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NASA NTRS2020

Streak Instabilities on HIFiRE-5 Elliptic Cone

The Hypersonic International Flight Research and Experimentation (HIFiRE) 5 flight experiment by the Air Force Research Laboratories and Australian Defense Science and Technology Organization yielded inflight, hypersonic transition data for a canonical, 3D configuration in the form of an elliptic cone at various combinations of angle-of-attack and yaw. Previous analysis has shown that boundary-layer stability calculations for the as-flown, zero-yaw flight conditions are able to capture the second mode dominated transition along the attachment line as well as the crossflow induced transition in between the attachment line and the minor axis symmetry plane. However, there is still a need to understand the transition in the vicinity of the minor axis plane of symmetry, where the boundary layer thickness exhibits an azimuthally compact bulge due to the collision of the secondary flow approaching from the attachment lines on both sides. This paper reports a computational analysis of the stability of the boundary layer flow along the bulge regions on both the leeward and windward sides of the vehicle surface. At a representative flight condition corresponding to a time instant of t = 514.813 seconds, computations are performed to identify several different unstable modes within the bulge regions, with the eventual goal of developing a linear stability correlation for the transition onset near the minor axis symmetry plane. The most amplified flow instabilities in the pretransitional region correspond to a “stem” mode that is concentrated within a pair of nearly vertical shear layers below the cap of the mushroom shaped bulge in the mean velocity contours. An excellent agreement is found between the predictions of instability amplification based on the plane marching parabolized stability equations (PSE) and the direct numerical solutions (DNS). Given the large number of unstable modes within the bulge region, the observed agreement demonstrates, for first time, that the PSE can provide accurate predictions for the development of flow instabilities in streak-like flow features over three-dimensional bodies. The peak N-factor of approximately 15 at the transition location estimated from the thermocouple measurements along the leeward centerline is close to the transition N-factor for Mack mode transition during the HIFiRE-1 circular cone flight experiment with nearly zero degrees angle of attack.

Meelan Choudhari↗

NASA NTRS1978

Turbulent boundary layers with large streamline curvature effects

It has been shown that turbulent flows are greatly affected by streamline curvature. In spite of this and the fact that curved shear flows are frequently encountered in engineering applications, the predictions of such flows are relatively less developed than the predictions of two-dimensional plane flows. Recently, various attempts were made by different investigators; however, their methods are only successful when the product of the boundary layer thickness to the local surface curvature is approximately 0.05. The present paper investigates the more general case where this product is in the range from 0.1 to 0.5. Results show that the calculated boundary-layer characteristics for arbitrary free stream conditions are in good agreement with measurements.

So, R. M. C.↗

NASA NTRS1980

The lunar magma ocean - A transient lunar phenomenon

The time required for the solidification of a lunar magma ocean is considered. In the absence of a thermal boundary crust, heat loss is by radiation and the ocean will solidify in a few decades. However, only a few millimeters of crust would effectively limit radiation. The current investigation has the objective to present estimates of conduction boundary (crust) thickness based on several models of the mechanism of crustal formation. Three different models for estimating conduction boundary layer thickness are discussed. They are based on the formation of a chill margin, a plagioclase flotation layer, and a layer which is continually destroyed by meteorite impacts and regrows by conductive heat loss. Based on these models, the maximum solidification time for a 200 km thick ocean is about 100 million years. A more probable solidification time based on a plagioclase flotation crust model is about 60 million years.

Minear, J. W.↗

NASA NTRS1972

Experimental evaluation of the aerodynamic damping of skin panels at low supersonic Mach numbers.

The aerodynamic damping of the first three vibration modes of a rectangular panel exposed to an attached turbulent boundary layer has been measured over the Mach number range of 1.10 to 1.40. Data showing that aerodynamic damping is a strong function of Mach number, dynamic pressure, mode shape, and boundary layer thickness are presented. At low supersonic Mach numbers, aerodynamic damping was found to be 20 to 100 times as large as common values of structural damping. Means of calculating aerodynamic damping, including effects of the boundary layer profile, are discussed. Calculated aerodynamic damping is compared with experimental data.

Muhlstein, L., Jr.↗

NASA NTRS1989

Experimental measurements of large scale structures in an incompressible turbulent boundary layer using correlated X-probes

Hot-wire anemometry measurements in an incompressible turbulent boundary-layer flow over a flat plate, at zero pressure gradient were made using two X-probes simultaneously. The over seven meters long flat plate installed within the wind tunnel generated an approximately 20-cm thick boundary layer, and R(theta) of about 4,000. The mean velocity and turbulence intensity data very close to the wall were measured with a single-wire. Space-time velocity fluctuation and shear-product correlation measurements enabled the calculation of large-scale structure convection velocity, inclination-angle to the wall, and spatial extent in space. The shear-product correlation results are reported for the first time.

Strataridakis, Constantine J.↗

NASA NTRS2018

Evaluation of Inflow Turbulence Methods in Large-Eddy Simulations of a Supersonic Boundary Layer

In the context of Large- Eddy Simulations (LES), Boundary-layer inflow turbulence is simulated using both the Synthetic Eddy Model (SEM) and Digital Filtering (DF). The effects of the projection error are investigated. The effect of the prescribed length scales on the adjustment region was found to be negligible for length scales less than one-tenth of the boundary-layer thickness. While it was conjectured that one method of the two might be more robust than the other, our results show that both the Digital Filtering Method and the Synthetic Eddy Method accurately replicate the boundary layer while successfully accounting for inflow turbulence.

Synthetic Eddy↗

NASA NTRS1985

Corrections for attached sidewall boundary-layer effects in 2-dimensional airfoil testing

The problems of sidewall boundary-layer effects in airfoil testing is treated by considering the changes in the flow area due to boundary-layer thinning under the influence of the airfoil flowfield. Using von Karman's momentum integral equation, it is shown that the sidewall boundary-layer thickness in the region of the airfoil can reduce to about half the undisturbed value under the conditions prevailing in testing of supercritical airfoils. A Mach number correction due to this increased width of the flow passage is proposed. Using the small disturbance approximation, the effect of the sidewall boundary-layers is shown to be equivalent to a change in the test Mach number and also in the airfoil thickness. Comparison of the results of this approach with other similarity rules and correlation of the experimental data demonstrate the applicability of the analysis presented from low speeds to transonic speeds.

Murthy, A. V.↗

NASA NTRS2003

Evaluation of Flush-Mounted, S-Duct Inlets With Large Amounts of Boundary Layer Ingestion

A new high Reynolds number test capability for boundary layer ingesting inlets has been developed for the NASA Langley Research Center 0.3-Meter Transonic Cryogenic Tunnel. Using this new capability, an experimental investigation of four S-duct inlet configurations with large amounts of boundary layer ingestion (nominal boundary layer thickness of about 40% of inlet height) was conducted at realistic operating conditions (high subsonic Mach numbers and full-scale Reynolds numbers). The objectives of this investigation were to 1) develop a new high Reynolds number, boundary-layer ingesting inlet test capability, 2) evaluate the performance of several boundary layer ingesting S-duct inlets, 3) provide a database for CFD tool validation, and 4) provide a baseline inlet for future inlet flow-control studies. Tests were conducted at Mach numbers from 0.25 to 0.83, Reynolds numbers (based on duct exit diameter) from 5.1 million to a fullscale value of 13.9 million, and inlet mass-flow ratios from 0.39 to 1.58 depending on Mach number. Results of this investigation indicate that inlet pressure recovery generally decreased and inlet distortion generally increased with increasing Mach number. Except at low Mach numbers, increasing inlet mass-flow increased pressure recovery and increased distortion. Increasing the amount of boundary layer ingestion (by decreasing inlet throat height and increasing inlet throat width) or ingesting a boundary layer with a distorted profile decreased pressure recovery and increased distortion. Finally, increasing Reynolds number had almost no effect on inlet distortion but increased inlet recovery by about one-half percent at a Mach number near cruise.

Berrier, Bobby L.↗

NASA NTRS2003

Evaluation of Flush-Mounted, S-Duct Inlets with Large Amounts of Boundary Layer Ingestion

A new high Reynolds number test capability for boundary layer ingesting inlets has been developed for the NASA Langley Research Center 0.3-Meter Transonic Cryogenic Tunnel. Using this new capability, an experimental investigation of four S-duct inlet configurations with large amounts of boundary layer ingestion (nominal boundary layer thickness of about 40% of inlet height) was conducted at realistic operating conditions (high subsonic Mach numbers and full-scale Reynolds numbers). The objectives of this investigation were to 1) provide a database for CFD tool validation on boundary layer ingesting inlets operating at realistic conditions and 2) provide a baseline inlet for future inlet flow-control studies. Tests were conducted at Mach numbers from 0.25 to 0.83, Reynolds numbers (based on duct exit diameter) from 5.1 million to a full-scale value of 13.9 million, and inlet mass-flow ratios from 0.39 to 1.58 depending on Mach number. Results of this investigation indicate that inlet pressure recovery generally decreased and inlet distortion generally increased with increasing Mach number. Except at low Mach numbers, increasing inlet mass-flow increased pressure recovery and increased distortion. Increasing the amount of boundary layer ingestion (by decreasing inlet throat height) or ingesting a boundary layer with a distorted (adverse) profile decreased pressure recovery and increased distortion. Finally, increasing Reynolds number had almost no effect on inlet distortion but increased inlet recovery by about one-half percent at a Mach number near cruise.

Berrier, Bobby L.↗

NASA NTRS1979

Decay of the zincate concentration gradient at an alkaline zinc cathode after charging

The transport of the zincate ion to the alkaline zinc cathode was studied by observing the decay of the zincate concentration gradient at a horizontal zinc cathode after charging. This decay was found to approximate first order kinetics as expected from a proposed boundary layer model. The concentrations were calculated from polarization voltages. The decay half life was shown to be a linear function of the thickness of porous zinc deposit on the cathode indicating a very rapid transport of zincate through porous zinc metal. The rapid transport is attributed to an electrochemical mechanism. From the linear dependence of the half life on the thickness the boundary layer thickness was found to be about 0.010 cm when the cathode was at the bottom of the cell. No significant dependence of the boundary layer thickness on the viscosity of electrolyte was observed. The data also indicated a relatively sharp transition between the diffusion and convection transport regions. When the cathode was at the top of the cell, the boundary layer thickness was found to be roughly 0.080 cm. The diffusion of zincate ion through asbestos submerged in alkaline electrolyte was shown to be comparable with that predicted from the bulk diffusion coefficient of the zincate ion in alkali.

Kautz, H. E.↗

NASA NTRS1975

Measurement of density and temperature in a hypersonic turbulent boundary layer using the electron beam fluorescence technique

Mean density and temperature fluctuations were measured across the turbulent, cooled-wall boundary layer in a continuous hypersonic (Mach 9.4) wind tunnel in air, using the nitrogen fluorescence excited by a 50 kV electron beam. Data were taken at three values of the tunnel stagnation pressure, the corresponding free stream densities being equivalent to 1.2, 4.0, and 7.4 torr at room temperature, and the boundary layer thicknesses about 4.0, 4.5, and 6.0 inches. The mean temperature and density profiles were similar to those previously determined in the same facility by conventional probes (static and pitot pressure, total temperature). A static pressure variation of about 50% across the boundary layer was found, the shape of the variation changing somewhat for the three stagnation pressure levels. The quadrupole model for rotational temperature spectra gave closer agreement with the free stream isentropic level (approximately 44 K) than the dipole model.

Mcronald, A. D.↗

NASA NTRS1984

Boundary layer simulator improvement

High chamber pressure expander cycles proposed for orbit transfer vehicles depend primarily on the heat energy transmitted from the combustion products through the thrust wall chamber wall. The heat transfer to the nozzle wall is affected by such variables as wall roughness, relamarization, and the presence of particles in the flow. Motor performance loss for these nozzles with thick boundary layers is inaccurate using the existing procedure coded BLIMPJ. Modifications and innovations to the code are examined. Updated routines are listed.

Praharaj, S. C.↗

NASA NTRSDate not supplied

BOLT II Roughness-Side Flight Results

An initial review of the roughness data from the BOLT II flight is provided. The BOLT II roughness experiment was designed to investigate discrete trips in flight based on the diamond configuration, which has been shown to be an efficient vortex generator and boundary layer trip from extensive ground-based testing. There were three trip locations chosen for the flight test and their size (height and width) were tailored to the local boundary layer thickness, but all three were expected to trip at the same time or flight condition. Details about the flight vehicle design, instrumentation, and best estimated trajectory are discussed. The present paper is limited to only a review and analysis of the thermocouple data. Boundary layer transition onset times are derived from the thermocouple analysis, thus allowing an initial assessment of the performance of these discrete trips. Since the three trips were sized to trip the boundary layer at the same time, based on a previous wind tunnel study, the present analysis indicates that they performed as expected.

Hypersonic↗

NASA NTRS2004

Simulation of Flow Through Breach in Leading Edge at Mach 24

A baseline solution for CFD Point 1 (Mach 24) in the STS-107 accident investigation was modified to include effects of holes through the leading edge into a vented cavity. The simulations were generated relatively quickly and early in the investigation by making simplifications to the leading edge cavity geometry. These simplifications in the breach simulations enabled: 1) A very quick grid generation procedure; 2) High fidelity corroboration of jet physics with internal surface impingements ensuing from a breach through the leading edge, fully coupled to the external shock layer flow at flight conditions. These simulations provided early evidence that the flow through a 2 inch diameter (or larger) breach enters the cavity with significant retention of external flow directionality. A normal jet directed into the cavity was not an appropriate model for these conditions at CFD Point 1 (Mach 24). The breach diameters were of the same order or larger than the local, external boundary-layer thickness. High impingement heating and pressures on the downstream lip of the breach were computed. It is likely that hole shape would evolve as a slot cut in the direction of the external streamlines. In the case of the 6 inch diameter breach the boundary layer is fully ingested.

Gnoffo, Peter A.↗

NASA NTRS2003

Effects of Wing Leading Edge Penetration with Venting and Exhaust Flow from Wheel Well at Mach 24 in Flight

A baseline solution for CFD Point 1 (Mach 24) in the STS-107 accident investigation was modified to include effects of: (1) holes through the leading edge into a vented cavity; and (2) a scarfed, conical nozzle directed toward the centerline of the vehicle from the forward, inboard corner of the landing gear door. The simulations were generated relatively quickly and early in the investigation because simplifications were made to the leading edge cavity geometry and an existing utility to merge scarfed nozzle grid domains with structured baseline external domains was implemented. These simplifications in the breach simulations enabled: (1) a very quick grid generation procedure; and (2) high fidelity corroboration of jet physics with internal surface impingements ensuing from a breach through the leading edge, fully coupled to the external shock layer flow at flight conditions. These simulations provided early evidence that the flow through a two-inch diameter (or larger) breach enters the cavity with significant retention of external flow directionality. A normal jet directed into the cavity was not an appropriate model for these conditions at CFD Point 1 (Mach 24). The breach diameters were of the same order or larger than the local, external boundary-layer thickness. High impingement heating and pressures on the downstream lip of the breach were computed. It is likely that hole shape would evolve as a slot cut in the direction of the external streamlines. In the case of the six-inch diameter breach the boundary layer is fully ingested. The intent of externally directed jet simulations in the second scenario was to approximately model aerodynamic effects of a relatively large internal wing pressure, fueled by combusting aluminum, which deforms the corner of the landing gear door and directs a jet across the windside surface. These jet interactions, in and of themselves, were not sufficiently large to explain observed aerodynamic behavior.

Gnoffo, Peter A.↗

NASA NTRS2019

The Effect of Incoming Boundary Layer Characteristics on the Performance of a Distributed Propulsion System

An experimental study is conducted in an effort to advance the understanding of flow physics associated with a boundary layer ingesting, distributed propulsion system. The influence of incoming boundary layer thickness and flow distortions are studied on the flow downstream and the overall performance of the system. The propulsion model, fabricated using additive manufacturing and integrated with electrical fans, is mounted on a flat plate and tested at subsonic speeds. Detailed characterization of the incoming boundary layer and subsequent assessment of the downstream flow field is performed using hotwire anemometry. Modification of the incoming boundary layer is achieved by placing tripping devices, such as rods and vortex generating ramps, near the leading edge of the flat plate. The overall performance of the system for different incoming flow conditions is analyzed by comparing magnitudes of exhaust velocities as well as estimated propulsive power to the corresponding baseline values. For a constant input power to the fans, smaller upstream flow distortions and moderately thickened boundary layers result in marginal changes in the flow field downstream. On the other hand, notable reductions in downstream flow velocities and propulsive power are observed in the case of a significantly thicker and/or distorted incoming boundary layer. It is hoped that this study will serve as a database for this technologically relevant flow field that has not been explored adequately before.

Propulsion↗

NASA NTRS2017

Development of a Flow Field for Testing a Boundary-Layer-Ingesting Propulsor

The test section of the 8- by 6-Foot Supersonic Wind Tunnel at NASA Glenn Research Center was modified to produce the test conditions for a boundary-layer-ingesting propulsor. A test was conducted to measure the flow properties in the modified test section before the propulsor was installed. Measured boundary layer and freestream conditions were compared to results from computational fluid dynamics simulations of the external surface for the reference vehicle. Testing showed that the desired freestream conditions and boundary layer thickness could be achieved; however, some non-uniformity of the freestream conditions, particularly the total temperature, were observed.

embedded propulsion↗

NASA NTRS1993

Response of the topography and gravity field on Venus to mantle upwelling beneath a chemical boundary layer

The long wavelength correlation of the gravity and topography and the large apparent depths of compensation (approximately 150-300 km) for large highland regions on Venus require significant differences between the interior structure of Earth and Venus. The morphology, geologic history, and large apparent depths of compensation for many highlands have been interpreted to indicate areas of mantle upwelling. A large apparent depth of compensation at a mantle upwelling is generally interpreted to indicate the base of the thermal boundary layer of convection. A boundary layer thickness of 150-300 km implies that the interior of Venus is presently much colder than Earth and thus tectonically less active. The recent Magellan mission has provided contradictory evidence regarding the present level of tectonic activity on Venus, prompting considerable debate. In this study, we investigate the possibility that a chemical boundary layer acts together with a thermal boundary layer to produce large apparent depths of compensation, or equivalently, large geoid-to-topography-ratios (GTR's). The crust of a planet forms through partial melting of mantle materials. Both the melt and the residuum are lower in density than unmelted (or undepleted) mantle. In the absence of vigorous plate tectonics, a thick layer of buoyant residuum, or depleted mantle, may collect beneath the lithosphere. In this scenario, the thermal lithosphere does not need to be thick and cold to match the GTR's. Cooling of the depleted layer may lead to overturn of the upper mantle and episodic resurfacing with time scales on the order of 300-500 MY, consistent with the resurfacing age of Venus.

Smrekar, Suzanne E.↗