A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

Progress in shock wave/boundary layer interactions

Conventional hypersonic wind tunnels and shock tunnels sufier from high levels of freestream ∞uctuations which are typically one to two orders of magnitude above ∞ight levels. These freestream ∞uctuations are generally dominated by acoustic noise radiated from the turbulent boundary layers on the nozzle walls. Although the efiects of the noise are often small, and so can be neglected, this noise often has a dramatic efiect on laminar-turbulent transition on models, and it can have an signiflcant efiect on other phenomena as well. Quiet-∞ow hypersonic tunnels with low noise levels comparable to ∞ight have therefore been sought for more than 50 years. The development of these tunnels is reviewed. The largest efiort was carried out at NASA Langley from the late 1960’s through the middle 1990’s, and resulted in successful quiet tunnels at Mach 3.5 and 6, although the Mach 6 tunnel was later decommissioned. The effort was then carried forward at Purdue University from 1990 through the present, leading to the nowsuccessful Boeing/AFOSR Mach-6 Quiet Tunnel.

Development of Hypersonic Quiet Tunnels

Ground Test Studies of the HIFiRE-1 Transition Experiment Part 2: Computational Analysis

Expansion tubes are an important type of test facility for the study of planetary entry flow-fields, being the only type of impulse facility capable of simulating the aerothermodynamics of superorbital planetary entry conditions from 10 to 20 km/s. However, the complex flow processes involved in expansion tube operation make it difficult to fully characterise flow conditions, with two-dimensional full facility computational fluid dynamics simulations often requiring tens or hundreds of thousands of computational hours to complete. In an attempt to simplify this problem and provide a rapid flow condition prediction tool, this paper presents a validated and comprehensive analytical framework for the simulation of an expansion tube facility. It identifies central flow processes and models them from state to state through the facility using established compressible and isentropic flow relations, and equilibrium and frozen chemistry. How the model simulates each section of an expansion tube is discussed, as well as how the model can be used to simulate situations where flow conditions diverge from ideal theory. The model is then validated against experimental data from the X2 expansion tube at the University of Queensland.

Implementation of a state-to-state analytical framework for the calculation of expansion tube flow properties

LENS XX, a new large-scale expansion tunnel facility, has been designed and constructed at CUBRC. This stand-alone facility was designed after successful testing in the prototype LENS X facility. This facility is the largest known expansion tunnel in the world with an inner diameter of 24 inches and an end to end length of more than 240 ft. With the addition of LENS XX, CUBRC now has the ability to test duplicated supersonic or hypersonic flight conditions at any practical flight condition from low supersonic launch trajectories to planetary reentry. Expansion tunnels have showed much promise in recent years with their ability to generate a wide range of hypervelocit y conditions with reduced chemistry effects at high-enthalpy conditions in comparison with shock tunnels; however, short test times and large-amplitude test gas disturbances are still practical limitations of this type of facility. The large scale of this new facility offers a large core-flow with increased test time far exceeding other expansion tubes/tunnels. The large diameter tube will generate lower frequency test gas disturbances and reduced viscous effects, resulting in a higher quality coreflow. Additionally, an electrically heated high-pressure hydrogen driver allows highenthalpy testing with stagnation enthalpies up to 90 MJ/kg in a standard configuration and up to 120 MJ/kg or more in a four-chamber configuration. LENS XX will also have test times over 4 ms, test gas Mach numbers over 30, Reynolds numbers over 10 7 per meter, test gas velocities greater 13 km/s and shock speeds up to 15 km/s are expected. Shock speeds up to 12.4 km/s have been successfully demonstrated. The present work is meant to validate and begin to characterize the large range of possible test conditions through shock speed and freestream pressure measurements. Shock speed measurements are constant from 5-25 tube diameters over a large range of conditions i ndicating that viscous effects are minimal. Additionally, facility operation has proven to be very repeatable with primary shock speeds varying less than ±1.5%.

Characterization of the New LENS Expansion Tunnel Facility

velocity measurements This work reports on freestream velocity measurements for a number of flows for velocities from 2,060 m/s to 5,350 m/s The measured velocity was compared to facility calculations that are based on the measured shock speed in the driven tube and measured reservoir conditions The calculations agree with the velocity measurements up to 10 MJ/kg At higher enthalpies the calculations under predict the actual velocity of the flow However, the velocity measurement provides a new capability to operate the tunnel in non-tailored mode to obtain velocities greater than 5,300 m/s for at least 2 milliseconds of steady flow Under most circumstances the LENS I and LENS II shock tunnels produce fully-duplicated conditions for various flight trajectories in the upper atmosphere At high enthalpy some of the dissociated products are frozen during the expansion into the test section, so non equilibrium chemistry models have been developed to predict the Nitric Oxide (NO) concentration in the free stream gas Since the presence of this contaminant in the flow changes the nature of the test gas, however slightly, computational fluid dynamic (CFD) calculations are used to compensate for these effects 2  The actual concentration of the gas must be known Also it is very desirable to measure the free stream velocity since it is a direct measure of the gas kinetic energy and thus connected to the total enthalpy of the flow, a basic operating parameter of the facility At CUBRC we have constructed a continuous wave Quantum

Measuring Nitric Oxide Freestream Velocity Using a Quantum Cascade Laser at CUBRC

An experimental program combined with numerical analysis has been conducted to examine real gas effects on the performance of hypervelocity re-entry vehicles. These studies which were conducted in the LENS I Shock Tunnel and LENS X Expansion Tunnel examine the flows over simple nose shapes and the Apollo, Mars Lander and Space Shuttle configurations. Measurements were made in air, nitrogen and CO2 at enthalpy levels from 2 MJ/kg to 12 MJ/kg to evaluate the nonequilibrium characteristics of the flow in the test facilities. The laser diode measurements which were made to determine the velocity and NO species concentration in the facility for the full range of enthalpies were in excellent agreement with predictions of freestream velocity but indicated NO mole fractions half of the predicted values. Measurements with the Apollo configuration in the LENS I Shock Tunnel and LENS X Expansion Tunnel were in good agreement with each other and with predictions of shock layer geometry. However, in the higher enthalpy flows, the heating levels were poorly predicted. Measurements in the two facilities with the Mars Lander configuration and CO2 as a test gas demonstrated that in high enthalpy flows there are significant differences in the standoff distances which are believed to result from a nonequilibrium nature of the CO2 flow in the shock tunnel. The measurements in the LENS X tunnel were in excellent agreement with DPLR predictions of the shock shape and standoff distance. Studies were also conducted to examine real gas effects on the control surface characteristics of a shuttle configuration. These studies which were conducted in air and nitrogen in the LENS I Shock Tunnel showed that real gas effects reduced the scale of the separated interaction region over the flap increasing its effectiveness. However, real gas effects reduce the pressure over the curved surface of the wing resulting in a reduced pitching moment and net reduction in vehicle stability.

Experimental Studies in LENS I and X to Evaluate Real Gas Effects on Hypervelocity Vehicle Performance

Measuring Nitric Oxide Freestream Concentration Using Quantum Cascade Lasers at CUBRC

A review has been presented detailing the comparisons between numerical prediction and experimental data collected in the LENS facilities for a program focusing on thermochemical modeling of the flow in the reflected shock tunnel facility at high enthalpy. Comparisons have been provided for several studies made in the LENS-I facility including fundamental laser diode measurements of freestream nitric oxide concentration, temperature, and velocity; measurements on a two-dimensional cylinder; and measurements of laminar shock-wave/boundary layer interaction on a double cone geometry. The freestream velocity of the facility is found to be predicted to an accuracy of 2.5% or better for well-tailored conditions at all enthalpy levels, but the static temperature is significantly over-predicted for high enthalpy flows. Despite this, good agreement is obtained with all measurements for a two-dimensional cylinder. For the double cone model, the effect of vibration-dissociation coupling with the T-TV and CVDV models has been investigated. The choice of coupling model has impact for the lower enthalpy case, but in the high enthalpy case, it is unclear whether the discrepancy with the measurements is attributable to the coupling in the interaction region or the understanding of the freestream conditions.

http://chimeracfd.com/professional/public/aiaa2007_0121.pdf

Ronald Parker

Papers

Characterization of the New LENS Expansion Tunnel Facility

Measuring Nitric Oxide Freestream Velocity Using a Quantum Cascade Laser at CUBRC

Experimental Studies in LENS I and X to Evaluate Real Gas Effects on Hypervelocity Vehicle Performance

Measuring Nitric Oxide Freestream Concentration Using Quantum Cascade Lasers at CUBRC

A Computational Analysis of Thermochemical Studies in the LENS Facilities