Robert D Rockwell

• PhD
• Senior Researcher at University of Virginia

The stiffness and damping coefficients of fluid film bearings play a key role in predicting levels of vibration and stability margins in high-performance industrial rotating machinery. However, variability in the coefficients calculated by numerical bearing codes creates inaccuracies in the rotodynamic predictions. Therefore, there is a strong need...

Closed-loop fueling control of a dual-mode scramjet was successfully demonstrated using optical emission spectroscopy as the sole sensor for controller feedback. The optical emission from species of interest ( ${{\rm OH}^*}$ , ${{\rm CH}^*}$ , ${\rm C}_2^*$ ) was first characterized throughout the combustor. The relative emission intensity between...

Closed-loop fueling control of a dual-mode scramjet was demonstrated using optical emission spectroscopy as the sole feedback to the controller. The optical emission from species of interest (OH*, CH*, C2*) was first characterized throughout the combustor. The relative emission intensity between species pairs was studied over a range of fueling con...

Closed-loop fueling control of a dual-mode scramjet was demonstrated using optical emission spectroscopy as the sole feedback to the controller. The optical emission from species of interest (OH*, CH*, C2*) was first characterized throughout the combustor. The relative emission intensity between species pairs was studied over a range of fueling con...

This paper explores the use of dual-mode scramjet shock train control taking an adaptive control approach known as characteristic model-based all-coefficient adaptive control. In this study a simple, semiempirical model of a dual-mode scramjet is developed. This model is suited to computationally efficient control simulation for the assessment of d...

A small-scale cavity flameholder for high-speed, premixed ethylene combustion has been designed, additively manufactured, and tested at Mach 5 enthalpy. The work has enabled a comprehensive study on the effects of flow compressibility and heat release on turbulent flame structures and stabilization mechanisms. The cavity is sized to produce a pract...

Hydrocarbon fuels offer optimal high energy per volume for scramjet applications for sustained hypersonic flight but require additional residence time due to slower ignition delays (compared with hydrogen fuel). The injection of ethylene at the start of the isolator of a dual-mode scramjet combustor, operating in ramjet mode, allows sufficient mixi...

The flame front of a premixed ethylene–air turbulent flame in a high-speed flowfield was imaged using hydroxyl radical (OH) planar laser-induced fluorescence (PLIF). An electrically heated continuous flow facility produced inflow conditions with a total temperature of 1200 K, corresponding to a flight Mach number of about five. A statistically stat...

In order to compensate for an extremely heavy journal, jacking pockets can be added to the surface of pads in fluid film bearings. Jacking pockets can range in size and shape and will have an influence on the hydrodynamic performance of the bearing. Computational fluid dynamics (CFD) was used to better understand the influence of the geometry of a...

Formaldehyde (CH2O) planar laser-induced fluorescence (PLIF) imaging was performed in a premixed, ethylene-fueled dual-mode scramjet combustor to study the flame structure and dynamic flame behavior. CH2O PLIF is used as a marker to provide information on the structure and position of the lower-temperature portion of the reaction zone. Low-repetiti...

Dual-pump coherent anti-Stokes Raman spectroscopy (CARS) was used to measure the mole fractions of major species as well as the rotational and vibrational temperatures of molecular nitrogen in a hydrogen-fueled dual-mode scramjet flowpath operated in the “ram” mode. Developments in CARS methods and uncertainties are described, including a detailed...

As part of a broader effort to provide detailed measurements of turbulent flames in dual-mode scramjets, promote a deeper understanding of the relevant combustion physics, and aid appropriate computational model development, a high-subsonic cavity-stabilized premixed ethylene–air flame (typical of ramjet operation) is studied using coherent anti-St...

Particle image velocimetry was performed in the spanwise centerplane of a scramjet cavity flameholder under premixed hydrocarbon-fueled dual-mode conditions, providing the first reported results of their kind. Graphite tracer particles were shown to offer suitable aerodynamic performance and durability in a high-enthalpy flow, overcoming restrictio...

Hypersonic airbreathing engines rely on scramjet combustion processes, which involve high-speed, compressible, and highly turbulent reacting flows. The combustion environment and the turbulent flames at the heart of these engines are difficult to simulate and study in the laboratory under well-controlled conditions. Typically, wind-tunnel testing i...

In the design phase of developing a rotating machine, it is important to consider the effect that the supporting structure has on the rotordynamic behavior of the system. The American Petroleum Institute’s (API) Standard Paragraphs state that if the support stiffness is greater than 3.5 times the bearing oil film stiffness, the designer may omit th...

Time-resolved CH* chemiluminescence imaging was performed at 50 kHz in order to study flame motion and stabilization in the axial flow direction in a dual-mode scramjet at the University of Virginia Supersonic Combustion Facility. The combustor was operated in a fully premixed mode at a global equivalence ratio of 0.40 using ethylene fuel and air w...

The combustion efficiency of a scramjet is ametric that evaluates the overall performance of the engine.Until recently, combustion efficiency was measured using indirect approaches such as a one-dimensional control volume calculation or a calorimeter and wall pressure tap measurements. A novel nonintrusive direct approach for the measurement of com...

Nitric oxide planar laser-induced fluorescence measurements have been performed in a small-scale scramjet combustor at the University of Virginia Aerospace Research Laboratory at nominal simulated Mach 5 flight. A mixture of nitric oxide and nitrogen was injected at the upstream end of the inlet isolator as a surrogate for ethylene fuel, and the mi...

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Formaldehyde (CH2O) planar laser-induced fluorescence (PLIF) and high-speed CH* chemiluminescence have been performed in a premixed, ethylene-fueled dual-mode scramjet combustor in order to study the dynamic flame behavior and structure. CH2O PLIF is used as a...

Flow visualization and statistical analysis of a supersonic, turbulent reacting flow from nonintrusive hydroxyl radical planar laser-induced fluorescence images are presented. The OH-PLIF images show instantaneous structures of turbulence in two combustor configurations at different fuel-equivalence ratios. Proper orthogonal decomposition and autoc...

Schlieren imaging is particularly suited to measuring density gradients in compressible flowfields and can be used to capture shock waves and expansion fans, as well as the turbulent structures of mixing and wake flows. Conventional schlieren imaging, however, has difficulty clearly capturing such structures in long-duration supersonic combustion t...

Testing of identical dual-mode scramjet flowpath geometries in the freejet and direct-connect configurations was conducted in two separate facilities. These tests enabled a comparison study between the two configurations, which was directed toward the determination of the effects of inlet distortion and backpressure on the performance and operabili...

Measurements were conducted at the University of Virginia Supersonic Combustion Facility of the flow in a constant-area duct downstream of a Mach 2 nozzle. The airflow was heated to approximately 1200 K in the facility heater upstream of the nozzle. Dual-pump coherent anti-Stokes Raman spectroscopy was used to measure the rotational and vibrational...

A two-color tunable diode laser sensor for detection of H2O absorption near 1.4 μm was used to simultaneously determine temperature, H2O column density, and velocity in a direct-connect scramjet combustor. Axial and transverse spatial resolutions were achieved by translating the measurement line of sight across and along the flowpath with measureme...

Spatially resolved laser absorption measurements of CO, CO2, and H2O within an ethylene-fueled direct-connect model scramjet combustor are presented. The sensors employ a variety of laser sources at midinfrared wavelengths to provide access to fundamental vibrational band absorption transitions for each species. Both scanned-wavelength modulation s...

The development and use of a tunable diode laser absorption spectroscopy sensor for combustion product water vapor in a hydrogen-fueled model scramjet combustor are presented. A pair of absorption transitions was selected from the combination bands of water vapor near 1.4 μm exploiting telecommunications diode laser and fiber technologies. Waveleng...

Advanced computational models of hypersonic air-breathing combustion processes are being developed to better understand and predict the complex flows within a dual-mode scramjet combustor. However, the accuracy of these models can only be quantified through comparison to experimental databases. Moreover, the quality of computational results is depe...

In this paper, the authors describe dual-pump coherent anti-Stokes Raman spectroscopy (CARS) measurements of mixing and combustion in a direct-connect scramjet combustor operating at equivalent flight Mach typical of the ramjet-scramjet transition, in the scram mode. Measurements were performed in the University of Virginia's scramjet test facility...

Numerical simulations of the turbulent reactive flow within a model scramjet combustor configuration, experimentally mapped at the University of Virginia's Scramjet Combustion Facility at an equivalence ratio of 0.17, are described in this paper. A hybrid large-eddy simulation/Reynolds-averaged Navier-Stokes method is used, with special attention f...

Hydroxyl radical (OH) planar laser-induced fluorescence (PLIF) visualizations were performed in the University of Virginia supersonic combustion experiment. The test section was set up in configuration A, which includes a Mach 2 nozzle, combustor, and extender section. Hydrogen fuel was injected through an unswept compression ramp at two different...

A two-color tunable diode laser sensor for detection of H2O absorption near 1.4 μm was used to simultaneously determine temperature, H2O column density, and velocity in a direct-connect scramjet combustor. Axial and transverse spatial resolution were achieved by translating the measurement line-of-sight (LOS) across and along the flow path with mea...

Despite over 50 years of research, the supersonic, turbulent, combusting flow field of a scramjet is not fully understood. This is particularly the case for the dual-mode scramjet (DMSJ) which operates in supersonic, subsonic, and mixed modes of combustion. This gap in knowledge stems from the inability to experimentally measure key flow properties...

Wind-tunnel tests were performed to determine the effect of vitiation on flameholding limits in a hydrocarbonfueled dual-mode scramjet flameholder. The test air was generated both clean and with 6.7% water by mole to examine the effect of hydrogen combustion vitiation on flameholding. The tests were performed in a direct-connect configuration with...

In this paper we describe efforts to obtain canonical data sets to assist computational modelers in their development of models for the prediction of mixing and combustion in scramjet combustors operating in the ramjet-scramjet transition regime. The CARS technique is employed to acquire temporally and spatially resolved measurements of temperature...

Non-intrusive hydroxyl radical (OH) planar laser-induced fluorescence (PLIF) measurements were obtained in configuration C of the University of Virginia supersonic combustion experiment. The combustion of hydrogen fuel injected through an unswept compression ramp into a supersonic cross-flow was imaged over a range of streamwise positions. Images w...

Measurements have been conducted at the University of Virginia Supersonic Combustion Facility in configuration C of the dual-mode scramjet. This is a continuation of previously published works on configuration A. The scramjet is hydrogen fueled and operated at two equivalence ratios, one representative of the "scram" mode and the other of the "ram"...

A three-flow-tube, quasi-one dimentional calculation was carried out to estimate modetransition fuel equivalence ratios under clean and vitiated inflow conditions. A simple flame holding model was used in the calculation. In cases of vitiated inflows, both total temperature and total enthalpy matched conditions to that of clean air were tested. Cal...

Schlieren imaging is particularly suited to measuring density gradients in compressible flowfields and can be used to capture shock waves and expansion fans, as well as the turbulent structures of mixing and wake flows. Conventional schlieren imaging, however, has difficulty clearly capturing such structures in long-duration supersonic combustion t...

Measurements have been conducted at the University of Virginia Supersonic Combustion Facility of the flow in a constant area duct downstream of a Mach 2 nozzle, where the airflow has first been heated to approximately 1200 K. Dual-pump CARS was used to acquire rotational and vibrational temperatures of N2and H2Oat two planes in the duct at differen...

Numerical simulations of reacting and non-reacting flows within a scramjet combustor configuration experimentally mapped at the University of Virginia's Scramjet Combustion Facility (operating with Configuration "A") are described in this paper. Reynolds-Averaged Navier-Stokes (RANS) and hybrid Large Eddy Simulation /Reynolds-Averaged Navier-Stokes...

The method of steam addition, and the associated makeup oxygen and optional carbon dioxide vitiation systems, is described. The tunable diode laser absorption spectroscopy (TDLAS) technique that was applied to the the University of Virginia Supersonic Combustion Facility (UVaSCF) is also described. It is also shown the first time that steam additio...

An experimental study was performed to characterize the effects of vitiation due to combustion-air preheating on dual-mode scramjet combustion. Major combustion vitiation species (H 2O and CO 2) were added to the freestream of an electrical-resistance-heated, direct-connect facility simulating Mach 5 flight enthalpy. With clean, dry air, the combus...

The present experimental study investigates the vitiation effects of heated test gas on combustor performance in a direct-connect dual-mode scramjet. Wall pressures were compared under two different types of heated gas conditions. One condition was generated with a combustion heater, and the other with an electric heater. Gaseous H2 was used as the...

To estimate the enthalpy effects of test gas in a direct-connect dual-mode combustor, an experimental study was conducted. Wall pressures were compared under two cases with different types of air heater (combustion heater and electric heater) at various H-2 fuel equivalence ratios. Considering flame holding, dual-mode transition and wall pressure v...

Reynolds-averaged Navier-Stokes (RANS) and hybrid large-eddy simulation / Reynolds-averaged Navier-Stokes strategies are applied to simulate hydrogen-air combustion in two flow paths (Configurations A and B) being tested at the University of Virginia's Scramjet Combustion Facility. The flow paths differ in that Configuration B includes a straight-w...

The design, fabrication, and test of a microelectromechanical-system-based millinewton-level hydrazine thruster were investigated. The designed operation temperature and pressure of the micro hydrazine thruster were set to 900 K and 690 kPa respectively. The dissociations of hydrazine at various flow rates and various numbers of reactor units were...

An experimental study was performed to characterize the effect of vitiates due to combustion air preheating on dual-mode scramjet combustion. Major vitiate species H 2O and CO 2 were added to the freestream of an electrically heated, direct connect facility simulating Mach 5 flight enthalpy. With dry air, the combustor operated in the supersonic mo...

Ever-increasing demands on the turbomachinery industry result in faster, lighter machines with higher rotational speeds and power densities. Modern, well-established thermoelastohydrodynamic (TEHD) analyses predict static and dynamic bearing characteristics in the presence of a turbulent lubricant and reduced lubricant flows. Proper design of tilti...

To design highly efficient and stable turbomachines, engineers require accurate methods to model seal flows and calculate clearance-excitation forces generated by the eccentric position of the rotor. One of the most widely used methods to predict leakage flow and dynamic coefficients is the use of computer codes developed based on bulk flow theory....

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1993. Includes bibliographical references (leaf 30).

No literature is currently available which has evaluated finite element power loss models for magnetic bearings and compared the results to experimental results. In this paper a finite element model of the magnetic and electric fields in magnetic bearings, including the motion of the magnetic material in the rotor, is developed. It evaluates the tw...

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