, the potential for virtual reality is increasingly realised. The costs associated with computing are now at a level where almost any individual can purchase a PC powerful enough to run simulations and modelling packages, and thus virtual reality is becoming more commonplace across all technology industries. The detailed and interactive models generated by individuals around the world, and indeed at the University of Queensland (UQ) illustrate the potential for this technology, and this thesis looks at how it can be used as an education tool within the mining engineering department. With safety the number one concern in mining, any developments that can lead to a safer working environment are being openly embraced. It is in this area, where virtual reality can be used as a “third eye” to help simulate situations and operations not visually seen in the physical world, that safety can be increased. If mining engineers can use the technology, then this will lead to a safer, better understood mining environment. This thesis aims to create a working model of the University of Queensland Experimental Mine (UQEM) that will be used by the mining department for years to come for the basis of both teaching and generating student interest. The University of Queensland Experimental Mine is an asset of the mining department that is widely used as an education source for student practicals and tutorials and thus, such a model has great potential in terms of student education within the department. With the hazardous nature of mining, and the increasing awareness of responsible risk management, then using virtual reality to model the mine provides the department with an educational tool for students to use, that is not only safer than being in the mine, but also a cheaper alternative. Virtual reality is a proven training, educational and safety tool, and it is important that students are exposed to the technology before entering the workforce. From a risk assessment perspective, hazards can be introduced into the model and, for subject work students must then identify them. The potential for this thesis is immense, and if the technology can be utilised more in the mining industry, then using virtual reality as a teaching basis at the university will greatly enhance the capabilities of graduation students. By increasing the use of virtual reality at the university and indeed within the mining department, the associated costs with teaching can be reduced and the quality of the education increased for what the UQ Mining Department has to offer.

Hydrodynamics of a pressurized fluidized bed with horizontal tubes: Influence of pressure, fluidization velocity and tube-bank geometry

To compare using computational fluid dynamics (CFD) the flow pattern, irrigant velocity, apical pressure and shear stress produced by negative (MiC) and positive pressure with different types of needles (side-vented (SV), front-vented (FV) and notched (N)) at two insertion depths in the apical ramification of oval root canals. The micro-CT of a mandibular molar with an oval root canal with an apical ramification was used for computational analysis after preparation and geometric reconstruction. Geometries with the needles in two positions (1 and 3mm from WL) were created to run the simulations. Key parameters of irrigation were displayed with CFD and compared. The penetration depth of the needle in the root canal strongly influenced shear stress and apical pressure. The three needles revealed that the highest shear stress, velocity and apical pressure were 1mm from the WL and generated medium velocities. In N simulations, the fluid flow did not reach the apical ramification and the lowest shear stress values for positive pressure needles were found. The predominant axial component for FV revealed a different pattern of irrigation with high shear stress values and higher apical pressures than those exerted by other needles. SV simulations had generalized fluid flow in most of the main canal, the highest shear stress values and lower apical pressure than the threshold determined for risk of extrusion. MiC was associated with low velocity, shear stress and apical pressure. The SV needle demonstrated a combination of low positive pressure and high shear stress; while N had the lowest shear stress and FV the highest apical pressure. MiC generated fluid flow in part of the apical ramification with negative apical pressure values but low shear stress and velocity.

Localized depletion of 180 and l3C in a thin subhorizontal marble layer in the Adamello contact aureole, Southern Alps, Italy, resulted from fluid infiltration focused along a crosscutting dike. Values of 0180 and ol3C in calcite from the 1 m long profile decrease systematically from sedimentary values of 0180 = 220/00 (SMOW) and Ol3C= 00/00 (PDB) to 0180 = 12.50/00 and ol3C -70/00near the dike. The presence of clinozoisite and garnet in the 5-15 cm thick marble layers near the granodiorite dike indicates H20-rich fluid conditions (XC02 0.01). The 0 and C isotope profiles were compared with one- and two-dimensional models of advective-dispersive isotope transport. Individually the isotope profiles fit one-dimensional transport models well. However one-dimensional models, using equilibrium fluidrock exchange or a kinetic formulation, do not explain the relative locations or shapes of the two isotope-exchange profiles given the petrologic constraint of XC02 0.01 for the infiltrating fluid. Excellent agreement with the 0180 and ol3C data is obtained using a twodimensional model that specifies (1) a high-permeability zone in marble near the dike that focuses fluid flow parallel to the dike and (2) a lower permeability zone in marble away from the dike where isotope exchange is dominated by molecular diffusion. The combined constraints imposed by phase equilibria and two isotope tracers allow two-dimensional fluid flow to be inferred from one-dimensional data. The results emphasize that isotope distributions resulting from multidimensional flow may fortuitously fit one-dimensional transport models if isotope tracers are considered independently. The use of multiple tracers coupled to fluid-composition constraints is therefore essential to discriminate between various transport models.

Dynamics of gas flow between interconnected vessels: Experiments and simulations