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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Observations of the magnetospheric boundary layers

Results on magnetospheric boundary layers are reviewed, emphasizing their dynamical importance based on hot plasma observations, energetic particle signatures, heavy ion contributions and the effects of wave-particle interactions. Satellite plasma observations show that 1% to 2% of the oncoming solar wind plasma enters the magnetosphere and is initially transported within the magnetospheric boundary layer. Some of this boundary layer plasma is entrained within the Earth's magnetotail where it can be accelerated. Tests are needed to determine the relative contributions of the primary acceleration processes whose effects are especially evident in the plasma sheet boundary layer.

Eastman, T. E.↗
NASA NTRS2012

RACORO Extended-Term Aircraft Observations of Boundary-Layer Clouds

Small boundary-layer clouds are ubiquitous over many parts of the globe and strongly influence the Earths radiative energy balance. However, our understanding of these clouds is insufficient to solve pressing scientific problems. For example, cloud feedback represents the largest uncertainty amongst all climate feedbacks in general circulation models (GCM). Several issues complicate understanding boundary-layer clouds and simulating them in GCMs. The high spatial variability of boundary-layer clouds poses an enormous computational challenge, since their horizontal dimensions and internal variability occur at spatial scales much finer than the computational grids used in GCMs. Aerosol-cloud interactions further complicate boundary-layer cloud measurement and simulation. Additionally, aerosols influence processes such as precipitation and cloud lifetime. An added complication is that at small scales (order meters to 10s of meters) distinguishing cloud from aerosol is increasingly difficult, due to the effects of aerosol humidification, cloud fragments and photon scattering between clouds.

boundary layer↗
NASA NTRS2018

Structure and Variability of the Martian Ion Composition Boundary Layer

A complex boundary layer with a variety of charged particle and electromagnetic field signatures, including a transition between plasma predominantly of solar wind origin and plasma of planetary origin, lies between the Martian bow shock and the ionosphere. In this paper, we develop and utilize algorithms to autonomously identify and characterize this ion composition boundary (ICB), using data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. We find an asymmetric ICB with a larger average thickness, lower altitude, and lower velocity shear in the hemisphere where the solar wind motional electric field points outward, as a result of the asymmetry of the mass loading process. The ICB thickness scales with the magnetosheath proton gyroradius at the top of the boundary layer but does not clearly vary with external drivers. The ICB location varies with solar wind ram pressure and crustal magnetic field strength, but does not clearly respond to solar wind Mach number or extreme ultraviolet irradiance. The ICB represents a distinct boundary for ion density and flow speed, but the magnetic field strength and direction typically do not vary significantly across the ICB. The plasma density and flow speed at the ICB vary seasonally, likely in response to variations in the neutral exosphere and/or atmosphere. However, the ICB on average remains at or below the altitude where pressure balance is achieved between the piled up magnetic field (MPB) and the solar wind ram pressure, regardless of season or crustal magnetic field strength.

Electromagnetic↗
NASA NTRS1986

Boundary layer transition

The boundary layer stability, its active control by sound and surface heating and the effect of curvature are studied numerically and experimentally for subsonic flow. In addition, the experimental and flight test data are correlated using the stability theory for supersonic Mach numbers. Active transition fixing and feedback control of boundary layer by sound interactions are experimentally investigated at low speed over an airfoil. Numerical simulation of active control by surface heating and cooling in air shows that by appropriate phase adjustment a reduction in the level of perturbation can be obtained. This simulation is based on the solution of two-dimensional compressible Navier-Stokes equations for a flat plate. Goertler vortices are studied experimentally on an airfoil in the Low Turbulence Pressure Tunnel (LTPT). The flow pattern was visualized using the sublimating chemical technique and data were obtained using a three component laser velocimeter. The effect of curvature on swept leading-edge stability on a cylinder was numerically studied. The results suggest that transition is dominated by traveling disturbance waves and that the waves with the greatest total amplification has an amplitude ratio of e sup 11. Experimental data from the quiet supersonic tunnel and flight tests are analyzed using linear compressible stability theory.

Maestrello, L.↗
NASA NTRS2013

Aeromechanics Analysis of a Boundary Layer Ingesting Fan

Boundary layer ingesting propulsion systems have the potential to significantly reduce fuel burn but these systems must overcome the challe nges related to aeromechanics-fan flutter stability and forced response dynamic stresses. High-fidelity computational analysis of the fan a eromechanics is integral to the ongoing effort to design a boundary layer ingesting inlet and fan for fabrication and wind-tunnel test. A t hree-dimensional, time-accurate, Reynolds-averaged Navier Stokes computational fluid dynamics code is used to study aerothermodynamic and a eromechanical behavior of the fan in response to both clean and distorted inflows. The computational aeromechanics analyses performed in th is study show an intermediate design iteration of the fan to be flutter-free at the design conditions analyzed with both clean and distorte d in-flows. Dynamic stresses from forced response have been calculated for the design rotational speed. Additional work is ongoing to expan d the analyses to off-design conditions, and for on-resonance conditions.

Bakhle, Milind A.↗
NASA NTRSDate not supplied

USM3D-ME Analyses Performed in Support of a Wind Tunnel Test of a Boundary-Layer Ingestion Configuration

Boundary Layer Ingestion (BLI) has been proposed as a technology with the potential to decrease fuel burn. However, one major concern for BLI configurations is the potential degradation of the flow quality, both on the airframe and at the fan face, resulting from the tightly integrated propulsor. A wind tunnel test was performed in the National Transonic Facility (NTF) at the NASA Langley Research Center to investigate the flow quality ingested by a tail cone thruster configuration, similar to the Single Aisle Turboelectric Aircraft Concept with Aft Boundary Layer Ingestion (STARC-ABL). The wind tunnel model was a modified version of the Common Research Model (CRM) to include an aft-mounted, flow-through propulsor. The experimental data obtained from the wind tunnel test provide insight into the flow and enables an assessment of the accuracy of the USM3D-ME flow solver for predicting the flow at the fan face, which will be crucial for fan design purposes. Both grid refinement and turbulence model studies were performed for the Clean and Cruise MFP configurations at the condition corresponding to ReMAC = 5 million, Mach = 0.8, and alpha = 2 deg. The selected grid refinement level and turbulence model were then used to perform simulations over the range of conditions considered in the NTF wind tunnel test. The condition sweep comparisons illustrate favorable agreement with the experimental data over the entire range of conditions and for all Mass Flow Plug (MFP) configurations. The largest differences were observed for the Idle MFP configuration, with approximately 3% difference observed between USM3D-ME and the experimental data. Future work should investigate the impact of higher fidelity turbulence models and grid adaptation on the USM3D-ME predictions.

CRM↗
NASA NTRSDate not supplied

USM3D-ME Analyses Performed in Support of a Wind Tunnel Test of a Boundary-Layer Ingestion Configuration

Boundary Layer Ingestion (BLI) has been proposed as a technology with the potential to decrease fuel burn. However, one major concern for BLI configurations is the potential degradation of the flow quality, both on the airframe and at the fan face, resulting from the tightly integrated propulsor. A wind tunnel test was performed in the National Transonic Facility (NTF) at the NASA Langley Research Center to investigate the flow quality ingested by a tail cone thruster configuration, similar to the Single Aisle Turboelectric Aircraft Concept with Aft Boundary Layer Ingestion (STARC-ABL). The wind tunnel model was a modified version of the Common Research Model (CRM) to include an aft-mounted, flow-through propulsor. The experimental data obtained from the wind tunnel test provide insight into the flow and enables an assessment of the accuracy of the USM3D-ME flow solver for predicting the flow at the fan face, which will be crucial for fan design purposes. Both grid refinement and turbulence model studies were performed for the Clean and Cruise MFP configurations at the condition corresponding to ReMAC = 5 million, Mach = 0.8, and alpha = 2 deg. The selected grid refinement level and turbulence model were then used to perform simulations over the range of conditions considered in the NTF wind tunnel test. The condition sweep comparisons illustrate favorable agreement with the experimental data over the entire range of conditions and for all Mass Flow Plug (MFP) configurations. The largest differences were observed for the Idle MFP configuration, with approximately 3% difference observed between USM3D-ME and the experimental data. Future work should investigate the impact of higher fidelity turbulence models and grid adaptation on the USM3D-ME predictions.

CRM↗
NASA NTRS1975

Mean and fluctuating flow measurements of a fully-developed, non-adiabatic, hypersonic boundary layer

Extensive boundary-layer measurements have been made on a cone-ogive-cylinder model at a free-stream Mach number of 7.0 and momentum-thickness Reynolds number of 8500. Mean flow transformations and calculated turbulence correlations are presented which are in good agreement with previous incompressible results. New quantitative turbulence measurements including measurements of the first higher moment and probability density of fluctuations in mass flow and total temperature in hypersonic flow are also presented. The higher moment and probability density data show that the characters of the fluctuation modes of the mass flow and total temperature are significantly different in the wall region and in the outer part of the boundary layer. These differences together with data on the turbulence scale and lifetime obtained from autocorrelation and space-time correlation measurements are discussed.

Owen, F. K.↗
NASA NTRS2004

Active Flow Control on a Boundary-Layer-Ingesting Inlet

Boundary layer ingestion (BLI) is explored as means to improve overall system performance for Blended Wing Body configuration. The benefits of BLI for vehicle system performance benefit are assessed with a process derived from first principles suitable for highly-integrated propulsion systems. This performance evaluation process provides framework within which to assess the benefits of an integrated BLI inlet and lays the groundwork for higher-fidelity systems studies. The results of the system study show that BLI provides a significant improvement in vehicle performance if the inlet distortion can be controlled, thus encouraging the pursuit of active flow control (AFC) as a BLI enabling technology. The effectiveness of active flow control in reducing engine inlet distortion was assessed using a 6% scale model of a 30% BLI offset, diffusing inlet. The experiment was conducted in the NASA Langley Basic Aerodynamics Research Tunnel with a model inlet designed specifically for this type of testing. High mass flow pulsing actuators provided the active flow control. Measurements were made of the onset boundary layer, the duct surface static pressures, and the mass flow through the duct and the actuators. The distortion was determined by 120 total pressure measurements located at the aerodynamic interface plane. The test matrix was limited to a maximum freestream Mach number of 0.15 with scaled mass flows through the inlet for that condition. The data show that the pulsed actuation can reduce distortion from 29% to 4.6% as measured by the circumferential distortion descriptor DC60 using less than 1% of inlet mass flow. Closed loop control of the actuation was also demonstrated using a sidewall surface static pressure as the response sensor.

Gorton, Susan Althoff↗
NASA NTRS1988

Analysis of wind-tunnel boundary-layer transition experiments on axisymmetric bodies at transonic speeds using compressible boundary-layer stability theory

The design of laminar flow fuselages and advanced swept wings at high-subsonic compressible speeds can benefit from a correlation of compressible transition experiments with the e exp n transition-prediction method. A computational analysis has been conducted to investigate the detailed transition measurements obtained by Boltz et al. (1956, 1960) for two bodies-of-revolution. Nonadiabatic wall conditions were included in the analysis when wall-temperature measurements were available.

Vijgen, P. M. H. W.↗
NASA NTRS1992

Turbulent spectra, fluxes, stability and growth of the mixed layer in the boundary layer of Mars

Spectra of wind and temperature from high frequency measurements in the atmospheric surface layer of Mars are presented for the first time. Heat and momentum fluxes, and stability are calculated for early spring from estimates of the surface temperature and mean Viking Lander 2 temperature and wind at 44 degrees N, using similarity theory. This study provides the first estimates of (1) the height of the mixed layer, (2) spectra of wind and temperature, (3) the validity of similarity theories on Mars, and (4) bounds of effective measuring height and surface roughness. It confirms and extends the universiality of model wind spectra. Finally and more important, we provide the ability to estimate and determine the self-consistency of Martian atmospheric mixed layer fluxes, stability and heights on a diurnal and annual basis. This can be used to initialize and validate the various models, which previously could only be compared with each other or the efforts of Sutton, Leovy and Tillman: these were restricted in season and limited by the results from the surface temperature model available at that time. Analysis of additional data can better estimate z(sub 0) values directly from the measurements and provide the parameters necessary to calculate the vertical profiles of wind and temperature on a daily, seasonal and annual basis.

Tillman, James E.↗
NASA NTRS1989

Flow unsteadiness effects on boundary layers

The development of boundary layers at high subsonic speeds in the presence of either mass flux fluctuations or acoustic disturbances (the two most important parameters in the unsteadiness environment affecting the aerodynamics of a flight vehicle) was investigated. A high quality database for generating detailed information concerning free-stream flow unsteadiness effects on boundary layer growth and transition in high subsonic and transonic speeds is described. The database will be generated with a two-pronged approach: (1) from a detailed review of existing literature on research and wind tunnel calibration database, and (2) from detailed tests in the Boundary Layer Apparatus for Subsonic and Transonic flow Affected by Noise Environment (BLASTANE). Special instrumentation, including hot wire anemometry, the buried wire gage technique, and laser velocimetry were used to obtain skin friction and turbulent shear stress data along the entire boundary layer for various free stream noise levels, turbulence content, and pressure gradients. This database will be useful for improving the correction methodology of applying wind tunnel test data to flight predictions and will be helpful for making improvements in turbulence modeling laws.

Murthy, Sreedhara V.↗
NASA NTRS2005

Receptivity of Supersonic Boundary Layers to Acoustic Disturbances

Boundary layer receptivity to two-dimensional slow and fast acoustic waves is investigated by solving Navier-Stokes equations for Mach 4.5 flow over a flat plate with a finite-thickness leading edge. Higher order spatial and temporal schemes are employed to obtain the solution whereby the flat-plate leading edge region is resolved by providing a sufficiently refined grid. The results show that the instability waves are generated in the leading edge region and that the boundary-layer is much more receptive to slow acoustic waves (by almost a factor of 20) as compared to the fast waves. Hence, this leading-edge receptivity mechanism is expected to be more relevant in the transition process for high Mach number flows. The effect of acoustic wave incidence angle is also studied and it is found that the receptivity of the boundary layer on the windward side (with respect to the acoustic forcing) decreases by more than a factor of 4 when the incidence angle is increased from 0 to 45 deg. However, the receptivity coefficient for the leeward side is found to vary relatively weakly with the incidence angle. The effect of leading-edge thickness is also studied and bluntness is found to stabilize the boundary layer. The relative significance of fast acoustic waves is enhanced in the presence of bluntness.

Malik, Mujeeb R.↗
NASA NTRS1958

Evaporation, Heat Transfer, and Velocity Distribution in Two-Dimensional and Rotationally Symmetrical Laminar Boundary-Layer Flow

The fundamental boundary layer equations for the flow, temperature and concentration fields are presented. Two dimensional symmetrical and unsymmetrical and rotationally symmetrical steady boundary layer flows are treated as well as the transfer boundary layer. Approximation methods for the calculation of the transfer layer are discussed and a brief survey of an investigation into the validity of the law that the Nusselt number is proportional to the cube root of the Prandtl number is presented.

Froessling, Nils↗