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Advanced Diagnostics For Megahertz Imaging Of Mixing, Fuel Spray, And Combustion Processes For Rotating Detonation Combustors

Recent advancements in megahertz rate, high-power, burst-mode laser technology are leveraged to perform and explore imaging measurements that spatially and temporally resolve the mixing, combustion, and detonation flow field in two laboratory-scale rotating detonation combustors (RDCs). In a non-premixed annular RDC, multiple imaging diagnostics are explored to investigate gaseous and liquid injector behavior, the detonation wave structure, and the propellant refill. In one instance, OH planar laser-induced fluorescence (OH-PLIF) imaging is performed up to a 2 MHz repetition rate to track the combustion products and reaction zone locations. In the same annular RDC, a single liquid fuel jet is injected, and laser-based 355-nm imaging of the fuel spray is performed up to a 1 MHz repetition rate. For this configuration, the annular RDC is used as a detonation driver to impose periodic detonation waves to interact with the fuel spray. Moreover, in this annular RDC, a range of tracer-based laser imaging measurements are explored to time-resolve the unsteady oxidizer air recovery and refill process. In a non-premixed linear RDC, planar imaging measurements of the fuel mixing are performed up to a 200 kHz repetition rate using PLIF of a tracer in the fuel supply. The fuel mixing imaging helps explain the origin of the observed pre and post wave burning, detonation structure, and enables quantifying injector recovery timescales. This paper will provide a high-level broad survey of diagnostics applied in these RDCs, lessons learned, and interesting observations.

Combustion↗

DOE OSTI2014

Glove port retrofit assembly and method of replacing components

What is disclosed is a system for retrofitting a sealed enclosure for performing work therein having an outer enclosure assembly configured to be clamped to the outer annular face of a port ring and form a sealed engagement with the outer annular surface of the port ring, a change assembly having an inner ring and an access element wherein the inner ring has a first annular cylinder body that is sized to be slidably received by the port ring and the access element is configured to be sealably and slidably positioned within the first annular cylinder body of the inner ring.

42 ENGINEERING↗

DOE OSTI2016

Assembly for directing combustion gas

An arrangement is provided for delivering gases from a plurality of combustors of a can-annular gas turbine combustion engine to a first row of turbine blades including a first row of turbine blades. The arrangement includes a gas path cylinder, a cone and an integrated exit piece (IEP) for each combustor. Each IEP comprises an inlet chamber for receiving a gas flow from a respective combustor, and includes a connection segment. The IEPs are connected together to define an annular chamber extending circumferentially and concentric to an engine longitudinal axis, for delivering the gas flow to the first row of blades. A radiused joint extends radially inward from a radially outer side of the inlet chamber to an outer boundary of the annular chamber, and a flared fillet extends radially inward from a radially inner side of the inlet chamber to an inner boundary of the annular chamber.

33 ADVANCED PROPULSION SYSTEMS↗

DOE OSTI2019

Check valve with pilot tube pressure sensing

A check valve's housing has a valve disposed therein to open or close a flow path from the housing's inlet to its outlet based on a difference between pressures at the inlet and outlet. The valve includes a bellows, a poppet, and a spring. The poppet includes a hollow structure extending through the poppet's plate and terminating in a first open end disposed within the bellows, an annular flange between the second face of the poppet's plate and the housing's outlet, and an open-ended tube extending from the annular flange into the housing's outlet. The spring, disposed within the hollow tubular structure, positions the annular flange to seal the outlet when the pressure difference is less than a predetermined amount and compresses when the difference exceeds the predetermined amount wherein the annular flange is unsealed from the housing's outlet to open the flow path.

42 ENGINEERING↗

DOE OSTI2016

Highlights from the Postirradiation Examination of AFC-3A and AFC-3B

Highlights from the postirradiation examination of the AFC-3A and AFC-3B irradiation test are presented. Baseline non-destructive and destructive examinations of these tests have been completed at this time. Results from visual examination, neutron radiography, gamma spectrometry, dimensional inspection, fission gas release, chemical burnup analysis, and optical microscopy have been collected. All the rodlets from these irradiations appear to have performed well during irradiation. Baseline PIE has been completed on rodlets from AFC- 3A, and AFC-3B. This includes visual exams, neutron radiography, gamma spectrometry. dimensional inspection, fission gas release evaluation, optical microscopy. microhardness evaluation. and chemical analysis. The results compiled here are a sampling of the full results. Baseline PIE provides an engineering or macroscopic scale evaluation of fuel performance and prepares samples for a more detailed phenomenological study of observed performance. Advanced PIE techniques are desired to obtain microscopic elemental and structural information both in the fuel, in the cladding, and in the interface where the composition of the FCCI layer is of great interest. The AFC-3 tests do appear to have performed roughly as designed during the irradiation. The FCCI behavior of Mo alloy metallic fuel versus Zr alloy metallic fuel has been confirmed. Results from this irradiation such as the FCCI observed in AFC-3A R1 and AFC-3A R2 can be used to eliminate Mo alloys as a choice in future irradiations where ultra-high burnup is a stated goal. Annular fuels are a preferred method for many high burnup core designs. The redistribution behavior of the annular U-Zr alloys should be studied further to better understand how this might impact high burnup annular fuel performance. The thermal bonding between annular fuel and cladding should also be studied further as there appear to be localized areas of FCCI forming in both AFC-3A R4 and AFC-3B R2, while no FCCI was observed in the Zr-based Na-bonded or Mo-based low smear density Na-bonded fuel. The performance of the low smear density. solid fuels is less clear. The neutron radiography and optical microscopy cross sections suggest the fuel is not forming a radially symmetric structure which may be causing undesirable localized temperature variations. Further study both by electron microscopy and by simulation to evaluate the implications of the non-symmetric fuel form are needed to better understand whether this fuel form merits further study under irradiation. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2018

Spark plasma sintering of structure-tailored ultrahigh-temperature components: First step to complex net shaping

The net-shaping capability in spark plasma sintering (SPS) of ultrahigh-temperature ceramics has been explored in this study. The annular or ring-like shape is considered here as the first step to a more complex geometry compared to a solid cylinder or disk. ZrC powders have been SPS processed in specially designed graphite tooling to achieve the annular shape geometry. Experimental runs have been carried out to determine the optimal processing parameters for producing highly dense ZrC specimens in this geometry. Finite-element modeling framework has been constructed to determine the internal stress evolution, as well as densification, during the SPS of the annular-shaped ZrC. The formulated processing schemes for ZrC have been adapted to process SiC/ZrB2 composite powder with the purpose of making tooling components for SPS applications. The applicability of the obtained composite SPS tooling has been evaluated at high temperature and high pressure associated with SPS regimes.

36 MATERIALS SCIENCE↗

DOE OSTI2015

3-60B Type-B shipping cask enhanced operational features to facilitate leakage rate testing - 15585

EnergySolutions is fabricating a new 3-60B Type B Shipping Cask that will be ready for use in spring 2015, designed for shipping Type B quantities of activated and/or non-fuel-bearing reactor or accelerator components. EnergySolutions, in consult with Leak Testing Specialists, Inc., has implemented an improved design of the 3-60B cask closures to better facilitate periodic and maintenance leakage rate testing and to allow end users to more easily perform pre-shipment leakage rate testing to confirm proper assembly of the cask closures. A typical Type B cask closure lid design incorporates a double O-ring configuration, where the inner O-ring provides containment and the outer O-ring is used for leakage rate testing of the containment O-ring seal. Leakage rate testing of a double O-ring configuration is typically accomplished by filling the cask cavity with helium, pulling a vacuum on the annular space between the two O-rings and monitoring for helium leakage through the containment O-ring. One issue is the potential for helium saturation of the O-ring elastomeric material, which can result in leakage rate test failures. The cask cavity volume is typically large, and takes a significant amount of time to fill with helium. As a result, the saturation time for certain elastomeric compounds may be exceeded, leading to potential false-negative leakage rate testing results. To avoid this, that the cask cavity typically is loaded with sealed container(s) to reduce the free volume and the fill time. The improved 3-60B cask closure lid incorporates a triple O-ring seal configuration that facilitates maintenance leak rate testing of the closure lid containment O-ring seal and eliminates the issues discussed above. The triple O-ring configuration uses the middle O-ring as the containment seal, with the inner and outer test O-rings creating relatively small annular volumes for testing purposes. These small annular volumes are quick to fill, minimizing the issue of Helium saturation of the O-ring material. This seal configuration also makes it possible to detect and replace a damaged O-ring seal during loading operations, or dress a damaged sealing surface, and perform the required maintenance leakage rate testing of the replacement O-ring at the plant site without the need to unload the cask and send it to a maintenance facility. Also, a second test port has been added to each O-ring annulus to allow leakage rate testing to be accomplished using a formal system calibration that complies with the requirements and recommendations of ASME Section V, Article 10 [4], ANSI N14.5-97 [2], and ANSI N14.5-2014 [3]. This provides a simple, reliable, and accurate means to perform leakage rate testing with a test confidence level that cannot be achieved without the second test port. The improved closure and test port design simplifies and shortens the time required to perform leakage testing, resulting in reduced operating costs, greater schedule security, and dose savings for the cask users. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2022

On the effects of reactant stratification and wall curvature in non-premixed rotating detonation combustors

The optimization of non-premixed rotating detonation combustors (RDCs) requires improved understanding of the coupled effects of reactant stratification, fluid property gradients, and complex shock-wave interactions on the detonation wave structure within annular geometries. In the current work, simultaneous orthogonal views of chemiluminescence and hydroxyl planar laser-induced fluorescence (PLIF) are utilized to establish the existence of a dual-wave system characterized by leading and trailing detonation waves that are closely coupled by the local flow physics. These features are persistent over a wide range of mass flow rates and are consistent with prior observations of non-premixed rotating detonations in annular geometries. The detailed instantaneous time sequences are compared with a 3D reactive unsteady Reynolds averaged Navier-Stokes (URANS) simulation to more clearly elucidate the in-situ combustion dynamics and the sensitivity to reactant inlet conditions. It is found that the dual-wave system results from unburned reactants that survive the leading detonation wave in the injector near field and are consumed within a trailing azimuthal reflected-shock combustion (ARSC) zone. By contrast, the injector far field is characterized by rapid mixing due to a sudden drop to subsonic conditions, and the bifurcated detonation wave structure collapses into a stronger, single-wave detonation front with higher overall pressure ratio as compared with the dual-wave system. While each RDC will have different inflow, mixing, and combustion characteristics, the underlying interactions between the stratified reactants and azimuthal wave dynamics identified through the combination of advanced MHz-rate diagnostics and 3D numerical simulations have important implications for the study of detonation wave stability, mode transition, and combustion efficiency in non-premixed annular RDCs.

3D URANS↗

DOE OSTI2025

Establishing a silica gel zone in well annulus and evaluating its performance in blocking vertical water flow

Wells are often constructed for monitoring purposes with relatively long screen lengths (e.g., >10 m). Vertical water flows can occur within the artificial or natural filterpack annulus that surrounds the screened interval, bypassing packer assemblies installed inside the wellbore. Attempts to isolate discrete vertical zones during groundwater sampling are unsuccessful when annular flow occurs and lead to remedy decisions based on biased or incorrect interpretations. Blocking vertical annular water flow and contaminant transport will help obtain more accurate concentrations of contaminants from sampling in targeted depth intervals. The application of silica gels formed from the injected colloidal silica CS suspensions is a novel approach to minimize or prevent movement of vertical movement of groundwater in the surrounding filterpack annulus. In this work, we tested the feasibility of injecting CS suspensions to target locations and developed a modified CS formulation that is injectable and prevents gravity sinking. We studied the distribution and penetration of silica gel at laboratory scale in mock well annulus with surrounding formations. We evaluated the performance of the silica gel in blocking vertical water flow in the annulus and in minimizing chemical transport through the gel zone. CS suspension formulations have been defined that are ready for injection, stay in target locations, and form gel within desired time frames. Injection of CS suspensions achieved uniform distribution in a well annulus filter pack, fully occupied the annulus pore space, and penetrated the formation surrounding the filter packer with a sufficient distance to create a hydraulic annular seal when the injection was applied at a sufficient rate. The depth of penetration into the formation was dependent on the permeability contrast between the filter pack and the surrounding formation. Silica gel that formed in the annulus blocked vertical water flow and stopped the chemical transport through the gel zone. In conclusion, this research reveals that using CS suspension injection and sequential gelation (CS-GEL) is a promising technology for blocking vertical water flow and chemical transport through the filter pack in targeted zones within the annulus of long-screened well systems.

Colloidal silica suspension↗

DOE OSTI2014

Features of space-charge-limited emission in foil-less diodes

Space-charge-limited (SCL) current can always be obtained from the blade surface of annular cathodes in foil-less diodes which are widely used in O-type relativistic high power microwave generators. However, there is little theoretical analysis regarding it due to the mathematical complexity, and almost all formulas about the SCL current in foil-less diodes are based on numerical simulation results. This paper performs an initial trial in calculation of the SCL current from annular cathodes theoretically under the ultra-relativistic assumption and the condition of infinitely large guiding magnetic field. The numerical calculation based on the theoretical research is coherent with the particle-in-cell (PIC) simulation result to some extent under a diode voltage of 850 kV. Despite that the theoretical research gives a much larger current than the PIC simulation (41.3 kA for the former and 9.7 kA for the latter), which is induced by the ultra-relativistic assumption in the theoretical research, they both show the basic characteristic of emission from annular cathodes in foil-less diodes, i.e., the emission enhancement at the cathode blade edges, especially at the outer edge. This characteristic is confirmed to some extent in our experimental research of cathode plasma photographing under the same diode voltage and a guiding magnetic field of 4 T.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2015

Spontaneous formation of circular and vortex ferroelectric domain structure in hexagonal YMnO{sub 3} and YMn{sub 0.9}Fe{sub 0.1}O{sub 3} prepared by low temperature solution synthesis

We report an experimental study of the domain structure of ferroelectric YMnO{sub 3} and YMn{sub 0.9}Fe{sub 0.1}O{sub 3} using polycrystalline samples prepared by direct hydrothermal crystallisation at 240 °C, well below their structural phase transition temperatures. Powder X-ray diffraction shows the expected P6{sub 3}cm space group for both samples with an increase in a and a small decrease in c with Fe incorporation, consistent with an adjustment of MnO{sub 5} tilting, while XANES spectra at the Mn and Fe K edges show the oxidation state of both metals are maintained at +3 in the doped sample. High resolution TEM shows that curved stripe, annular and vortex domains can all be observed in the YMnO{sub 3} crystals, proving that the structural phase transition is not the only driving force for the occurrence of the annular and vortex domains. Furthermore, the absence of the annular and vortex domains in YMn{sub 0.9}Fe{sub 0.1}O{sub 3} indicates that the tilting state of MnO{sub 5} bipyramids plays an important role in the domain formation. Atomic resolution STEM images confirm that the ferroelectric domain walls correspond to structural antiphase boundaries similar to the crystals made via high temperature solid-state reactions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

MODELING MULTI-WAVELENGTH PULSE PROFILES OF THE MILLISECOND PULSAR PSR B1821–24

PSR B1821–24 is a solitary millisecond pulsar that radiates multi-wavelength pulsed photons. It has complex radio, X-ray, and γ-ray pulse profiles with distinct peak phase separations that challenge the traditional caustic emission models. Using the single-pole annular gap model with a suitable magnetic inclination angle (α = 40°) and viewing angle (ζ = 75°), we managed to reproduce its pulse profiles of three wavebands. It is found that the middle radio peak originated from the core gap region at high altitudes, and the other two radio peaks originated from the annular gap region at relatively low altitudes. Two peaks of both X-ray and γ-ray wavebands basically originated from the annular gap region, while the γ-ray emission generated from the core gap region contributes somewhat to the first γ-ray peak. Precisely reproducing the multi-wavelength pulse profiles of PSR B1821–24 enables us to understand emission regions of distinct wavebands and justify pulsar emission models.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Star formation in CALIFA survey perturbed galaxies – II. Star-formation histories and oxygen abundances

ABSTRACT Galaxy evolution is generally affected by tidal interactions. First, in this series, we reported several effects that suggest that tidal interactions contribute to the regulation of star formation (SF). To confirm this, we now compare stellar mass assembly histories and SF look-back time annular profiles between CALIFA survey tidally and non-tidally perturbed galaxies. We pair their respective star-forming regions at the closest stellar mass surface densities to reduce the influence of stellar mass. The assembly histories and annular profiles show statistically significant differences so that higher star-formation rates characterize regions in tidally perturbed galaxies. These regions underwent a more intense (re)activation of SF in the last 1 Gyr. Varying shapes of the annular profiles also reflect fluctuations between suppression and (re)activation of SF. Since gas-phase abundances used to be lower in more actively than in less actively star-forming galaxies, we further explore the plausible presence of metal-poor gas inflows able to dilute such abundances. The resolved relations of oxygen (O) abundance with stellar mass density and with total gas fraction show slightly lower O abundances for regions in tidally perturbed galaxies. The single distributions of O abundances statistically validate this. Moreover, from a metallicity model based on stellar feedback, the mass rate differentials (inflows−outflows) show statistically valid higher values for regions in tidally perturbed galaxies. These differentials, and the metal fractions from the population synthesis, suggest dominant gas inflows in these galaxies. This dominance and the differences in SF through time confirm the previously reported effects of tidal interactions on SF.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2025

Theoretical description of atomtronic Josephson junctions in an optical lattice

Experimental realizations of “atomtronic” Josephson junctions have recently been created in annular traps in relative rotation with respect to potential barriers that generate the weak links. If these devices are additionally subjected to an optical lattice potential, then they can incorporate strong-coupling Mott physics within the design, which can modify the behavior and can allow for interesting new configurations of barriers and of superfluid flow patterns. We examine theoretically the behavior of a Bose superfluid in an optical lattice in the presence of an annular trap and a barrier across the annular region which acts as a Josephson junction. As the superfluid is rotated, circulating super-currents appear. Beyond a threshold superfluid velocity, phase slips develop, which generate vortices. We use a finite temperature strong-coupling expansion about the mean-field solution of the Bose Hubbard model to calculate various properties of such devices. Additionally, we discuss some of the rich behavior that can result when there are Mott regions within the system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2025

Modal focal adaptive optics for Bessel-focus two-photon fluorescence microscopy

Adaptive optics (AO) improves the spatial resolution of microscopy by correcting optical aberrations. While its application has been well established in microscopy modalities utilizing a circular pupil, its adaptation to systems with non-circular pupils, such as Bessel-focus two-photon fluorescence microscopy (2PFM) with an annular pupil, remains relatively uncharted. Herein, we present a modal focal AO (MFAO) method for Bessel-focus 2PFM. Measuring and correcting aberration using a spatial light modulator placed in conjugation with the focal plane of the microscope objective, MFAO employs Zernike annular polynomials — a first in AO implementation — to achieve performance on par with a previous zonal AO method, but with a notably simplified optical configuration. We validated the performance of MFAO in correcting artificial and sample-induced aberrations, as well as in in vivo imaging of zebrafish larvae and mouse brains. By expanding the application of modal AO to annular pupils as well as aberration measurement and correction to a wavefront modulator at the objective focal plane, MFAO represents a notable advancement in the implementation of AO in microscopy.

47 OTHER INSTRUMENTATION↗

DOE OSTI2014

Low Frequency Modulation of Extreme Temperature Regimes in a Changing Climate

The project examines long-term changes in extreme temperature episodes (ETE) associated with planetary climate modes (PCMs) in both the real atmospheric and climate model simulations. The focus is on cold air outbreaks (CAOs) and warm waves (WWs) occurring over the continental US during the past 60 winters. No significant long-term trends in either WWs or CAOs are observed over the US. The annual frequency of CAOs is affected by the (i) North Atlantic Oscillation (NAO) over the Southeast US and (ii) Pacific–North American (PNA) pattern over the Northwest US. WW frequency is influenced by the (i) NAO over the eastern US and (ii) combined influence of PNA, Pacific decadal oscillation (PDO), and ENSO over the southern US. The collective influence of PCMs accounts for as much as 50% of the regional variability in ETE frequency. During CAO (WW) events occurring over the southeast US, there are low (high) pressure anomalies at higher atmospheric levels over the southeast US with oppositely-signed pressure anomalies in the lower atmosphere over the central US. These patterns lead to anomalous northerly (for CAOs) or southerly (for WWs) flow into the southeast leading to cold or warm surface air temperature anomalies, respectively. One distinction is that CAOs involve substantial air mass transport while WW formation is more local in nature. The primary differences among event categories are in the origin and nature of the pressure anomaly features linked to ETE onset. In some cases, PCMs help to provide a favorable environment for event onset. Heat budget analyses indicate that latitudinal transport in the lower atmosphere is the main contributor to regional cooling during CAO onset. This is partly offset by adiabatic warming associated with subsiding air. Additional diagnoses reveal that this latitudinal transport is partly due to the remote physical influence of a shallow cold pool of air trapped along the east side of the Rocky Mountains. ETE and PCM behavior is also studied in (CMIP5) climate model simulations. Although the climate models considered are able to represent the overall behavior of ETEs, the frequency of WWs (CAOs) is too high (low) in many models. While all models qualitatively replicate the overall structure of the PNA pattern, a small minority of models fails to properly simulate the NAO pattern. Model shortcomings in representing the NAO and PNA patterns have important consequences for simulating associated regional variability in surface air temperature and storm track behavior. The influence of PCMs on ETEs is underestimated in most CMIP5 models. In particular, none of the models are able to accurately simulate observed linkages between ETEs and the PDO, due to a gross misrepresentation of the PDO pattern in most models. Our results indicate that predictions of future CAO and WW behavior are currently limited by the ability of climate models to accurately represent PCM characteristics. Our study also considers the behavior of PCMs known as annular modes. It is determined that north-south movements in the stratospheric jet stream (related to the Polar Annular Mode) result in long-lasting impacts upon surface weather conditions including regional air temperature anomalies. The structure and dynamics of the stratospheric northern annular mode (or SNAM, related to changes in the strength of the stratospheric jet stream) was studied in CMIP5 models. In models with poorly-resolved stratospheres, the amplitude of SNAM at stratospheric altitudes is typically too weak, consistent with weaker stratospheric jet variability. However, this distinction does not carry over to the associated tropospheric signature of SNAM. A regional analysis illustrates that most CMIP5 models (regardless of whether the stratosphere is well-resolved) have anomalously weak and eastward shifted (compared to observed SNAM events) storm track and sea level pressure anomaly patterns during SNAM events. Analyses of stratosphere–troposphere coupling reveal that large-scale wave activity in the stratosphere is anomalously weak in CMIP5 models having poorly-resolved stratospheres, due to correspondingly weak upward propagation of wave activity from the troposphere. This suggests that such models have anomalously weak stratosphere-troposphere coupling in association with SNAM events. Paradoxically, however, there is little apparent impact upon the attendant tropospheric variability.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2016

Kick Detection at the Bit: Early Detection via Low Cost Monitoring

Formation fluid influxes (i.e. kicks) pose persistent challenges and operational costs during drilling operations. Implications of kicks range in scale but cumulatively result in substantial costs that affect drilling safety, environment, schedule, and infrastructure. Early kick detection presents a low-cost, easily adopted solution for avoiding well control challenges associated with kicks near the bit. Borehole geophysical tools used during the drilling process as part of the logging-while-drilling (LWD) and measurement-while-drilling (MWD) provide the advantage of offering real-time downhole data. LWD/MWD collect data on both the annulus and borehole wall. The annular data are normally treated as background, and are filtered out to isolate the formation measurements. Because kicks will change the local physical properties of annular fluids, bottom-hole measurements are among the first indicators that a formation fluid has invaded the wellbore. This report describes and validates a technique for using the annular portion of LWD/MWD data to facilitate early kick detection using first order principles. The detection technique leverages data from standard and cost-effective technologies that are typically implemented during well drilling, such as MWD/LWD data in combination with mud-pulse telemetry for data transmission.

42 ENGINEERING↗

NASA NTRS1972

Fluid flow analysis of a hot-core hypersonic wind-tunnel nozzle concept

A hypersonic-wind-tunnel nozzle concept which incorporates a hot-core flow surrounded by an annular flow of cold air offers a promising technique for maximizing the model size while minimizing the power required to heat the test core. This capability becomes especially important when providing the true-temperature duplication needed for hypersonic propulsion testing. Several two-dimensional wind-tunnel nozzle configurations that are designed according to this concept are analyzed by using recently developed analytical techniques for prediction of the boundary-layer growth and the mixing between the hot and cold coaxial supersonic airflows. The analyses indicate that introduction of the cold annular flow near the throat results in an unacceptable test core for the nozzle size and stagnation conditions considered because of both mixing and condensation effects. Use of a half-nozzle with a ramp on the flat portion does not appear promising because of the thick boundary layer associated with the extra length. However, the analyses indicate that if the cold annular flow is introduced at the exit of a full two-dimensional nozzle, an acceptable test core will be produced. Predictions of the mixing between the hot and cold supersonic streams for this configuration show that mixing effects from the cold flow do not appreciably penetrate into the hot core for the large downstream distances of interest.

Anders, J. B.↗