An experimental study involving the interaction between high-temperature real gas effects and turbulence was conducted in the T4 Stalker reflected shock tunnel, using a flat plate model angled 10 degrees to the free stream with a 5mm blunted leading edge. For Air, N-2 and a 'mixture' of N-2 and 10%O-2/90%N-2 (by volume) test gases, the total enthalpy of the test condition was between 8.3 and 11.3 MJ/kg, with post shock temperatures in excess of 6000K. Subsequently, significant chemical and thermal non-equilibrium conditions were present in the leading edge region. Due to excessively bright post shock region, a high-speed luminosity technique was used to image the shock layer, which showed that the post shock oxygen dissociation in the air results in reduced shock standoff distances for the Air and mixture test gases as compared to the N-2 test gas. Preliminary, heat transfer results show that transition for a wedge geometry occurs between 0.9 and 1.2 million Reynolds number, however further analysis is required.

This paper presents the noise levels generated inside a two-dimensional scramjet combustor at Mach 7.3 freestream using the focused laser differential interferometric (FLDI) technique. FLDI measurements were taken at the front, middle, and rear of the combustor’s center plane under unfueled, combustion-suppressed, and combustion-on conditions. Spectral analysis of the FLDI signal shows density fluctuations inside the scramjet combustor are almost two times higher than the freestream and confirms the capability of this technique for measuring the disturbances in a complex hypersonic flowfield. Though combustion-induced pressure rise is low, a trend in the increase in the normalized density fluctuations/noise levels due to supersonic combustion is observed across the measurement locations for the combustion-on condition. However, the overall increment in the noise level is modest between the three conditions and across the three probing locations. This infers that, for the current scramjet geometry, fueling rates, fuel–air mixing, and supersonic combustion are not the dominant noise sources in the scramjet combustor. Instead, the base hypersonic flowfield inside the scramjet combustor is the main contributor to the noise field. Noting that there is relatively large uncertainty in the measured noise levels and that the combustion-induced pressure rise is modest in the present study, further investigation is needed to check the applicability of these results to the scramjet engines with flow paths having more complex flowfields, fueling schemes, and fueling rates.

A modification to cylindrical focused laser differential interferometry (CFLDI) that, without beam intersection, can achieve smaller stand-off distances from flat geometries than conventional FLDI is presented. The modified system uses a cylindrical lens pair to expand and collimate the beam in a single direction, parallel to the model surface, forming a long, flat, elliptical profile. Subsequently, a spherical lens focuses the beam. Mach 7.3 hypersonic flow, produced by the T4 Stalker Reflected Shock Tunnel, was used for an experimental comparison between the responses of the modified CFLDI and a similar FLDI system in the freestream and just above the boundary-layer edge. Good agreement between the modified CFLDI and FLDI among all measured frequencies was observed when probing near the boundary-layer edge. The comparison in the freestream had good agreement up to 1500 kHz, and higher frequencies saw the modified CFLDI response attenuated at a shallower angle than the FLDI. A combination of different system parameters and base noise levels between the experiments is believed to account for this difference. The modified CFLDI system was used to probe inside the boundary layer, achieving a [Formula: see text] of approximately 0.4, where broadband turbulence is detected.

A 3/8th scale model of the BoLT II hypersonic flight experiment geometry was tested in the T4 Stalker Tube at The University of Queensland. Thin-film heat-transfer gauges were installed at some of the locations where similar instrumentation was used to measure heat-transfer rates in the flight. The freestream Reynolds number was varied at similar total enthalpies and flight Mach number to the flight test. Over the range of conditions tested, the boundary layer on the test surface of the model ranged from laminar to transitional and fully turbulent. The temporal variations of surface heat transfer show intermittent turbulent spots in the transitional regions and the turbulent fluctuations in the fully turbulent regions. The results show how the transition front and extent vary with Reynolds number. Results are also compared with some heat transfer measurements made at different Reynolds numbers in the CUBRC LENS II facility in which the flight model and instrumentation was tested prior to the flight. Results show that transition occurred in the T4 tests at lower Reynolds numbers than in the LENS II tests.

Electrification of remote communities is a great challenge worldwide. Their reliance on economically and environmentally unfavourable diesel generators makes these communities attractive target markets for renewables. Concentrating solar thermal (CST) plants operating on supercritical CO2 (s-CO2) Brayton power cycles have been proposed for their high efficiency, compactness, compatibility with natural air-cooling, and capability of being built at a small size without significant efficiency penalties. Thermal energy storage (TES) technology can mitigate intermittency problems. This study aims to identify the optimal configuration of hybrid CST and diesel generation (DG) for different types of remote locations based on annual simulations involving key system design features including solar multiple, TES size, and CST size. One novelty in this study is the inclusion of actual weather information and load demand profiles for selected potential locations. Another is that a realistic economic model for s-CO2 power blocks for small to medium sizes, based on accurate cost data, is presented. More importantly, a realistic representation of the s-CO2 turbine, which includes isentropic efficiencies varying at off-design conditions, is used. This facilitates a study into the effects that the inclusion of realistic off-design turbine information has on the thermodynamic and techno-economic performances of the system. This is done by comparing the simulation results with results obtained using a conventional method that uses a constant turbine efficiency. This paper presents the optimal system configurations offering the lowest levelised cost of energy (LCOE) obtained using three-variable exhaustive search optimisation. The results show that the system is an economically favourable option and provides substantial environmental benefits.

Interpreting the results of boundary Layer transition studies and testing scramjets at realistic flight conditions in impulse facilities like the T4 Stalker tube requires prior knowledge of freestream noise levels. To quantify these noise levels, an experimental study was conducted using a focused laser differential interferometer (FLDI) and density fluctuations in the core flow of T4's Mach 6b, 7, and 8b nozzles were determined. FLDI also probed inside and outside the Mach 6b nozzle core flow. When probing outside the nozzle core flow, the FLDI results show increased fluctuations for frequencies above 400 kHz. Such behaviour is not observed in the spectra measured inside the core flow, demonstrating that the current FLDI instrument has an adequate spatial resolution to attenuate far-field disturbances generated outside the nozzle core flow. T4's noise level is quantified by determining the RMS of the density fluctuations normalised by mean density in Octave bands for frequencies ranging between 22 and 22 kHz. For this frequency range, the noise level typically ranges between 0.1% and 0.6% for the Mach 6b and 7 nozzle flows. For the Mach 8b nozzle, the noise level is between 0.2% and 1.7%. The freestream sound pressure levels (SPLs), determined from the density fluctuations using isentropic relations, are between 105 and 130 dB for all three nozzle flows. The measured noise levels indicate that T4 is suitable for conducting fundamental studies in the hypersonic flow regime and for scramjet testing.

The initiation and growth of turbulent spots in transitional hypersonic boundary layers can influence the transition length and the distribution of heat transfer and skin friction through the transitional region. There is debate in the literature about whether spots initiate in a small band at the start of transition or throughout the transitional region. This paper presents a new design of arrays of thin-film heat transfer specifically designed to detect whether spots initiate in a small band. The gauges were arranged in two spanwise rows at different streamwise locations and were tested on a 7° blunt cone in the T4 Stalker Tube. It is shown that such instrumentation is capable of identifying that some spots initiate between the rows when other spots have already formed upstream of the first row. This demonstrates that the breakdown of laminar boundary layers is not concentrated in a region of small streamwise extent in the current hypersonic flows.

This paper presents two-dimensional heat transfer results for the first time in an expansion tube, using infrared thermography at a Mars entry condition. Experiments were performed in the X2 expansion tube at The University of Queensland in a Martian (CO2/N-2) test gas on a wedge model. Infrared filtering from 3.5 to 4 mu m was performed in data acquisition to remove significant radiation from the shock layer. Thermal images of a preheated surface from the infrared camera were used together with measurements from a fast response infrared sensor to obtain heat flux maps at a hypervelocity condition with flight duplicated enthalpy. Experimental heat flux results have an uncertainty of less than 10% and agreed with laminar convective theoretical correlations to within 16%, making thermography suitable for heat transfer measurements in expansion tubes. This technique has potential for future applications in studying wall/near-wall viscous phenomena dependent on surface temperatures in expansion tubes.

Concentrating solar thermal (CST) operating on supercritical CO 2 (s-CO 2 ) Brayton power cycles have been proposed as the next generation thermal energy conversion alternative. The most critical component in the cycles is a turbine. A turbine design should achieve good performance at its design operating conditions and maintain acceptable performance at off-design conditions. This paper presents 1D off-design s-CO 2 radial turbine performance prediction model for s-CO 2 turbines. The model is adjusted from the novel 1D part-load performance prediction model developed by the authors. While the part-load performance prediction model considers turbine inlet temperature as constant variable, in this study, the assumption is relaxed as some forms of sensible thermal storage (e.g. particulate solid) allow fluctuation in the turbine inlet temperature. The 1D performance prediction results were checked against 3D CFD simulation for validation and the agreement was acceptable except for some explainable features. Comprehensive turbine performance maps combining the effect of the mass flow rate and turbine inlet temperature are presented. The maps provide an insight into the combined impact of the part-load control and the operation under the off-design operating conditions.

There is recent focus on supercritical CO2 (s-CO2) Brayton power cycles as the next-generation thermal energy conversion choice. They are efficient, compact, economic, and environmentally friendly. They are also scalable without efficiency penalties and suitable for small and large sizes. The most critical component is reported to be the turbine. A turbine design should achieve good performance at its design operating conditions and maintain acceptable performance at off-design conditions. Off-design operating conditions are relevant because thermal power plants are increasingly required to meet varying electricity demand in continuously changing environments. This paper presents a novel one-dimensional part-load performance prediction model for s-CO2 turbines. The novelty of the present model comes from the accurate prediction of the part-load s-CO2 turbine performance with less than 10% deviation, validated against reliable three-dimensional computational fluid dynamics simulation. Furthermore, the proposed model uses fundamental fluid dynamic equations and a real gas property library and does not require calibration. A Python code based on the proposed model can generate a full list of essential performance variables and internal flow information.

Infrared thermography is a well-established heat transfer measurement technique in hypersonic wind tunnels but it has only recently been applied in expansion tubes for heat transfer measurements at hypervelocity conditions with full flight enthalpy. Heat transfer experiments at a Mars entry condition were performed in the X2 Expansion Tube at The University of Queensland on a heated wedge model. This paper describes the procedure that was used to calibrate the infrared camera and infrared sensor to obtain surface temperature measurements over a heated model, where the surface temperatures of interest cannot be completely covered by the blackbody calibrator of a known temperature. The uncertainties present during calibration are discussed and quantified. It is expected that findings from this calibration will allow improvement in the calibration procedure for future thermography experiments in expansion tubes.

two dimensional heat transfer measurements at planetary re-entry conditons. Experiments were performed in the X2 Expansion Tube at The University of Queensland in a simulated Martian (CO2/N2) test gas on a wedge model. An infrared camera and sensor were used in these experiments. Infrared filtering to remove radiation outside of the 3.5 -4 µm waveband was found to be sufficient to eliminate direct radiation from the shock layer. The infrared camera was used for radiation measurements from which surface temperature maps were deduced. The infrared sensor was used to obtain a time resolved variation of the surface temperatures from which heat flux can be deduced. The model surface was pre-heated to two different temperatures to assess the signal to background ratios for infrared thermography. These results indicate infrared thermography can be used for obtaining two dimensional heat transfer on blunt bodies at speeds of ∼ 5.6 km/s in a Mars test gas.

A better estimate of the transition length can greatly increase the efficiency of thermal protection systems in hypersonic flying vehicles. Recent efforts have been made to fit models to experimental data available in the literature for different types of facilities, flow conditions and model geometries with zero pressure gradient. Experimental results from new transition experiments on a flared cone are compared with predictions from these models. The model predicts the transition length quite well. Due to the model’s sensitivity to spot initiation rate, the predictions of the transition length when transition started well within the flared portion of the cone do not agree with the predictions as well.

Magnetohydrodynamic (MHD) aerobraking has the potential to significantly reduce peak heat loads for high-speed planetary entry, due to increases in total drag force in the early phase of the trajectory. Establishing accurate techniques for measuring MHD drag force in ground testing facilities is a necessary first step for investigating this phenomenon. The objective of this paper is to demonstrate the methodology required for using a stress wave force balance (SWFB) to measure MHD drag force in an expansion tunnel. Whilst the SWFB is an established technique for measurement of short duration forces in impulse wind tunnel facilities, conventional designs exhibit unusually low signal-to-noise ratios in MHD ground testing flow fields, due to electromagnetic interference from the plasma in the shock layer. This paper investigates the effect that sting design, amplifier setup, and strain gauge location have on the signal-to-noise ratio of a SWFB. Experimental validation of each design was undertaken in the X2 expansion tunnel with a high enthalpy ( $$\sim 16\,\hbox {MJ}\,\hbox {kg}^{-1}$$ ) argon test flow by comparing the results to those obtained using an accelerometer-based force balance. The results demonstrate that maximum signal-to-noise ratio is obtained when: the sting is made from a low stiffness material such as polycarbonate to maximise strain; the charge amplifier is located near the strain gauge inside the model and is grounded at the data acquisition system to minimise electrical noise; the strain gauge is located close to the applied load to delay the return of reflected stress waves from the free end. MHD drag forces measured in this study varied up to approximately 3 N, and measurement uncertainty was found to be approximately $$\pm \, 0.2\,\hbox {N}$$ . Overall, successful adaptation of the stress wave force balance technique to MHD ground testing was achieved, and it has been shown to be a viable alternative to accelerometer-based techniques.

The process via which a hypersonic boundary layer transitions from laminar to turbulent flow is important in determining the length of transitional flow regions which is important information for designers of hypersonic vehicles. The effects of bluntness of the leading edge of the hypersonic body on the unsteady processes in the transitional region have not received much attention in the literature. This paper compares the unsteady processes in the transitional region for a slender cone with both a sharp and a blunted tip at hypersonic flow conditions in the T4 Stalker Tube. Fewer, more isolated turbulent spots were observed for the blunted than for the sharp cone when tested at similar or higher Reynolds number conditions.

An accelerometer-based force balance has been used to measure the magnetohydrodynamic (MHD) drag force which arises when a magnetic field is present in a high-enthalpy ionised flow. This has been conducted using two expansion tunnels, with periods of steady test flow as low as $$40\,\upmu \hbox {s}$$. The use of this technique for MHD drag measurements is demonstrated and limitations are discussed. The results show that there is a measurable component of MHD drag in a flow-field where electrodynamic boundary conditions are matched to true flight. Furthermore, it is demonstrated that the measured forces can be attributed exclusively to the MHD effect, with good repeatability. The results indicated that at least $$100\, \upmu \hbox {s}$$ of steady flow is required before the MHD force stabilises.

This paper presents experimentally measured shock layer radiation data relevant to a Mars Science Laboratory trajectory point in a 96% CO2, 4% N2 mixture. Tests were performed in the X2 expansion tube at The University of Queensland to characterise shock layer radiation. Results from these tests will assist in determining if infrared thermography can be used in expansion tubes for measuring heat transfer at Martian entry conditions. The radiance data was spectrally and spatially resolved and ranges the near to mid infrared region from 0.78 - 5.1 µm. Results indicated that the ideal region to perform thermography was from 3.5 - 4 µm as the shock layer radiation was found to be a minimum in this region. A pre-heat surface temperature of 1800 K is deemed to be necessary to obtain a good signal to noise ratio, so that the thermally emitted surface radiation was much higher than that from the gas in the shock layer. It was also found that using an Aluminium diaphragm rather than Mylar resulted in higher shock layer radiation.

Experimental evidence indicates that boundary layers in hypersonic flows transition from being laminar to turbulent via the mechanism of formation and propagation of turbulent spots. Turbulent spots have been detected using either surface heat transfer gauge signals or pressure traces, or they have been visualized using high-speed schlieren techniques. The extent of the transition zone is strongly dependent on the rate of initiation of turbulent spots and spot propagation parameters. However, it is not possible at present to predict the turbulent spot initiation rates in hypersonic transitional flows. As a first step toward developing an effective predictive model for the purpose, a methodology is developed to enable estimation of the spot initiation rate and intermittency distribution from experimental heat transfer data. The methodology is validated by comparison with experimental data where both the heat transfer and intermittency were measured. The methodology is then used in a predictive mode on three experimental datasets, and it is found to give good agreement. This enables prediction of other important variables as well, including skin friction and a wide variety of other boundary-layer properties in the transition zone at hypersonic Mach numbers.