1. 5)inFigures 17and 18. Figure 18shows a similar correlation for the transitional measurements at our highest velocity condition. It can be seenthat, for fullyturbulent flows,the break point was moved to lower levels of the correlation parameter, indicating a higher cooling requirement underhigh-velocityconditions. Themeasurementsin transitionalflows showbreak-pointvalues similarto those observedwith studiesatlowerenthalpies. The measurements that are shown correlatedin terms of theHEDIcorrelationparameterinFigure 19indicate that the effectiveness of film cooling was significantly decreased with the increase in the freestream velocity and decrease in shock-layer density. These same parameters also exhibited significanteffect ontheaero-opticalperformanceofa seeker-headaperture. 3.3 Base Flow Studies with METT Model Confieuration
2. Weconcludefromtheseteststhatatleast 40 flow lengths are required to establish the turbulent flowover thislarge-scalemodel. However,because of the long run times that can be generated in the LENS facility, we have an additional 6-10 milliseconds over which this complex base flow is fully established and remains steady. Our measurementsalsoindicatethattheReynoldsnumber capabilityof the LENS facility is such that, on this large-scale model, fully turbulent flows can be generated in the baseregion at Mach numbers of up to 18. 3.4 StudieswiththePlanetarvProbeConfieuratiw
3. Atypical set of heat transfer and pressure records onthe front and back face of the model as well asalongthestingisshowninFigure 30. Itcan be seenthatwhiletheflowoverthefrontfaceof the model was established during the establishment of thenozzleflow(-1 millisecond),theflowinthebase regiontook 2to 3milliseconds(-50-60 flowlengths) to stabilize. The time-dependent pressure distributions along the sting indicate that the separatedbase flow began with a smaller separated region, which expanded to a steady configuration duringflowestablishment,asillustratedinFigure 31. Comoarison With DSMC and Navier-Stokes Codc .Solutions d
4. Measurementsweremadeatenthalpylevels of 5 MJkg and 10MJkg at a stagnationpressureof 500 atmospheres so that common measurements could be made in the LENS, HEG,andAmesshock tunnels. The distributions of pressure and heat transfer obtained for the 5MJkg case are shownin Figure 34aand 34b. We seefortheseflowsthatthe interactionregionassociatedwiththe separatedbaseregionflowextended IOnoseradiifromthetipofthe model, which is significantly longer than the measurements at lower Reynolds numbers for the code-validationstudiesshowninFigures 33aand 33b in section 3.4. For the measurementsmadeatthe IO MJkg test case (showninFigures 35a and 35b). we see that the interactionregion extendedeven further downstream,reachingcloseto 11noseradiifromthe tip of the model. The increase in size of the interactionregion isconsistentwithanincreaseinthe Reynolds number, providing the flow remains d Amodelsupportandopticalbench systemandsuitse ofaero-thermalandaero-opticalinstrumentationhave been developed to evaluate the performance of hypewelocity-vehicleconfigurations. An aggressive program isbeingconductedtodevelopthick doublediaphragm technology, address severe throat and reservoir heating problems, and construct a fastacting throat valve that survives under very high enthalpy conditions. Studies employing a simple seeker-head aperture configuration are being conducted to validate the performance of the LENS facility and the aerothermal and aero-optical instrumentation developed for seeker-head evaluation. Aerotherrnal studies are also being conducted to examine the time establishment of the base-regionflowbehind asimplifiedconfigurationof a hypersonic airbreathing vehicle. Measurements madeinthesestudiesindicatethat 50-60flowlengths arerequired to stabilize the base-region flow. Heat transfer and pressure measurements on a sting supported planetary probe configuration were obtainedat 5MJkgand 10MJkgenthalpylevelsat stagnation pressures of 500 atmospheres for comparions with measurements to be made in the HEGandAMES facilities. Measurementswerealso obtained in low-density and laminar flows for comparisonswithsolutions totheDSMCandNavier-Stokes codes for conditions where vibrational nonequilibrium and dissociation effects are important. Time-resolved pressure and heat transfer measurements in the base region of the probe, together with high-speed schlieren photography indicated that flow lengths of 50 or more were required to fully establish the recirculating flow in thebase region. Thelow-densityflowmeasurements were found to be in good agreement with Moss's DSMC code predictions. The measurements in continuum flow indicated that the base-region separated flow was longer than that predicted with the Navier-Stokes code. Preliminary studies have been conducted to examine hydrogen mixing and combustioninahypervelocityenvironment.