Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “boundary layer”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,711 records · Page 95
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Wall pressure spectra calculations for equilibrium boundary layers

Calculation of the flow direction wave-number spectrum of pressure fluctuations on the wall under a turbulent boundary layer. Particular attention is paid to finding the spectral density of the wall pressure fluctuations as a function of the streamwise wave number. For this purpose a five-dimensional integration is employed in which the equilibrium boundary layers are assumed to have velocity profiles given by the law of the wall plus Cole's wake function.

Panton, R. L.↗
NASA NTRS1974

Interference heating from interactions of shock waves with turbulent boundary layers at Mach 6

An experimental investigation of interference heating resulting from interactions of shock waves and turbulent boundary layers was conducted. Pressure and heat-transfer distributions were measured on a flat plate in the free stream and on the wall of the test section of the Langley Mach 6 high Reynolds number tunnel for Reynolds numbers ranging from 2 million to 400 million. Various incident shock strengths were obtained by varying a wedge-shock generator angle (from 10 deg to 15 deg) and by placing a spherical-shock generator at different vertical positions above the instrumented flat plate and tunnel wall. The largest heating-rate amplification factors obtained for completely turbulent boundary layers were 22.1 for the flat plate and 11.6 for the tunnel wall experiments. Maximum heating correlated with peak pressures using a power law with a 0.85 exponent. Measured pressure distributions were compared with those calculated using turbulent free-interaction pressure rise theories, and separation lengths were compared with values calculated by using different methods.

Johnson, C. B.↗
NASA NTRS1988

An arrayed hot-film sensor for detection of laminar boundary-layer flow disturbance spatial characteristics

An arrayed hot-film sensor has been developed for use in laminar boundary-layer research for the detection of crossflow or Goertler vortices. This sensor has been developed to detect spatial variations in heat transfer which are characteristic of crossflow or Goertler vortices. The sensor is ultimately intended for flight research applications. This paper describes the sensor, its priciples of operation, signal analysis techniques, and experimental results illustrating the spatial detection capabilities of this specialized hot-film device. Discretely placed spheres placed in the boundary layer created alternating regions of undisturbed and disturbed laminar flow over a prototype sensor. Flow visualization results were correlated with the sensor output to demonstrate the ability of the sensor to determine the spatial boundaries of localized disturbances in laminar flow. This work represents the initial steps toward the validation and calibration of an arrayed hot-film sensor for the detection of crossflow or Goertler vorticity wavelength and/or wave frequency.

Wusk, M. S.↗
NASA NTRS1991

Nonlinear disturbances in a hypersonic laminar boundary layer

Three separate but similar experiments on the growth of naturally-occurring instability waves in the laminar boundary-layers on sharp cones at hypersonic Mach numbers have been conducted. Each provided clear evidence that the theoretically-predicted second mode of instability was responsible for high-amplitude wave trains observed to prevail upstream of boundary-layer transition to turbulence. However, each also seemed to reveal the presence of an additional instability not accounted for by the linear theory. Here, examination is made of the tape-recorded hot-wire anemometer signals of one experiment on a sharp cone at Mach 8 for evidence of nonlinearity, the finding of which would explain the presence of the additional mode as a consequence of harmonic generation. Several approaches for identification of the residual effects of nonlinearity are described and utilized. Also, a simplified model describing certain fluctuation characteristics has been developed. Altogether, the evidence of nonlinear wave development is found to be strong. Quantitative comparisons of linear theory to experiments must be made with caution when nonlinearity is present in the experiment.

Kimmel, Roger L.↗
NASA NTRS1986

Coherent structures in a turbulent boundary layer. I - Generation of 'artificial' bursts

In an effort to better understand the physics and structure of coherent events in a turbulent boundary layer, an attempt is made to produce 'artificial' bursts. These are generated in a turbulent boundary layer developed on a flat plate towed in an 18 m water channel and thus with negligible freestream turbulence. The burstlike events are produced by either withdrawing near-wall fluid from two minute holes separated in the spanwise direction or by pitching a miniature delta wing that is flush-mounted to the wall. Either of these two actions generates a hairpinlike vortex and low-speed streak that resemble naturally occurring structures. The resulting sequence of events that occur at a given location can be uniquely controlled, thus allowing detailed examination via phase-locked measurements and flow visualization. In this paper, the proof of concept of artificial burst generation is established by comparing the artificial events with natural, random bursts using flow visualization and hot-film signals.

Gad-El-hak, M.↗
NASA NTRS1985

ISEE particle observations of surface waves at the magnetopause boundary layer

The dual-spacecraft ISEE mission provides a unique opportunity to study the motions of the magnetopause and adjacent boundary layer. By comparing high-time-resolution energetic particle data from ISEE 1 to those of ISEE 2, the velocity and orientation of the inner boundary of the boundary layer can be determined. Two cases are presented. In one, tailward propagating sinusoidally shaped surface waves with a wavelength in excess of 42,000 km and an amplitude of approximately 5000 km are found. In the other, surface waves are indicated with a wavelength of approximately 40,000 km and an amplitude of approximately 11,000 km having steepened nonsinusoidal shapes. The existence of such large-amplitude waves suggests that the particle dynamics near the magnetopause support nonlinear processes.

Couzens, D.↗
NASA NTRS1986

On the instability of a three-dimensional attachment-line boundary layer - Weakly nonlinear theory and a numerical approach

The instability of a three-dimensional attachment-line boundary layer is considered in the nonlinear regime. Using weakly nonlinear theory, it is found that, apart from a small interval near the (linear) critical Reynolds number, finite-amplitude solutions bifurcate subcritically from the upper branch of the neutral curve. The time-dependent Navier-Stokes equations for the attachment-line flow have been solved using a Fourier-Chebyshev spectral method and the subcritical instability is found at wavenumbers that correspond to the upper branch. Both the theory and the numerical calculations show the existence of supercritical finite-amplitude (equilibrium) states near the lower branch which explains why the observed flow exhibits a preference for the lower branch modes. The effect of blowing and suction on nonlinear stability of the attachment-line boundary layer is also investigated.

Hall, P.↗
NASA NTRS1956

The Compressible Laminar Boundary Layer with Heat Transfer and Arbitrary Pressure Gradient

An approximate method for the calculation of the compressible laminar boundary layer with heat transfer and arbitrary pressure gradient, based on Thwaites' correlation concept, is presented. With the definition of dimensionless shear and heat-transfer parameters and an assumed correlation of these parameters in terms of a momentum parameter, a complete system of relations for calculating skin friction and heat transfer results. Knowledge of velocity or temperature profiles is not necessary in using this calculation method. When the method is applied to a convergent-divergent, axially symmetric rocket nozzle, it shows that high rates of heat transfer are obtained at the initial stagnation point and at the throat of the nozzle. Also indicated are negative displacement thicknesses in the convergent portion of the nozzle; these occur because of the high density within the lower portions of the cooled boundary layer. (author)

Cohen, Clarence B↗
DOE OSTI2025

Best estimate of the planetary boundary layer height from multiple remote sensing measurements

Remote sensing measurements have been widely used to estimate the planetary boundary layer height (PBLHT). Each remote sensing approach offers unique strengths and faces different limitations. In this study, we use machine learning (ML) methods to produce a best-estimate PBLHT (PBLHT-BE-ML) by integrating four PBLHT estimates derived from remote sensing measurements at the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) observatory. Three ML models – random forest (RF) classifier, RF regressor, and light gradient-boosting machine (LightGBM) – were trained on a dataset from 2017 to 2023 that included radiosonde, various remote sensing PBLHT estimates, and atmospheric meteorological conditions. Evaluations indicated that PBLHT-BE-ML from all three models improved alignment with the PBLHT derived from radiosonde data (PBLHT-SONDE), with LightGBM demonstrating the highest accuracy under both stable and unstable boundary layer conditions. Feature analysis revealed that the most influential input features at the SGP site were the PBLHT estimates derived from (a) potential temperature profiles retrieved using Raman lidar (RL) and atmospheric emitted radiance interferometer (AERI) measurements (PBLHT-THERMO), (b) vertical velocity variance profiles from Doppler lidar (PBLHT-DL), and (c) aerosol backscatter profiles from micropulse lidar (PBLHT-MPL). The trained models were then used to predict PBLHT-BE-ML at a temporal resolution of 10 min, effectively capturing the diurnal evolution of PBLHT and its significant seasonal variations, with the largest diurnal variation observed over summer at the SGP site. We applied these trained models to data from the ARM Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) field campaign (EPC), where the PBLHT-BE-ML, particularly with the LightGBM model, demonstrated improved accuracy against PBLHT-SONDE. Analyses of model performance at both the SGP and EPC sites suggest that expanding the training dataset to include various surface types, such as ocean and ice-covered areas, could further enhance ML model performance for PBLHT estimation across varied geographic regions.

Zhang, Damao [Pacific Northwest National Laborator↗
NASA NTRS2011

Receptivity to Roughness, Acoustic, and Vortical Disturbances in Supersonic Boundary Layers Over Swept Wings

The receptivity and interaction of stationary and traveling crossflow instability of three-dimensional supersonic boundary layers over a swept biconvex wing with a blunt leading edge are numerically investigated for a freestream Mach number of 3. The steady and unsteady flow fields are obtained by solving the full Navier-Stokes equations. The receptivity of the boundary layer to surface roughness, freestream acoustic waves, and freestream vorticity waves are numerically investigated. The initial amplitudes of the stationary vortices generated by 1 micron roughness elements is about 2000 times larger than the initial amplitudes of the traveling disturbances generated by vortical disturbances. The interaction of stationary and traveling disturbances was investigated by solving the equations with both surface roughness and vortical disturbances. When the initial amplitudes of the stationary disturbances are large compared to the traveling disturbances, the stationary vortex dominates the perturbation field. When the amplitudes are comparable, the traveling vortex prevails and the stationary vortex is suppressed.

Balakumar, Ponnampalam↗
NASA NTRS2016

Optimal Growth in Hypersonic Boundary Layers

The linear form of the parabolized linear stability equations is used in a variational approach to extend the previous body of results for the optimal, nonmodal disturbance growth in boundary-layer flows. This paper investigates the optimal growth characteristics in the hypersonic Mach number regime without any high-enthalpy effects. The influence of wall cooling is studied, with particular emphasis on the role of the initial disturbance location and the value of the spanwise wave number that leads to the maximum energy growth up to a specified location. Unlike previous predictions that used a basic state obtained from a self-similar solution to the boundary-layer equations, mean flow solutions based on the full Navier-Stokes equations are used in select cases to help account for the viscous- inviscid interaction near the leading edge of the plate and for the weak shock wave emanating from that region. Using the full Navier-Stokes mean flow is shown to result in further reduction with Mach number in the magnitude of optimal growth relative to the predictions based on the self-similar approximation to the base flow.

Navier Stokes equations↗
NASA NTRS1989

A nonlinear investigation of the stationary modes of instability of the three-dimensional compressible boundary layer due to a rotating disc

The effects of compressibility on a stationary mode of instability of the 3-D boundary layer due to a rotating disc are investigated. The aim is to determine whether this mode will be important in the finite amplitude destabilization of the boundary layer. This stationary mode is characterized by the effective velocity profile having zero shear stress at the wall. Triple-deck solutions are presented for an adiabatic wall and an isothermal wall. It is found that this stationary mode is only possible over a finite range of Mach numbers. Asymptotic solutions are obtained which describe the structure of the wavenumber and the orientation of these modes as functions of the local Mach number. The effects of nonlinearity are investigated allowing the finite amplitude growth of a disturbance close to the neutral location to be described.

Seddougui, Sharon O.↗
NASA NTRS1993

Aerothermodynamic heating due to shock wave/laminar boundary-layer interactions in high-enthalpy hypersonic flow

The interaction between a swept shock wave and a laminar boundary layer was investigated experimentally in high-enthalpy hypersonic flow. The effect of high-temperature, real gas physics on the interaction was examined by conducting tests in air and helium. Heat transfer measurements were made on the surface of a flat plate and a shock-generating fin using thin-film resistance sensors for fin incidence angles of 0, 5, and 10 deg at Mach numbers of 6.9 in air and 7.2 in helium. The experiments were conducted in the NASA HYPULSE expansion tube, an impulse-type facility capable of generating high-enthalpy, high-velocity flow with freestream levels of dissociated species that are particularly low. The measurements indicate that the swept shock wave creates high local heat transfer levels in the interaction region, with the highest heating found in the strongest interaction. The maximum measured heating rates in the interaction are order of magnitude greater than laminar flat plate boundary layer heating levels at the same location.

Hackett, Charles M.↗
NASA NTRS1973

Local skin friction coefficients and boundary layer profiles obtained in flight from the XB-70-1 airplane at Mach numbers up to 2.5

Boundary-layer and local friction data for Mach numbers up to 2.5 and Reynolds numbers up to 3.6 x 10 to the 8th power were obtained in flight at three locations on the XB-70-1 airplane: the lower forward fuselage centerline (nose), the upper rear fuselage centerline, and the upper surface of the right wing. Local skin friction coefficients were derived at each location by using (1) a skin friction force balance, (2) a Preston probe, and (3) an adaptation of Clauser's method which derives skin friction from the rake velocity profile. These three techniques provided consistent results that agreed well with the von Karman-Schoenherr relationship for flow conditions that are quasi-two-dimensional. At the lower angles of attack, the nose-boom and flow-direction vanes are believed to have caused the momentum thickness at the nose to be larger than at the higher angles of attack. The boundary-layer data and local skin friction coefficients are tabulated. The wind-tunnel-model surface-pressure distribution ahead of the three locations and the flight surface-pressure distribution ahead of the wing location are included.

Fisher, D. F.↗
NASA NTRS1986

Unsteady separated boundary layer in a transonic diffuser flow with self-excited oscillations

A numerical investigation of two-dimensional unsteady boundary layer in a transonic diffuser flow with self-excited oscillations and strong flow separation by solving the compressible, Reynolds-averaged, thin-layer Navier-Stokes equations with two-equations turbulence model is described. Three different meshes with constant streamwise mesh distribution and varying vertical mesh distribution were used. Results obtained indicate that a refinement of mesh studied here has minimal effect on the mean boundary layer flow but significantly increases the amplitude of oscillation of all flow variables. Comparisons of unsteady wall pressure, velocity profile, terminal shock, and separation pocket among computations and with experiment are presented.

Hsieh, T.↗