The predictions of non-equilibrium radiation for a Titan aerocapture aeroshell vary significantly amongst Computational Fluid Dynamics (CFD) analyses and are limited by the physical models of the non-equilibrium flow. Of particular interest are the non-equilibrium processes associated with the cyanogen (CN) molecule which is known to be a strong radiator. It is therefore important to have experimental data for these radiating shock layers which will allow for validation of CFD models. Furthermore, a more detailed understanding of the chemical processes that lead to the formation of CN above equilibrium concentration is required. This thesis describes the modelling of the radiation behind a shock using a collisional-radiative (CR) model and presents measurements of radiation intensity behind a shock in simulated Titan and Martian atmospheres. The uncertainties in radiation is more significant at lower speeds (around 5-8 km/s) with these atmospheres when compared to Earth entry. This is due to the formation of CN and because of the highly non-equilibrium nature of the flow. The motivation for this work began with the successful landing of the Huygens probe on the surface of Titan which led to the renewed interest in inter-planetary missions. Thus radiative heating during atmospheric entry to Titan and Mars was the subject of several experimental campaigns and extensive computational analyses. In order to better understand the formation of CN, and the nonequilibrium radiation emitted under such atmospheric conditions, NASA Ames Research Center conducted a series of experiments on their Electric Arc Shock Tube facility, EAST. Furthermore, several research groups in Europe and the United States independently developed CR models to predict the measured levels of radiation. The results from these simulations showed some ma jor discrepancies and highlighted a lack of knowledge and understanding about the fundamental physics behind the formation and decay of the CN molecule and its associated excited states. Based on a comparison of the various simulations with the CR models and the EAST experimental data, it was concluded that the absolute level of peak radiation was well predicted, however, there was a significant discrepancy related to the decay rate of the radiation. Therefore, to add to the relatively small amount of experimental data for these highly non-equilibrium radiating flow conditions, experiments were performed on the X2 shock tube at The University of Queensland with the aim of producing a comprehensive set of benchmark data for Titan entry. The data obtained from these experiments have been used to validate the results from the NASA Ames testing, and due to the large parametric variation, as a source for code validation. In addition to the experimental component of this thesis, an investigation into the simulation of CN non-equilibrium radiation was conducted. It has been previously concluded that there was a significant discrepancy between the experimentally measured radiation decay rate and the predicted value from CR models. Therefore, the primary aim of the simulation work presented in this thesis is to explain the reason behind this discrepancy. Through a parametric study of important reactions combined with an analysis of the reaction set, it was concluded that the coupling between the dissociation of N2 and the formation of CN (through the reaction N2 + C ↔ CN + N) controlled the radiation decay rate. The reason for the super equilibrium concentrations was identified to be a result of the N2 + C ↔ CN + N reaction continuing to over-produce CN after nominal equilibrium values are reached. This is due to the slow build up of N to drive the reverse reaction. Thus it has been shown in this thesis that the behaviour of the CN concentration is controlled by the rate of N2 dissociation. This led to the implementation of a more thorough method for simulating the dissociation process of molecular nitrogen. Therefore, a mono-quantum vibration state specific model that includes excitation and de-excitation reactions for all the vibrational states of nitrogen was incorporated into the CR model developed by Magin et al. The nitrogen vibration state specific model that was implemented was developed by Pierott and is based on SSH theory. The model developed in this thesis is known as the ViSpeN CR model (Vibrationally Specific Nitrogen). The ViSpeN results show significantly better agreement with experimental data in terms of the decay rate, initial rise of the radiation and the overall trends in the data. However, the work in this thesis has shown there are still discrepancies in predicting the absolute level of radiation measured in shock tunnel experiments. This led to the development of a modification to the ViSpeN model (known as ViSpeN-L) which includes a proposed new value for the radiative lifetime of the CN violet transition. The agreement between the experimental data and the ViSpeN-L model is excellent for conditions relevant to Titan entry.

No description available.

No description available.

The emerging paradigms of shockwave research have opened up new horizons for interdisciplinary applications. This has inevitably driven research towards studying the propagation of shockwaves in miniature shock tubes (tube diameters typically in the range of 1−10 ). Studies have revealed that while operating at this diameter range and low initial pressures (typically 1 < 100 ) leading to low values of characteristic Reynolds numbers (typically ′ < 23,000 −1), results in the boundary layer playing a major role in shockwave attenuation. But there are very few studies addressing shockwave attenuation when shock tubes are operated at higher Reynolds number. Pressure measurements and visualization studies in shock tubes of these length scales are also seldom attempted due to practical difficulties. Given that premise, in the present work the shockwave attenuation due to wall effects and non-ideal diaphragm rupture in shock tubes of hydraulic diameters 2 , 6 and 10 has been investigated at ambient initial driven section conditions ( 1 = 300 and 1 = 1 resulting in Reynolds number in the range 70,212 −1 – 888,627 −1). In this study pressure measurements and high-speed visualization have been carried out to find the effect of the pressure ratio, temperature ratio and molecular weights of driver gas on the shock attenuation processes. In order to study the effects of the driver/driven gas temperature ratios on the shock attenuation process, a new in-situ oxyhydrogen (hydrogen and oxygen gases in the ratio 2:1) generator has been developed. Using this innovative device, the miniature shock tubes are also run in the detonation mode (forward facing detonation wave). The results obtained using helium and nitrogen driver gases for these shock tubes reveal that as the hydraulic diameter of the shock tube is reduced, a larger diaphragm pressure ratio is required to obtain a particular strength of shockwave. The attenuation in the shockwave is found to be a function of the driver gas properties namely specific heat ratio ( 4), molecular weight ( 4), temperature ( 4) as well as the diaphragm opening time of the shock tube in addition to the parameters , 21, / , and 1 as already suggested in previous reports. The visualization studies reveal that the effect of diaphragm opening time leading to longer shock formation distances appears to influence the shockwave attenuation process at these shock tube diameters. Further, it is also found that the strength of the shockwave reduces when the ratio 4/ 1 is higher. It is also seen that the length of the driven sections must be less than twice the length of the driver sections to reduce attenuation. Based on the understanding of the nature of supersonic flow in a miniature shock tubes, a novel shock/blast wave device has been developed for certain innovative biotechnology applications such as needleless vaccine delivery and cell transformations. The new device has an internal diameter of 6 and by varying the length of the driver/driven sections either shock or blast waves of requisite strength and impulse can be generated at the open end of the tube. In the shock tube mode of operation, shockwaves with steady time duration of up to 30 have been generated. In the blast tube mode of operation, where the entire tube is filled with oxyhydrogen mixture, shockwaves with peak pressures of up to 550 have been obtained with good repeatability. An attempt to power this device using solar energy has also given successful results. Visualization of the open end of the detonation driven shock tube reveals features typical of flow from the open end of shock tubes and has helped in quantifying the density field. The subsequent instants of the flow resemble a precursor flow in gun muzzle blast and flash. Typical energy levels of the shock/blast waves coming out this device is found to be about 34 for an oxyhydrogen fill pressure of 5.1 in the shock tube operation mode. Transformation of E.coli, Salmonella Typhimurium and Pseudomonas aeruginosa bacterial strains using the device by introducing plasmid DNA through their cell walls has been successfully carried out. There is more than twofold increase in the transformation efficiency using the device as compared to conventional methods. Using the same device, needleless vaccine delivery in mice using Salmonella has also been demonstrated successfully. Overall, in the present thesis, a novel method for generating shockwaves in a repeatable and controllable manner in miniature scales for interdisciplinary applications has been proposed. Also, it is the first time that experiments with the different diameter miniature shock tubes have been carried out to demonstrate the attenuation of shockwaves as the hydraulic diameter of the shock tube decreases. Future research endeavors will focus on quantitative measurement of the particle velocity behind the shock waves, and also on the nature of the boundary layers to further resolve the complex flow physics associated with supersonic flows in these miniature shock tubes.

Thesis (M.Sc.) - University of Queensland, 2004. / Includes bibliography.

Richtmyer-Meshkov instability is studied in shock tube experiments with an Atwood number of 0.7. The interface is formed in a vertical shock tube using opposed gas flows, and three-dimensional random initial interface perturbations are generated by the vertical oscillation of gas column producing Faraday waves. Planar Laser Mie scattering is used for flow visualization and for measurements of the mixing process. Experimental image sequences are recorded at 6 kHz frequency and processed to obtain the time dependent variation of the integral mixing layer width. Measurements of the mixing layer width are compared with Mikaelian's [1] model in order to extract the growth exponent. where a fairly wide range of values is found varying from theta approximate to 0.2 to 0.6.

This thesis focuses on ignition of diisopropyl ketone (DIPK), a new biofuel candidate that is produced by endophytic conversion. The ignition delay times behind reflected shockwaves were modeled in a high-pressure shock tube. The ignition delay times were compared to other biofuels and gasoline surrogates. Parametric studies of the ignition delay experiments were performed between 1-10 atm and 900 -1200K. An OH optical sensor was developed in conjunction for the ignition delay experiments. The OH optical sensor uses a microwave discharge lamp to generate light at 308 nm that will then be shined through the combustion reaction. Using Beer-Lambert law the concentration of OH can be obtained during ignition and oxidation of hydrocarbon fuels in a shock tube. DIPK ignition delay time experiments are planned in two shock tubes (located at UCF and UF) to provide ignition and OH time-histories data for model validation.

The design, development, construction, and instrumentation features of a supersonic shock tunnel that produced high temperature supersonic flow for a short duration, on the order of 2 msec, are presented. The shock tunnel was equipped with a Mach 3 supersonic 2-D nozzle. Test runs were conducted using air and helium drivers at driving pressures varying from 200-450 psig (1.4-3.1 MPa gage), with the driven gas in all the cases being ambient air. Pressure and temperature measurements were made to document the operating conditions of the tunnel. Total pressure measurements were made in the settling chamber of the nozzle where the flow Mach number is 0.14 (weakly subsonic). Static pressure measurements were made at the exit of the nozzle to establish the unsteady starting process of the nozzle. Total temperature measurements using thermocouples were made in the settling chamber of the nozzle to identify the maximum temperature attained in the flow. Surface heat flux measurements were made at the exit of the nozzle and compared with previous skin friction measurements. The measured pressures and temperatures compared well with the predicted values for the air driver. In the case of the test runs with the helium driver the nozzle started, but the flow was unsteady. Consequently, there were difficulties in making measurements and interpreting them. The surface heat flux and skin friction followed the Reynold's analogy within 50% during the steady run time of the shock tunnel. / M.S.

Part 1 The coupled shock-tube/mass spectrometer apparatus is characterized in terms of its capabilities for chemical kinetic studies. Criteria for doing kinetic measurements by this experimental technique are discussed. The characterization experiments showed that our apparatus was capable of giving plausible signal shapes for non-reactive dynamic shots at P₁ = 5 torr. Measurements of ion current under static conditions showed that response of the quadrupole mass spectrometer was linear over a range of P₁ = 0-5 torr. Schlieren measurements indicated that the shock wave velocity was erratic and non-reproducible over the last 5 feet of the test section and that the velocity at the endwall could not be predicted from the schlieren data. The electron beam width was found to be ~.1" and the implications of this measurement for further studies on the free jet are outlined. The present beam width is suitable for jet studies in which bulk ionization of gas from a cross-section of the jet is performed. Design improvements needed for future reactive studies on our system are reviewed. In addition, experimental studies of jet risetime with a pulsed molecular beam apparatus showed poor agreement between the experimental and theoretical jet risetimes. The apparent discrepancy is discussed and possible explanations for it are given. Part 2 The rate constant k₁ for the reaction C₅H₁₂ → C₄H₉ + CH₃ was determined from reflected shock experiments (1100-1300°K) in which the progress of reaction was monitored by the appearance of H atoms. Atomic resonance absorption spectrophotometry at the Lyman-α line was performed on three mixtures (20 ppm, 10 ppm, 5 ppm) of neopentane in argon to give k₁ = .17 x 10¹⁸ exp (-84800±6200/RT) sec⁻¹. This result is in very good agreement with earlier single pulse shock tube experiments. In addition, calibration experiments for H atom were performed by shock-heating two mixtures (10 ppm and 5 ppm) of neopentane in argon. The results obtained were in good agreement with previous calibration data. / Doctor of Philosophy

The growing requirements to achieve hypersonic flights, as in the case of reentry vehicles, pose a serious challenge to the designers. This demands an understanding of the features of hypersonic flow and its effect on hypersonic vehicles. Hypersonic shock tunnels are one of the most widely used facilities for the purpose of obtaining valuable design data by conducting experiments on scaled down models. They are operated by conventional shock tubes by rupturing metal diaphragms placed between the driver and driven sections of the shock tube. Shock tunnels are being extensively used in spite of some of the drawbacks they possess. Due to the varying nature of metal diaphragm rupture, reproducibility of the experiment results is difficult to obtain. Damage to model and inner surface of the shock tube can happen when the diaphragm petal breaks away from the diaphragm. Lastly the time consuming diaphragm replacement process is not desired in applications which require quick loading of shock waves on the specimen. All these disadvantages call for the replacement of the diaphragm mode of operation with a diaphragmless mode of operation for the generation of shock waves. The main objective of the present study is to design and demonstrate the working of a diaphragmless hypersonic shock tunnel. The motivation for the present study comes from the fact that the diaphragmless operation of a shock tunnel has not been reported so far in the open literature. All the research works carried out deal with diaphragmless drivers operating only a shock tube. In the present work, the conventional metal diaphragm is substituted by fast acting pneumatic valves which serve the purpose of quickly opening the driven section of the shock tube to allow the driver gas to rush in, resulting in the formation of a shock wave. To design a diaphragmless driver, a detailed study of the shock formation process is accomplished which helps in understanding the effect of valve opening time on the shock formation distance. Also the theoretical basis for the design of a pneumatic cylinder is understood. Following the theoretical studies, three types of diaphragmless drivers are designed and tested. The first setup incorporates a rubber membrane, which acts as a valve. The rubber membrane when bulged closes the mouth of the driven section and on retraction the driven section is opened to the driver gas. The second and the third setups utilise two different types of double acting pneumatic cylinders. Experimental results of the three diaphragmless drivers operating a shock tube are analysed and compared with the ideal shock tube theory. Better repeatability in terms of shock Mach number is shown with all three diaphragmless shock tubes when compared with a conventionally operated shock tube. Finally, the best among the three systems is identified to operate the hypersonic shock tunnel 2 (HST2) facility of the Shock Waves laboratory, IISc. Demonstration of the working of the diaphragmless shock tunnel is shown by performing heat transfer measurements on a 3 mm backward facing step flat plate model. The experimental results are compared with those obtained in a conventional shock tunnel. CFD studies on diaphragmless shock tube model are done to have an idea on the flow in the shock tube there by identifying the shock formation distance. ANSYS-CFX package is used for this purpose. Further, results from the numerical simulation of hypersonic flow over the backward facing step model are compared with the experimental results thus validating the code.