SEARCH · Engineering Papers

Results for “Boundary Layer Stability”

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.

SourceResearch connectionFrom yearThrough year

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

At least 217 records · Page 12

All sources NASA NTRS DOE OSTI

NASA NTRS1987

Linear stability analysis of three-dimensional compressible boundary layers

A compressible stability analysis computer code is developed. The code uses a matrix finite-difference method for local eigenvale solution when a good guess for the eigenvalue is available and is significantly more computationally efficient than the commonly used inital-value approach. The local eigenvalue search procedure also results in eigenfunctions and, at little extra work, group velocities. A globally convergent eigenvalue procedure is also developed that may be used when no guess for the eigenvalue is available. The global problem is formulated in such a way that no unstable spurious modes appear so that the method is suitable for use in a black-box stability code. Sample stability calculations are presented for the boundary layer profiles of an LFC swept wing.

Malik, Mujeeb R.↗

NASA NTRS1950

On stability of free laminar boundary layer between parallel streams

An analysis and calculations on the stability of the free laminar boundary layer between parallel streams were made for an incompressible fluid using the Tollmien-Schlichting theory of small disturbances. Because the boundary conditions are at infinity, two solutions of the Orr-Sommerfeld stability equations need not be considered, and the remaining two solutions are exponential in character at the infinite boundaries. The calculations show that the flow is unstable except for very low Reynolds numbers.

Lessen, Martin↗

NASA NTRS2004

LASTRAC.3d: Transition Prediction in 3D Boundary Layers

Langley Stability and Transition Analysis Code (LASTRAC) is a general-purpose, physics-based transition prediction code released by NASA for laminar flow control studies and transition research. This paper describes the LASTRAC extension to general three-dimensional (3D) boundary layers such as finite swept wings, cones, or bodies at an angle of attack. The stability problem is formulated by using a body-fitted nonorthogonal curvilinear coordinate system constructed on the body surface. The nonorthogonal coordinate system offers a variety of marching paths and spanwise waveforms. In the extreme case of an infinite swept wing boundary layer, marching with a nonorthogonal coordinate produces identical solutions to those obtained with an orthogonal coordinate system using the earlier release of LASTRAC. Several methods to formulate the 3D parabolized stability equations (PSE) are discussed. A surface-marching procedure akin to that for 3D boundary layer equations may be used to solve the 3D parabolized disturbance equations. On the other hand, the local line-marching PSE method, formulated as an easy extension from its 2D counterpart and capable of handling the spanwise mean flow and disturbance variation, offers an alternative. A linear stability theory or parabolized stability equations based N-factor analysis carried out along the streamline direction with a fixed wavelength and downstream-varying spanwise direction constitutes an efficient engineering approach to study instability wave evolution in a 3D boundary layer. The surface-marching PSE method enables a consistent treatment of the disturbance evolution along both streamwise and spanwise directions but requires more stringent initial conditions. Both PSE methods and the traditional LST approach are implemented in the LASTRAC.3d code. Several test cases for tapered or finite swept wings and cones at an angle of attack are discussed.

Chang, Chau-Lyan↗

NASA NTRS1947

The stability of the laminar boundary layer in a compressible fluid

Report is a continuation of a theoretical investigation of the stability of the laminar boundary layer in a compressible fluid. An approximate estimate for the minimum critical Reynolds number, or stability limit, is obtained in terms of the distribution of the kinematic viscosity and the product of the mean density and mean vorticity across the boundary layer. The extension of the results of the stability analysis to laminar boundary-layer gas flows with a pressure gradient in the direction of the free stream is discussed. (author)

Lees, Lester↗

NASA NTRS2017

Stabilization of Hypersonic Boundary Layers by Linear and Nonlinear Optimal Perturbations

The effect of stationary, finite-amplitude, linear and nonlinear optimal perturbations on the modal disturbance growth in a Mach 6 axisymmetric flow over a 7 deg. half-angle cone with 0:126 mm nose radius and 0:305 m length is investigated. The freestream parameters (M = 6, Re(exp 1) = 18 x 10(exp. 6) /m) are selected to match the flow conditions of a previous experiment in the VKI H3 hypersonic tunnel. Plane-marching parabolized stability equations are used in conjunction with a partial-differential equation based planar eigenvalue analysis to characterize the boundary layer instability in the presence of azimuthally periodic streaks. The streaks are observed to stabilize nominally planar Mack mode instabilities, although oblique Mack mode and first-mode disturbances are destabilized. Experimentally measured transition onset in the absence of any streaks correlates with an amplification factor of N = 6 for the planar Mack modes. For high enough streak amplitudes, the transition threshold of N = 6 is not reached by the Mack mode instabilities within the length of the cone; however, subharmonic first-mode instabilities, which are destabilized by the presence of the streaks, do reach N = 6 near the end of the cone. The highest stabilization is observed at streak amplitudes of approximately 20 percent of the freestream velocity. Because the use of initial disturbance profiles based on linear optimal growth theory may yield suboptimal control in the context of nonlinear streaks, the computational predictions are extended to nonlinear optimal growth theory. Results show that by using nonlinearly optimal perturbation leads to slightly enhanced stabilization of plane Mack mode disturbances as well as reduced destabilization of subharmonic first-mode disturbances.

Incompressible boundary layer↗

NASA NTRS1989

Stability of compressible boundary layers over a smooth backward-facing step

An investigation is conducted into the determination of the credibility of interacting boundary layers in predicting compressible subsonic flows over smooth surface imperfections. The case of smooth backward-facing steps is considered. The predicted mean flows are compared with those obtained using a Navier-Stokes solver. Moreover, the linear 2-D compressible stability characteristics of both mean flows are compared. The results show that the interacting boundary-layer formulation produces accurate mean flows that yield accurate linear stability characteristics, such as growth rates and amplification factors.

Ragab, S. A.↗

NASA NTRS1990

Stability of compressible boundary layers over a smooth backward-facing step

Ragab, S. A.↗

NASA NTRS1974

On the application of linear stability theory to the problem of supersonic boundary-layer transition

Linear stability theory is used to calculate the amplitude ratio of constant-frequency disturbances as a function of Reynolds number for insulated and cooled-wall flat-plate boundary layers between Mach numbers 1.3 and 5.8. The growth curves are used to examine the consequences of using a fixed amplitude of the most unstable frequency as a transition criterion. The effect of free-stream Mach number on insulated-wall boundary layers is calculated, assuming that the initial disturbance level is constant, is proportional to the square of the free-stream Mach number and to the square root of the energy density of the one-dimensional power spectra of free-stream disturbances measured in supersonic wind tunnels.

Mack, L. M.↗

NASA NTRS1980

On the stability of three-dimensional compressible nonparallel boundary layers

A compressible linear stability theory is presented for three-dimensional nonuniform boundary layers. The amplitude, phase, and wavenumber equations which govern the motion of the disturbance are obtained by using the method of multiple scales. Group velocity trajectories are used to identify the disturbance growth direction. The spatial stability theory is applied to the flow on a laminar flow control supercritical sweptback wing of infinite span. Three different methods are used to calculate the absolute maximum logarithmic amplitude ratio N. In the front crossflow instability region, the method of maximum spatial growth rate predicts large difference in N compared with the method of fixed wavelength and the method of fixed spanwise component of wavelength. This difference decreases in the middle streamwise instability region, and almost vanishes in the rear crossflow instability region. Compressibility of the medium reduces N by about 15% in both the front and rear regions, and by about 40% in the middle region of the wing. Nonuniformity of the medium has large effects specially in the rear region.

El-Hady, N. M.↗

NASA NTRS1979

Stability of three-dimensional boundary layers

A theory is presented for the three-dimensional stability of boundary layers. Equations are derived for the evolution of a disturbance having a given frequency and originating at a given curve. These equations are used to determine the rays along which the disturbance energy propagates. It is shown that the results can be obtained by using the saddle-point method, or kinematic wave theory, or the method of multiple scales. Extension of the theory to the case of a wave packet is also presented.

Nayfeh, A. H.↗

NASA NTRS1980

Neutral stability calculations for boundary-layer flows

An analysis is presented of the parallel neutral stability of three-dimensional incompressible, isothermal boundary-layer flows. A Taylor-series expansion of the dispersion relation is used to derive the general eigenvalues. These equations are functions of the complex group velocity. These relations are verified by numerical results obtained for two- and three-dimensional disturbances in two- and three-dimensional flows.

Nayfeh, A. H.↗

NASA NTRS2019

A New Method to Retrieve the Diurnal Variability of Planetary Boundary Layer Height from Lidar Under Different Thermodynamic Stability Conditions

The planetary boundary layer height (PBLH) is an important parameter for understanding the accumulation of pollutants and the dynamics of the lower atmosphere. Lidar has been used for tracking the evolution of PBLH by using aerosol backscatter as a tracer, assuming aerosol is generally well-mixed in the PBL; however, the validity of this assumption actually varies with atmospheric stability. This is demonstrated here for stable boundary layers (SBL), neutral boundary layers (NBL), and convective boundary layers (CBL) using an 8-year dataset of micropulse lidar (MPL) and radiosonde (RS) measurements at the ARM Southern Great Plains, and MPL at the GSFC site. Due to weak thermal convection and complex aerosol stratification, traditional gradient and wavelet methods can have difficulty capturing the diurnal PBLH variations in the morning and forenoon, as well as under stable conditions generally. A new method is developed that combines lidar-measured aerosol backscatter with a stability dependent model of PBLH temporal variation (DTDS). The latter helps “recalibrate” the PBLH in the presence of a residual aerosol layer that does not change in harmony with PBL diurnal variation. The hybrid method offers significantly improved PBLH detection, with better correlation and smaller biases, under most thermodynamic conditions, especially for SBL and CBL. Relying on the physical process of PBL diurnal development, different schemes are developed for growing, maintenance, and decaying periods. Comprehensive evaluation of this new method shows much better tracking of diurnal PBLH variation and significantly smaller biases under various pollution levels.

Tianning Su↗

NASA NTRS1992

Instability and transition in three-dimensional supersonic boundary layers

Linear stability of three-dimensional flow past a 5 deg semi-vertex sharp cone at 2 deg incidence in Mach 3.5 free-stream is studied. Computed laminar mean flow profiles along the leeward line of symmetry are highly inflectional and, hence, much more unstable than the profiles along the windward line of symmetry. Accordingly, transition occurs much earlier along the leeward line both in the present calculations (based upon eN approach) and in the experiments of King (1991) performed in NASA Langley 'quiet' tunnel. Boundary-layer transition in the region between the two symmetry lines is influenced by the crossflow generated due to the angle of attack and, as a consequence, it progressively moves upstream with increasing azimuthal angle measured from the windward line. The computed transition front is qualitatively similar to the experimental results, although some differences remain.

Malik, M. R.↗

NASA NTRS1988

Numerical experiments on the stability of controlled boundary layers

Nonlinear simulations are presented for instability and transition in parallel water boundary layers subjected to pressure gradient, suction, or heating control. In the nonlinear regime, finite amplitude, 2-D Tollmein-Schlichting waves grow faster than is predicted by linear theory. Moreover, this discrepancy is greatest in the case of heating control. Likewise, heating control is found to be the least effective in delaying secondary instabilities of both the fundamental and subharmonic type. Flow field details (including temperature profiles) are presented for both the uncontrolled boundary layer and the heated boundary layer.

Zang, Thomas A.↗

NASA NTRS1991