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Results for “Stability and transition”

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.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Nonuniform concentration - A mechanism for drag reduction.

A large reduction in drag coefficient has been observed in certain external flows of aqueous solutions with high molecular weight polymer additives. A change in the near wake configuration is phenomenologically responsible for the drag reduction, but the underlying mechanism is presently unknown. An analogy to known phenomena in particulate suspensions is drawn which suggests nonuniform concentration of the polymer additive as an explanation. An analysis of the boundary layer on a sphere with varying viscosity was made to investigate the effect. The results indicate early transition to turbulence for concentration variations whose length scale is small compared with the momentum boundary layer thickness. Stabilization and delayed transition are indicated for thicker concentration layers. Observations are suggested for the thin concentration layers.

Rivard, W. C.↗
NASA NTRS2011

Assessing Uncertainties in Boundary Layer Transition Predictions for HIFiRE-1 at Non-zero Angles of Attack

Boundary layer stability was analyzed for the HIFiRE-1 flight vehicle geometry for ground tests conducted at the CUBRC LENS I hypersonic shock test facility and the Langley Research Center (LaRC) 20- inch Mach 6 Tunnel. Boundary layer stability results were compared to transition onset location obtained from discrete heat transfer measurements from thin film gauges during the CUBRC test and spatially continuous heat transfer measurements from thermal phosphor paint data during the LaRC test. The focus of this analysis was on conditions at non-zero angles of attack as stability analysis has already been performed at zero degrees angle of attack. Also, the transition onset data obtained during flight testing was at nonzero angles of attack, so this analysis could be expanded in the future to include the results of the flight test data. Stability analysis was performed using the 2D parabolized stability software suite STABL (Stability and Transition Analysis for Hypersonic Boundary Layers) developed at the University of Minnesota and the mean flow solutions were computed using the DPLR finite volume Navier-Stokes computational fluid dynamics (CFD) solver. A center line slice of the 3D mean flow solution was used for the stability analysis to incorporate the angle of attack effects while still taking advantage of the 2D STABL software suite. The N-factors at transition onset and the value of Re(sub theta)/M(sub e), commonly used to predict boundary layer transition onset, were compared for all conditions analyzed. Ground test data was analyzed at Mach 7.2 and Mach 6.0 and angles of attack of 1deg, 3deg and 5deg. At these conditions, the flow was found to be second mode dominant for the HIFiRE-1 slender cone geometry. On the leeward side of the vehicle, a strong trend of transition onset location with angle of attack was observed as the boundary layer on the leeward side of the vehicle developed inflection points at streamwise positions on the vehicle that correlated to angle of attack. Inflection points are a strong instability mechanism that lead to rapid breakdown and transition to turbulence. The transition onset location on the windward side of the vehicle displayed no trend with angle of attack or freestream Reynolds number and transition was observed farther down the vehicle than observed on the leeward side of the vehicle. In analysis of both windward and leeward sides of the vehicle, use of the N factor methodology to develop trends to predict boundary layer transition onset showed improvements over the Re(sub theta)/M(sub e) empirical correlation methodology. Stronger correlations and less scatter in the data were observed when using the N factor method for these cases.

Marek, Lindsay C.↗
NASA NTRS1988

Transition prediction in external flows via linear stability theory

Linear stability theory results are presented for flight and low-disturbance wind tunnels, at low and high speeds, and for T-S, Gortler, and cross-flow modes. Results show that, in the absence of Morkovin 'bypasses', transition at low background disturbance levels corresponds to N-factors of the order of 9 to 11, provided that phenomena such as curvature effects are included. The results point to a wider range of applicability for the e exp N method than previously conjectured, and suggest that the e exp N method can be used to parametrize transition predictions as a function of parameters which affect the mean flow profiles for such purposes as LFC and minimum drag design.

Bushnell, D. M.↗
NASA NTRS1982

The condensational instability in the solar transition region and corona

The stability of plasmas at temperatures and densities typical of the solar transition region and corona is investigated using both a linear analysis and nonlinear time-dependent numerical simulations. Growth rates, decay rates, and oscillation frequencies of the perturbations determined from the linear analysis are in excellent agreement with the simulations. The nonlinear regime is characterized by a bifurcation of the plasma into a cool dense condensation surrounded by a hot tenuous corona. The condensation may then be accelerated by forces in the plasma such as those arising from gravity or differential heating. Finally, the results of the detailed simulation show that the transition region is a dynamically stable structure which is the result of the nonlinear evolution of the condensational instability.

Oran, E. S.↗
NASA NTRS1987

Lanthanide-containing polyimides

The preparation of a variety of lanthanide-containing polyimide films is described, and results of their characterization are presented. The properties investigated include the glass transition temperature, thermooxidative stability, magnetic susceptibility, and electrical conductivity of the polymer. Films containing lanthanide chlorides, fluorides, and sulfides are flexible, but those containing lanthanide nitrates are extremely brittle. The addition of lanthanide acetates and acetylacetonates caused immediate gelation of two of the synthesis-mixture ingredients. It was found that, in general, the addition of lanthanide to the polyimide increases the density and glass transition temperature of the polymer but slightly decreases the thermooxidative stability.

Stoakley, D. M.↗
NASA NTRS1991

A numerical investigation of supersonic nozzle boundary layer transition

The boundary layer stability within the high-area-ratio nozzle at NASA Lewis was tested at five chamber pressure conditions. For all nozzle conditions examined, Taylor-Goertler vortices grew more rapidly than Tollmien-Schlichting waves. The experimental heat flux was accurately predicted by a laminar boundary layer computation, thereby confirming the laminar nature of the nozzle boundary layer flow. When the chamber pressure was increased in a series of cases, the transition point occurred farther upstream. The number of vortices contained in the dominant instability increased with chamber pressure.

Pauley, Laura L.↗
NASA NTRSDate not supplied

Eigenvalue Sensitivity Computations for Linear Stability Theory

To realize the drag reduction benefit of boundary-layer transition control strategies, it is crucial to integrate transition prediction into the vehicle design through an optimization process. The integration of transition prediction based on linear stability analysis into adjoint d design optimization requires coupling an adjoint enabled computational fluid dynamics (CFD) solver with an adjoint enabled linear stability code. In particular, the boundary-layer transition location is often predicted using the N-factor method based on linear stability theory (LST). Thus, sensitivity of the linear-stability eigenvalues constitute an essential building block for optimizing the laminar flow performance. The present paper describes an implementation of LST eigenvalue sensitivity analysis that can be easily coupled with a CFD solver. Specifically, we describe a discrete adjoint formulation for the transition location prediction based on the N-factor method. The verification of this formulation is carried out by comparing the adjoint-based sensitivity of the local growth rate of a given instability mode with respect to the disturbance frequency, and the adjoint-based sensitivity of the transition location with respect to spanwise wavenumber with those sensitivities computed using a finite-difference approximation. Finally, the adjoint LST formulation is applied to flat-plate boundary-layer flows at transonic, supersonic, and hypersonic conditions, to determine the behavior and sensitivities of the transition location with respect to a range of disturbance spanwise wavenumbers.

Boundary Layer Transition↗
NASA NTRS1992

Validation of three-dimensional incompressible spatial direct numerical simulation code: A comparison with linear stability and parabolic stability equation theories for boundary-layer transition on a flat plate

Spatially evolving instabilities in a boundary layer on a flat plate are computed by direct numerical simulation (DNS) of the incompressible Navier-Stokes equations. In a truncated physical domain, a nonstaggered mesh is used for the grid. A Chebyshev-collocation method is used normal to the wall; finite difference and compact difference methods are used in the streamwise direction; and a Fourier series is used in the spanwise direction. For time stepping, implicit Crank-Nicolson and explicit Runge-Kutta schemes are used to the time-splitting method. The influence-matrix technique is used to solve the pressure equation. At the outflow boundary, the buffer-domain technique is used to prevent convective wave reflection or upstream propagation of information from the boundary. Results of the DNS are compared with those from both linear stability theory (LST) and parabolized stability equation (PSE) theory. Computed disturbance amplitudes and phases are in very good agreement with those of LST (for small inflow disturbance amplitudes). A measure of the sensitivity of the inflow condition is demonstrated with both LST and PSE theory used to approximate inflows. Although the DNS numerics are very different than those of PSE theory, the results are in good agreement. A small discrepancy in the results that does occur is likely a result of the variation in PSE boundary condition treatment in the far field. Finally, a small-amplitude wave triad is forced at the inflow, and simulation results are compared with those of LST. Again, very good agreement is found between DNS and LST results for the 3-D simulations, the implication being that the disturbance amplitudes are sufficiently small that nonlinear interactions are negligible.

Joslin, Ronald D.↗
NASA NTRS1961

Operational Technique for Transition of Several Types of V/Stol Aircraft

Flight test experience has been obtained with five test bed aircraft which employed widely differing principles of V/STOL operation. speeds these aircraft were supported by wing lift and in the hovering condition they were supported by engine-produced thrust. used to transfer the lift from the wing to the engine are examined. primary items considered in the transition region are longitudinal trim changes, stability , stalled flow during descending transitions, and the flexibility of the transition procedure of each type of aircraft.

Drinkwater, Fred J., III↗
NASA NTRSDate not supplied

Transition Prediction for the 30P30N Airfoil and the CRM-HL using FUN3D

The ability to accurately model transition over high-lift configurations can lead to improved agreement between stationary Reynolds-Averaged Navier-Stokes (RANS) computations and experimental measurements. In this work, selected transport-equation-based RANS models for transition prediction in the NASA FUN3D flow solver are used to simulate flow over the 30P30N three-element airfoil and the High-Lift Common Research Model (CRM-HL). The primary RANS-based transition model is the Langtry-Menter (LM) 𝜸-Re𝜽𝒕 model coupled with the Menter shear-stress transport model. Additionally, the existing capability for transition prediction based on linear stability correlations is used to allow the modeling of transition over multiple elements of the 30P30N configuration. This approach pairs an algebraic transition model with the Spalart-Allmaras (SA) turbulence model that relies on an imposed transition location in FUN3D and the parabolized stability equations as implemented in the LASTRAC code. Predictions based on these different transition prediction approaches and models are compared with each other, experimental data, and previous simulations by evaluating the lift and drag coefficients, the surface-pressure/skin-friction distributions, and the locations of transition onset. Results are presented for multiple angles of attack for the 30P30N airfoil and CRM-HL. For the CRM-HL, a grid resolution study is performed for the LM transition model and the SA turbulence model.

High Lift↗
NASA NTRS1987

Wind-tunnel investigation of a full-scale general aviation airplane equipped with an advanced natural laminar flow wing

An investigation was conducted in the Langley 30- by 60-Foot Wind Tunnel to evaluate the performance, stability, and control characteristics of a full-scale general aviation airplane equipped with an advanced laminar flow wing. The study focused on the effects of natural laminar flow and advanced boundary layer transition on performance, stability, and control, and also on the effects of several wing leading edge modifications on the stall/departure resistance of the configuration. Data were measured over an angle-of-attack range from -6 to 40 deg and an angle-of-sideslip range from -6 to 20 deg. The Reynolds number was varied from 1.4 to 2.4 x 10 to the 6th power based on the mean aerodynamic chord. Additional measurements were made using hot-film and sublimating chemical techniques to determine the condition of the wing boundary layer, and wool tufts were used to study the wing stall characteristics. The investigation showed that large regions of natural laminar flow existed on the wing which would significantly enhance cruise performance. Also, because of the characteristics of the airfoil section, artificially tripping the wing boundary layer to a turbulent condition did not significantly effect the lift, stability, and control characteristics. The addition of a leading-edge droop arrangement was found to increase the stall angle of attack at the wingtips and, therefore, was considered to be effective in improving the stall/departure resistance of the configuration. Also the addition of the droop arrangement resulted in only minor increases in drag.

Murri, Daniel G.↗
NASA NTRS1985

Flap-Lag-Torsion Stability in Forward Flight

An aeroelastic stability of three-degree flap-lag-torsion blade in forward flight is examined. Quasisteady aerodynamics with a dynamic inflow model is used. The nonlinear time dependent periodic blade response is calculated using an iterative procedure based on Floquet theory. The periodic perturbation equations are solved for stability using Floquet transition matrix theory as well as constant coefficient approximation in the fixed reference frame. Results are presented for both stiff-inplane and soft-inplane blade configurations. The effects of several parameters on blade stability are examined, including structural coupling, pitch-flap and pitch-lag coupling, torsion stiffness, steady inflow distribution, dynamic inflow, blade response solution and constant coefficient approximation.

Panda, B.↗
NASA NTRS1983

Vortices, stability, and turbulence

The transition process between laminar flow to turbulent flow is discussed in terms of a third state of fluid motion, vortical motion that is approximately periodic in space and/or time and displays symmetrical properties. The possibility that the transition from laminar to turbulent flow is accompanied by intermediate vortical states, with turbulence being an instability of the vortical states, is examined, with consideration given to the hypothesis that the turbulent state retains a memory of the vortex structures. Solutions are sought for the Navier-Stokes equations for a viscous liquid in a channel. Instances of inviscid vortical states and the presence of a three-dimensional instability are studied, demonstrating that transition phenomena can be explained qualitatively in terms of vortical state characteristics.

Saffman, P. G.↗
NASA NTRS1984

Boundary-layer linear stability theory

Most fluid flows are turbulent rather than laminar and the reason for this was studied. One of the earliest explanations was that laminar flow is unstable, and the linear instability theory was first developed to explore this possibility. A series of early papers by Rayleigh produced many notable results concerning the instability of inviscid flows, such as the discovery of inflectional instability. Viscosity was commonly thought to act only to stabilize the flow, and flows with convex velocity profiles appeared to be stable. The investigations that led to a viscous theory of boundary layer instability was reported. The earliest application of linear stability theory to transition prediction calculated the amplitude ratio of the most amplified frequency as a function of Reynolds number for a Blasius boundary layer, and found that this quantity had values between five and nine at the observed Ret. The experiment of Schubauer and Skramstad (1947) completely reversed the prevailing option and fully vindicated the Gottingen proponents of the theory. This experiment demonstrated the existence of instability waves in a boundary layer, their connection with transition, and the quantitative description of their behavior by the theory of Tollmien and Schlichting. It is generally accepted that flow parameters such as pressure gradient, suction and heat transfer qualitatively affect transition in the manner predicted by the linear theory, and in particular that a flow predicted to be stable by the theory should remain laminar. The linear theory, in the form of the e9, or N-factor is today in routine use in engineering studies of laminar flow. The stability theory to boundary layers with pressure gradients and suction was applied. The only large body of numerical results for exact boundary layer solutions before the advent of the computer age by calculating the stability characteristics of the Falkner-Skan family of velocity profiles are given. When the digital computer reached a stage of development which permit the direct solution of the primary differential equations, numerical results were obtained from the linear theory during the next 10 years for many different boundary layer flows: three dimensional boundary layers; free convention boundary layers; compressible boundary layers; boundary layers on compliant walls; a recomputation of Falkner-Skan flows; unsteady boundary layers; and heated wall boundary layers.

Leslie M Mack↗
NASA NTRS1987

Application of stability theory to laminar flow control - Progress and requirements

Paper briefly summarizes the current status of linear stability theory as applied to laminar flow control for aerodynamics. Results indicate that the conventional 'N factor' method of correlating stability theory and transition has a broad application range, including low- and high-speeds, two- and three-dimensional mean flow and TS, Gortler and crossflow disturbance modes. Linear theory is particularly applicable to the laminar flow control problem as, for system efficiency, control must be exercised and disturbances maintained in the linear regime. Current areas of concern for LFC, which require further stability theory research, include TS-crossflow interaction, combined disturbance fields (roughness, waviness, noise) and suction-induced disturbances. Some results on wave-interactions are presented.

Bushnell, D. M.↗
NASA NTRS1984

Quantum chemical studies of a model for peptide bond formation. 3. Role of magnesium cation in formation of amide and water from ammonia and glycine

The SN2 reaction between glycine and ammonia molecules with magnesium cation Mg2+ as a catalyst has been studied as a model reaction for Mg(2+)-catalyzed peptide bond formation using the ab initio Hartree-Fock molecular orbital method. As in previous studies of the uncatalyzed and amine-catalyzed reactions between glycine and ammonia, two reaction mechanisms have been examined, i.e., a two-step and a concerted reaction. The stationary points of each reaction including intermediate and transition states have been identified and free energies calculated for all geometry-optimized reaction species to determine the thermodynamics and kinetics of each reaction. Substantial decreases in free energies of activation were found for both reaction mechanisms in the Mg(2+)-catalyzed amide bond formation compared with those in the uncatalyzed and amine-catalyzed amide bond formation. The catalytic effect of the Mg2+ cation is to stabilize both the transition states and intermediate, and it is attributed to the neutralization of the developing negative charge on the electrophile and formation of a conformationally flexible nonplanar five-membered chelate ring structure.

Magnesium/chemistry↗
NASA NTRS1991

Evaluation of the longitudinal stability and control characteristics of a mixed-flow remote-lift STOVL aircraft in transition and hover

An evaluation of the longitudinal stability and control characteristics of a mixed-flow remote-lift (MFRL) STOVL aircraft in the powered-lift portion of the flight envelope is presented. A stabilization and command augmentation system was implemented on the MFRL aircraft to meet the requirements for satisfactory flying qualities. The pitch portion of this control system uses a state-rate feedback implicit model following controller to achieve the desired flying qualities and to suppress the effects of external variations and disturbances in the aircrafts characteristics over the low speed envelope.

Engelland, Shawn A.↗