Boundary layer transition studies
NASA Technical Reports Server (NTRS)
Watmuff, Jonathan H.
1995-01-01
A small-scale wind tunnel previously used for turbulent boundary layer experiments was modified for two sets of boundary layer transition studies. The first study concerns a laminar separation/turbulent reattachment. The pressure gradient and unit Reynolds number are the same as the fully turbulent flow of Spalart and Watmuff. Without the trip wire, a laminar layer asymptotes to a Falkner & Skan similarity solution in the FPG. Application of the APG causes the layer to separate and a highly turbulent and approximately 2D mean flow reattachment occurs downstream. In an effort to gain some physical insight into the flow processes a small impulsive disturbance was introduced at the C(sub p) minimum. The facility is totally automated and phase-averaged data are measured on a point-by-point basis using unprecedently large grids. The evolution of the disturbance has been tracked all the way into the reattachment region and beyond into the fully turbulent boundary layer. At first, the amplitude decays exponentially with streamwise distance in the APG region, where the layer remains attached, i.e. the layer is viscously stable. After separation, the rate of decay slows, and a point of minimum amplitude is reached where the contours of the wave packet exhibit dispersive characteristics. From this point, exponential growth of the amplitude of the disturbance is observed in the detached shear layer, i.e. the dominant instability mechanism is inviscid. A group of large-scale 3D vortex loops emerges in the vicinity of the reattachment. Remarkably, the second loop retains its identify far downstream in the turbulent boundary layer. The results provide a level of detail usually associated with CFD. Substantial modifications were made to the facility for the second study concerning disturbances generated by Suction Holes for laminar flow Control (LFC). The test section incorporates suction through interchangeable porous test surfaces. Detailed studies have been made using isolated
Modelling the transitional boundary layer
NASA Technical Reports Server (NTRS)
Narasimha, R.
1990-01-01
Recent developments in the modelling of the transition zone in the boundary layer are reviewed (the zone being defined as extending from the station where intermittency begins to depart from zero to that where it is nearly unity). The value of using a new non-dimensional spot formation rate parameter, and the importance of allowing for so-called subtransitions within the transition zone, are both stressed. Models do reasonably well in constant pressure 2-dimensional flows, but in the presence of strong pressure gradients further improvements are needed. The linear combination approach works surprisingly well in most cases, but would not be so successful in situations where a purely laminar boundary layer would separate but a transitional one would not. Intermittency-weighted eddy viscosity methods do not predict peak surface parameters well without the introduction of an overshooting transition function whose connection with the spot theory of transition is obscure. Suggestions are made for further work that now appears necessary for developing improved models of the transition zone.
Boundary Layers, Transitions and Separation
NASA Technical Reports Server (NTRS)
2010-01-01
Effects of roughness in boundary layers have to be addressed. Until adverse pressure gradient effects are understood, roughness will not significantly drive design. Mechanisms responsible for separation not understood. Effects on Zero Pressure Gradient boundary layers (shear stress). Effects on separation in pressure gradient (prediction of separation). Effect on scalar transport (heat transfer) not understood. Model for skin friction needed in simulations - first grid point likely to be in buffer layer. Definition of roughness important for useful experiments. A lot of validation experiments will be needed. How to get to ks for roughness of engineering interest? - depends on wavelength height, etc. for engineering interest? Re-discovering the wheel should be avoided: existing knowledge (theoretical and experimental) should find its way into the engineering models. It is a task of the industry to filter out the existing information in the literature for results relevant to its application, being external or internal.
Interactions in boundary-layer transition
NASA Technical Reports Server (NTRS)
Smith, Frank T.
1989-01-01
Certain theoretical studies of boundary-layer transition are described, based on high Reynolds numbers and with attention drawn to the various nonlinear interactions and scales present. The article concentrates in particular on theories for which the mean-flow profile is completely altered from its original state. Two- and three-dimensional flow theory and conjectures on turbulent-boundary-layer structures are included. Specific recent findings noted, and in qualitative agreement with experiments, are: nonlinear finite-time break-ups in unsteady interactive boundary layers; strong vortex/wave interactions; and prediction of turbulent boundary-layer displacement- and stress sublayer-thicknesses.
Nonlinear breakdowns in boundary layer transition
NASA Technical Reports Server (NTRS)
Smith, Frank T.
1990-01-01
Theoretical studies of boundary-layer transition are described, based on high Reynolds numbers and with attention drawn to nonlinear interactions, breakdowns and scales. The article notes in particular truly nonlinear theories for which the mean-flow profile is completely altered from its original state. Two- and three-dimensional flow theory and conjectures on turbulent boundary-layer structures are included. Specific recent findings noted, and in qualitative agreement with experiments, are: nonlinear finite-time break-ups in unsteady interactive boundary layers; strong vortex/wave interactions; and prediction of turbulent boundary-layer displacement- and stress sublayer-thicknesses.
Dynamic Acoustic Detection of Boundary Layer transition
NASA Technical Reports Server (NTRS)
Grohs, Jonathan R.
1995-01-01
The wind tunnel investigation into the acoustic nature of boundary layer transition using miniature microphones. This research is the groundwork for entry into the National Transonic Facility (NTF) at the NASA Langley Research Center (LaRC). Due to the extreme environmental conditions of NTF testing, low temperatures and high pressures, traditional boundary layer detection methods are not available. The emphasis of this project and further studies is acoustical sampling of a typical boundary layer and environmental durability of the miniature microphones. The research was conducted with the 14 by 22 Foot Subsonic Tunnel, concurrent with another wind tunnel test. Using the resources of LaRC, a full inquiry into the feasibility of using Knowles Electronics, Inc. EM-3086 microphones to detect the surface boundary layer, under differing conditions, was completed. This report shall discuss the difficulties encountered, product performance and observations, and future research adaptability of this method.
Boundary Layer Transition on X-43A
NASA Technical Reports Server (NTRS)
Berry, Scott; Daryabeigi, Kamran; Wurster, Kathryn; Bittner, Robert
2008-01-01
The successful Mach 7 and 10 flights of the first fully integrated scramjet propulsion systems by the Hyper-X (X-43A) program have provided the means with which to verify the original design methodologies and assumptions. As part of Hyper-X s propulsion-airframe integration, the forebody was designed to include a spanwise array of vortex generators to promote boundary layer transition ahead of the engine. Turbulence at the inlet is thought to provide the most reliable engine design and allows direct scaling of flight results to groundbased data. Pre-flight estimations of boundary layer transition, for both Mach 7 and 10 flight conditions, suggested that forebody boundary layer trips were required to ensure fully turbulent conditions upstream of the inlet. This paper presents the results of an analysis of the thermocouple measurements used to infer the dynamics of the transition process during the trajectories for both flights, on both the lower surface (to assess trip performance) and the upper surface (to assess natural transition). The approach used in the analysis of the thermocouple data is outlined, along with a discussion of the calculated local flow properties that correspond to the transition events as identified in the flight data. The present analysis has confirmed that the boundary layer trips performed as expected for both flights, providing turbulent flow ahead of the inlet during critical portions of the trajectory, while the upper surface was laminar as predicted by the pre-flight analysis.
Orbiter Boundary Layer Transition Prediction Tool Enhancements
NASA Technical Reports Server (NTRS)
Berry, Scott A.; King, Rudolph A.; Kegerise, Michael A.; Wood, William A.; McGinley, Catherine B.; Berger, Karen T.; Anderson, Brian P.
2010-01-01
Updates to an analytic tool developed for Shuttle support to predict the onset of boundary layer transition resulting from thermal protection system damage or repair are presented. The boundary layer transition tool is part of a suite of tools that analyze the local aerothermodynamic environment to enable informed disposition of damage for making recommendations to fly as is or to repair. Using mission specific trajectory information and details of each d agmea site or repair, the expected time (and thus Mach number) of transition onset is predicted to help define proper environments for use in subsequent thermal and stress analysis of the thermal protection system and structure. The boundary layer transition criteria utilized within the tool were updated based on new local boundary layer properties obtained from high fidelity computational solutions. Also, new ground-based measurements were obtained to allow for a wider parametric variation with both protuberances and cavities and then the resulting correlations were calibrated against updated flight data. The end result is to provide correlations that allow increased confidence with the resulting transition predictions. Recently, a new approach was adopted to remove conservatism in terms of sustained turbulence along the wing leading edge. Finally, some of the newer flight data are also discussed in terms of how these results reflect back on the updated correlations.
Boundary layer transition detection by luminescence imaging
NASA Technical Reports Server (NTRS)
Mclachlan, B. G.; Bell, J. H.; Gallery, J.; Gouterman, M.; Callis, J.
1993-01-01
In recent experiments we have demonstrated the feasibility of a new approach to boundary layer transition detection. This new approach employs the temperature dependence of certain photoluminescent materials in the form of a surface coating or 'paint' to detect the change in heat transfer characteristics that accompany boundary layer transition. The feasibility experiments were conducted for low subsonic to transonic Mach numbers on two-dimensional airfoil and flat plate configurations. Paint derived transition locations were determined and compared to those obtained from Preston pressure probe measurements. Artificial heating of the models was used to obtain transition temperature signatures suitable for the instrumentation available to us. Initial estimates show, however, that passive kinetic heating at high Mach numbers is a promising alternative.
Nonlinear Transient Growth and Boundary Layer Transition
NASA Technical Reports Server (NTRS)
Paredes, Pedro; Choudhari, Meelan M.; Li, Fei
2016-01-01
Parabolized stability equations (PSE) are used in a variational approach to study the optimal, non-modal disturbance growth in a Mach 3 at plate boundary layer and a Mach 6 circular cone boundary layer. As noted in previous works, the optimal initial disturbances correspond to steady counter-rotating streamwise vortices, which subsequently lead to the formation of streamwise-elongated structures, i.e., streaks, via a lift-up effect. The nonlinear evolution of the linearly optimal stationary perturbations is computed using the nonlinear plane-marching PSE for stationary perturbations. A fully implicit marching technique is used to facilitate the computation of nonlinear streaks with large amplitudes. To assess the effect of the finite-amplitude streaks on transition, the linear form of plane- marching PSE is used to investigate the instability of the boundary layer flow modified by spanwise periodic streaks. The onset of bypass transition is estimated by using an N- factor criterion based on the amplification of the streak instabilities. Results show that, for both flow configurations of interest, streaks of sufficiently large amplitude can lead to significantly earlier onset of transition than that in an unperturbed boundary layer without any streaks.
Numerical simulation of supersonic boundary layer transition
NASA Technical Reports Server (NTRS)
Guo, Y.; Adams, N. A.; Sandham, N. D.; Kleiser, L.
1994-01-01
The present contribution reviews some of the recent progress obtained at our group in the direct numerical simulation (DNS) of compressible boundary layer transition. Elements of the different simulation approaches and numerical techniques employed are surveyed. Temporal and spatial simulations, as well as comparisons with results obtained from Parabolized Stability Equations, are discussed. DNS results are given for flat plate boundary layers in the Mach number range 1.6 to 4.5. A temporal DNS at Mach 4.5 has been continued through breakdown all the way to the turbulent stage. In addition results obtained with a recently developed extended temporal DNS approach are presented, which takes into account some nonparallel effects of a growing boundary layer. Results from this approach are quite close to those of spatial DNS, while preserving the efficiency of the temporal DNS.
Boundary-layer Transition at Supersonic Speeds
NASA Technical Reports Server (NTRS)
Low, George M
1956-01-01
Recent results of the effects of Mach number, stream turbulence, leading-edge geometry, leading-edge sweep, surface temperature, surface finish, pressure gradient, and angle of attack on boundary-layer transition are summarized. Factors that delay transition are nose blunting, surface cooling, and favorable pressure gradient. Leading-edge sweep and excessive surface roughness tend to promote early transition. The effects of leading-edge blunting on two-dimensional surfaces and surface cooling can be predicted adequately by existing theories, at least in the moderate Mach number range.
Numerical simulation of boundary-layer transition
NASA Technical Reports Server (NTRS)
Spalart, P. R.
1984-01-01
The transition to turbulence in boundary layers was investigated by direct numerical solution of the nonlinear, three-dimensional, incompressible Navier-Stokes equations in the half-infinite domain over a flat plate. Periodicity was imposed in the streamwise and spanwise directions. A body force was applied to approximate the effect of a nonparallel mean flow. The numerical method was spectra, based on Fourier series and Jacobi polynomials, and used divergence-free basis functions. Extremely rapid convergence was obtained when solving the linear Orr-Sommerfeld equation. The early nonlinear and three-dimensional stages of transition, in a boundary layer disturbed by a vibrating ribbon, were successfully simulated. Excellent qualitative agreement was observed with either experiments or weakly nonlinear theories. In particular, the breakdown pattern was staggered or nonstaggered depending on the disturbance amplitude.
Sound radiation due to boundary layer transition
NASA Technical Reports Server (NTRS)
Wang, Meng
1993-01-01
This report describes progress made to date towards calculations of noise produced by the laminar-turbulence transition process in a low Mach number boundary layer formed on a rigid wall. The primary objectives of the study are to elucidate the physical mechanisms by which acoustic waves are generated, to clarify the roles of the fluctuating Reynolds stress and the viscous stress in the presence of a solid surface, and to determine the relative efficiency as a noise source of the various transition stages. In particular, we will examine the acoustic characteristics and directivity associated with three-dimensional instability waves, the detached high-shear layer, and turbulent spots following a laminar breakdown. Additionally, attention will be paid to the unsteady surface pressures during the transition, which provide a source of flow noise as well as a forcing function for wall vibration in both aeronautical and marine applications.
Simulations of Boundary-Layer Transition
NASA Technical Reports Server (NTRS)
Herbert, Thorwald
2007-01-01
For incompressible benchmark flows, we have demonstrated the capability of the parabolized stability equations (PSE) to simulate the transition process in excellent agreement with microscopic experiments and direct Navier-Stokes simulations at modest computational cost. Encouraged by these results, we have developed the PSE methodology of three-dimensional boundary-layers in general curvilinear coordinates for the range from low to hypersonic speeds, and for both linear and nonlinear problems. For given initial and boundary conditions, the approach permits simulations from receptivity through linear and secondary instabilities into the late stages of transition where significant changes in skin friction and heat transfer coefficients occur. We have performed transition simulations for a variety of two- and three-dimensional similarity solutions and for realistic flows over swept wings at subsonic and supersonic speeds, the pressure ans suction side of turbine blades at low and medium turbulence levels, and over a blunt cone at Mach number Ma = 8. We present selected results for different transition mechanisms with emphasis on the late stage of transition and the evolution of wall-shear stress and heat transfer.
Large Eddy Simulation of Transitional Boundary Layer
NASA Astrophysics Data System (ADS)
Sayadi, Taraneh; Moin, Parviz
2009-11-01
A sixth order compact finite difference code is employed to investigate compressible Large Eddy Simulation (LES) of subharmonic transition of a spatially developing zero pressure gradient boundary layer, at Ma = 0.2. The computational domain extends from Rex= 10^5, where laminar blowing and suction excites the most unstable fundamental and sub-harmonic modes, to fully turbulent stage at Rex= 10.1x10^5. Numerical sponges are used in the neighborhood of external boundaries to provide non-reflective conditions. Our interest lies in the performance of the dynamic subgrid scale (SGS) model [1] in the transition process. It is observed that in early stages of transition the eddy viscosity is much smaller than the physical viscosity. As a result the amplitudes of selected harmonics are in very good agreement with the experimental data [2]. The model's contribution gradually increases during the last stages of transition process and the dynamic eddy viscosity becomes fully active and dominant in the turbulent region. Consistent with this trend the skin friction coefficient versus Rex diverges from its laminar profile and converges to the turbulent profile after an overshoot. 1. Moin P. et. al. Phys Fluids A, 3(11), 2746-2757, 1991. 2. Kachanov Yu. S. et. al. JFM, 138, 209-247, 1983.
Boundary Layer Transition Flight Experiment Overview
NASA Technical Reports Server (NTRS)
Berger, Karen T.; Anderson, Brian P.; Campbell, Charles H.; Garske, Michael T.; Saucedo, Luis A.; Kinder, Gerald R.; Micklos, Ann M.
2011-01-01
In support of the Boundary Layer Transition Flight Experiment (BLT FE) Project, a manufactured protuberance tile was installed on the port wing of Space Shuttle Orbiter Discovery for STS-119, STS-128, STS-131 and STS-133 as well as Space Shuttle Endeavour for STS-134. Additional instrumentation was installed in order to obtain more spatially resolved measurements downstream of the protuberance. This paper provides an overview of the BLT FE Project with emphasis on the STS-131 and STS-133 results. A high-level overview of the in-situ flight data is presented, along with a summary of the comparisons between pre- and post-flight analysis predictions and flight data. Comparisons show that empirically correlated predictions for boundary layer transition onset time closely match the flight data, while predicted surface temperatures were significantly higher than observed flight temperatures. A thermocouple anomaly observed on a number of the missions is discussed as are a number of the mitigation actions that will be taken on the final flight, STS-134, including potential alterations of the flight trajectory and changes to the flight instrumentation.
X-33 Hypersonic Boundary Layer Transition
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Horvath, Thomas J.; Hollis, Brian R.; Thompson, Richard A.; Hamilton, H. Harris, II
1999-01-01
Boundary layer and aeroheating characteristics of several X-33 configurations have been experimentally examined in the Langley 20-Inch Mach 6 Air Tunnel. Global surface heat transfer distributions, surface streamline patterns, and shock shapes were measured on 0.013-scale models at Mach 6 in air. Parametric variations include angles-of-attack of 20-deg, 30-deg, and 40-deg; Reynolds numbers based on model length of 0.9 to 6.6 million; and body-flap deflections of 0, 10 and 20-deg. The effects of discrete and distributed roughness elements on boundary layer transition, which included trip height, size, location, and distribution, both on and off the windward centerline, were investigated. The discrete roughness results on centerline were used to provide a transition correlation for the X-33 flight vehicle that was applicable across the range of reentry angles of attack. The attachment line discrete roughness results were shown to be consistent with the centerline results, as no increased sensitivity to roughness along the attachment line was identified. The effect of bowed panels was qualitatively shown to be less effective than the discrete trips; however, the distributed nature of the bowed panels affected a larger percent of the aft-body windward surface than a single discrete trip.
NASA Technical Reports Server (NTRS)
Mack, L. M.
1967-01-01
The fundamentals of stability theory, its chief results, and the physical mechanisms at work are presented. The stability theory of the laminar boundary determines whether a small disturbance introduced into the boundary layer will amplify or damp. If the disturbance damps, the boundary layer remains laminar. If the disturbance amplifies, and by a sufficient amount, then transition to turbulence eventually takes place. The stability theory establishes those states of the boundary layer which are most likely to lead to transition, identifys those frequencies which are the most dangerous, and indicates how the external parameters can best be changed to avoid transition.
Boundary Layer Transition Flight Experiment Implementation on OV-103
NASA Technical Reports Server (NTRS)
Spanos, Theodoros A.
2009-01-01
This slide presentation reviews the boundary layer transition experiment flown on Discovery. The purpose of the boundary layer transition flight experiment was to obtain hypersonic aero-thermodynamic data for the purpose of better understanding the flow transition from a laminar to turbulent boundary layer using a known height protuberance. The preparation of the shuttle is described, with the various groups responsibilities outlined. Views of the shuttle in flight with the experimental results are shown.
Boundary-layer transition effects on airplane stability and control
NASA Technical Reports Server (NTRS)
Van Dam, C. P.; Holmes, B. J.
1986-01-01
Surface contamination of laminar-flow airfoils can significantly modify the location of transition from laminar-to-turbulent boundary-layer flow. The contamination can be the result of insect debris, environmental effects such as ice crystals and moisture due to mist or rain, surface damage, or other contamination adhering to the surface. Location and mode of transition have a dominant effect on the lift-and-drag characteristics of a lifting surface. The influences of laminar boundary-layer flow behavior on airplane stability and control are examined through theoretical results and experimental (wind-tunnel and free-flight) data. For certain airfoils with a relatively steep pressure recovery it is shown that loss of laminar flow near the leading edge can result in premature separation of the turbulent boundary layer and, consequently, in loss of lift and control effectiveness. Aerodynamic modifications which minimize boundary-layer transition effects on airplane stability and control are also discussed.
A study of methods to investigate nozzle boundary layer transition
NASA Technical Reports Server (NTRS)
Pauley, Laura L.
1991-01-01
To further investigate nozzle flow, numerical computations are employed. The computations produce complete flow velocity and temperature fields within the nozzle. As a check, these results can be compared with experimental data at the wall. Once an accurate numerical scheme has been validated, it can be used as a design tool to predict the performance of other nozzle designs without the cost of experimental testing. Typically, the numerical analysis assumes either a laminar boundary layer or a fully turbulent boundary layer which is steady and two-dimensional. Boundary layer transition is not considered. Computing both the completely laminar boundary layer and the completely turbulent boundary layer conditions gives the minimum and maximum wall heat flux possible for a specified geometry. When the experimental heat flux measurements lie between these two values, the nature of the boundary layer is unknown. The boundary layer may have transitioned from laminar to turbulent; three-dimensional structures may be present in the boundary layer, or the inlet flow conditions may not be correctly specified in the computation.
Trends in hypersonic boundary layer stability and transition research
NASA Astrophysics Data System (ADS)
Kimmel, Roger L.
1999-01-01
Boundary layer transition impacts hypersonic vehicle performance more profoundly than low speed vehicle performance. Accurate prediction is difficult due to the sensitivity of transition to initial conditions. Computational tools continue to improve, but their use is limited largely to specialists. Ground testing continues to be a valuable tool, but new facility development is slow. Emphasis on transition control methods will increase as our understanding of the physics of hypersonic transition improves.
Physical description of boundary-layer transition: Experimental evidence
NASA Technical Reports Server (NTRS)
Saric, William S.
1994-01-01
The problems of understanding the origins of turbulent flow and transition to turbulent flow are the most important unsolved problems of fluid mechanics and aerodynamics. It is well known that the stability, transition, and turbulent characteristics of bounded shear layers are fundamentally different from those of free shear layers. Likewise, the stability, transition, and turbulent characteristics of open systems are fundamentally different from those of closed systems. Because of the influence of indigenous disturbances, surface geometry and roughness, sound, heat transfer, and ablation, it is not possible to develop general prediction schemes for transition location and the nature of turbulent structures in boundary-layer flows. At the present time no mathematical model exists that can predict the transition Reynolds number on a flat plate. The recent progress in this area is encouraging, in that a number of distinct transition mechanisms have been found experimentally. The theoretical work finds them to be amplitude and Reynolds-number dependent. The theory remains rather incomplete with regard to predicting transition. Amplitude and spectral characteristics of the disturbances inside the laminar viscous layer strongly influence which type of transition occurs. The major need in this area is to understand how freestream disturbances are entrained into the boundary layer, i.e., to answer the question of receptivity. We refer receptivity to the mechanism(s) that cause freestream disturbances to enter the boundary layer and create the initial amplitudes for unstable waves.
Feasibility study of optical boundary layer transition detection method
NASA Technical Reports Server (NTRS)
Azzazy, M.; Modarress, D.; Trolinger, J. D.
1986-01-01
A high sensitivity differential interferometer was developed to locate the region where the boundary layer flow undergoes transition from laminar to turbulent. Two laboratory experimental configurations were used to evaluate the performance of the interferometer: open shear layer, and low speed wind tunnel turbulent spot configuration. In each experiment, small temperature fluctuations were introduced as the signal source. Simultaneous cold wire measurements were compared with the interferometer data. The comparison shows that the interferometer is sensitive to very weak phase variations in the order of 0.001 the laser wavelength. An attempt to detect boundary layer transition over a flat plate at NASA-Langley Unitary Supersonic Wind Tunnel using the interferometer system was performed. The phase variations during boundary layer transition in the supersonic wind tunnel were beyond the minimum signal-to-noise level of the instrument.
Orbiter Boundary Layer Transition Stability Modeling at Flight Entry Conditions
NASA Technical Reports Server (NTRS)
Bartkowicz, Matt; Johnson, Heath; Candler, Graham; Campbell, Charles H.
2009-01-01
State of the art boundary layer stability modeling capabilities are increasingly seeing application to entry flight vehicles. With the advent of user friendly and robust implementations of two-dimensional chemical nonequilibrium stability modeling with the STABL/PSE-CHEM software, the need for flight data to calibrate such analyses capabilities becomes more critical. Recent efforts to perform entry flight testing with the Orbiter geometry related to entry aerothermodynamics and boundary layer transition is allowing for a heightened focus on the Orbiter configuration. A significant advancement in the state of the art can likely be achieved by establishing a basis of understanding for the occurrence of boundary layer transition on the Orbiter due to discrete protruding gap fillers and the nominal distributed roughness of the actual thermal protection system. Recent success in demonstrating centerline two-dimensional stability modeling on the centerline of the Orbiter at flight entry conditions provides a starting point for additional investigations. The more detailed paper will include smooth Orbiter configuration boundary layer stability results for several typical orbiter entry conditions. In addition, the numerical modeling approach for establishing the mean laminar flow will be reviewed and the method for determining boundary layer disturbance growth will be overviewed. In addition, if actual Orbiter TPS surface data obtained via digital surface scans become available, it may be possible to investigate the effects of an as-flown flight configuration on boundary layer transition compared to a smooth CAD reference.
Flight Experiment Verification of Shuttle Boundary Layer Transition Prediction Tool
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Berger, Karen T.; Horvath, Thomas J.; Wood, William A.
2016-01-01
Boundary layer transition at hypersonic conditions is critical to the design of future high-speed aircraft and spacecraft. Accurate methods to predict transition would directly impact the aerothermodynamic environments used to size a hypersonic vehicle's thermal protection system. A transition prediction tool, based on wind tunnel derived discrete roughness correlations, was developed and implemented for the Space Shuttle return-to-flight program. This tool was also used to design a boundary layer transition flight experiment in order to assess correlation uncertainties, particularly with regard to high Mach-number transition and tunnel-to-flight scaling. A review is provided of the results obtained from the flight experiment in order to evaluate the transition prediction tool implemented for the Shuttle program.
Bypass transition and spot nucleation in boundary layers
NASA Astrophysics Data System (ADS)
Kreilos, Tobias; Khapko, Taras; Schlatter, Philipp; Duguet, Yohann; Henningson, Dan S.; Eckhardt, Bruno
2016-08-01
The spatiotemporal aspects of the transition to turbulence are considered in the case of a boundary-layer flow developing above a flat plate exposed to free-stream turbulence. Combining results on the receptivity to free-stream turbulence with the nonlinear concept of a transition threshold, a physically motivated model suggests a spatial distribution of spot nucleation events. To describe the evolution of turbulent spots a probabilistic cellular automaton is introduced, with all parameters directly obtained from numerical simulations of the boundary layer. The nucleation rates are then combined with the cellular automaton model, yielding excellent quantitative agreement with the statistical characteristics for different free-stream turbulence levels. We thus show how the recent theoretical progress on transitional wall-bounded flows can be extended to the much wider class of spatially developing boundary-layer flows.
Rough-wall turbulent boundary layers in the transition regime
NASA Technical Reports Server (NTRS)
Bandyopadhyay, Promode R.
1987-01-01
An experimental investigation of turbulent boundary layers over two-dimensional spanwise groove and three-dimensional sandgrain roughnesses in the transition regime between hydraulically smooth and fully rough conditions is presented. It is found that a self-preserving state can be reached in boundary layers developing over both d-type groove and sandgrain roughnesses, and that the drag of a k-type rough wall can be reduced by lowering the spanwise aspect ratio of the roughness elements. The two roughness Reynolds numbers defining the boundaries of the transition regime of the k-type roughnesses are shown to decrease with increasing roughness-element spanwise aspect ratio, and the upper critical transition Reynolds number is shown to determine the roughness behavior in both the transition and fully rough regime.
Simulating Dispersion in the Evening-Transition Boundary Layer
NASA Astrophysics Data System (ADS)
Taylor, Alexander C.; Beare, Robert J.; Thomson, David J.
2014-12-01
We investigate dispersion in the evening-transition boundary layer using large-eddy simulation (LES). In the LES, a particle model traces pollutant paths using a combination of the resolved flow velocities and a random displacement model to represent subgrid-scale motions. The LES is forced with both a sudden switch-off of the surface heat flux and also a more gradual observed evolution. The LES shows `lofting' of plumes from near-surface releases in the pre-transition convective boundary layer; it also shows the subsequent `trapping' of releases in the post-transition near-surface stable boundary layer and residual layer above. Given the paucity of observations for pollution dispersion in evening transitions, the LES proves a useful reference. We then use the LES to test and improve a one-dimensional Lagrangian Stochastic Model (LSM) such as is often used in practical dispersion studies. The LSM used here includes both time-varying and skewed turbulence statistics. It is forced with the vertical velocity variance, skewness and dissipation from the LES for particle releases at various heights and times in the evening transition. The LSM plume spreads are significantly larger than those from the LES in the post-transition stable boundary-layer trapping regime. The forcing from the LES was thus insufficient to constrain the plume evolution, and inclusion of the significant stratification effects was required. In the so-called modified LSM, a correction to the vertical velocity variance was included to represent the effect of stable stratification and the consequent presence of wave-like motions. The modified LSM shows improved trapping of particles in the post-transition stable boundary layer.
The role of nonlinear critical layers in boundary layer transition
NASA Technical Reports Server (NTRS)
Goldstein, M.E.
1995-01-01
Asymptotic methods are used to describe the nonlinear self-interaction between pairs of oblique instability modes that eventually develops when initially linear spatially growing instability waves evolve downstream in nominally two-dimensional laminar boundary layers. The first nonlinear reaction takes place locally within a so-called 'critical layer', with the flow outside this layer consisting of a locally parallel mean flow plus a pair of oblique instability waves - which may or may not be accompanied by an associated plane wave. The amplitudes of these waves, which are completely determined by nonlinear effects within the critical layer, satisfy either a single integro-differential equation or a pair of integro-differential equations with quadratic to quartic-type nonlinearities. The physical implications of these equations are discussed.
Atmospheric boundary layer evening transitions over West Texas
Technology Transfer Automated Retrieval System (TEKTRAN)
A systemic analysis of the atmospheric boundary layer behavior during some evening transitions over West Texas was done using the data from an extensive array of instruments which included small and large aperture scintillometers, net radiometers, and meteorological stations. The analysis also comp...
Detection of boundary-layer transitions in wind tunnels
NASA Technical Reports Server (NTRS)
Wood, W. R.; Somers, D. M.
1978-01-01
Accelerometer replaces stethoscope in technique for detection of laminar-to-turbulent boundary-layer transitions on wind-tunnel models. Technique allows measurements above or below atmospheric pressure because human operator is not required within tunnel. Data may be taken from accelerometer, and pressure transducer simultaneously, and delivered to systems for analysis.
Numerical simulation of transition control in boundary layers
NASA Astrophysics Data System (ADS)
Laurien, E.; Kleiser, L.
The transition process from laminar to turbulent boundary layers is simulated by numerical integration of the 3D incompressible Navier-Stokes equations. Spatially periodic wave disturbances in a parallel Blasius flow are assumed. A spectral method with real-space Chebyshev collocation in the normal direction is employed. Both the classical K-type and the subharmonic type of transition are investigated. Good agreement with measurements and flow visualizations of transition experiments is obtained. Control of transition by wave superposition is simulated using periodic wall suction/blowing. It is shown that 2D control works well at an early stage but fails after significant 3D disturbances have developed.
Evolutionary geometry of Lagrangian structures in a transitional boundary layer
NASA Astrophysics Data System (ADS)
Zheng, Wenjie; Yang, Yue; Chen, Shiyi
2016-03-01
We report a geometric study of Lagrangian structures in a weakly compressible, spatially evolving transitional boundary layer at the Mach number 0.7. The Lagrangian structures in the transition process are extracted from the Lagrangian scalar field by a sliding window filter at a sequence of reference times. The multi-scale and multi-directional geometric analysis is applied to characterize the geometry of spatially evolving Lagrangian structures, including the averaged inclination and sweep angles at different scales ranging from one half of the boundary layer thickness to several viscous length scales. Here, the inclination angle is on the plane of the streamwise and wall-normal directions, and the sweep angle is on the plane of the streamwise and spanwise directions. In general, the averaged inclination angle is increased and the sweep angle is decreased with the reference time. The variation of the angles for large-scale structures is smaller than that for small-scale structures. Before the transition, the averaged inclination and sweep angles are only slightly altered for all the scales. As the transition occurs, averaged inclination angles increase and sweep angles decrease rapidly for small-scale structures. In the late transitional stage, the averaged inclination angle of small-scale structures with 30 viscous length scales is approximately 42°, and the averaged sweep angle in the logarithm law region is approximately 30°. Additionally, the geometry of Lagrangian structures in transitional boundary layer flow is compared with that in the fully developed turbulent channel flow.
On the Effects of Surface Roughness on Boundary Layer Transition
NASA Technical Reports Server (NTRS)
Choudhari, Meelan M.; Li, Fei; Chang, Chau-Lyan; Edwards, Jack
2009-01-01
Surface roughness can influence laminar-turbulent transition in many different ways. This paper outlines selected analyses performed at the NASA Langley Research Center, ranging in speed from subsonic to hypersonic Mach numbers and highlighting the beneficial as well as adverse roles of the surface roughness in technological applications. The first theme pertains to boundary-layer tripping on the forebody of a hypersonic airbreathing configuration via a spanwise periodic array of trip elements, with the goal of understanding the physical mechanisms underlying roughness-induced transition in a high-speed boundary layer. The effect of an isolated, finite amplitude roughness element on a supersonic boundary layer is considered next. The other set of flow configurations examined herein corresponds to roughness based laminar flow control in subsonic and supersonic swept wing boundary layers. A common theme to all of the above configurations is the need to apply higher fidelity, physics based techniques to develop reliable predictions of roughness effects on laminar-turbulent transition.
Grain-boundary layering transitions and phonon engineering
NASA Astrophysics Data System (ADS)
Rickman, J. M.; Harmer, M. P.; Chan, H. M.
2016-09-01
We employ semi-grand canonical Monte Carlo simulation to investigate layering transitions at grain boundaries in a prototypical binary alloy. We demonstrate the existence of such transitions among various interfacial states and examine the role of elastic fields in dictating state equilibria. The results of these studies are summarized in the form of diagrams that highlight interfacial state coexistence in this system. Finally, we examine the impact of layering transitions on the phononic properties of the system, as given by the specific heat and, by extension, the thermal conductivity. Thus, it is suggested that by inducing interfacial layering transitions via changes in temperature or pressure, one can thereby engineer thermodynamic and transport properties in materials.
Studying the Afternoon Transition of the Planetary Boundary Layer
NASA Astrophysics Data System (ADS)
Lothon, Marie; Lenschow, Donald H.
2010-07-01
The planetary boundary layer is the part of the atmosphere that interacts directly with the Earth's surface on a time scale of a few hours or less. In daytime, solar heating of the surface can generate buoyant turbulent eddies that efficiently mix the air through a depth of more than a kilometer. This convective boundary layer (CBL) is a conduit for trace gases such as water vapor and carbon dioxide that are emitted or absorbed by the surface (and surface vegetation) to be transported into or out of the layer nearest the surface. The CBL has been extensively observed and relatively successfully modeled. But the early morning transition—when the CBL emerges from the nocturnal boundary layer—and the late afternoon transition—when the CBL decays to an intermittently turbulent “residual layer” overlying a shallower, stably stratified boundary layer—are difficult to observe and model due to turbulence intermittency and anisotropy, horizontal heterogeneity, and rapid time changes. Even the definition of the boundary layer during these transitional periods is fuzzy; there is no consensus on what criteria to use and no simple scaling laws, as there are for the CBL, that apply during these transitions.
Minnowbrook II 1997 Workshop on Boundary Layer Transition in Turbomachines
NASA Technical Reports Server (NTRS)
LaGraff John E. (Editor); Ashpis, David E. (Editor)
1998-01-01
The volume contains materials presented at the Minnowbrook II - 1997 Workshop on Boundary Layer Transition in Turbomachines, held at Syracuse University Minnowbrook Conference Center, New York, on September 7-10, 1997. The workshop followed the informal format at the 1993 Minnowbrook I workshop, focusing on improving the understanding of late stage (final breakdown) boundary layer transition, with the engineering application of improving design codes for turbomachinery in mind. Among the physical mechanisms discussed were hydrodynamic instabilities, laminar to turbulent transition, bypass transition, turbulent spots, wake interaction with boundary layers, calmed regions, and separation, all in the context of flow in turbomachinery, particularly in compressors and high and low pressure turbines. Results from experiments, DNS, computation, modeling and theoretical analysis were presented. Abstracts and copies of viewgraphs, a specifically commissioned summation paper prepared after the workshop, and a transcript of the extensive working group reports and discussions are included in this volume. They provide recommendations for future research and clearly highlight the need for continued vigorous research in the technologically important area of transition in turbomachines.
Advanced boundary layer transition measurement methods for flight applications
NASA Technical Reports Server (NTRS)
Holmes, B. J.; Croom, C. C.; Gail, P. D.; Manuel, G. S.; Carraway, D. L.
1986-01-01
In modern laminar flow flight research, it is important to understand the specific cause(s) of laminar to turbulent boundary-layer transition. Such information is crucial to the exploration of the limits of practical application of laminar flow for drag reduction on aircraft. The transition modes of interest in current flight investigations include the viscous Tollmien-Schlichting instability, the inflectional instability at laminar separation, and the crossflow inflectional instability, as well as others. This paper presents the results to date of research on advanced devices and methods used for the study of laminar boundary-layer transition phenomena in the flight environment. Recent advancements in the development of arrayed hot-film devices and of a new flow visualization method are discussed. Arrayed hot-film devices have been designed to detect the presence of laminar separation, and of crossflow vorticity. The advanced flow visualization method utilizes color changes in liquid-crystal coatings to detect boundary-layer transition at high altitude flight conditions. Flight and wind tunnel data are presented to illustrate the design and operation of these advanced methods. These new research tools provide information on disturbance growth and transition mode which is essential to furthering our understanding of practical design limits for applications of laminar flow technology.
Review of Orbiter Flight Boundary Layer Transition Data
NASA Technical Reports Server (NTRS)
Mcginley, Catherine B.; Berry, Scott A.; Kinder, Gerald R.; Barnell, maria; Wang, Kuo C.; Kirk, Benjamin S.
2006-01-01
In support of the Shuttle Return to Flight program, a tool was developed to predict when boundary layer transition would occur on the lower surface of the orbiter during reentry due to the presence of protuberances and cavities in the thermal protection system. This predictive tool was developed based on extensive wind tunnel tests conducted after the loss of the Space Shuttle Columbia. Recognizing that wind tunnels cannot simulate the exact conditions an orbiter encounters as it re-enters the atmosphere, a preliminary attempt was made to use the documented flight related damage and the orbiter transition times, as deduced from flight instrumentation, to calibrate the predictive tool. After flight STS-114, the Boundary Layer Transition Team decided that a more in-depth analysis of the historical flight data was needed to better determine the root causes of the occasional early transition times of some of the past shuttle flights. In this paper we discuss our methodology for the analysis, the various sources of shuttle damage information, the analysis of the flight thermocouple data, and how the results compare to the Boundary Layer Transition prediction tool designed for Return to Flight.
Roughness Induced Transition in a Supersonic Boundary Layer
NASA Technical Reports Server (NTRS)
Balakumar, Ponnampalam; Kergerise, Michael A.
2013-01-01
Direct numerical simulation is used to investigate the transition induced by threedimensional isolated roughness elements in a supersonic boundary layer at a free stream Mach number of 3.5. Simulations are performed for two different configurations: one is a square planform roughness and the other is a diamond planform roughness. The mean-flow calculations show that the roughness induces counter rotating streamwise vortices downstream of the roughness. These vortices persist for a long distance downstream and lift the low momentum fluid from the near wall region and place it near the outer part of the boundary layer. This forms highly inflectional boundary layer profiles. These observations agree with recent experimental observations. The receptivity calculations showed that the amplitudes of the mass-flux fluctuations near the neutral point for the diamond shape roughness are the same as the amplitude of the acoustic disturbances. They are three times smaller for the square shape roughness.
Experiments on the active control of transitional boundary layers
NASA Astrophysics Data System (ADS)
Nelson, P. A.; Rioual, J.-L.; Fisher, M. J.
Experimental results are presented which demonstrate that the streamwise position of the transition region of a flat plate boundary layer can be actively controlled. The means of control is through the application of suction through the surface of the plate, a progressive increase in suction rate being capable of producing transition at progressively larger distances downstream from the plate leading edge. A simple digital feedback regulator based on an integral control law is shown to be most effective in regulating the position of transition, an error signal being derived from measurements of pressure fluctuations on the surface of the plate.
Fluid Mechanics and Heat Transfer in Transitional Boundary Layers
NASA Technical Reports Server (NTRS)
Wang, Ting
2007-01-01
Experiments have been performed to investigate the effects of elevated free-stream turbulence and streamwise acceleration on flow and thermal structures in transitional boundary layers. The free-stream turbulence ranges from 0.5 to 6.4% and the streamwise acceleration ranges from K = 0 to 0.8 x 10(exp -6). The onset of transition, transition length and the turbulent spot formation rate are determined. The statistical results and conditionally sampled results of th streamwise and cross-stream velocity fluctuations, temperature fluctuations, Reynolds stress and Reynolds heat fluxes are presented.
Boundary-Layer Receptivity and Integrated Transition Prediction
NASA Technical Reports Server (NTRS)
Chang, Chau-Lyan; Choudhari, Meelan
2005-01-01
The adjoint parabold stability equations (PSE) formulation is used to calculate the boundary layer receptivity to localized surface roughness and suction for compressible boundary layers. Receptivity efficiency functions predicted by the adjoint PSE approach agree well with results based on other nonparallel methods including linearized Navier-Stokes equations for both Tollmien-Schlichting waves and crossflow instability in swept wing boundary layers. The receptivity efficiency function can be regarded as the Green's function to the disturbance amplitude evolution in a nonparallel (growing) boundary layer. Given the Fourier transformed geometry factor distribution along the chordwise direction, the linear disturbance amplitude evolution for a finite size, distributed nonuniformity can be computed by evaluating the integral effects of both disturbance generation and linear amplification. The synergistic approach via the linear adjoint PSE for receptivity and nonlinear PSE for disturbance evolution downstream of the leading edge forms the basis for an integrated transition prediction tool. Eventually, such physics-based, high fidelity prediction methods could simulate the transition process from the disturbance generation through the nonlinear breakdown in a holistic manner.
A complex-lamellar description of boundary layer transition
NASA Astrophysics Data System (ADS)
Kolla, Maureen Louise
Flow transition is important, in both practical and phenomenological terms. However, there is currently no method for identifying the spatial locations associated with transition, such as the start and end of intermittency. The concept of flow stability and experimental correlations have been used, however, flow stability only identifies the location where disturbances begin to grow in the laminar flow and experimental correlations can only give approximations as measuring the start and end of intermittency is difficult. Therefore, the focus of this work is to construct a method to identify the start and end of intermittency, for a natural boundary layer transition and a separated flow transition. We obtain these locations by deriving a complex-lamellar description of the velocity field that exists between a fully laminar and fully turbulent boundary condition. Mathematically, this complex-lamellar decomposition, which is constructed from the classical Darwin-Lighthill-Hawthorne drift function and the transport of enstrophy, describes the flow that exists between the fully laminar Pohlhausen equations and Prandtl's fully turbulent one seventh power law. We approximate the difference in enstrophy density between the boundary conditions using a power series. The slope of the power series is scaled by using the shape of the universal intermittency distribution within the intermittency region. We solve the complex-lamellar decomposition of the velocity field along with the slope of the difference in enstrophy density function to determine the location of the laminar and turbulent boundary conditions. Then from the difference in enstrophy density function we calculate the start and end of intermittency. We perform this calculation on a natural boundary layer transition over a flat plate for zero pressure gradient flow and for separated shear flow over a separation bubble. We compare these results to existing experimental results and verify the accuracy of our transition
Characteristics of Mach 10 transitional and turbulent boundary layers
NASA Technical Reports Server (NTRS)
Watson, R. D.
1978-01-01
Measurements of the mean flow properties of transitional and turbulent boundary layers in helium on 4 deg and 5 deg wedges were made for flows with edge Mach numbers from 9.5 to 11.3, ratios of wall temperature to total temperature of 0.4 to 0.95, and maximum length Reynolds numbers of one hundred million. The data include pitot and total temperature surveys and measurements of heat transfer and surface shear. In addition, with the assumption of local similarity, turbulence quantities such as the mixing length were derived from the mean flow profiles. Low Reynolds number and precursor transition effects were significant factors at these test conditions and were included in finite difference boundary layer predictions.
Modeling Disturbance Dynamics in Transitional and Turbulent Boundary Layers
NASA Technical Reports Server (NTRS)
Grosch, C. E.; Gatski, T. B. (Technical Monitor)
2002-01-01
The dynamics of an ensemble of linear disturbances in boundary-layer flows at various Reynolds numbers is studied through an analysis of the transport equations for the mean disturbance kinetic energy and energy dissipation rate. Effects of adverse and favorable pressure-gradients on the disturbance dynamics are also included in the analysis. Unlike the fully turbulent regime where nonlinear phase scrambling of the fluctuations affects the flow field even in proximity to the wall, the early stage transition regime fluctuations studied here are influenced across the boundary layer by the solid boundary. In addition, the dominating dynamics in the disturbance kinetic energy equation is governed by the energy production, pressure-transport and viscous diffusion - also in contrast to the fully turbulent regime. For the disturbance dissipation rate, a dynamic balance exists between the destruction and diffusion of dissipation.
Boundary Layer Transition Experiments in Support of the Hypersonics Program
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Chen, Fang-Jenq; Wilder, Michael C.; Reda, Daniel C.
2007-01-01
Two experimental boundary layer transition studies in support of fundamental hypersonics research are reviewed. The two studies are the HyBoLT flight experiment and a new ballistic range effort. Details are provided of the objectives and approach associated with each experimental program. The establishment of experimental databases from ground and flight are to provide better understanding of high-speed flows and data to validate and guide the development of simulation tools.
Characterization of structural response to hypersonic boundary-layer transition
Riley, Zachary B.; Deshmukh, Rohit; Miller, Brent A.; McNamara, Jack J.; Casper, Katya M.
2016-05-24
The inherent relationship between boundary-layer stability, aerodynamic heating, and surface conditions makes the potential for interaction between the structural response and boundary-layer transition an important and challenging area of study in high-speed flows. This paper phenomenologically explores this interaction using a fundamental two-dimensional aerothermoelastic model under the assumption of an aluminum panel with simple supports. Specifically, an existing model is extended to examine the impact of transition onset location, transition length, and transitional overshoot in heat flux and fluctuating pressure on the structural response of surface panels. Transitional flow conditions are found to yield significantly increased thermal gradients, and theymore » can result in higher maximum panel temperatures compared to turbulent flow. Results indicate that overshoot in heat flux and fluctuating pressure reduces the flutter onset time and increases the strain energy accumulated in the panel. Furthermore, overshoot occurring near the midchord can yield average temperatures and peak displacements exceeding those experienced by the panel subject to turbulent flow. Lastly, these results suggest that fully turbulent flow does not always conservatively predict the thermo-structural response of surface panels.« less
Infrared Imaging of Boundary Layer Transition Flight Experiments
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Horvath, Thomas J., Jr.; Schwartz, Richard; Ross, Martin; Anderson, Brian; Campbell, Charles H.
2008-01-01
The Hypersonic Thermodynamic Infrared Measurement (HYTHIRM) project is presently focused on near term support to the Shuttle program through the development of an infrared imaging capability of sufficient spatial and temporal resolution to augment existing on-board Orbiter instrumentation. Significant progress has been made with the identification and inventory of relevant existing optical imaging assets and the development, maturation, and validation of simulation and modeling tools for assessment and mission planning purposes, which were intended to lead to the best strategies and assets for successful acquisition of quantitative global surface temperature data on the Shuttle during entry. However, there are longer-term goals of providing global infrared imaging support to other flight projects as well. A status of HYTHIRM from the perspective of how two NASA-sponsored boundary layer transition flight experiments could benefit by infrared measurements is provided. Those two flight projects are the Hypersonic Boundary layer Transition (HyBoLT) flight experiment and the Shuttle Boundary Layer Transition Flight Experiment (BLT FE), which are both intended for reducing uncertainties associated with the extrapolation of wind tunnel derived transition correlations for flight application. Thus, the criticality of obtaining high quality flight data along with the impact it would provide to the Shuttle program damage assessment process are discussed. Two recent wind tunnel efforts that were intended as risk mitigation in terms of quantifying the transition process and resulting turbulent wedge locations are briefly reviewed. Progress is being made towards finalizing an imaging strategy in support of the Shuttle BLT FE, however there are no plans currently to image HyBoLT.
Transition experiments in a boundary layer with embedded streamwise vortices
NASA Astrophysics Data System (ADS)
Bakchinov, A. A.; Grek, G. R.; Klingmann, B. G. B.; Kozlov, V. V.
1995-04-01
The stability of a flat plate boundary layer modulated by stationary streamwise vortices was studied experimentally in the T-324 low speed wind tunnel in Novosibirsk. Vortices were generated inside the boundary layer by means of roughness elements arranged in a regular array along the spanwise (z-) direction. Transition is not caused directly by these structures, but by the growth of small amplitude traveling waves riding on top of the steady vortices. This situation is analogous to the transition process in Görtler and cross-flows. The waves were found to amplify up to a stage where higher harmonics are generated, leading to turbulent breakdown and disintegration of the spanwise boundary layer structure. For strong modulations, the observed instability is quite powerful, and can be excited ``naturally'' by small uncontrollable background disturbances. Controlled oscillations were then introduced by means of a vibrating ribbon, allowing a detailed investigation of the wave characteristics. The instability seems to be associated with the spanwise gradients of the mean flow, ∂U/∂z, and at all z-positions, the maximum wave amplitude was found at a wall-normal position where the mean velocity is equal to the phase velocity of the wave, U(y)=c, i.e., at the local critical layer. Unstable waves were observed at frequencies well above those for which Tollmien-Schlichting (TS) waves amplify in the Blasius boundary layer. Excitation at lower frequencies and milder basic flow modulations showed that TS-type waves may also develop. The relation between TS-type waves and the observed high-frequency instability is discussed in the light of previous authors' findings.
Analysis of the photodiode boundary layer transition indicator
Kuntz, D.W.; Wilken, A.C.; Payne, J.L.
1994-01-01
The photodiode transition indicator is a device which has been successfully used to determine the onset of boundary layer transition on numerous hypersonic flight vehicles. The exact source of the electromagnetic radiation detected by the photodiode at transition was not understood. In some cases early saturation of the device occurred, and the device failed to detect transition. Analyses have been performed to determine the source of the radiation producing the photodiode signal. The results of these analyses indicate that the most likely source of the radiation is blackbody emission from the heatshield material bordering the quartz window of the device. Good agreement between flight data and calculations based on this radiation source has been obtained. Analyses also indicate that the most probable source of the radiation causing early saturation is blackbody radiation from carbon particles which break away from the nosetip during the ablation process.
Transition Delay in Hypersonic Boundary Layers via Optimal Perturbations
NASA Technical Reports Server (NTRS)
Paredes, Pedro; Choudhari, Meelan M.; Li, Fei
2016-01-01
The effect of nonlinear optimal streaks on disturbance growth in a Mach 6 axisymmetric flow over a 7deg half-angle cone is investigated in an e ort to expand the range of available techniques for transition control. Plane-marching parabolized stability equations are used 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 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, but subharmonic first mode instabilities, which are destabilized by the presence of the streaks, reach N = 6 near the end of the cone. These results suggest a passive flow control strategy of using micro vortex generators to induce streaks that would delay transition in hypersonic boundary layers.
Characteristics of turbulent spots in transitional boundary layers
NASA Astrophysics Data System (ADS)
Marxen, Olaf; Zaki, Tamer
2015-11-01
The laminar-turbulent transition process in a flat-plate boundary layer beneath free-stream turbulence takes place through the inception and spreading of confined patches of turbulence in an otherwise laminar flow. These patches, also referred to as turbulent spots, result from a secondary instability of the Klebanoff streaks in the pre-transitional region. The dynamics of turbulence in the spots are investigated by analyzing data sets obtained from direct numerical simulations. Conditionally-averaged and spot-ensemble-averaged statistics are evaluated and describe the flow in the intermittent transition zone. Both mean-flow and disturbance root mean square levels obtained from conditional averaging agree very well with results for fully turbulent flows, in particular near the wall and at high intermittency levels. At relatively low intermittency, the spatial inhomogeneity of turbulence within the spots is important, and is examined using ensemble averaging of turbulent patches that have comparable volume and a similar streamwise location.
A cloudiness transition in a marine boundary layer
NASA Technical Reports Server (NTRS)
Betts, Alan K.; Boers, Reinout
1990-01-01
Boundary layer cloudiness plays several important roles in the energy budget of the earth. Low level stratocumulus are highly reflective clouds which reduce the net incoming shortwave radiation at the earth's surface. Climatically, the transition to a small area fraction of scattered cumulus clouds occurs as the air flows over warmer water. Although these clouds reflect less sunlight, they still play an important role in the boundary layer equilibrium by transporting water vapor upwards, and enhancing the surface evaporation. The First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment (FIRE) included a marine stratocumulus experiment off the southern California coast from June 29 to July 19, 1987. The objectives of this experiment were to study the controls on fractional cloudiness, and to assess the role of cloud-top entrainment instability (CTEI) and mesoscale structure in determining cloud type. The focus is one research day, July 7, 1987, when coordinated aircraft missions were flown by four research aircraft, centered on a LANDSAT scene at 1830 UTC. The remarkable feature of this LANDSAT scene is the transition from a clear sky in the west through broken cumulus to solid stratocumulus in the east. The dynamic and thermodynamic structure of this transition in cloudiness is analyzed using data from the NCAR Electra. By averaging the aircraft data, the internal structure of the different cloud regimes is documented, and it is shown that the transition between broken cumulus and stratocumulus is associated with a change in structure with respect to the CTEI condition. However, this results not from sea surface temperature changes, but mostly from a transition in the air above the inversion, and the breakup appears to be at a structure on the unstable side of the wet virtual adiabat.
Bypass transition of the bottom boundary layer under solitary wave
NASA Astrophysics Data System (ADS)
Sadek, Mahmoud; Diamessis, Peter; Parras, Luis; Liu, Philip
2015-11-01
The transition to turbulence in the bottom boundary layer (BBL) flow driven by a soliton-like pressure gradient in an oscillating water tunnel (an approximation for the BBL under solitary waves) is investigated using hydrodynamic linear stability theory and DNS. As observed in the laboratory experiment by Sumer et al. (2010), two possible transition scenarios exist. The first scenario is associated with the classical transition resulting from the breakdown of the exponentially growing 2-D Tollmien-Schlichting waves. The alternative scenario; i.e., bypass transition; takes place through formation of localized turbulent spots. The investigation of the latter transition scenario is performed in two steps. The first step consists of reformulating the linear stability analysis in the non-modal framework for the purpose of finding the optimum disturbance characteristics which lead to the formation of those turbulent spots. In the second step, the computed optimum noise structure is inserted in the 3D DNS in order to induce the formation of the turbulent spots and effectively simulate the bypass transition observed experimentally.
Space Shuttle Boundary Layer Transition Flight Experiment Ground Testing Overview
NASA Technical Reports Server (NTRS)
Berger, Karen T.; Anderson, Brian P.; Campbell, Charles H.
2014-01-01
In support of the Boundary Layer Transition (BLT) Flight Experiment (FE) Project in which a manufactured protuberance tile was installed on the port wing of Space Shuttle Orbiter Discovery for STS-119, STS- 128, STS-131 and STS-133 as well as Space Shuttle Orbiter Endeavour for STS-134, a significant ground test campaign was completed. The primary goals of the test campaign were to provide ground test data to support the planning and safety certification efforts required to fly the flight experiment as well as validation for the collected flight data. These test included Arcjet testing of the tile protuberance, aerothermal testing to determine the boundary layer transition behavior and resultant surface heating and planar laser induced fluorescence (PLIF) testing in order to gain a better understanding of the flow field characteristics associated with the flight experiment. This paper provides an overview of the BLT FE Project ground testing. High-level overviews of the facilities, models, test techniques and data are presented, along with a summary of the insights gained from each test.
Coastal boundary layer transition within tropical cyclones at landfall
NASA Astrophysics Data System (ADS)
Howard, James Robert
Hurricanes pose a great risk to life and property with their high winds, excessive rainfall, wave action, and storm surge. Predicting changes within hurricanes at and near the time of landfall requires an understanding of the dynamics that drive the boundary layer flow. Forecasters predict the timing, duration, and effects of the intense winds associated with a hurricane when it comes ashore, while emergency management officials call for public evacuations based upon these forecasts. One region where understanding the magnitude and structure of the wind is critical is within the surface layer just downstream of the coastline in the onshore flow. Within this region the flow begins to adjust to changes in surface triggered by its passage from the shallow coastal waters to the less homogeneous and rougher land. This adjustment may include a slowing of the mean wind with an increase in turbulence, both resulting from the increased friction of the man-made and natural terrain. Hurricane observing programs consisting of portable and mobile equipment and regional coastal mesoscale observing networks are leading to a better understanding of the processes involved with these flow modifications. The Texas Tech University Wind Engineering Mobile Instrumented Tower Experiment (WEMITE) continues to play a leading role in the observation and analysis of the boundary layer of tropical cyclones at landfall. In order to gain further insight into the characteristics of this coastal transition zone, experiments were planned utilizing portable in-situ and remote measuring devices to be placed within the onshore flow at landfall. Experiment plan designs along with results from these experiments are discussed, including the analysis of a dataset collected by multiple institutions during the landfall of Hurricane Lili (2002) along the south-central Louisiana coast. Investigation reveals the existence of frictionally-induced changes in the boundary layer downwind of the coastline within
Transition and Breakdown to Turbulence in Incompressible Boundary Layers
NASA Technical Reports Server (NTRS)
Balakumar, Ponnampalam
1998-01-01
We have developed a code where the nonlinear terms are treated implicitly. The equations are discretized using the two-point fourth order compact scheme in the y-direction and the backward Euler method in the x-direction. We investigated the transition process in a Blasius boundary layer due to fundamental type breakdown. With 8 modes in the w and 3 planes, we could compute the evolution of disturbances up to Re(x)=910, which is well into the strongly nonlinear region. The transition onset point is located around Re(x)=850. The comparison with the measurements and with the DNS computations are very good up to Re(x)=880.
Recommendations for Hypersonic Boundary Layer Transition Flight Testing
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Kimmel, Roger; Reshotko, Eli
2011-01-01
Much has been learned about the physics underlying the transition process at supersonic and hypersonic speeds through years of analysis, experiment and computation. Generally, the application of this knowledge has been restricted to simple shapes like plates, cones and spherical bodies. However, flight reentry vehicles are in reality never simple. They typically are highly complex geometries flown at angle of attack so three-dimensional effects are very important, as are roughness effects due to surface features and/or ablation. This paper will review our present understanding of the physics of the transition process and look back at some of the recent flight test programs for their successes and failures. The goal of this paper is to develop rationale for new hypersonic boundary layer transition flight experiments. Motivations will be derived from both an inward look at what we believe constitutes a good flight test program as well as an outward review of the goals and objectives of some recent US based unclassified proposals and programs. As part of our recommendations, this paper will address the need for careful experimental work as per the guidelines enunciated years ago by the U.S. Transition Study Group. Following these guidelines is essential to obtaining reliable, usable data for allowing refinement of transition estimation techniques.
Structure Identification Within a Transitioning Swept-Wing Boundary Layer
NASA Technical Reports Server (NTRS)
Chapman, Keith; Glauser, Mark
1996-01-01
Extensive measurements are made in a transitioning swept-wing boundary layer using hot-film, hot-wire and cross-wire anemometry. The crossflow-dominated flow contains stationary vortices that breakdown near mid-chord. The most amplified vortex wavelength is forced by the use of artificial roughness elements near the leading edge. Two-component velocity and spanwise surface shear-stress correlation measurements are made at two constant chord locations, before and after transition. Streamwise surface shear stresses are also measured through the entire transition region. Correlation techniques are used to identify stationary structures in the laminar regime and coherent structures in the turbulent regime. Basic techniques include observation of the spatial correlations and the spatially distributed auto-spectra. The primary and secondary instability mechanisms are identified in the spectra in all measured fields. The primary mechanism is seen to grow, cause transition and produce large-scale turbulence. The secondary mechanism grows through the entire transition region and produces the small-scale turbulence. Advanced techniques use Linear Stochastic Estimation (LSE) and Proper Orthogonal Decomposition (POD) to identify the spatio-temporal evolutions of structures in the boundary layer. LSE is used to estimate the instantaneous velocity fields using temporal data from just two spatial locations and the spatial correlations. Reference locations are selected using maximum RMS values to provide the best available estimates. POD is used to objectively determine modes characteristic of the measured flow based on energy. The stationary vortices are identified in the first laminar modes of each velocity component and shear component. Experimental evidence suggests that neighboring vortices interact and produce large coherent structures with spanwise periodicity at double the stationary vortex wavelength. An objective transition region detection method is developed using
Numerical Simulations of the Boundary Layer Transition Flight Experiment
NASA Technical Reports Server (NTRS)
Tang, Chun Y.; Trumble, Kerry A.; Campbell, Charles H.; Lessard, Victor R.; Wood, William A.
2010-01-01
Computational Fluid Dynamics (CFD) simulations were used to study the possible effects that the Boundary Layer Transition (BLT) Flight Experiments may have on the heating environment of the Space Shuttle during its entry to Earth. To investigate this issue, hypersonic calculations using the Data-Parallel Line Relaxation (DPLR) and Langley Aerothermodynamic Upwind Relaxation (LAURA) CFD codes were computed for a 0.75 tall protuberance at flight conditions of Mach 15 and 18. These initial results showed high surface heating on the BLT trip and the areas surrounding the protuberance. Since the predicted peak heating rates would exceed the thermal limits of the materials selected to construct the BLT trip, many changes to the geometry were attempted in order to reduce the surface heat flux. The following paper describes the various geometry revisions and the resulting heating environments predicted by the CFD codes.
Comparison of Methods for Determining Boundary Layer Edge Conditions for Transition Correlations
NASA Technical Reports Server (NTRS)
Liechty, Derek S.; Berry, Scott A.; Hollis, Brian R.; Horvath, Thomas J.
2003-01-01
Data previously obtained for the X-33 in the NASA Langley Research Center 20-Inch Mach 6 Air Tunnel have been reanalyzed to compare methods for determining boundary layer edge conditions for use in transition correlations. The experimental results were previously obtained utilizing the phosphor thermography technique to monitor the status of the boundary layer downstream of discrete roughness elements via global heat transfer images of the X-33 windward surface. A boundary layer transition correlation was previously developed for this data set using boundary layer edge conditions calculated using an inviscid/integral boundary layer approach. An algorithm was written in the present study to extract boundary layer edge quantities from higher fidelity viscous computational fluid dynamic solutions to develop transition correlations that account for viscous effects on vehicles of arbitrary complexity. The boundary layer transition correlation developed for the X-33 from the viscous solutions are compared to the previous boundary layer transition correlations. It is shown that the boundary layer edge conditions calculated using an inviscid/integral boundary layer approach are significantly different than those extracted from viscous computational fluid dynamic solutions. The present results demonstrate the differences obtained in correlating transition data using different computational methods.
Characteristics of transition in a flat-plate boundary layer
NASA Astrophysics Data System (ADS)
Choi, Myung-Ryul; Choi, Haecheon; Kang, Shin-Hyoung
1998-11-01
A direct numerical simulation of the spatially evolving transition in a flat-plate boundary layer is performed in the region of ( 115000<= Re_x<= 340000 ) with ( 1537× 99× 128 ) grid points. Inflow disturbances, similar to the two dimensional T-S wave combined with three dimensional waves, are generated on the upstream wall through time-dependent localized blowing and suction. A ( Λ ) vortex, consisting of two legs, is identified at a downstream location of blowing and suction. Soon a hairpin vortex, consisting of a head and two legs, is formed from the ( Λ ) vortex through the self induction mechanism. At a later time new hairpin vortices are successively produced behind the first hairpin vortex. At the final stage six hairpin vortices are observed. As the vortices move downstream in time, the legs of the ( Λ ) vortex get stronger and become quasi-streamwise vortices, while the head of the hairpin vortex changes into an ( Ω ) shape. Near the end of the computational domain the hairpin vortices and quasi-streamwise vortices are entangled with each other and convect downstream together; these phenomena are compared with the characteristics of a turbulent spot. It is shown that the spikes and saw-tooth like jumps in the streamwise velocity signals, observed in experiments, are associated with the heads and legs of the hairpin vortices, respectively.
Laminar boundary layer in conditions of natural transition to turbulent flow
NASA Technical Reports Server (NTRS)
Polyakov, N. F.
1986-01-01
Results of experimental study of regularities of a natural transition of a laminar boundary layer to a turbulent layer at low subsonic air flow velocities are presented, analyzed and compared with theory and model experiments.
Bypass transition in boundary layers including curvature and favorable pressure gradient effects
NASA Technical Reports Server (NTRS)
Volino, R. J.; Simon, T. W.
1991-01-01
Recent studies of 2-D boundary layers undergoing bypass transition were reviewed. Bypass transition is characterized by the sudden appearance of turbulent spots in boundary layer without first the regular, observable growth of disturbances predicted by linear stability theory. There are no standard criteria or parameters for defining bypass transition, but it is known to be the mode of transition when the flow is disturbed by perturbations of sufficient amplitude.
Orbiter Entry Aeroheating Working Group Viscous CFD Boundary Layer Transition Trailblazer Solutions
NASA Technical Reports Server (NTRS)
Wood, William A.; Erickson, David W.; Greene, Francis A.
2007-01-01
Boundary layer transition correlations for the Shuttle Orbiter have been previously developed utilizing a two-layer boundary layer prediction technique. The particular two-layer technique that was used is limited to Mach numbers less than 20. To allow assessments at Mach numbers greater than 20, it is proposed to use viscous CFD to the predict boundary layer properties. This report addresses if the existing Orbiter entry aeroheating viscous CFD solutions, which were originally intended to be used for heat transfer rate predictions, adequately resolve boundary layer edge properties and if the existing two-layer results could be leveraged to reduce the number of needed CFD solutions. The boundary layer edge parameters from viscous CFD solutions are extracted along the wind side centerline of the Space Shuttle Orbiter at reentry conditions, and are compared with results from the two-layer boundary layer prediction technique. The differences between the viscous CFD and two-layer prediction techniques vary between Mach 6 and 18 flight conditions and Mach 6 wind tunnel conditions, and there is not a straightforward scaling between the viscous CFD and two-layer values. Therefore: it is not possible to leverage the existing two-layer Orbiter flight boundary layer data set as a substitute for a viscous CFD data set; but viscous CFD solutions at the current grid resolution are sufficient to produce a boundary layer data set suitable for applying edge-based boundary layer transition correlations.
Free-stream disturbances, continuous eigenfunctions, boundary-layer instability and transition
NASA Technical Reports Server (NTRS)
Salwen, H.
1980-01-01
A rational foundation is provided for the application of the linear stability theory of parallel shear flows to transition prediction. An explicit method is given for carrying out the necessary calculations. The expansions are shown to be complete. Sample calculations show that a typical boundary layer is very sensitive to vorticity disturbance in the inner boundary layer near the critical layer. Vorticity disturbances three or four boundary layer thicknesses above the boundary are nearly uncoupled from the boundary layer, in that the amplitudes of the discrete Tollmein-Schlichting waves are an extremely small fraction of the amplitude of the disturbance.
Free-stream disturbance, continuous Eigenfunctions, boundary-layer instability and transition
NASA Technical Reports Server (NTRS)
Grosch, C. E.
1980-01-01
A rational foundation is presented for the application of the linear shear flows to transition prediction, and an explicit method is given for carrying out the necessary calculations. The expansions used are shown to be complete. Sample calculations show that a typical boundary layer is very sensitive to vorticity disturbances in the inner boundary layer, near the critical layer. Vorticity disturbances three or four boundary layer thicknesses above the boundary are nearly uncoupled from the boundary layer in that the amplitudes of the discrete Tollmien-Schlicting waves are an extremely small fraction of the amplitude of the disturbance.
Identifying Boundary-Layer Transitions on Aircraft Skin
NASA Technical Reports Server (NTRS)
Holmes, B. J.; Croom, C. C.; Kelliher, W. C.; Obara, C. J.
1984-01-01
Sublimating chemicals offer accurate, low-cost way of indicating laminarto-turbulent flow transisions on surfaces of aircraft. Aerodynamic surfaces coated with thin film of such volatile chemical solids as naphthalene, diphenyl, acenaphthene, or fluorene. Film sublimes rapidly because of high local shear stress and heat transfer in boundary layer. Coating appears white in regions where chemical remained on surface indicating laminar flow; regions where chemical disappeared indicate turbulent flow.
NASA Technical Reports Server (NTRS)
Martellucci, A.; Maguire, B. L.; Neff, R. S.
1972-01-01
The objective of the study was to provide a detailed post flight evaluation of ballistic vehicle flight test boundary layer transition data. A total of fifty-five vehicles were selected for analysis. These vehicles were chosen from a data sampling of roughly two hundred flights and the criteria for vehicle selection is delineated herein. The results of the analysis indicate that frustum transition of re-entry vehicles appears to be nose tip dominated. Frustum related parameters and materials apparently have a second order effect on transition. This implies that local viscous parameters on the frustum should not correlate flight test transition data, and in fact they do not. Specific parameters relative to the nose tip have been identified as the apparent dominant factors that characterize the transition phenomena and a correlation of flight test data is presented.
Effect of Protuberance Shape and Orientation on Space Shuttle Orbiter Boundary-Layer Transition
NASA Technical Reports Server (NTRS)
King, RUdolph A.; Berry, Scott A.; Kegerise, Michael A.
2008-01-01
This document describes an experimental study conducted to examine the effects of protuberances on hypersonic boundary-layer transition. The experiment was conducted in the Langley 20-Inch Mach 6 Tunnel on a series of 0.9%-scale Shuttle Orbiter models. The data were acquired to complement the existing ground-based boundary-layer transition database that was used to develop Version 1.0 of the boundary-layer transition RTF (return-to-flight) tool. The existing ground-based data were all acquired on 0.75%-scale Orbiter models using diamond-shaped ( pizza-box ) trips. The larger model scale facilitated in manufacturing higher fidelity protuberances. The end use of this experimental database will be to develop a technical basis (in the form of a boundary-layer transition correlation) to assess representative protrusion shapes, e.g., gap fillers and protrusions resulting from possible tile repair concepts. The primary objective of this study is to investigate the effects of protuberance-trip location and geometry on Shuttle Orbiter boundary-layer transition. Secondary goals are to assess the effects of gap-filler orientation and other protrusion shapes on boundary-layer transition. Global heat-transfer images using phosphor thermography of the Orbiter windward surface and the corresponding streamwise and spanwise heating distributions were used to infer the state of the boundary layer, i.e., laminar, transitional, or turbulent.
NASA Technical Reports Server (NTRS)
Reshotko, E.
1974-01-01
Review of the nature and goals of the NASA Transition Study program aimed at developing procedures yielding information relevant to anomalies in boundary layer transition data and future estimation of transition Reynolds numbers. Specific experimental programs have been formulated that emphasize careful and redundant measurements, documentation of the disturbance environment, and elimination of facility induced transition, whenever possible.
NASA Technical Reports Server (NTRS)
Weilmuenster, K. J.
1974-01-01
Experimental measurements of boundary-layer transition in an expansion-tube test-gas flow are presented along with radial distributions of pitot pressure. An integral method for calculating constant Reynolds number lines for an expansion-tube flow is introduced. Comparison of experimental data and constant Reynolds number calculations has shown that for given conditions, wall boundary-layer transition occurs at a constant Reynolds number in an expansion-tube flow. Operating conditions in the expansion tube were chosen so that the effects of test-gas nonequilibrium on boundary-layer transition could be studied.
Transition in a Supersonic Boundary Layer due to Acoustic Disturbances
NASA Technical Reports Server (NTRS)
Balakumar, Ponnampalam
2004-01-01
The boundary layer receptivity process due to the interaction of three-dimensional slow and fast acoustic disturbances with a blunted flat plate is numerically investigated at a free stream Mach number of 3.5 and at a high Reynolds number of 106/inch. The computations are performed with and without two-dimensional isolated roughness element located near the leading edge. Both the steady and unsteady solutions are obtained by solving the full Navier-Stokes equations using the 5th-order accurate weighted essentially non-oscillatory (WENO) scheme for space discretization and using third-order total-variation-diminishing (TVD) Runge-Kutta scheme for time integration. The simulations showed that the linear instability waves are generated very close to the leading edge. The wavelength of the disturbances inside the boundary layer first increases gradually and becomes longer than the wavelength for the instability waves within a short distance from the leading edge. The wavelength then decreases gradually and merges with the wavelength for the Tollmien_Schlichting wave. The initial amplitudes of the instability waves near the neutral points, the receptivity coefficients, are about 1.20 and 0.07 times the amplitude of the free-stream disturbances for the slow and the fast waves respectively. It was also revealed that small isolated roughness element does not enhance the receptivity process for the given nose bluntness.
Transition in a Supersonic Boundary Layer Due to Acoustic Disturbances
NASA Technical Reports Server (NTRS)
Balakumar, P.
2005-01-01
The boundary layer receptivity process due to the interaction of three-dimensional slow and fast acoustic disturbances with a blunted flat plate is numerically investigated at a free stream Mach number of 3.5 and at a high Reynolds number of 10(exp 6)/inch. The computations are performed with and without two-dimensional isolated roughness element located near the leading edge. Both the steady and unsteady solutions are obtained by solving the full Navier-Stokes equations using the fifth-order accurate weighted essentially non-oscillatory (WENO) scheme for space discretization and using third-order total-variation-diminishing (TVD) Runge-Kutta scheme for time integration. The simulations showed that the linear instability waves are generated very close to the leading edge. The wavelength of the disturbances inside the boundary layer first increases gradually and becomes longer than the wavelength for the instability waves within a short distance from the leading edge. The wavelength then decreases gradually and merges with the wavelength for the Tollmien-Schlichting wave. The initial amplitudes of the instability waves near the neutral points, the receptivity coefficients, are about 1.20 and 0.07 times the amplitude of the free-stream disturbances for the slow and the fast waves respectively. It was also revealed that small isolated roughness element does not enhance the receptivity process for the given nose bluntness.
NASA Technical Reports Server (NTRS)
Walker, G. J.; Solomon, W. J.
2007-01-01
Quantitative observations of transitional boundary layers in regions of strong flow deceleration on an axial compressor stator blade are reported. Measurements are obtained at a fixed chordwise position, and the blade incidence was varied by changing the compressor throughflow so as to move the transition region relative to the stationary probe. It was thus possible to observe typical boundary layer behavior at various stages of transition in the turbomachine environment. The range of observations covers separating laminar flow at transition onset, and reattachment of intermittently turbulent periodically separated shear layers.
NASA Technical Reports Server (NTRS)
Boldman, D. R.; Brinich, P. F.
1974-01-01
The boundary-layer transition on a short plate was studied by means of the china-clay visual technique. The plate model was mounted in a wind tunnel so that it was subjected to small simultaneous spanwise and chordwise pressure gradients. Results of the experimental study, which was performed at three subsonic velocities, indicated that the transition pattern was appreciably curved in the spanwise direction but quite smooth and well behaved. Reasonable comparisons between predictions of transition and experiment were obtained from two finite-difference two-dimensional boundary-layer calculation methods which incorporated transition models based on the concept of a transition intermittency factor.
Shuttle Return To Flight Experimental Results: Protuberance Effects on Boundary Layer Transition
NASA Technical Reports Server (NTRS)
Liechty, Derek S.; Berry, Scott A.; Horvath, Thomas J.
2006-01-01
The effect of isolated roughness elements on the windward boundary layer of the Shuttle Orbiter has been experimentally examined in the Langley Aerothermodynamic Laboratory in support of an agency-wide effort to prepare the Shuttle Orbiter for return to flight. This experimental effort was initiated to provide a roughness effects database for developing transition criteria to support on-orbit decisions to repair damage to the thermal protection system. Boundary layer transition results were obtained using trips of varying heights and locations along the centerline and attachment lines of 0.0075-scale models. Global heat transfer images using phosphor thermography of the Orbiter windward surface and the corresponding heating distributions were used to infer the state of the boundary layer (laminar, transitional, or turbulent). The database contained within this report will be used to formulate protuberance-induced transition correlations using predicted boundary layer edge parameters.
NASA Technical Reports Server (NTRS)
Von Doenhoff, Albert E
1938-01-01
Boundary-layer surveys were made throughout the transition region along a smooth flat plate placed in an airstream of practically zero turbulence and with an adverse pressure gradient. The boundary-layer Reynolds number at the laminar separation point was varied from 1,800 to 2,600. The test data, when considered in the light of certain theoretical deductions, indicated that transition probably began with separation of the laminar boundary layer. The extent of the transition region, defined as the distance from a calculated laminar separation point to the position of the first fully developed turbulent boundary-layer profile, could be expressed as a constant Reynolds number run of approximately 70,000. Some speculations are presented concerning the application of the foregoing concepts, after certain assumptions have been made, to the problem of the connection between transition on the upper surface of an airfoil at high angles of attack and the maximum lift.
Computer graphic visualization of orbiter lower surface boundary-layer transition
NASA Technical Reports Server (NTRS)
Throckmorton, D. A.; Hartung, L. C.
1984-01-01
Computer graphic techniques are applied to the processing of Shuttle Orbiter flight data in order to create a visual presentation of the extent and movement of the boundary-layer transition front over the orbiter lower surface during entry. Flight-measured surface temperature-time histories define the onset and completion of the boundary-layer transition process at any measurement location. The locus of points which define the spatial position of the boundary-layer transition front on the orbiter planform is plotted at each discrete time for which flight data are available. Displaying these images sequentially in real-time results in an animated simulation of the in-flight boundary-layer transition process.
Study of boundary-layer transition using transonic-cone preston tube data
NASA Technical Reports Server (NTRS)
Reed, T. D.; Moretti, P. M.
1980-01-01
The laminar boundary layer on a 10 degree cone in a transonic wind tunnel was studied. The inviscid flow and boundary layer development were simulated by computer programs. The effects of pitch and yaw angles on the boundary layer were examined. Preston-tube data, taken on the boundary-layer-transition cone in the NASA Ames 11 ft transonic wind tunnel, were used to develope a correlation which relates the measurements to theoretical values of laminar skin friction. The recommended correlation is based on a compressible form of the classical law-of-the-wall. The computer codes successfully simulates the laminar boundary layer for near-zero pitch and yaw angles. However, in cases of significant pitch and/or yaw angles, the flow is three dimensional and the boundary layer computer code used here cannot provide a satisfactory model. The skin-friction correlation is thought to be valid for body geometries other than cones.
High-resolution PIV measurements of a transitional shock wave-boundary layer interaction
NASA Astrophysics Data System (ADS)
Giepman, R. H. M.; Schrijer, F. F. J.; van Oudheusden, B. W.
2015-06-01
This study investigates the effects of boundary layer transition on an oblique shock wave reflection. The Mach number was 1.7, the unit Reynolds number was 35 × 106 m-1, and the pressure ratio over the interaction was 1.35. Particle image velocimetry is used as the main flow diagnostics tool, supported by oil-flow and Schlieren visualizations. At these conditions, the thickness of the laminar boundary layer is only 0.2 mm, and seeding proved to be problematic as practically no seeding was recorded in the lower 40 % of the boundary layer. The top 60 % could, however, still be resolved with good accuracy and is found to be in good agreement with the compressible Blasius solution. Due to the effects of turbulent mixing, the near-wall seeding deficiency disappears when the boundary layer transitions to a turbulent state. This allowed the seeding distribution to be used as an indicator for the state of the boundary layer, permitting to obtain an approximate intermittency distribution for the boundary layer transition region. This knowledge was then used for positioning the oblique shock wave in the laminar, transitional (50 % intermittency) or turbulent region of the boundary layer. Separation is only recorded for the laminar and transitional interactions. For the laminar interaction, a large separation bubble is found, with a streamwise length of 96. The incoming boundary layer is lifted over the separation bubble and remains in a laminar state up to the impingement point of the shock wave. After the shock, transition starts and a turbulent profile is reached approximately 80-90 downstream of the shock. Under the same shock conditions, the transitional interaction displays a smaller separation bubble (43), and transition is found to be accelerated over the separation bubble.
NASA Technical Reports Server (NTRS)
Loitsianskii. L. G.
1956-01-01
The fundamental, practically the most important branch of the modern mechanics of a viscous fluid or a gas, is that branch which concerns itself with the study of the boundary layer. The presence of a boundary layer accounts for the origin of the resistance and lift force, the breakdown of the smooth flow about bodies, and other phenomena that are associated with the motion of a body in a real fluid. The concept of boundary layer was clearly formulated by the founder of aerodynamics, N. E. Joukowsky, in his well-known work "On the Form of Ships" published as early as 1890. In his book "Theoretical Foundations of Air Navigation," Joukowsky gave an account of the most important properties of the boundary layer and pointed out the part played by it in the production of the resistance of bodies to motion. The fundamental differential equations of the motion of a fluid in a laminar boundary layer were given by Prandtl in 1904; the first solutions of these equations date from 1907 to 1910. As regards the turbulent boundary layer, there does not exist even to this day any rigorous formulation of this problem because there is no closed system of equations for the turbulent motion of a fluid. Soviet scientists have done much toward developing a general theory of the boundary layer, and in that branch of the theory which is of greatest practical importance at the present time, namely the study of the boundary layer at large velocities of the body in a compressed gas, the efforts of the scientists of our country have borne fruit in the creation of a new theory which leaves far behind all that has been done previously in this direction. We shall herein enumerate the most important results by Soviet scientists in the development of the theory of the boundary layer.
Effect of adverse pressure gradient on high speed boundary layer transition
NASA Astrophysics Data System (ADS)
Franko, Kenneth J.; Lele, Sanjiva
2014-02-01
The effect of adverse pressure gradients (APG) on boundary layer stability, breakdown, and heat-transfer overshoot is investigated. Flat plate isothermal boundary layers initially at Mach 6 with APG imposed through the freestream boundary condition are simulated using suction and blowing to produce boundary layer instabilities. The three different transition mechanisms compared are first mode oblique breakdown, second mode oblique breakdown, and second mode fundamental resonance. For all of the transition mechanisms, an adverse pressure gradient increases the linear growth rates and quickens the transition to turbulence. However, the nonlinear breakdown for all three transition mechanisms is qualitatively the same as for a zero pressure gradient boundary layer. First mode oblique breakdown leads to the earliest transition location and an overshoot in heat transfer in the transitional region. Both types of Mack second mode forcing lead to a transitional boundary layer but even with the increased growth rates and N factors produced by the adverse pressure gradient, the breakdown process is still more gradual than first mode oblique breakdown because the primary Mack second mode instabilities saturate and produce streaks that breakdown further downstream.
Measurements in a Transitional Boundary Layer Under Low-Pressure Turbine Airfoil Conditions
NASA Technical Reports Server (NTRS)
Simon, Terrence W.; Qiu, Songgang; Yuan, Kebiao; Ashpis, David (Technical Monitor); Simon, Fred (Technical Monitor)
2000-01-01
This report presents the results of an experimental study of transition from laminar to turbulent flow in boundary layers or in shear layers over separation zones on a convex-curved surface which simulates the suction surface of a low-pressure turbine airfoil. Flows with various free-stream turbulence intensity (FSTI) values (0.5%, 2.5% and 10%), and various Reynolds numbers (50,000, 100,000 200,000 and 300,000) are investigated. Reynold numbers in the present study are based on suction surface length and passage exit mean velocity. Flow separation followed by transition within the separated flow region is observed for the lower-Re cases at each of the FSTI levels. At the highest Reynolds numbers and at elevated FSn, transition of the attached boundary layer begins before separation, and the separation zone is small. Transition proceeds in the shear layer over the separation bubble. For both the transitional boundary layer and the transitional shear layer, mean velocity, turbulence intensity and intermittency (the fraction of the time the flow is turbulent) distributions are presented. The present data are compared to published distribution models for bypass transition, intermittency distribution through transition, transition start position, and transition length. A model developed for transition of separated flows is shown to adequately predict the location of the beginning of transition, for these cases, and a model developed for transitional boundary layer flows seems to adequately predict the path of intermittency through transition when the transition start and end are known. These results are useful for the design of low-pressure turbine stages which are known to operate under conditions replicated by these tests.
NASA Technical Reports Server (NTRS)
Bathel, Brett F.; Johansen, Craig T.; Danehy, Paul M.; Inman, Jennifer A.; Jones, Stephen B.; Goyne, Christopher P.
2011-01-01
Measurements of instantaneous and mean streamwise velocity profiles in a hypersonic laminar boundary layer as well as a boundary layer undergoing laminar-to-turbulent transition were obtained over a 10-degree half-angle wedge model. A molecular tagging velocimetry technique consisting of a NO2 approaches?NO photo-dissociation reaction and two subsequent excitations of NO was used. The measurement of the transitional boundary layer velocity profiles was made downstream of a 1-mm tall, 4-mm diameter cylindrical trip along several lines lying within a streamwise measurement plane normal to the model surface and offset 6-mm from the model centerline. For laminar and transitional boundary layer measurements, the magnitudes of streamwise velocity fluctuations are compared. In the transitional boundary layer the fluctuations were, in general, 2-4 times larger than those in the laminar boundary layer. Of particular interest were fluctuations corresponding to a height of approximately 50% of the laminar boundary layer thickness having a magnitude of nearly 30% of the mean measured velocity. For comparison, the measured fluctuations in the laminar boundary layer were approximately 5% of the mean measured velocity at the same location. For the highest 10% signal-to-noise ratio data, average single-shot uncertainties using a 1 ?Es and 50 ?Es interframe delay were 115 m/s and 3 m/s, respectively. By averaging single-shot measurements of the transitional boundary layer, uncertainties in mean velocity as low as 39 m/s were obtained in the wind tunnel. The wall-normal and streamwise spatial resolutions were 0.14-mm (2 pixel) and 0.82-mm (11 pixels), respectively. These measurements were performed in the 31-inch Mach 10 Air Wind Tunnel at the NASA Langley Research Center.
Effect of a 3D surface depression on boundary layer transition
NASA Astrophysics Data System (ADS)
Xu, Hui; Mughal, Shahid; Sherwin, Spencer J.
2015-11-01
The influence of a three-dimensional surface depression on the transitional boundary layer is investigated numerically. In the boundary layer transition, the primary mode is a Tollmien-Schlichting (TS) wave which is a viscous instability. These modes are receptive to surface roughness interacting with free stream disturbances and/or surface vibrations. In this paper, numerical calculations are carried out to investigate the effect of the depression on instability of the boundary layer. In order to implement linear analysis, two/three (2D/3D)-dimensional nonlinear Navier-Stokes equations are solved by spectral element method to generate base flows in a sufficient large domain. The linear analyses are done by the parabolic stability equations (PSE). Finally, a DNS calculation is done to simulate the boundary layer transition.
NASA Astrophysics Data System (ADS)
Zhao, Yunfei; Liu, Wei; Xu, Dan; Gang, Dundian; Yi, Shihe
2016-01-01
The effect of surface roughness on boundary layer transition is of great importance to hypersonic vehicles. In this paper, both experimental and numerical methods are used to investigate the laminar-turbulent transition of a Mach 3 flat-plate boundary layer induced by isolated roughness element. Good agreements are achieved between experimental data and high-order numerical simulations. It is observed that, with increasing height of roughness, the transition tends to move forward. Two different types of transition mechanisms are found according to the height of the roughness elements. For the smallest roughness height of h=1 mm, the shear layer instability in the wake region appears to be the leading mechanism for transition to turbulence. For two larger roughness elements of h=2 mm and h=4 mm, strong unsteadiness is developed from the upstream separation zone and transition is immediately accomplished, which indicates that the absolute instability in upstream separation zone dominates the transition.
Modeling of the heat transfer in bypass transitional boundary-layer flows
NASA Technical Reports Server (NTRS)
Simon, Frederick F.; Stephens, Craig A.
1991-01-01
A low Reynolds number k-epsilon turbulence model and conditioned momentum, energy and turbulence equations were used to predict bypass transition heat transfer on a flat plate in a high-disturbance environment with zero pressure gradient. The use of conditioned equations was demonstrated to be an improvement over the use of the global-time-averaged equations for the calculation of velocity profiles and turbulence intensity profiles in the transition region of a boundary layer. The approach of conditioned equations is extended to include heat transfer and a modeling of transition events is used to predict transition onset and the extent of transition on a flat plate. The events, which describe the boundary layer at the leading edge, result in boundary-layer regions consisting of: (1) the laminar, (2) pseudolaminar, (3) transitional, and (4) turbulent boundary layers. The modeled transition events were incorporated into the TEXSTAN 2-D boundary-layer code which is used to numerically predict the heat transfer. The numerical predictions in general compared well with the experimental data and revealed areas where additional experimental information is needed.
Flight-measured laminar boundary-layer transition phenomena including stability theory analysis
NASA Technical Reports Server (NTRS)
Obara, C. J.; Holmes, B. J.
1985-01-01
Flight experiments were conducted on a single-engine turboprop aircraft fitted with a 92-in-chord, 3-ft-span natural laminar flow glove at glove section lift coefficients from 0.15 to 1.10. The boundary-layer transition measurement methods used included sublimating chemicals and surface hot-film sensors. Transition occurred downstream of the minimum pressure point. Hot-film sensors provided a well-defined indication of laminar, laminar-separation, transitional, and turbulent boundary layers. Theoretical calculations of the boundary-layer parameters provided close agreement between the predicted laminar-separation point and the measured transition location. Tollmien-Schlichting (T-S) wave growth n-factors between 15 and 17 were calculated at the predicted point of laminar separation. These results suggest that for many practical airplane cruise conditions, laminar separation (as opposed to T-S instability) is the major cause of transition in predominantly two-dimensional flows.
Assessment of a transitional boundary layer theory at low hypersonic Mach numbers
NASA Technical Reports Server (NTRS)
Shamroth, S. J.; Mcdonald, H.
1972-01-01
An investigation was carried out to assess the accuracy of a transitional boundary layer theory in the low hypersonic Mach number regime. The theory is based upon the simultaneous numerical solution of the boundary layer partial differential equations for the mean motion and an integral form of the turbulence kinetic energy equation which controls the magnitude and development of the Reynolds stress. Comparisions with experimental data show the theory is capable of accurately predicting heat transfer and velocity profiles through the transitional regime and correctly predicts the effects of Mach number and wall cooling on transition Reynolds number. The procedure shows promise of predicting the initiation of transition for given free stream disturbance levels. The effects on transition predictions of the pressure dilitation term and of direct absorption of acoustic energy by the boundary layer were evaluated.
Three-dimensional boundary layer stability and transition
NASA Technical Reports Server (NTRS)
Malik, M. R.; Li, F.
1992-01-01
Nonparallel and nonlinear stability of a three-dimensional boundary layer, subject to crossflow instability, is investigated using parabolized stability equations (PSEs). Both traveling and stationary disturbances are considered and nonparallel effect on crossflow instability is found to be destabilizing. Our linear PSE results for stationary disturbances agree well with the results from direct solution of Navier-Stokes equations obtained by Spalart (1989). Nonlinear calculations have been carried out for stationary vortices and the computed wall vorticity pattern results in streamwise streaks which resemble remarkably well with the surface oil-flow visualizations in swept-wing experiments. Other features of the stationary vortex development (half-mushroom structure, inflected velocity profiles, vortex doubling, etc.) are also captured in our nonlinear calculations. Nonlinear interaction of the stationary amplitude of the stationary vortex is large as compared to the traveling mode, and the stationary vortex dominates most of the downstream development. When the two modes have the same initial amplitude, the traveling mode dominates the downstream development owing to its higher growth rate, and there is a tendency for the stationary mode to be suppressed. The effect of nonlinear wave development on the skin-friction coefficient is also computed.
Flight and wind-tunnel correlation of boundary-layer transition on the AEDC transition cone
NASA Technical Reports Server (NTRS)
Fisher, D. L.; Dougherty, N. S., Jr.
1982-01-01
Transition and fluctuating surface pressure data were acquired on a 10 deg included angle cone, using the same instrumentation and technique over a wide range of Mach and Reynolds numbers in 23 wind tunnels and in flight. Transition was detected with a traversing pitot-pressure probe in contact with the surface. The surface pressure fluctuations were measured with microphones set flush in the cone surface. Good correlation of end of transition Reynolds number RE(T) was obtained between data from the lower disturbance wind tunnels and flight up to a boundary layer edge Mach number, M(e) = 1.2. Above M(e) = 1.2, however, this correlation deteriorates, with the flight Re(T) being 25 to 30% higher than the wind tunnel Re(T) at M(e) = 1.6. The end of transition Reynolds number correlated within + or - 20% with the surface pressure fluctuations, according to the equation used. Broad peaks in the power spectral density distributions indicated that Tollmien-Schlichting waves were the probable cause of transition in flight and in some of the wind tunnels.
NASA Technical Reports Server (NTRS)
Volino, Ralph J.; Hultgren, Lennart .
2000-01-01
Detailed velocity measurements were made along a flat plate subject to the same dimensionless pressure gradient as the suction side of a modern low-pressure turbine airfoil. Reynolds numbers based on wetted plate length and nominal exit velocity were varied from 50,000 to 300,000, covering cruise to takeoff conditions. Low and high inlet free-stream turbulence intensities (0.2% and 7%) were set using passive grids. The location of boundary-layer separation does not depend strongly on the free-stream turbulence level or Reynolds number, as long as the boundary layer remains non-turbulent prior to separation. Strong acceleration prevents transition on the upstream part of the plate in all cases. Both free-stream turbulence and Reynolds number have strong effects on transition in the adverse pressure gradient region. Under low free-stream turbulence conditions transition is induced by instability waves in the shear layer of the separation bubble. Reattachment generally occurs at the transition start. At Re = 50,000 the separation bubble does not close before the trailing edge of the modeled airfoil. At higher Re, transition moves upstream, and the boundary layer reattaches. With high free-stream turbulence levels, transition appears to occur in a bypass mode, similar to that in attached boundary layers. Transition moves upstream, resulting in shorter separation regions. At Re above 200,000, transition begins before separation. Mean velocity, turbulence and intermittency profiles are presented.
Optical boundary-layer transition detection in a transonic wind tunnel
NASA Technical Reports Server (NTRS)
Azzazy, M.; Modarress, D.; Hall, R. M.
1987-01-01
A high-sensitivity interferometer has been developed and used to detect boundary-layer transitions over a symmetric airfoil. The tests, which included both natural and roughness-induced transitions, were performed in a transonic wind tunnel. The measurements showed a peak amplitude rms and higher energy in the spectrum of the signal associated with transition. The tests revealed that the interferometer system can be used to locate the transition region over three-dimensional aerodynamic models.
NASA Astrophysics Data System (ADS)
Volino, Ralph John
1995-01-01
Measurements from transitional, heated boundary layers along a concave-curved test wall are presented and discussed. A boundary layer subject to low free-stream turbulence intensity (FSTI), which contains stationary streamwise (Gortler) vortices, is documented. The low FSTI measurements are followed by measurements in boundary layers subject to high (initially 8%) free-stream turbulence intensity and moderate to strong (K = {nuover U_sp{infty} {2}}{dUinftyover dx} as high as 9times 10^{ -6}) acceleration. The high FSTI experiments are the main focus of the work. Conditions were chosen to simulate those present on the downstream half of the pressure side of a gas turbine airfoil. The high FSTI boundary layers undergo transition from a strongly disturbed non-turbulent state to a fully-turbulent state. Due to the stabilizing effect of strong acceleration, the transition zones are of extended length in spite of the high FSTI. Transitional values of skin friction coefficients and Stanton numbers drop below flat-plate, low FSTI, turbulent flow correlations, but remain well above laminar flow values. Mean velocity and temperature profiles exhibit clear changes in shape as the flow passes through transition. Turbulence statistics, including the turbulent shear stress, turbulent heat flux, and turbulent Prandtl number, are documented. Turbulent transport is strongly suppressed below values in unaccelerated turbulent boundary layers. A technique called "octant analysis" is introduced and applied to several cases from the literature as well as to data from the present study. Octant analysis shows a fundamental difference between transitional and fully-turbulent boundary layers. Transitional boundary layers are characterized by incomplete mixing compared to fully-turbulent boundary layers. Similar octant analysis results are observed in both low and high FSTI cases. Spectral analysis suggests that the non-turbulent zone of the high FSTI flow is dominated by large scale
Effect of Far-Field Boundary Conditions on Boundary-Layer Transition
NASA Technical Reports Server (NTRS)
Bertolotti, Fabio P.; Joslin, Ronald D.
1994-01-01
The effect of far-field boundary conditions on the evolution of a finite-amplitude two-dimensional wave in the Blasius boundary layer is assessed. With the use of the parabolized stability equations (PSE) theory for the numerical computations, either asymptotic, Dirichlet, Neumann or mixed boundary conditions are imposed at various distances from the wall. The results indicate that asymptotic and mixed boundary conditions yield the most accurate mean-flow distortion and unsteady instability modes in comparison with the results obtained with either Dirichlet or Neumann conditions.
Effect of Far-Field Boundary Conditions on Boundary-Layer Transition
NASA Technical Reports Server (NTRS)
Bertolotti, Fabio P.; Joslin, Ronald D.
1995-01-01
The effect of far-field boundary conditions on the evolution of a finite-amplitude two-dimensional wave in the Blasius boundary layer is assessed. With the use of the parabolized stability equations (PSE) theory for the numerical computations, either asymptotic, Dirichlet, Neumann or mixed boundary conditions are imposed at various distances from the wall. The results indicate that asymptotic and mixed boundary conditions yield the most accurate mean-flow distortion and unsteady instability modes in comparison with the results obtained with either Dirichlet or Neumann conditions.
Effect of Surface Waviness on Transition in Three-Dimensional Boundary-Layer Flow
NASA Technical Reports Server (NTRS)
Masad, Jamal A.
1996-01-01
The effect of a surface wave on transition in three-dimensional boundary-layer flow over an infinite swept wing was studied. The mean flow computed using interacting boundary-layer theory, and transition was predicted using linear stability theory coupled with the empirical eN method. It was found that decreasing the wave height, sweep angle, or freestream unit Reynolds number, and increasing the freestream Mach number or suction level all stabilized the flow and moved transition onset to downstream locations.
Shuttle Return To Flight Experimental Results: Cavity Effects on Boundary Layer Transition
NASA Technical Reports Server (NTRS)
Liechty, Derek S.; Horvath, Thomas J.; Berry, Scott A.
2006-01-01
The effect of an isolated rectangular cavity on hypersonic boundary layer transition of the windward surface of the Shuttle Orbiter has been experimentally examined in the Langley Aerothermodynamics Laboratory in support of an agency-wide effort to prepare the Shuttle Orbiter for return to flight. This experimental study was initiated to provide a cavity effects database for developing hypersonic transition criteria to support on-orbit decisions to repair a damaged thermal protection system. Boundary layer transition results were obtained using 0.0075-scale Orbiter models with simulated tile damage (rectangular cavities) of varying length, width, and depth. The database contained within this report will be used to formulate cavity-induced transition correlations using predicted boundary layer edge parameters.
Experimental studies on the stability and transition of 3-dimensional boundary layers
NASA Technical Reports Server (NTRS)
Nitschke-Kowsky, P.
1987-01-01
Three-dimensional unstable boundary layers were investigated as to their characteristic instabilities, leading to turbulence. Standing cross-flow instabilities and traveling waves preceding the transition were visualized with the hydrogen bubble technique in the boundary layer above the wall of a swept cylinder. With the sublimation method and hot film technique, a model consisting of a swept flat plate with a pressure-inducing displacement body in the 1 m wind tunnel was studied. Standing waves and traveling waves in a broad frequency are observed. The boundary layer of this model is close to the assumptions of the theory.
Roles of Engineering Correlations in Hypersonic Entry Boundary Layer Transition Prediction
NASA Technical Reports Server (NTRS)
Campbell, Charles H.; King, Rudolph A.; Kergerise, Michael A.; Berry, Scott A.; Horvath, Thomas J.
2010-01-01
Efforts to design and operate hypersonic entry vehicles are constrained by many considerations that involve all aspects of an entry vehicle system. One of the more significant physical phenomenon that affect entry trajectory and thermal protection system design is the occurrence of boundary layer transition from a laminar to turbulent state. During the Space Shuttle Return To Flight activity following the loss of Columbia and her crew of seven, NASA's entry aerothermodynamics community implemented an engineering correlation based framework for the prediction of boundary layer transition on the Orbiter. The methodology for this implementation relies upon the framework of correlation techniques that have been in use for several decades. What makes the Orbiter boundary layer transition correlation implementation unique is that a statistically significant data set was acquired in multiple ground test facilities, flight data exists to assist in establishing a better correlation and the framework was founded upon state of the art chemical nonequilibrium Navier Stokes flow field simulations. The basic tenets that guided the formulation and implementation of the Orbiter Return To Flight boundary layer transition prediction capability will be reviewed as a recommended format for future empirical correlation efforts. The validity of this approach has since been demonstrated by very favorable comparison of recent entry flight testing performed with the Orbiter Discovery, which will be graphically summarized. These flight data can provide a means to validate discrete protuberance engineering correlation approaches as well as high fidelity prediction methods to higher confidence. The results of these Orbiter engineering and flight test activities only serve to reinforce the essential role that engineering correlations currently exercise in the design and operation of entry vehicles. The framework of information-related to the Orbiter empirical boundary layer transition
Overview of Boundary Layer Transition Research in Support of Orbiter Return To Flight
NASA Technical Reports Server (NTRS)
Berry, Scott A.; Horvath, Thomas J.; Greene, Francis A.; Kinder, Gerald R.; Wang, K. C.
2006-01-01
A predictive tool for estimating the onset of boundary layer transition resulting from damage to and/or repair of the thermal protection system was developed in support of Shuttle Return to Flight. The boundary layer transition tool is part of a suite of tools that analyze the aerothermodynamic environment to the local thermal protection system to allow informed disposition of damage for making recommendations to fly as is or to repair. Using mission specific trajectory information and details of each damage site or repair, the expected time (and thus Mach number) at transition onset is predicted to help define the aerothermodynamic environment to use in the subsequent thermal and stress analysis of the local thermal protection system and structure. The boundary layer transition criteria utilized for the tool was developed from ground-based measurements to account for the effect of both protuberances and cavities and has been calibrated against select flight data. Computed local boundary layer edge conditions were used to correlate the results, specifically the momentum thickness Reynolds number over the edge Mach number and the boundary layer thickness. For the initial Return to Flight mission, STS-114, empirical curve coefficients of 27, 100, and 900 were selected to predict transition onset for protuberances based on height, and cavities based on depth and length, respectively.
NASA Technical Reports Server (NTRS)
Liepmann, Hans W; Fila, Gertrude H
1947-01-01
The laminar boundary layer and the position of the transition point were investigated on a heated flat plate. It was found that the Reynolds number of transition decreased as the temperature of the plate is increased. It is shown from simple qualitative analytical considerations that the effect of variable viscosity in the boundary layer due to the temperature difference produces a velocity profile with an inflection point if the wall temperature is higher than the free-stream temperature. This profile is confirmed by measurements. The instability of inflection-point profiles is discussed. Studies of the flow in the wake of large, two-dimensional roughness elements are presented. It is shown that a boundary-layer can separate and reattach itself to the wall without having transition take place.
Version 2 of the Protuberance Correlations for the Shuttle-Orbiter Boundary Layer Transition Tool
NASA Technical Reports Server (NTRS)
King, Rudolph A.; Kegerise, Michael A.; Berry, Scott A.
2009-01-01
Orbiter-specific transition data, acquired in four ground-based facilities (LaRC 20-Inch Mach 6 Air Tunnel, LaRC 31-Inch Mach 10 Air Tunnel, LaRC 20-Inch Mach 6 CF4 Tunnel, and CUBRC LENS-I Shock Tunnel) with three wind tunnel model scales (0.75, 0.90, and 1.8%) and from Orbiter historical flight data, have been analyzed to improve a pre-existing engineering tool for reentry transition prediction on the windward side of the Orbiter. Boundary layer transition (BLT) engineering correlations for transition induced by isolated protuberances are presented using a laminar Navier-Stokes (N-S) database to provide the relevant boundary-layer properties. It is demonstrated that the earlier version of the BLT correlation that had been developed using parameters derived from an engineering boundary-layer code has improved data collapse when developed with the N-S database. Of the new correlations examined, the proposed correlation 5, based on boundary-layer edge and wall properties, was found to provide the best overall correlation metrics when the entire database is employed. The second independent correlation (proposed correlation 7) selected is based on properties within the boundary layer at the protuberance height. The Aeroheating Panel selected a process to derive the recommended coefficients for Version 2 of the BLT Tool. The assumptions and limitations of the recommended protuberance BLT Tool V.2 are presented.
Advanced IR System For Supersonic Boundary Layer Transition Flight Experiment
NASA Technical Reports Server (NTRS)
Banks, Daniel W.
2008-01-01
Infrared thermography is a preferred method investigating transition in flight: a) Global and non-intrusive; b) Can also be used to visualize and characterize other fluid mechanic phenomena such as shock impingement, separation etc. F-15 based system was updated with new camera and digital video recorder to support high Reynolds number transition tests. Digital Recording improves image quality and analysis capability and allows for accurate quantitative (temperature) measurements and greater enhancement through image processing allows analysis of smaller scale phenomena.
Measurement of transitional boundary layer on a flat plate using a computational Preston tube method
NASA Astrophysics Data System (ADS)
Jeon, W. P.; Kang, S. H.
1995-11-01
The development of the transitional boundary layers on a flat plate in uniform and non-uniform incoming flows was experimentally investigated. The mean velocity profiles and the wall shear stresses on a flat plate were measured in the wakes which were generated by circular cylinders and a flat plate ahead of the test plate. A computational Preston tube method (CPM) originally proposed by Nitsche et al. (1983) was adopted and refined to measure the skin friction coefficients in the transitional boundary layer. The CPM was verified as a useful tool to measure the skin-friction over the transitional boundary layer with reasonable accuracy. As the turbulence level in the wakes increased, the starting and ending points of the transition moved progressively upstream. For the same turbulence intensities, the transition was delayed with increase of the length scale. The skin-friction coefficients at the downstream stations in the wake flow were considerably and consistently smaller than the values in the equilibrium turbulent boundary layer of the uniform flow. The transition length for the cases of the plate-wake were shorter than those for the cases of the cylinder-wake as well as the uniform flow.
Minnowbrook I: 1993 Workshop on End-Stage Boundary Layer Transition
NASA Technical Reports Server (NTRS)
LaGraff, John E. (Editor)
2007-01-01
This volume contains materials presented at the Minnowbrook I-1993 Workshop on End-Stage Boundary Layer Transition, held at the Syracuse University Minnowbrook Conference Center, New York, from August 15 to 18, 1993. This volume was previously published as a Syracuse University report edited by John E. LaGraff. The workshop organizers were John E. LaGraff (Syracuse University), Terry V. Jones (Oxford University), and J. Paul Gostelow (University of Technology, Sydney). The workshop focused on physical understanding of the late stages of transition from laminar to turbulent flows, with the specific goal of contributing to improving engineering design of turbomachinery and wing airfoils. The workshop participants included academic researchers from the United States and abroad, and representatives from the gas-turbine industry and U.S. government laboratories. To improve interaction and discussions among the participants, no formal papers were required. The physical mechanisms discussed were related to natural and bypass transition, wake-induced transition, effects of freestream turbulence, turbulent spots, hairpin vortices, nonlinear instabilities and breakdown, instability wave interactions, intermittency, turbulence, numerical simulation and modeling of transition, heat transfer in boundary-layer transition, transition in separated flows, laminarization, transition in turbomachinery compressors and turbines, hypersonic boundary-layer transition, and other related topics. This volume contains abstracts and copies of the viewgraphs presented, organized according to the workshop sessions. The workshop summary and the plenary discussion transcript clearly outline future research needs.
Influence of a heated leading edge on boundary layer growth, stability, and transition
Landrum, D.B.; Macha, J.M.
1987-01-01
This paper presents the results of a combined theoretical and experimental study of the influence of a heated leading edge on the growth, stability, and transition of a two-dimensional boundary layer. The findings are directly applicable to aircraft wings and nacelles that use surface heating for anti-icing protection. The potential effects of the non-adiabatic condition are particularly important for laminar-flow sections where even small perturbations can result in significantly degraded aerodynamic performance. The results of the study give new insight to the fundamental coupling between streamwise pressure gradient and surface heat flux in laminar and transitional boundary layers.
Influence of a heated leading edge on boundary layer growth, stability, and transition
Landrum, D.B.; Macha, J.M.
1987-06-01
This paper presents the results of a combined theoretical and experimental study of the influence of a heated leading edge on the growth, stability, and transition of a two-dimensional boundary layer. The findings are directly applicable to aircraft wings and nacelles that use surface heating for anti-icing protection. The potential effects of the non-adiabatic condition are particularly important for laminar-flow sections where even small perturbations can result in significantly degraded aerodynamic performance. The results of the study give new insight to the fundamental coupling between streamwise pressure gradient and surface heat flux in laminar and transitional boundary layers. 13 references.
Holt film wall shear instrumentation for boundary layer transition research
NASA Technical Reports Server (NTRS)
Schneider, Steven P.
1994-01-01
Measurements of the performance of hot-film wall-shear sensors were performed to aid development of improved sensors. The effect of film size and substrate properties on the sensor performance was quantified through parametric studies carried out both electronically and in a shock tube. The results show that sensor frequency response increases with decreasing sensor size, while at the same time sensitivity decreases. Substrate effects were also studied, through parametric variation of thermal conductivity and heat capacity. Early studies used complex dual-layer substrates, while later studies were designed for both single-layer and dual-layer substrates. Sensor failures and funding limitations have precluded completion of the substrate thermal-property tests.
Hypersonic Boundary-Layer Transition for X-33 Phase 2 Vehicle
NASA Technical Reports Server (NTRS)
Thompson, Richard A.; Hamilton, Harris H., II; Berry, Scott A.; Horvath, Thomas J.; Nowak, Robert J.
1998-01-01
A status review of the experimental and computational work performed to support the X-33 program in the area of hypersonic boundary-layer transition is presented. Global transition fronts are visualized using thermographic phosphor measurements. Results are used to derive transition correlations for "smooth body" and discrete roughness data and a computational tool is developed to predict transition onset for X-33 using these results. The X-33 thermal protection system appears to be conservatively designed for transition effects based on these studies. Additional study is needed to address concerns related to surface waviness. A discussion of future test plans is included.
Boundary Layer Transition in the Leading Edge Region of a Swept Cylinder in High Speed Flow
NASA Technical Reports Server (NTRS)
Coleman, Colin P.
1998-01-01
Experiments were conducted on a 76 degree swept cylinder to establish the behavior of the attachment line transition process in a low-disturbance level, Mach number 1.6 flow. For a near adiabatic wall condition, the attachment-line boundary layer remained laminar up to the highest attainable Reynolds number. The attachment-line boundary layer transition under the influence of trip wires depended on wind tunnel disturbance level, and a transition onset condition for this flow is established. Internal heating raised the surface temperature of the attachment line to induce boundary layer instabilities. This was demonstrated experimentally for the first time and the frequencies of the most amplified disturbances were determined over a range of temperature settings. Results were in excellent agreement to those predicted by a linear stability code, and provide the first experimental verification of theory. Transition onset along the heated attachment line at an R-bar of 800 under quiet tunnel conditions was found to correlate with an N factor of 13.2. Increased tunnel disturbance levels caused the transition onset to occur at lower cylinder surface temperatures and was found to correlate with an approximate N factor of 1 1.9, so demonstrating that the attachment-line boundary layer is receptive to increases in the tunnel disturbance level.
Modeling of transition and surface roughness effects in boundary-layer flows
NASA Technical Reports Server (NTRS)
Feiereisen, W. J.; Acharya, M.
1986-01-01
Experiments were carried out to examine the influence of three-dimensional, stochastic roughness on the growth of incompressible turbulent boundary layers, as well as the effect of streamwise pressure gradients and freestream turbulence intensity on smooth-wall boundary-layer transition. The modeling of these effects in a two-dimensional boundary-layer computation program was examined with the help of the experiments. A model for surface roughness was developed that relates directly measurable statistical parameters quantifying the roughness geometry to the aerodynamic effects. This model should be valid for a limited class of surfaces found on turbomachinery blading and in other engineering applications. Commonly used criteria for the transition onset performed poorly and presumably need to be modified to account for other factors influencing the process.
Derivation of generalized transition/boundary conditions for planar multiple-layer structures
NASA Technical Reports Server (NTRS)
Ricoy, M. A.; Volakis, J. L.
1990-01-01
Infinite-order generalized impedance boundary conditions (GIBCs) and generalized sheet transition conditions (GSTCs) for planar multilayer configurations are developed via the Taylor series expansion method. The conditions are derived in a matrix product form where each matrix corresponds to a specific layer. An overall composite boundary/transition condition is obtained by making finite-order approximations to the elements of each matrix for the cases of 'low-contrast' and 'high-contrast' material layers. The accuracy of the truncated boundary conditions is examined by comparing their implied reflection and transmission coefficients with the corresponding exact coefficients. Design curves are also given which relate the maximum order of the conditions required to simulate a coating or layer of specific thickness and contrast. Expressions are then derived for the reflection and transmission coefficients of the GIBC/GSTC sheets, and these are compared to exact coefficients to demonstrate the validity of the derived GIBCs/GSTCs.
Boundary Layer Transition During the Orion Exploration Flight Test 1 (EFT-1)
NASA Technical Reports Server (NTRS)
Kirk, Lindsay C.
2016-01-01
Boundary layer transition was observed in the thermocouple data on the windside backshell of the Orion reentry capsule. Sensors along the windside centerline, as well as off-centerline, indicated transition late in the flight at approximately Mach 4 conditions. Transition progressed as expected, beginning at the sensors closest to the forward bay cover (FBC) and moving towards the heatshield. Sensors placed in off-centerline locations did not follow streamlines, so the progression of transition observed in these sensors is less intuitive. Future analysis will include comparisons to pre-flight predictions and expected transitional behavior will be investigated. Sensors located within the centerline and off-centerline launch abort system (LAS) attach well cavities on the FBC also showed indications of boundary layer transition. The transition within the centerline cavity was observed in the temperature traces prior to transition onset on the sensors upstream of the cavity. Transition behavior within the off centerline LAS attach well cavity will also be investigated. Heatshield thermocouples were placed within Avcoat plugs to attempt to capture transitional behavior as well as better understand the aerothermal environments. Thermocouples were placed in stacks of two or five vertically within the plugs, but the temperature data obtained at the sensors closest to the surface did not immediately indicate transitional behavior. Efforts to use the in depth thermocouple temperatures to reconstruct the surface heat flux are ongoing and any results showing the onset of boundary layer transition obtained from those reconstructions will also be included in this paper. Transition on additional features of interest, including compression pad ramps, will be included if it becomes available.
Characteristics of the laminar-turbulent edge in transitional boundary layers
NASA Astrophysics Data System (ADS)
Lee, Jin; Zaki, Tamer
2015-11-01
Characteristics of the boundary separating the laminar and turbulent regions in a transitional boundary layer are examined using a time series of three-dimensional flow fields extracted from direct numerical simulations (DNS). In order to accurately mimic boundary-layer experiments perturbed by grid turbulence, the current simulation includes the leading edge of the flat plate and the incoming homogeneous isotropic turbulence. The Reynolds number based on the momentum thickness reaches up to 1400, and high-resolution three-dimensional flow fields of the DNS data will be publicly accessible via the Johns Hopkins Turbulence Database (JHTDB). The laminar-turbulence discrimination algorithm isolates the turbulence spots within the transition zone and the bounding surface of the fully-turbulent flow. Attention is placed on the cross-stream surface between the transition zone and fully-turbulent boundary layer. The shape of this interface is dictated by a balance between downstream advection, destabilization of upstream flow and merging of turbulence spots. Conditionally sampled statistics are examined across the interface, and are also compared to the downstream equilibrium turbulent boundary layer.
In-Flight Boundary-Layer Transition of a Large Flat Plate at Supersonic Speeds
NASA Technical Reports Server (NTRS)
Banks, D. W.; Frederick, M. A.; Tracy, R. R.; Matisheck, J. R.; Vanecek, N. D.
2012-01-01
A flight experiment was conducted to investigate the pressure distribution, local-flow conditions, and boundary-layer transition characteristics on a large flat plate in flight at supersonic speeds up to Mach 2.00. The tests used a NASA testbed aircraft with a bottom centerline mounted test fixture. The primary objective of the test was to characterize the local flow field in preparation for future tests of a high Reynolds number natural laminar flow test article. A second objective was to determine the boundary-layer transition characteristics on the flat plate and the effectiveness of using a simplified surface coating. Boundary-layer transition was captured in both analog and digital formats using an onboard infrared imaging system. Surface pressures were measured on the surface of the flat plate. Flow field measurements near the leading edge of the test fixture revealed the local flow characteristics including downwash, sidewash, and local Mach number. Results also indicated that the simplified surface coating did not provide sufficient insulation from the metallic structure, which likely had a substantial effect on boundary-layer transition compared with that of an adiabatic surface. Cold wall conditions were predominant during the acceleration to maximum Mach number, and warm wall conditions were evident during the subsequent deceleration.
NASA Astrophysics Data System (ADS)
Sayadi, Taraneh; Hamman, Curtis W.; Moin, Parviz
2012-09-01
In this fluid dynamics video, recent simulations of transition to turbulence in compressible (M = 0.2), zero-pressure-gradient flat-plate boundary layers triggered by fundamental (Klebanoff K-type) and subharmonic (Herbert H-type) secondary instabilities of Tollmien-Schlichting waves are highlighted.
Predicting Boundary-Layer Transition on Space-Shuttle Re-Entry
NASA Technical Reports Server (NTRS)
Berry, Scott; Horvath, Tom; Merski, Ron; Liechty, Derek; Greene, Frank; Bibb, Karen; Buck, Greg; Hamilton, Harris; Weilmuenster, Jim; Campbell, Chuck; Bouslog, Stan; Kirk, Ben; Bourland, Garry; Cassady, Amy; Anderson, Brian; Reda, Dan; Reuther, James; Kinder, Gerry; Chao, Dennis; Hyatt, Jay; Barnwell, Maria; Wang, K. C.; Schneider, Steve
2008-01-01
The BLT Prediction Tool ("BLT" signifies "Boundary Layer Transition") is provided as part of the Damage Assessment Team analysis package, which is utilized for analyzing local aerothermodynamics environments of damaged or repaired space-shuttle thermal protection tiles. Such analyses are helpful in deciding whether to repair launch-induced damage before re-entering the terrestrial atmosphere.
Application of a transitional boundary-layer theory in the low hypersonic Mach number regime
NASA Technical Reports Server (NTRS)
Shamroth, S. J.; Mcdonald, H.
1975-01-01
An investigation is made to assess the capability of a finite-difference boundary-layer procedure to predict the mean profile development across a transition from laminar to turbulent flow in the low hypersonic Mach-number regime. The boundary-layer procedure uses an integral form of the turbulence kinetic-energy equation to govern the development of the Reynolds apparent shear stress. The present investigation shows the ability of this procedure to predict Stanton number, velocity profiles, and density profiles through the transition region and, in addition, to predict the effect of wall cooling and Mach number on transition Reynolds number. The contribution of the pressure-dilatation term to the energy balance is examined and it is suggested that transition can be initiated by the direct absorption of acoustic energy even if only a small amount (1 per cent) of the incident acoustic energy is absorbed.
NASA Technical Reports Server (NTRS)
Lewis, T. L.; Banner, R. D.
1971-01-01
A flush-mounted microphone on the vertical fin of an X-15 airplane was used to investigate boundary layer transition phenomenon during flights to peak altitudes of approximately 70,000 meters. The flight results were compared with those from wind tunnel studies, skin temperature measurements, and empirical prediction data. The Reynolds numbers determined for the end of transition were consistent with those obtained from wind tunnel studies. Maximum surface-pressure-fluctuation coefficients in the transition region were about an order of magnitude greater than those for fully developed turbulent flow. This was also consistent with wind tunnel data. It was also noted that the power-spectral-density estimates of the surface-pressure fluctuations were characterized by a shift in power from high frequencies to low frequencies as the boundary layer changed from turbulent to laminar flow. Large changes in power at the lowest frequencies appeared to mark the beginning of transition.
NASA Technical Reports Server (NTRS)
Wang, T.; Simon, T. W.
1987-01-01
The test section of the present experiment to ascertain the effects of convex curvature and freestream turbulence on boundary layer momentum and heat transfer during natural transition provided a two-dimensional boundary layer flow on a uniformly heated curved surface, with bending to various curvature radii, R. Attention is given to results for the cases of R = infinity, 180 cm, and 90 cm, each with two freestream turbulence intensity levels. While the mild convex curvature of R = 180 cm delays transition, further bending to R = 90 cm leads to no signifucant further delay of transition. Cases with both curvature and higher freestream disturbance effects exhibit the latter's pronounced dominance. These data are pertinent to the development of transition prediction models for gas turbine blade design.
Application of vortex identification schemes to DNS data of transitional boundary layer
NASA Astrophysics Data System (ADS)
Pierce, Brian; Moin, Parviz; Sayadi, Taraneh
2012-11-01
We have demonstrated how various vortex identification and visualization criteria perform using DNS data from a transitional and turbulent boundary layer by Sayadi et al. (submitted to J. Fluid Mech.). The presence of well-known Λ vortices in the transitional region provides a well defined and yet realistic benchmark for evaluation of various criteria. We investigate the impact of changing the threshold used for iso-surface plotting. Brian Pierce acknowledges the support from the Stanford Graduate Fellowship.
Boundary layer transition: A review of theory, experiment and related phenomena
NASA Technical Reports Server (NTRS)
Kistler, E. L.
1971-01-01
The overall problem of boundary layer flow transition is reviewed. Evidence indicates a need for new, basic physical hypotheses in classical fluid mechanics math models based on the Navier-Stokes equations. The Navier-Stokes equations are challenged as inadequate for the investigation of fluid transition, since they are based on several assumptions which should be expected to alter significantly the stability characteristics of the resulting math model. Strong prima facie evidence is presented to this effect.
NASA Technical Reports Server (NTRS)
Banks, Daniel W.
2008-01-01
Infrared thermography is a powerful tool for investigating fluid mechanics on flight vehicles. (Can be used to visualize and characterize transition, shock impingement, separation etc.). Updated onboard F-15 based system was used to visualize supersonic boundary layer transition test article. (Tollmien-Schlichting and cross-flow dominant flow fields). Digital Recording improves image quality and analysis capability. (Allows accurate quantitative (temperature) measurements, Greater enhancement through image processing allows analysis of smaller scale phenomena).
NASA Astrophysics Data System (ADS)
Higuchi, Hiroshi; Kiura, Toshiro; Goto, Yuichiro; Hiramoto, Riho
2001-11-01
In spite of their popularity, flow structures over common baseball and flying disks have not been studied in detail. A slowly rotating baseball is subject to erratic flight paths, and is known as a knuckleball. In the present experiment, the characteristic of force acting on a baseball was obtained and the velocity vector field near the surface of the ball and the wake were measured with the DPIV technique. The seam triggered the boundary layer transition or caused the boundary layer separation itself. The laminar/turbulent boundary layer separations were identified with specific ball orientations. Corresponding three-dimensional wake pattern and the side force result in unpredictable trajectories. In the second part of the talk, flow physics regarding a spin-stabilized flying disk is addressed. The roll-up of trailing vortices was visualized in detail and their vorticity field was measured with the DPIV. The vortical flow over the disk produced flow reattachment at a very high angle of attack. The boundary layer at low angles of attack was affected by the surface motion with asymmetric boundary layer transitions as evidenced by the flow visualization and the hot wire survey. The flow separation and attachment on the underside cavity were also affected by the rotation.
Numerical modeling of the transitional boundary layer over a flat plate
NASA Astrophysics Data System (ADS)
Ivanov, Dimitry; Chorny, Andrei
2015-11-01
Our example is connected with fundamental research on understanding how an initially laminar boundary layer becomes turbulent. We have chosen the flow over a flat plate as a prototype for boundary-layer flows around bodies. Special attention was paid to the near-wall region in order to capture all levels of the boundary layer. In this study, the numerical software package OpenFOAM has been used in order to solve the flow field. The results were used in a comparative study with data obtained from Large Eddy Simulation (LES). The composite SGS-wall model is presently incorporated into a computer code suitable for the LES of developing flat-plate boundary layers. Presently this model is extended to the LES of the zero-pressure gradient, flat-plate turbulent boundary layer. In current study the time discretization is based on a second order Crank-Nicolson/Adams-Bashforth method. LES solver using Smagorinsky and the one-equation LES turbulence models. The transition models significantly improve the prediction of the onset location compared to the fully turbulent models.LES methods appear to be the most promising new tool for the design and analysis of flow devices including transition regions of the turbulent flow.
Shuttle orbiter boundary layer transition at flight and wind tunnel conditions
NASA Technical Reports Server (NTRS)
Goodrich, W. D.; Derry, S. M.; Bertin, J. J.
1983-01-01
Hypersonic boundary layer transition data obtained on the windward centerline of the Shuttle orbiter during entry for the first five flights are presented and analyzed. Because the orbiter surface is composed of a large number of thermal protection tiles, the transition data include the effects of distributed roughness arising from tile misalignment and gaps. These data are used as a benchmark for assessing and improving the accuracy of boundary layer transition predictions based on correlations of wind tunnel data taken on both aerodynamically rough and smooth orbiter surfaces. By comparing these two data bases, the relative importance of tunnel free stream noise and surface roughness on orbiter boundary layer transition correlation parameters can be assessed. This assessment indicates that accurate predications of transition times can be made for the orbiter at hypersonic flight conditions by using roughness dominated wind tunnel data. Specifically, times of transition onset and completion is accurately predicted using a correlation based on critical and effective values of a roughness Reynolds number previously derived from wind tunnel data.
Experimental Study of Bypass Transition in a Boundary Layer. M.S. Thesis
NASA Technical Reports Server (NTRS)
Suder, Kenneth L.; Obrien, James E.; Reshotko, Eli
1988-01-01
A detailed investigation to compare the boundary layer transition process in a low intensity disturbance environment to that in an environment in which the disturbances are initially non-linear in amplitude was conducted using a flat plate model. The transition mechanism based on linear growth of Tollmien Schlichting (T-S) waves was associated with a freestream turbulence level of 0.3 percent; however, for a freestream turbulence intensity of 0.65 percent and higher, the bypass transition mechanism prevailed. The results of detailed measurements acquired to study and compare the two transition mechanisms indicate that there exists a critical value for the peak rms of the velocity fluctuations within the boundary layer of approximately 3 to 3.5 percent of the freestream velocity. Once the unsteadiness within the boundary layer reached this critical value, turbulent bursting initiated, regardless of the transition mechanism. The two point correlations and simultaneous time traces within the transition region illustrate the features of a turbulent burst and its effect on the surrounding flowfield.
In-Flight Boundary-Layer Transition on a Large Flat Plate at Supersonic Speeds
NASA Technical Reports Server (NTRS)
Banks, Daniel W.; Fredericks, Michael Alan; Tracy, Richard R.; Matisheck, Jason R.; Vanecek, Neal D.
2012-01-01
A flight experiment was conducted to investigate the pressure distribution, local flow conditions, and boundary-layer transition characteristics on a large flat plate in flight at supersonic speeds up to Mach 2.0. The primary objective of the test was to characterize the local flow field in preparation for future tests of a high Reynolds number natural laminar flow test article. The tests used a F-15B testbed aircraft with a bottom centerline mounted test fixture. A second objective was to determine the boundary-layer transition characteristics on the flat plate and the effectiveness of using a simplified surface coating for future laminar flow flight tests employing infrared thermography. Boundary-layer transition was captured using an onboard infrared imaging system. The infrared imagery was captured in both analog and digital formats. Surface pressures were measured with electronically scanned pressure modules connected to 60 surface-mounted pressure orifices. The local flow field was measured with five 5-hole conical probes mounted near the leading edge of the test fixture. Flow field measurements revealed the local flow characteristics including downwash, sidewash, and local Mach number. Results also indicated that the simplified surface coating did not provide sufficient insulation from the metallic structure, which likely had a substantial effect on boundary-layer transition compared with that of an adiabatic surface. Cold wall conditions were predominant during the acceleration to maximum Mach number, and warm wall conditions were evident during the subsequent deceleration. The infrared imaging system was able to capture shock wave impingement on the surface of the flat plate in addition to indicating laminar-to-turbulent boundary-layer transition.
NASA Technical Reports Server (NTRS)
Sohn, Ki-Hyeon; Reshotko, Eli
1991-01-01
A detailed investigation to document momentum and thermal development of boundary layers undergoing natural transition on a heated flat plate was performed. Experimental results of both overall and conditionally sampled characteristics of laminar, transitional, and low Reynolds number turbulent boundary layers are presented. Measurements were acquired in a low-speed, closed-loop wind tunnel with a freestream velocity of 100 ft/s and zero pressure gradient over a range of freestream turbulence intensities (TI) from 0.4 to 6 percent. The distributions of skin friction, heat transfer rate and Reynolds shear stress were all consistent with previously published data. Reynolds analogy factors for R(sub theta) is less than 2300 were found to be well predicted by laminar and turbulent correlations which accounted for an unheated starting length. The measured laminar value of Reynolds analogy factor was as much as 53 percent higher than the Pr(sup -2/3). A small dependence of turbulent results on TI was observed. Conditional sampling performed in the transitional boundary layer indicated the existence of a near-wall drop in intermittency, pronounced at certain low intermittencies, which is consistent with the cross-sectional shape of turbulent spots observed by others. Non-turbulent intervals were observed to possess large magnitudes of near-wall unsteadiness and turbulent intervals had peak values as much as 50 percent higher than were measured at fully turbulent stations. Non-turbulent and turbulent profiles in transitional boundary layers cannot be simply treated as Blasius and fully turbulent profiles, respectively. The boundary layer spectra indicate predicted selective amplification of T-S waves for TI is approximately 0.4 percent. However, for TI is approximately 0.8 and 1.1 percent, T-S waves are localized very near the wall and do not play a dominant role in transition process.
Observations of the Early Morning Boundary-Layer Transition with Small Remotely-Piloted Aircraft
NASA Astrophysics Data System (ADS)
Wildmann, Norman; Rau, Gerrit Anke; Bange, Jens
2015-12-01
A remotely-piloted aircraft (RPA), equipped with a high resolution thermodynamic sensor package, was used to investigate physical processes during the morning transition of the atmospheric boundary layer over land. Experiments were conducted at a test site in heterogeneous terrain in south-west Germany on 5 days from June to September 2013 in an evolving shallow convective boundary layer, which then developed into a well-mixed layer later in the day. A combination of vertical profiling and constant-altitude profiling (CAP) at 100 m height above ground level was chosen as the measuring strategy throughout the experiment. The combination of flight strategies allows the application of mixed-layer scaling using the boundary-layer height z_i, convective velocity scale w_* and convective temperature scale θ _*. The hypothesis that mixed-layer theory is valid during the whole transition was not confirmed for all parameters. A good agreement is found for temperature variances, especially in the upper half of the boundary layer, and the normalized heat-flux profile. The results were compared to a previous study with the helicopter-borne turbulence probe Helipod, and it was found that similar data quality can be achieved with the RPA. On all days, the CAP flight level was within the entrainment zone for a short time, and the horizontal variability of temperature and water vapour along the flight path is presented as an example of the inhomogeneity of layer interfaces in the boundary layer. The study serves as a case study of the possibilities and limitations with state-of-the-art RPA technology in micrometeorology.
NASA Technical Reports Server (NTRS)
Volino, Ralph J.; Simon, Terrence W.
1995-01-01
Measurements from transitional, heated boundary layers along a concave-curved test wall are presented and discussed. A boundary layer subject to low free-stream turbulence intensity (FSTI), which contains stationary streamwise (Gortler) vortices, is documented. The low FSTI measurements are followed by measurements in boundary layers subject to high (initially 8%) free-stream turbulence intensity and moderate to strong streamwise acceleration. Conditions were chosen to simulate those present on the downstream half of the pressure side of a gas turbine airfoil. Mean flow characteristics as well as turbulence statistics, including the turbulent shear stress, turbulent heat flux, and turbulent Prandtl number, are documented. A technique called "octant analysis" is introduced and applied to several cases from the literature as well as to data from the present study. Spectral analysis was applied to describe the effects of turbulence scales of different sizes during transition. To the authors'knowledge, this is the first detailed documentation of boundary layer transition under such high free-stream turbulence conditions.
A DNS study of supersonic boundary layer trip induced transition and turbulence
NASA Astrophysics Data System (ADS)
Beekman, Izaak; Martin, M. Pino
2014-11-01
We perform the direct numerical simulation (DNS) of a Mach 7 . 2 , turbulent boundary layer, with a laminar inflow. A two-dimensional, semi-circular, bar-type roughness element is introduced near the inlet to hasten transition to turbulence. We choose this geometry because two-dimensional trip-wire-type devices have been used extensively by the experimental community, but we know of no computational studies to simulate transition behind such a roughness element in supersonic flow. We vary the trip size to investigate how size and trip-imposed length scales affect the transition process and the resulting turbulence. The incoming boundary layer conditions are matched to those of experiments being conducted at Princeton University Gas Dynamics Laboratory, where the free stream Mach number is 7 . 2 . This work is sponsored by the USAF under Grant AF/9550-10-1-0535 STW 21 - Revitalization of the Hypersonics Testing and Evaluation Workforce.
Some Effects of Bluntness on Boundary-Layer Transition and Heat Transfer at Supersonic Speeds
NASA Technical Reports Server (NTRS)
Moeckel, W E
1957-01-01
Large downstream movements of transition observed when the leading edge of a hollow cylinder or a flat plate is slightly blunted are explained in terms of the reduction in Reynolds number at the outer edge of the boundary layer due to the detached shock wave. The magnitude of this reduction is computed for cones and wedges for Mach numbers to 20. Concurrent changes in outer-edge Mach number and temperature occur in the direction that would increase the stability of the laminar boundary layer. The hypothesis is made that transition Reynolds number is substantially unchanged when a sharp leading edge or tip is blunted. This hypothesis leads to the conclusion that the downstream movement of transition is inversely proportional to the ratio of surface Reynolds number with blunted tip or leading edge to surface Reynolds number with sharp tip or leading edge. The conclusion is in good agreement with the hollow-cylinder result at Mach 3.1.
NASA Technical Reports Server (NTRS)
Hall, R. M.; Carraway, D. L.; Johnson, C. B.; Wright, R. E., Jr.; Obara, C. J.
1989-01-01
Four different boundary-layer transition detection techniques, namely liquid crystals, very thin hot films, IR photography, and an optical interferometer, were compared using the same flat plate model for the same tunnel conditions. The comparisons, conducted at NASA-Langley, involved not only their sensitivity to transition but also their ease of use. The thin films, as expected, gave excellent quantitative information and were used as the standard for evaluating the other techniques. Both the liquid crystals and IR photography were able to detect transition before the boundary-layer intermittency factor had reached 50 percent. The optical interferometer was unsuccessful. Conditions sampled included a range of Mach numbers from 1.5 to 2.5 and unit Reynolds numbers from 1.0 to 4.0 million/foot.
A purely nonlinear route to transition approaching the edge of chaos in a boundary layer
NASA Astrophysics Data System (ADS)
Cherubini, S.; De Palma, P.; Robinet, J.-Ch; Bottaro, A.
2012-06-01
The understanding of transition in shear flows has recently progressed along new paradigms based on the central role of coherent flow structures and their nonlinear interactions. We follow such paradigms to identify, by means of a nonlinear optimization of the energy growth at short time, the initial perturbation which most easily induces transition in a boundary layer. Moreover, a bisection procedure has been used to identify localized flow structures living on the edge of chaos, found to be populated by hairpin vortices and streaks. Such an edge structure appears to act as a relative attractor for the trajectory of the laminar base state perturbed by the initial finite-amplitude disturbances, mediating the route to turbulence of the flow, via the triggering of a regeneration cycle of Λ and hairpin structures at different space and time scales. These findings introduce a new, purely nonlinear scenario of transition in a boundary-layer flow.
NASA Technical Reports Server (NTRS)
LaGraff, John E. (Editor); Ashpis, David E. (Editor)
2002-01-01
This volume and its accompanying CD-ROM contain materials presented at the Minnowbrook III-2000 Workshop on Boundary Layer Transition and Unsteady Aspects of Turbomachinery Flows held at the Syracuse University Minnowbrook Conference Center, Blue Mountain Lake, New York, August 20-23, 2000. Workshop organizers were John E. LaGraff (Syracuse University), Terry V Jones (Oxford University), and J. Paul Gostelow (University of Leicester). The workshop followed the theme, venue, and informal format of two earlier workshops: Minnowbrook I (1993) and Minnowbrook II (1997). The workshop was focused on physical understanding the late stage (final breakdown) boundary layer transition, separation, and effects of unsteady wakes with the specific goal of contributing to engineering application of improving design codes for turbomachinery. The workshop participants included academic researchers from the USA and abroad, and representatives from the gas-turbine industry and government laboratories. The physical mechanisms discussed included turbulence disturbance environment in turbomachinery, flow instabilities, bypass and natural transition, turbulent spots and calmed regions, wake interactions with attached and separated boundary layers, turbulence and transition modeling and CFD, and DNS. This volume contains abstracts and copies of the viewgraphs presented, organized according to the workshop sessions. The viewgraphs are included on the CD-ROM only. The workshop summary and the plenary-discussion transcripts clearly highlight the need for continued vigorous research in the technologically important area of transition, separated and unsteady flows in turbomachines.
Heat transfer and fluid mechanics measurements in transitional boundary layer flows
NASA Technical Reports Server (NTRS)
Wang, T.; Simon, T. W.; Buddhavarapu, J.
1985-01-01
Experimental results are presented to document hydrodynamic and thermal development of flat-plate boundary layers undergoing natural transition. Local heat transfer coefficients, skin friction coefficients and profiles of velocity, temperature and Reynolds normal and shear stresses are presented. A case with no transition and transitional cases with 0.68% and 2.0% free-stream disturbance intensities were investigated. The locations of transition are consistent with earlier data. A late-laminar state with significant levels of turbulence is documented. In late-transitional and early-turbulent flows, turbulent Prandtl number and conduction layer thickness values exceed, and the Reynolds analogy factor is less than, values previously measured in fully turbulent flows.
Heat transfer and fluid mechanics measurements in transitional boundary layer flows
NASA Technical Reports Server (NTRS)
Wang, T.; Simon, T. W.; Buddhavarapu, J.
1985-01-01
Experimental results are presented to document hydrodynamic and thermal development of flat-plate boundary layers undergoing natural transition. Local heat transfer coefficients, skin friction coefficients and profiles of velocity, temperature and Reynolds normal and shear stresses are presented. A case with no transition and transitional cases with 0.68 percent and 2.0 percent free-stream disturbance intensities were investigated. The locations of transition are consistent with earlier data. A late-laminar state with significant levels of turbulence is documented. In late-transitional and early-turbulent flows, turbulent Prandtl number and conduction layer thickness values exceed, and the Reynolds analogy factor is less than, values previously measured in fully turbulent flows.
NASA Technical Reports Server (NTRS)
Li, Fei; Choudhari, Meelan; Chang, Chau-Lyan; White, Jeffery
2011-01-01
Computations are performed to study the boundary layer instability mechanisms pertaining to hypersonic flow over blunt capsules. For capsules with ablative heat shields, transition may be influenced both by out-gassing associated with surface pyrolysis and the resulting modification of surface geometry including the formation of micro-roughness. To isolate the effects of out-gassing, this paper examines the stability of canonical boundary layer flows over a smooth surface in the presence of gas injection into the boundary layer. For a slender cone, the effects of out-gassing on the predominantly second mode instability are found to be stabilizing. In contrast, for a blunt capsule flow dominated by first mode instability, out-gassing is shown to be destabilizing. Analogous destabilizing effects of outgassing are also noted for both stationary and traveling modes of crossflow instability over a blunt sphere-cone configuration at angle of attack.
NASA Astrophysics Data System (ADS)
Pierce, Brian; Moin, Parviz; Sayadi, Taraneh
2013-01-01
We have demonstrated how various vortex identification and visualization criteria perform using direct numerical simulation data from a transitional and turbulent boundary layer by Sayadi, Hamman, and Moin ["Direct numerical simulation of complete transition to turbulence via h-type and k-type secondary instabilities," Technical Report, Stanford University, CTR Annual Research Briefs, 2011]. The presence of well-known Λ vortices in the transitional region provides a well defined and yet realistic benchmark for evaluation of various criteria. We investigate the impact of changing the threshold used for iso-surface plotting.
Laminar Turbulent Transition in a Boundary Layer Subjected to Weak Free Stream Turbulence
NASA Astrophysics Data System (ADS)
Kenchi, Toshiaki; Matsubara, Masaharu; Ikeda, Toshihiko
For revealing the transition process in a flat plate boundary layer subjected to a weak free stream turbulence, flow visualization and hot-wire measurements were performed. A weak free stream turbulence was generated by a turbulence grid mounted upstream of the contraction. The flow visualization clearly displayed a transition scenario in which a local two-dimensional wave packet rapidly forms a Λ shape structure and then breaks down to turbulence, resulting in the generation of a turbulent spot. Quantitative measurements performed by using a hot-wire anemometer also confirmed the existence of local Tollmien-Schlichting waves that agreed with the parallel linear theory in terms of their frequency, phase velocity, and the wall-normal distribution of band-pass-filtered fluctuations. For comparison, a boundary layer subjected to a moderate-intensity free stream turbulence was investigated. This investigation showed that streaky structures play an important role in the boundary layer transition, as shown by Matsubara et al. [J. Fluid Mech., 430, (2001), 149-168.] A drastic change occurred in the transition process and this change could be sensitively determined by employing the intensity and/or spectra of the free stream turbulence.
High-Speed Boundary-Layer Transition Induced by an Isolated Roughness Element
NASA Technical Reports Server (NTRS)
Kegerise, Michael A.; Owens, Lewis R.; King, Rudolph A.
2010-01-01
Progress on an experimental effort to quantify the instability mechanisms associated with roughness-induced transition in a high-speed boundary layer is reported in this paper. To simulate the low-disturbance environment encountered during high-altitude flight, the experimental study was performed in the NASA-Langley Mach 3.5 Supersonic Low-Disturbance Tunnel. A flat plate trip sizing study was performed first to identify the roughness height required to force transition. That study, which included transition onset measurements under both quiet and noisy freestream conditions, confirmed the sensitivity of roughness-induced transition to freestream disturbance levels. Surveys of the laminar boundary layer on a 7deg half-angle sharp-tipped cone were performed via hot-wire anemometry and pitot-pressure measurements. The measured mean mass-flux and Mach-number profiles agreed very well with computed mean-flow profiles. Finally, surveys of the boundary layer developing downstream of an isolated roughness element on the cone were performed. The measurements revealed an instability in the far wake of the roughness element that grows exponentially and has peak frequencies in the 150 to 250 kHz range.
Transition induced by fixed and freely convecting spherical particles in laminar boundary layers
NASA Astrophysics Data System (ADS)
Petrie, H. L.; Morris, P. J.; Bajwa, A. R.; Vincent, D. C.
1993-08-01
An experimental and analytical study of aspects of transition induced by disturbances from spherical particles in laminar boundary layers is discussed. The generation of turbulent wedges by fixed spherical particles in a laminar boundary layer on or near the surface of a flat plate is considered experimentally using flow visualization with fluorescent dye and laser Doppler velocimetry. Turbulent spots generated by freely convecting spherical particles that are released in the freestream to fall into a flat plate laminar boundary layer and impact the plate are also discussed. A combination of dye flow visualization and a video based particle tracking technique was used to study the convecting particle problem. Although the Reynolds number at the critical condition for turbulent wedge generation by fixed particles and turbulent spot generation by convecting particles are similar, transition in these two situations appears to be fundamentally different. The development of a turbulent wedge near the critical condition is a relatively gradual process. In contrast, turbulent spots form relatively quickly after the convecting particles enter the boundary layer and impact the plate. Turbulent wedge formation downstream of a fixed particle results from the destabilization of the near wall flow by the vortical structures shed into particle wake. This shedding process is dominated by periodically shed loop shaped hairpin vortices. Observation of subharmonic oscillations at 1/2 and 1/4 of this shedding frequency suggest that a chaotic route to turbulence by a series of period doubling bifurcations is possible.
Laminar-Turbulent Transition Behind Discrete Roughness Elements in a High-Speed Boundary Layer
NASA Technical Reports Server (NTRS)
Choudhari, Meelan M.; Li, Fei; Wu, Minwei; Chang, Chau-Lyan; Edwards, Jack R., Jr.; Kegerise, Michael; King, Rudolph
2010-01-01
Computations are performed to study the flow past an isolated roughness element in a Mach 3.5, laminar, flat plate boundary layer. To determine the effects of the roughness element on the location of laminar-turbulent transition inside the boundary layer, the instability characteristics of the stationary wake behind the roughness element are investigated over a range of roughness heights. The wake flow adjacent to the spanwise plane of symmetry is characterized by a narrow region of increased boundary layer thickness. Beyond the near wake region, the centerline streak is surrounded by a pair of high-speed streaks with reduced boundary layer thickness and a secondary, outer pair of lower-speed streaks. Similar to the spanwise periodic pattern of streaks behind an array of regularly spaced roughness elements, the above wake structure persists over large distances and can sustain strong enough convective instabilities to cause an earlier onset of transition when the roughness height is sufficiently large. Time accurate computations are performed to clarify additional issues such as the role of the nearfield of the roughness element during the generation of streak instabilities, as well as to reveal selected details of their nonlinear evolution. Effects of roughness element shape on the streak amplitudes and the interactions between multiple roughness elements aligned along the flow direction are also investigated.
Experiments on transitional shock wave--boundary layer interactions at Mach 5
NASA Astrophysics Data System (ADS)
Erdem, E.; Kontis, K.; Johnstone, E.; Murray, N. P.; Steelant, J.
2013-10-01
An experimental campaign was carried out to investigate transitional shock wave--boundary layer interactions (SWBLI) at Mach and unit Reynolds numbers of 5 and 15.9 × 106 1/m, respectively. An impinging shock that generates 7° flow deflection resulted in separated SWBLI flowfield on axisymmetric centrebody. Various flow diagnostics were utilised such as schlieren photography, quantitative infrared thermography, shear sensitive liquid crystals, pressure sensitive paints and particle image velocimetry (PIV) to provide a complete time-averaged experimental data set. One nominally laminar case (with triggered transition due to SWBLI) and four natural transition cases with varying intermittency were tested. Heat transfer and shear stress peaks occurred around the reattachment point. For nominally laminar case, the separation induces transition, and thus, heat transfer and pressure peaks were found to be the highest. For the cases with natural transition with different intermittency levels, where incoming boundary layer is in state of transition, the magnitude of pressure and heat transfer peaks initially started to increase reaching a maximum and afterwards decreased towards the highest intermittency case. The presence of streamwise vortices was apparent for laminar case. Pressure peaks were found to occur slightly downstream of heat flux/shear stress peaks. PIV results (for laminar case only) showed high levels of turbulence above the separation region, proving triggered transition behaviour.
Observations of the Early Evening Boundary-Layer Transition Using a Small Unmanned Aerial System
NASA Astrophysics Data System (ADS)
Bonin, Timothy; Chilson, Phillip; Zielke, Brett; Fedorovich, Evgeni
2013-01-01
The evolution of the lower portion of the planetary boundary layer is investigated using the Small Multifunction Research and Teaching Sonde (SMARTSonde), an unmanned aerial vehicle developed at the University of Oklahoma. The study focuses on the lowest 200 m of the atmosphere, where the most noticeable thermodynamic changes occur during the day. Between October 2010 and February 2011, a series of flights was conducted during the evening hours on several days to examine the vertical structure of the lower boundary layer. Data from a nearby Oklahoma Mesonet tower was used to supplement the vertical profiles of temperature, humidity, and pressure, which were collected approximately every 30 min, starting 2 h before sunset and continuing until dusk. From the profiles, sensible and latent heat fluxes were estimated. These fluxes were used to diagnose the portion of the boundary layer that was most affected by the early evening transition. During the transition period, a shallow cool and moist layer near the ground was formed, and as the evening progressed the cooling affected an increasingly shallower layer just above the surface.
NASA Technical Reports Server (NTRS)
Schneider, Steven P.
1991-01-01
Laminar-turbulent transition in high speed boundary layers is a complicated problem which is still poorly understood, partly because of experimental ambiguities caused by operating in noisy wind tunnels. The NASA Langley experience with quiet tunnel design has been used to design a quiet flow tunnel which can be constructed less expensively. Fabrication techniques have been investigated, and inviscid, boundary layer, and stability computer codes have been adapted for use in the nozzle design. Construction of such a facility seems feasible, at a reasonable cost. Two facilities have been proposed: a large one, with a quiet flow region large enough to study the end of transition, and a smaller and less expensive one, capable of studying low Reynolds number issues such as receptivity. Funding for either facility remains to be obtained, although key facility elements have been obtained and are being integrated into the existing Purdue supersonic facilities.
A quiet-flow Ludwieg tube for experimental study of high speed boundary layer transition
NASA Technical Reports Server (NTRS)
Schneider, Steven P.
1991-01-01
Laminar-turbulent transition in high speed boundary layers is a complicated problem which is still poorly understood, partly because of experimental ambiguities caused by operating in noisy wind tunnels. The NASA Langley experience with quiet tunnel design has been used to design a quiet flow tunnel which can be constructed less expensively. Fabrication techniques have been investigated, and inviscid, boundary layer, and stability computer codes have been adapted for use in the nozzle design. Construction of such a facility seems feasible, at a reasonable cost. Two facilities have been proposed: a large one, with a quiet flow region large enough to study the end of transition, and a smaller and less expensive one, capable of studying low Reynolds number issues such as receptivity. Funding for either facility remains to be obtained, although key facility elements have been obtained and are being integrated into the existing Purdue supersonic facilities.
Experimental study of boundary layer transition on a heated flat plate
NASA Technical Reports Server (NTRS)
Sohn, K. H.; Reshotko, E.; Zaman, K. B. M. Q.
1991-01-01
A detailed investigation to the document momentum and thermal development of boundary layers undergoing natural transition on a heated flat plate was performed. Experimental results of both overall and conditionally sampled characteristics of laminar, transitional, and low Reynolds number turbulent boundary layers are presented. Measurements were done in a low-speed, closed-loop wind tunnel with a freestream velocity of 100 ft/s and zero pressure gradient over a range of freestream turbulence intensities from 0.4 to 6 percent. The distributions of skin friction, heat transfer rate, and Reynolds shear stress were all consistent with previously published data. Reynolds analogy factors for momentum thickness Reynolds number, Re(sub theta) less than 2300 were found to be well predicted by laminar and turbulent correlations which accounted for an unheated starting length and uniform heat flux. A small dependence of turbulence results on the freestream turbulence intensity was observed.
NASA Technical Reports Server (NTRS)
Horvath, Thomas J.; Berry, Scott A.; Merski, N. Ronald; Berger, Karen T.; Buck, Gregory M.; Liechty, Derek S.; Schneider, Steven P.
2006-01-01
An overview is provided of the experimental wind tunnel program conducted at the NASA Langley Research Center Aerothermodynamics Laboratory in support of an agency-wide effort to prepare the Shuttle Orbiter for Return-to-Flight. The effect of an isolated protuberance and an isolated rectangular cavity on hypersonic boundary layer transition onset on the windward surface of the Shuttle Orbiter has been experimentally characterized. These experimental studies were initiated to provide a protuberance and cavity effects database for developing hypersonic transition criteria to support on-orbit disposition of thermal protection system damage or repair. In addition, a synergistic experimental investigation was undertaken to assess the impact of an isolated mass-flow entrainment source (simulating pyrolysis/outgassing from a proposed tile repair material) on boundary layer transition. A brief review of the relevant literature regarding hypersonic boundary layer transition induced from cavities and localized mass addition from ablation is presented. Boundary layer transition results were obtained using 0.0075-scale Orbiter models with simulated tile damage (rectangular cavities) of varying length, width, and depth and simulated tile damage or repair (protuberances) of varying height. Cavity and mass addition effects were assessed at a fixed location (x/L = 0.3) along the model centerline in a region of near zero pressure gradient. Cavity length-to-depth ratio was systematically varied from 2.5 to 17.7 and length-to-width ratio of 1 to 8.5. Cavity depth-to-local boundary layer thickness ranged from 0.5 to 4.8. Protuberances were located at several sites along the centerline and port/starboard attachment lines along the chine and wing leading edge. Protuberance height-to-boundary layer thickness was varied from approximately 0.2 to 1.1. Global heat transfer images and heating distributions of the Orbiter windward surface using phosphor thermography were used to infer the
NASA Astrophysics Data System (ADS)
Sastre, Mariano; Viana, Samuel; Maqueda, Gregorio; Yagüe, Carlos
2010-05-01
Turbulence is probably the most important feature dealing with the diffusion of contaminants in the planetary boundary layer. The main characteristics of turbulence are governed, apart from synoptic conditions, by the daily cycle of the Earth surface heating and cooling, so that, simplifying, two configurations are often found: convective and stable. The transition from a diurnal convective boundary layer to a typically stable nocturnal one is not still well understood (Edwards, 2009). Different micrometeorological conditions at sunset or a few hours previously may be critical for the establishment of a strong surface-based stability or a weak one, even for similar synoptic conditions. This work focuses on the characterization of the evening transition which takes place at the atmospheric boundary layer, considering the temporal interval 17.00-23.00 GMT. The methodology includes looking for some relations between meteorological variables, turbulent parameters and particulate matter (PM10, PM2.5 and PM1) concentrations measured by a GRIMM particle monitor (MODEL 365). Observational data (Summer 2009) is provided from permanent instrumentation at the Research Centre for the Lower Atmosphere (CIBA) in Valladolid (Spain), which is on a quite flat terrain (Cuxart et al., 2000). A 10m height mast equipped with temperature, wind speed and direction, and moisture sensors at several levels are available. Also two sonic anemometers (20 Hz sampling rate) at 1.5 and 10m were deployed in the mast. The database is complemented by a triangle of microbarometers installed next to the surface, and another three microbarometers placed in a 100m meteorological tower at 20, 50 and 100m respectively, which are ideal to study coherent structures present in the boundary layer. Statistical parameters of meteorological variables have been calculated and studied in order to find out connections with the most relevant physical processes. Moreover different cases studies will be analyzed
Gortler vortices and transition in wall boundary layers of two Mach 5 nozzles
NASA Technical Reports Server (NTRS)
Beckwith, I. E.; Holley, B. B.
1981-01-01
The onset of transition in the wall boundary layers of two axisymmetric Mach 5 wind-tunnel nozzles has been measured under conditions of extremely low incident disturbance levels. The range of test unit Reynolds numbers, based on conditions at the nozzle exit, was from 6 x 10 to the 6th power m to 2.5 x 10 to the 7th power m. When the nozzle walls were maintained in a polished and clean condition, transition moved gradually upstream as the test Reynolds number was increased. When transition occurred in the supersonic concave wall region, the values of the local Gortler parameter at transition varied from about 5 to 6, whereas the momentum thickness Reynolds number varied from about 750 to 1050. Oil flow patterns obtained near the exit of the nozzles indicated that Gortler vortices were always present when the wall boundary layers were laminar. Calculations for the growth of Gortler vortices based on new results from linear theory for supersonic flat-plate profiles gave amplification ratios to transition from e to the 4th power to e to the 15th power. Possible reasons for this wide range in amplification ratios are discussed, but no definite conclusions are yet possible regarding the values of n in a simple e to the nth power type theory for the assumed linear amplification of Gortler vortices to transition in supersonic nozzles.
NASA Technical Reports Server (NTRS)
Choudhari, Meelan M.; Tokugawa, Naoko; Li, Fei; Chang, Chau-Lyan; White, Jeffery A.; Ishikawa, Hiroaki; Ueda, Yoshine; Atobe, Takashi; Fujii, Keisuke
2012-01-01
Boundary layer transition over axisymmetric bodies at non-zero angle of attack in supersonic flow is numerically investigated as part of joint research between the National Aeronautics and Space Administration (NASA) and Japan Aerospace Exploration Agency (JAXA). Transition over four axisymmetric bodies (namely, Sears-Haack body, semi-Sears-Haack body, 5-degree straight cone and flared cone) with different axial pressure gradients has been studied at Mach 2 in order to understand the effect of axial pressure gradient on instability amplification along the leeward symmetry plane and in the region of nonzero crossflow away from it. Comparisons are made with measured transition data in Mach 2 facilities as well as with predicted and measured transition characteristics for a 5-degree straight cone in a Mach 3.5 low disturbance tunnel. Limitations of using linear stability correlations for predicting transition over axisymmetric bodies at angle of attack are pointed out.
Relationship between transition and modes of instability in supersonic boundary layers
NASA Technical Reports Server (NTRS)
Masad, Jamal A.
1993-01-01
The relationship between the predicted transition location and the first and second modes of instability in two-dimensional supersonic boundary-layer flow on a flat plate is examined. Linear stability theory and the N-factor criterion are used to predict transition location. The effect of heat transfer is also studied; the results demonstrate that the transition reversal phenomenon can be explained by the opposite effect of cooling on the first and second modes of instability. Compressibility of destabilizing at free-stream Mach numbers of 2 to 3.5. The predicted transition location is due to the oblique first modes of instability, up to free-stream Mach numbers between 6 and 6.5. At higher Mach numbers, the predicted transition location is due to a combination of two-dimensional first and second modes of instability.
NASA Astrophysics Data System (ADS)
Cherubini, S.; De Palma, P.; Robinet, J.-Ch.
2015-03-01
The effect of a constant homogeneous wall suction on the nonlinear transient growth of localized finite amplitude perturbations in a boundary-layer flow is investigated. Using a variational technique, nonlinear optimal disturbances are computed for the asymptotic suction boundary layer (ASBL) flow, defined as those finite amplitude disturbances yielding the largest energy growth at a given target time T. It is found that homogeneous wall suction remarkably reduces the optimal energy gain in the nonlinear case. Furthermore, mirror-symmetry breaking of the shape of the optimal perturbation appears when decreasing the Reynolds number from 10 000 to 5000, whereas spanwise mirror-symmetry was a robust feature of the nonlinear optimal perturbations found in the Blasius boundary-layer flow. Direct numerical simulations show that the different evolutions of the symmetric and of the non-symmetric initial perturbations are linked to different mechanisms of transport and tilting of the vortices by the mean flow. By bisecting the initial energy of the nonlinear optimal perturbations, minimal energy thresholds for subcritical transition to turbulence have been obtained. These energy thresholds are found to be 1-4 orders of magnitude smaller than those provided in the literature for other transition scenarios. For low to moderate Reynolds numbers, the energy thresholds are found to scale with Re-2, suggesting a new scaling law for transition in the ASBL.
Boundary Layer Transition Correlations and Aeroheating Predictions for Mars Smart Lander
NASA Technical Reports Server (NTRS)
Hollis, Brian R.; Liechty, Derek S.
2002-01-01
Laminar and turbulent perfect-gas air, Navier-Stokes computations have been performed for a proposed Mars Smart Lander entry vehicle at Mach 6 over a free stream Reynolds number range of 6.9 x 10(exp 6/m to 2.4 x 10(exp 7)m(2.1 x 10(exp 6)/ft to 7.3 x 10(exp 6)ft) for angles-of-attack of 0-deg, 11-deg, 16-deg, and 20-deg, and comparisons were made to wind tunnel heating data obtained at the same conditions. Boundary layer edge properties were extracted from the solutions and used to correlate experimental data on the effects of heat-shield penetrations (bolt-holes where the entry vehicle would be attached to the propulsion module during transit to Mars) on boundary-layer transition. A non-equilibrium Martian-atmosphere computation was performed for the peak heating point on the entry trajectory in order to determine if the penetrations would produce boundary-layer transition by using this correlation.
Boundary Layer Transition Correlations and Aeroheating Predictions for Mars Smart Lander
NASA Technical Reports Server (NTRS)
Hollis, Brian R.; Liechty, Derek S.
2002-01-01
Laminar and turbulent perfect-gas air, Navier-Stokes computations have been performed for a proposed Mars Smart Lander entry vehicle at Mach 6 over a free stream Reynolds number range of 6.9 x 10(exp 6)/m to 2.4 x 10(exp 7)/m (2.1 x 10(exp 6)/ft to 7.3 x 10(exp 6)/ft) for angles-of-attack of 0-deg, 11-deg, 16-deg, and 20-deg, and comparisons were made to wind tunnel heating data obtained a t the same conditions. Boundary layer edge properties were extracted from the solutions and used to correlate experimental data on the effects of heat-shield penetrations (bolt-holes where the entry vehicle would be attached to the propulsion module during transit to Mars) on boundary-layer transition. A non-equilibrium Martian-atmosphere computation was performed for the peak heating point on the entry trajectory in order to determine if the penetrations would produce boundary-layer transition by using this correlation.
NASA Astrophysics Data System (ADS)
Sastre, Mariano; Yagüe, Carlos; Román-Cascón, Carlos; Maqueda, Gregorio; Ander Arrillaga, Jon
2015-04-01
In this work we study the temporal evolution of the Atmospheric Boundary Layer (ABL) along the transition period from a diurnal typical convection to a nocturnal more frequently stable situation. This period is known as late afternoon or evening transition, depending on the specific definitions employed by different authors [1]. In order to obtain a proper characterization, we try to learn whether or not the behaviour of these transitional boundary layers is strongly dependent on local conditions. To do so, two sets of evening transitions are studied from data collected at two different experimental sites. These locations correspond to research facilities named CIBA (Spain) and CRA (France), which are the places where atmospheric field campaigns have been conducted during the last years, such as CIBA2008 and BLLAST 2011, respectively. In order to get comparable situations, we focus especially on transitions with weak synoptic forcing, and consider daily astronomical sunset as a reference time. A statistical analysis on main parameters related to the transition is carried out for both locations, and the average behaviour is shown as well as extreme values according to the timing. A similar pattern in the qualitative evolution of many variables is found. Nevertheless, several relevant differences in the progress of key variables are obtained too. Moisture, both from the soil and the air, is thought to have great relevance in explaining many of the differences found between the two sites. Some case studies are explored, focusing on the role played by the atmospheric turbulence. Complementary, numerical experiments are also performed using the Weather Research and Forecast (WRF) mesoscale model, in order to test the role of humidity, by artificially varying it in some of the simulations. [1] Lothon, M. and coauthors (2014): The BLLAST field experiment: Boundary-Layer Late Afternoon and Sunset Turbulence. Atmos. Chem. Phys., 14, 10931-10960.
Numerical investigation of the three-dimensional development in boundary layer transition
NASA Astrophysics Data System (ADS)
Fasel, H. F.; Rist, U.; Konzelmann, U.
1987-06-01
A numerical method for solving the complete Navier-Stokes equations for incompressible flows is introduced that is applicable for investigating three-dimensional transition phenomena in a spatially-growing boundary layer. Results are discussed for a test case with small three-dimensional disturbances for which detailed comparison to linear stability theory is possible. The validity of this numerical model for investigating nonlinear transition phenomena is demonstrated by realistic spatial simulations of the experiments by Kachanov and Levchenko (1984) for a subharmonic resonance breakdown and of the experiments of Klebanoff et al. (1962) for a fundamental resonance breakdown.
An experimental investigation of boundary layer transition in an adverse pressure gradient
NASA Technical Reports Server (NTRS)
Watmuff, Jonathan H.
1991-01-01
The evolution of a small perturbation introduced periodically into a boundary layer with a moderately strong adverse pressure gradient (APG) was investigated experimentally using the hot-wire method. The magnitude of the disturbance is found to decay with the streamwise distance in the APG before undergoing rapid growth and triggering transition in a very repetitive manner. The evidence suggests that the laminar layer separates and that the transition mechanism is an inviscid shear-layer type of instability. Contours of spanwise vorticity in the plane of the disturbance show the formation of roll-ups in the initial stages. Subsequent interaction with the wall leads to the formation of large-scale vortex loops which merge into a single vortex loop further downstream.
NASA Astrophysics Data System (ADS)
Sastre, Mariano; Román-Cascón, Carlos; Yagüe, Carlos; Arrillaga, Jon A.; Maqueda, Gregorio
2016-04-01
From a typically convective diurnal situation to a stably stratified nocturnal one, the atmospheric boundary layer (ABL) experiences the so-called afternoon and evening transition. This period is complex to study due to the presence of many different forcings, usually weak and opposite [1]. In this work, the transitional processes are studied by using 6-year data from permanent instrumentation at CIBA, a research center located in the Spanish Northern plateau. These measurements include particulate matter (PM) and turbulent records. Certain variables display a twin pattern in their time evolution for all the seasons, only differing in their absolute values. On the contrary, the air specific humidity behaves differently for each season, which is distinct to the results from a previous study at a different location [2]. Besides, a common pattern of increasing PM values near sunset is found, with a number of influences playing a role in PM concentrations: stability, turbulence and ABL thickness among others. In particular, the competing thermal and mechanical turbulent effects result in PM concentration reduction (settling on the ground or being advected) or increase, depending in each case on the specific season and particle group. Furthermore, the relative importance of the bigger PM (between 2.5 and 10 μm) is linked to the wind minimum around sunset, especially during summer. [1] Lothon, M. and coauthors (2014): The BLLAST field experiment: Boundary-Layer Late Afternoon and Sunset Turbulence, Atmos. Chem. Phys., 14, 10931-10960. [2] Wingo, S. M. and Knupp, K. R. (2015): Multi-platform observations characterizing the afternoon-to-evening transition of the planetary boundary layer in Northern Alabama, USA, Boundary-Layer Meteorol., 155, 29-53.
Mixed mode transition in zero and adverse pressure gradient boundary layers
NASA Astrophysics Data System (ADS)
Bose, Rikhi; Durbin, Paul
2015-11-01
Flow regimes exist where interaction of Klebanoff streaks and the Tollmien-Sclichting waves trigger transition but either mode is individually insufficient. Such interaction between orderly and bypass routes of transition is called Mixed mode transition. In zero pressure gradient boundary layers, mixed mode transition follows three routes depending upon strength of these perturbation modes. At high free-stream turbulence intensity (Tu), bypass transition is dominant and the flow is very weakly sensitive to the TS mode strength. In the presence of a strong TS mode, low Tu triggers secondary instability of the TS wave forming Λ vortices. The Λ vortices are forced response due to the weak streaks rather than resonance mechanism seen in monochromatic excitations. When both of these modes are weak, secondary instability of streaks trigger consequent breakdown to turbulent spots. Three-dimensional visualization of the perturbation fields shows toroidal n = 0 and helical n = 1 modes observed in instability of axisymmetric jets and wakes. In adverese pressure gradient boundary layers, the presence of an inflection point significantly increases the growth rate of TS mode thereby strengthening the secondary instability route and the interaction is more interesting. This work was supported by NSF grant CBET-1228195. Computer time was provided by the Extreme Science and Engineering Discovery Environment (XSEDE).
Analysis of the photodiode boundary layer transition indicator. LDRD final report
Kuntz, D.W.; Wilken, A.C.; Payne, J.L.
1994-06-01
The photodiode transition indicator is a device which has been successfully used to determine the onset of boundary layer transition on numerous hypersonic flight vehicles. The exact source of the electromagnetic radiation detected by the photodiode at transition was not understood. In some cases early saturation of the device occurred, and the device failed to detect transition. Analyses have been performed to determine the source of the radiation producing the photodiode signal. The results of these analyses indicate that the most likely source of the radiation is blackbody emission from the heatshield material bordering the quartz window of the device. Good agreement between flight data and calculations based on this radiation source has been obtained. Analyses also indicate that the most probable source of the radiation causing early saturation is blackbody radiation from carbon particles which break away from the nosetip during the ablation process.
Analysis of flight data on boundary layer transition at high angles of attack
NASA Technical Reports Server (NTRS)
Haigh, W. W.; Lake, B. M.; Ko, D. R. S.
1972-01-01
Boundary layer transition data were obtained on the flight of two cones which reentered at velocities of about 7.0 km/sec. One cone reentered at a nominal zero degree angle of attack and the other, due to an anomaly above the earth atmosphere, reentered at local angles of attack up to 7.0 km/sec. The transition data were obtained from on-board acoustic and electrostatic sensors. A description of the design, calibration, and method used to detect transition from the sensors is included. The flow field calculation used to obtain the local flow properties on the cones is described. Finally, the transition data found from both cone flights is correlated.
Edmond J. Walsh; Kevin P. Nolan; Donald M. McEligot; Ralph J. Volino; Adrian Bejan
2007-05-01
Conditionally-sampled boundary layer data for an accelerating transitional boundary layer have been analyzed to calculate the entropy generation rate in the transition region. By weighing the nondimensional dissipation coefficient for the laminar-conditioned-data and turbulent-conditioned-data with the intermittency factor the average entropy generation rate in the transition region can be determined and hence be compared to the time averaged data and correlations for steady laminar and turbulent flows. It is demonstrated that this method provides, for the first time, an accurate and detailed picture of the entropy generation rate during transition. The data used in this paper have been taken from detailed boundary layer measurements available in the literature. This paper provides, using an intermittency weighted approach, a methodology for predicting entropy generation in a transitional boundary layer.
Multigrid methods for flow transition in three-dimensional boundary layers with surface roughness
NASA Technical Reports Server (NTRS)
Liu, Chaoqun; Liu, Zhining; Mccormick, Steve
1993-01-01
The efficient multilevel adaptive method has been successfully applied to perform direct numerical simulations (DNS) of flow transition in 3-D channels and 3-D boundary layers with 2-D and 3-D isolated and distributed roughness in a curvilinear coordinate system. A fourth-order finite difference technique on stretched and staggered grids, a fully-implicit time marching scheme, a semi-coarsening multigrid method associated with line distributive relaxation scheme, and an improved outflow boundary-condition treatment, which needs only a very short buffer domain to damp all order-one wave reflections, are developed. These approaches make the multigrid DNS code very accurate and efficient. This allows us not only to be able to do spatial DNS for the 3-D channel and flat plate at low computational costs, but also to do spatial DNS for transition in the 3-D boundary layer with 3-D single and multiple roughness elements, which would have extremely high computational costs with conventional methods. Numerical results show good agreement with the linear stability theory, the secondary instability theory, and a number of laboratory experiments. The contribution of isolated and distributed roughness to transition is analyzed.
NASA Astrophysics Data System (ADS)
Sastre Marugán, Mariano; Steeneveld, Gert-Jan; Yagüe, Carlos; Román-Cascón, Carlos; Maqueda, Gregorio; van de Boer, Anneke
2013-04-01
The Planetary Boundary Layer (PBL) is mainly ruled by both mechanical and thermal turbulence, and shows an evident diurnal cycle. In the evening transitional period, decay in turbulent kinetic energy occurs, but all the mechanisms behind this decay are still not well understood. In this framework, the BLLAST (Boundary Layer Late Afternoon and Sunset Turbulence) project aims to improve the knowledge on the physical processes taking place during the late afternoon and evening transition in the lower troposphere. The BLLAST field campaign was organized in Lannemezan (France) from 14th June to 8th July 2011 [1]. Both in situ measurements (i.e., with meteorological towers, surface based instruments, tethered balloons…) and remote sensors (i.e., SODAR, scintillometer…) were used for this purpose, and two different approaches were developed: vertical structure of the boundary layer and spatial heterogeneity. Besides, Numerical Weather Prediction (NWP) models have exhibited substantial difficulties to properly simulate the diurnal cycle in the atmosphere and also the PBL afternoon and evening transition. Typically, some errors are found in air temperature and wind speed close to the surface. Regarding this fact, the main goal of this work is to study how the mesoscale model WRF (Weather Research and Forecast) performs simulations of the evening transition during the BLLAST field campaign. In particular, it is tested for permutations of different PBL and Land Surface Model (LSM) schemes. We try to understand why some differences in model results appear. A comparison between observations and combinations of PBL and LSM parameterizations is shown, testing the sensitivity to these options. We specifically evaluate the surface radiation budget (out- and incoming long- and shortwave radiation), and the surface energy budget variables (latent and sensible heat fluxes, as well as soil heat flux). Furthermore, the vertical profiles of some key variables (such as potential
NASA Technical Reports Server (NTRS)
Campbell, Charles H.; Berger, Karen; Anderson, Brian
2012-01-01
Hypersonic entry flight testing motivated by efforts seeking to characterize boundary layer transition on the Space Shuttle Orbiters have identified challenges in our ability to acquire high quality quantitative surface temperature measurements versus time. Five missions near the end of the Space Shuttle Program implemented a tile surface protuberance as a boundary layer trip together with tile surface thermocouples to capture temperature measurements during entry. Similar engineering implementations of these measurements on Discovery and Endeavor demonstrated unexpected measurement voltage response during the high heating portion of the entry trajectory. An assessment has been performed to characterize possible causes of the issues experienced during STS-119, STS-128, STS-131, STS-133 and STS-134 as well as similar issues encountered during other orbiter entries.
On strongly nonlinear vortex/wave interactions in boundary-layer transition
NASA Technical Reports Server (NTRS)
Hall, Philip; Smith, Frank T.
1989-01-01
The interactions between longitudinal vortices and accompanying waves considered are strongly nonlinear, in the sense that the mean-flow profile throughout the boundary layer is completely altered from its original undisturbed state. Nonlinear interactions between vortex flow and Tollmien-Schlichting waves are addressed first, and some analytical and computational properties are described. These include the possibility in the spatial-development case of a finite-distance break-up, inducing a singularity in the displacement thickness. Second, vortex/Rayleigh wave nonlinear interactions are considered for the compressible boundary-layer, along with certain special cases of interest and some possible solution properties. Both types, vortex/Tollmien-Schlichting and vortex/Rayleigh, are short-scale/long-scale interactions and they have potential applications to many flows at high Reynolds numbers. The strongly nonlinear nature is believed to make them very relevant to fully fledged transition to turbulence.
Physics of unsteady cylinder-induced transitional shock wave boundary layer interactions
NASA Astrophysics Data System (ADS)
Murphree, Zachary Ryan
The mean flowfield and time-dependent characteristics of a Mach 5 cylinder-induced transitional shock-wave/boundary-layer interaction have been studied experimentally. The interactions were generated with a right circular cylinder mounted on a flat plate. The Reynolds number based on distance from the leading edge of the plate to the cylinder leading edge ranged from 4.5 x 106 to 6.1 x 106, and the incoming boundary-layer was transitional. The objectives of the study were to: (i) provide a detailed description of the mean flow structure of the interaction, and (ii) characterize the unsteadiness of the interaction based on fluctuating pressure measurements. Mean wall-pressure measurements coupled with planar laser scattering and surface visualization showed that the transitional interaction exhibits characteristics that are essentially a "composite" of an upstream laminar interaction and a downstream turbulent interaction. In the upstream region there is a laminar separation bubble that is characterized by a weak separation shock, a pressure plateau, and low relative mass/heat flux. The separated boundary-layer reattaches downstream of this bubble, about 4 diameters upstream of the cylinder. This reattached flow is characterized by high relative mass/heat flux, an increase in pressure and a rapidly thickening boundary-layer. The flow then separates again in a manner very similar to a low Reynolds number turbulent interaction. Statistical analysis of the pressure histories suggest that the entire interaction stretches and contracts in concert. Power spectral densities of the pressure fluctuations showed unsteadiness throughout the interaction with energy content in one of two frequency bands: one with a sharp peak from 1-2 kHz and the other with a broader peak at 7-10 kHz. The lower frequency is attributed to the interaction motion, whereas the higher frequency is found underneath the reattached boundary-layer. Cross-correlations and coherence functions in the
NASA Technical Reports Server (NTRS)
Saric, W. S.; Reynolds, G. A.
1979-01-01
The preliminary experimental development work directed towards the understanding of transition in boundary layers with suction is presented. The basic stability experiment was established and the facility was certified.
Experiments on hypersonic boundary layer transition on blunt cones with acoustic-absorption coating
NASA Astrophysics Data System (ADS)
Shiplyuk, A.; Lukashevich, S.; Bountin, D.; Maslov, A.; Knaus, H.
2012-01-01
The laminar-turbulent transition is studied experimentally on a cone with an acoustic-absorption coating and with different nose bluntness in a high-speed flow. The acoustic-absorption coating is a felt metal sheet with a random microstructure. Experiments were carried out on a 1-meter length 7 degree cone at free-stream Mach number M = 8 and zero angle of attack. Locations of the laminar-turbulent transition are detected using heat flux distributions registered by calorimeter sensors. In addition, boundary layer pulsations are measured by means of ultrafast heat flux sensors. It is shown that the laminar-turbulent transition is caused by the second-mode instability, and the laminar run extends as the bluntness is increased. The porous coating effectively suppresses this instability for all tested bluntness values and 1.3-1.85 times extends the laminar run.
NASA Astrophysics Data System (ADS)
Asbik, M.; Ansari, O.; Zeghmati, B.
2005-03-01
A numerical study of the onset of longitudinal transition between turbulent and laminar regimes during the evaporation of a water film is presented. These water film streams along a horizontal elliptical tube under the simultaneous effects of gravity, pressure gradients, caused by the vapor flow and curvature, and viscous forces. At the interface of water vapor, the shear stress is supposed to be negligible. Outside the boundary layer, the vapor phase velocity is obtained from potential flow. In the analysis Von Karman’s turbulence model is used and the inertia and convection terms are retained. Transfers equations are discretised by using the implicit Keller method. The effects of an initial liquid flow rate per unit of length, Froude number, temperature difference between the wall and the liquid vapor interface and ellipticity on the transition position have been evaluated. The transition criterion has been given in term of the critical film Reynolds number (ReΓ)C.
Controlling forebody asymmetries in flight: Experience with boundary layer transition strips
NASA Technical Reports Server (NTRS)
Fisher, David F.; Cobleigh, Brent R.
1994-01-01
The NASA Dryden Flight Research Center has an ongoing program to investigate aircraft flight characteristics at high angles of attack. As part of this investigation, longitudinal boundary layer transition strips were installed on the F-18 HARV forebody, a preproduction F/A-18 radome with a nose-slice tendency, and the X-31 aircraft forebody and noseboom to reduce asymmetric yawing moments at high angles of attack. The transition strips were effective on the F-18 HARV at angles of attack above 60 deg. On the preproduction F/A-18 radome at an angle of attack near 50 deg the strips were not effective. When the transition strips were installed on the X-31 noseboom, a favorable effect was observed on the yawing moment dynamics but the magnitude of the yawing moment was not decreased.
Laminar-Boundary-Layer Oscillations and Transition on a Flat Plate
NASA Technical Reports Server (NTRS)
Schubauer, G B; Skramstad, H K
1948-01-01
This is an account of an investigation in which oscillations were discovered in the laminar boundary layer along a flat plate. These oscillations were found during the course of an experiment in which transition from laminar to turbulent flow was being studied on the plate as the turbulence in the wind stream was being reduced to unusually low values by means of damping screens. The first part of the paper deals with experimental methods and apparatus, measurements of turbulence and sound, and studies of transition. A description is then given of the manner in which oscillations were discovered and how they were found to be related to transition, and then how controlled oscillations were produced and studied in detail.
Experimental analysis of the boundary layer transition with zero and positive pressure gradient
NASA Technical Reports Server (NTRS)
Arnal, D.; Jullen, J. C.; Michel, R.
1980-01-01
The influence of a positive pressure gradient on the boundary layer transition is studied. The mean velocity and turbulence profiles of four cases are examined. As the intensity of the pressure gradient is increased, the Reynolds number of the transition onset and the length of the transition region are reduced. The Tollmein-Schlichting waves disturb the laminar regime; the amplification of these waves is in good agreement with the stability theory. The three dimensional deformation of the waves leads finally to the appearance of turbulence. In the case of zero pressure gradient, the properties of the turbulent spots are studied by conditional sampling of the hot-wire signal; in the case of positive pressure gradient, the turbulence appears in a progressive manner and the turbulent spots are much more difficult to characterize.
Direct Numerical Simulation of Transition in a Swept-Wing Boundary Layer
NASA Technical Reports Server (NTRS)
Duan, Lian; Choudhari, Meelan M.; Li, Fei
2013-01-01
Direct numerical simulation (DNS) is performed to examine laminar to turbulent transition due to high-frequency secondary instability of stationary crossflow vortices in a subsonic swept-wing boundary layer for a realistic natural-laminar-flow airfoil configuration. The secondary instability is introduced via inflow forcing derived from a two-dimensional, partial-differential-equation based eigenvalue computation; and the mode selected for forcing corresponds to the most amplified secondary instability mode which, in this case, derives a majority of its growth from energy production mechanisms associated with the wall-normal shear of the stationary basic state. Both the growth of the secondary instability wave and the resulting onset of laminar-turbulent transition are captured within the DNS computations. The growth of the secondary instability wave in the DNS solution compares well with linear secondary instability theory when the amplitude is small; the linear growth is followed by a region of reduced growth resulting from nonlinear effects before an explosive onset of laminar breakdown to turbulence. The peak fluctuations are concentrated near the boundary layer edge during the initial stage of transition, but rapidly propagates towards the surface during the process of laminar breakdown. Both time-averaged statistics and flow visualization based on the DNS reveal a sawtooth transition pattern that is analogous to previously documented surface flow visualizations of transition due to stationary crossflow instability. The memory of the stationary crossflow vortex is found to persist through the transition zone and well beyond the location of the maximum skin friction.
Free-stream turbulence and concave curvature effects on heated, transitional boundary layers
NASA Technical Reports Server (NTRS)
Kim, J.; Simon, T. W.
1991-01-01
An experimental investigation of the transition process on flat-plate and concave curved-wall boundary layers for various free-stream turbulence levels was performed. Results show that for transition of a flat-plate, the two forms of boundary layer behavior, identified as laminar-like and turbulent-like, cannot be thought of as separate Blasius and fully-turbulent profiles, respectively. Thus, simple transition models in which the desired quantity is assumed to be an average, weighted on intermittency, of the theoretical laminar and fully turbulent values is not expected to be successful. Deviation of the flow identified as laminar-like from theoretical laminar behavior is shown to be due to recovery after the passage of a turbulent spot, while deviation of the flow identified as turbulent-like from the full-turbulent values is thought to be due to incomplete establishment of the fully-turbulent power spectral distribution. Turbulent Prandtl numbers for the transitional flow, computed from measured shear stress, turbulent heat flux and mean velocity and temperature profiles, were less than unity. For the curved-wall case with low free-stream turbulence intensity, the existence of Gortler vortices on the concave wall within both laminar and turbulent flows was established using liquid crystal visualization and spanwise velocity and temperature traverses. Transition was found to occur via a vortex breakdown mode. The vortex wavelength was quite irregular in both the laminar and turbulent flows, but the vortices were stable in time and space. The upwash was found to be more unstable, with higher levels of u' and u'v', and lower skin friction coefficients and shape factors. Turbulent Prandtl numbers, measured using a triple-wire probe, were found to be near unity for all post-transitional profiles, indicating no gross violation of Reynolds analogy. No evidence of streamwise vortices was seen in the high turbulence intensity case.
DNS of Laminar-Turbulent Transition in Swept-Wing Boundary Layers
NASA Technical Reports Server (NTRS)
Duan, L.; Choudhari, M.; Li, F.
2014-01-01
Direct numerical simulation (DNS) is performed to examine laminar to turbulent transition due to high-frequency secondary instability of stationary crossflow vortices in a subsonic swept-wing boundary layer for a realistic natural-laminar-flow airfoil configuration. The secondary instability is introduced via inflow forcing and the mode selected for forcing corresponds to the most amplified secondary instability mode that, in this case, derives a majority of its growth from energy production mechanisms associated with the wall-normal shear of the stationary basic state. An inlet boundary condition is carefully designed to allow for accurate injection of instability wave modes and minimize acoustic reflections at numerical boundaries. Nonlinear parabolized stability equation (PSE) predictions compare well with the DNS in terms of modal amplitudes and modal shape during the strongly nonlinear phase of the secondary instability mode. During the transition process, the skin friction coefficient rises rather rapidly and the wall-shear distribution shows a sawtooth pattern that is analogous to the previously documented surface flow visualizations of transition due to stationary crossflow instability. Fully turbulent features are observed in the downstream region of the flow.
Analysis of velocity and thermal structures in a transitionally rough turbulent boundary layer
NASA Astrophysics Data System (ADS)
Doosttalab, Ali; Dharmarathne, Suranga; Araya, Guillermo; Tutkun, Murat; Adrian, Ronald; Castillo, Luciano
2015-11-01
A zero pressure gradient turbulent boundary layer flowing over a transitionally rough surface (24-grit sandpaper) with k+ = 11 and Reynolds numbers based on momentum thickness of around 2400 is studied using direct numerical simulation (DNS). Heat transfer between the isothermal rough surface and the turbulent flow with molecular Prandtl number Pr = 0 . 71 is simulated. The dynamic multi-scale approach developed by Araya et al. (2011) is employed to prescribe realistic time-dependent thermal inflow boundary conditions. Above the roughness sub-layer (3 - 5 k) it is found that statistics of the temperature field, including higher order moments and conditional averages, are the same for the smooth and rough surface flow, showing that the Townsend's Reynolds number similarity hypothesis applies for the thermal field as well as the velocity field for the Reynolds number and k+ considered in this study. Also the velocity and thermal structures of the developing boundary layer were studied by means of multi-point correlations and POD analysis.
Wavelet-based identification of localized turbulent regions in a transitional boundary layer
NASA Astrophysics Data System (ADS)
Yoshikawa, Joe; Nishio, Yu; Izawa, Seiichiro; Fukunishi, Yu
2014-11-01
A numerical study in order to develop a method to identify localized turbulent regions in a transitional boundary layer is carried out using a wavelet transformation. Finding the onset of turbulence is quite difficult because it is not easy to distinguish the localized turbulent regions from ``non-active'' groups of vortices. The base flow with low-speed streaks is generated by placing an array of obstacles. Then a short duration jet is ejected from the wall into the low-speed streak. First, a hairpin vortex appears in the laminar boundary layer which travels downstream growing up. Downstream, localized turbulent regions appear in the boundary layer, where a lot of vortices are entangled with each other. A wavelet analysis is applied to the spatial waveforms of streamwise velocity fluctuations obtained from these two flow fields. It is shown that the hairpin vortex appears as a high amplitude spot in the wavelet spectrum, which is small in both wavenumber-wise and streamwise scales. On the other hand, the isolated turbulent region appears more wide spread in the wavenumber-wise scale. So, using this method, localized turbulent regions can be identified.
Use of Boundary Layer Transition Detection to Validate Full-Scale Flight Performance Predictions
NASA Technical Reports Server (NTRS)
Hamner, Marvine; Owens, L. R., Jr.; Wahls, R. A.; Yeh, David
1999-01-01
Full-scale flight performance predictions can be made using CFD or a combination of CFD and analytical skin-friction predictions. However, no matter what method is used to obtain full-scale flight performance predictions knowledge of the boundary layer state is critical. The implementation of CFD codes solving the Navier-Stokes equations to obtain these predictions is still a time consuming, expensive process. In addition, to ultimately obtain accurate performance predictions the transition location must be fixed in the CFD model. An example, using the M2.4-7A geometry, of the change in Navier-Stokes solution with changes in transition and in turbulence model will be shown. Oil flow visualization using the M2.4-7A 4.0% scale model in the 14'x22' wind tunnel shows that fixing transition at 10% x/c in the CFD model best captures the flow physics of the wing flow field. A less costly method of obtaining full-scale performance predictions is the use of non-linear Euler codes or linear CFD codes, such as panel methods, combined with analytical skin-friction predictions. Again, knowledge of the boundary layer state is critical to the accurate determination of full-scale flight performance. Boundary layer transition detection has been performed at 0.3 and 0.9 Mach numbers over an extensive Reynolds number range using the 2.2% scale Reference H model in the NTF. A temperature sensitive paint system was used to determine the boundary layer state for these conditions. Data was obtained for three configurations: the baseline, undeflected flaps configuration; the transonic cruise configuration; and, the high-lift configuration. It was determined that at low Reynolds number conditions, in the 8 to 10 million Reynolds number range, the baseline configuration has extensive regions of laminar flow, in fact significantly more than analytical skin-friction methods predict. This configuration is fully turbulent at about 30 million Reynolds number for both 0.3 and 0.9, Mach numbers
NASA Technical Reports Server (NTRS)
Carter, J. E.
1977-01-01
A computer program called STAYLAM is presented for the computation of the compressible laminar boundary-layer flow over a yawed infinite wing including distributed suction. This program is restricted to the transonic speed range or less due to the approximate treatment of the compressibility effects. The prescribed suction distribution is permitted to change discontinuously along the chord measured perpendicular to the wing leading edge. Estimates of transition are made by considering leading edge contamination, cross flow instability, and instability of the Tollmien-Schlichting type. A program listing is given in addition to user instructions and a sample case.
NASA Technical Reports Server (NTRS)
Kim, J.; Simon, T. W.
1991-01-01
An experimental investigation of the transition process on flat-plate and concave curved-wall boundary layers for various free-streem turbulence levels was performed. Where possible, sampling according to the intermittency function was made. Such sampling allowed segregation of the signal into two types of behavior: laminar-like and turbulent-like. The results from the investigation are discussed. Documentation is presented in two volumes. Volume one contains the text of the report including figures and supporting appendices. Volume two contains data reduction program listings and tabulated data.
Experimental analysis and computation of the onset and development of the boundary layer transition
NASA Technical Reports Server (NTRS)
Arnal, D.; Juillen, J. C.; Michel, R.
1978-01-01
The transition of an incompressible boundary layer, with zero pressure gradient and low free-stream turbulence is studied. Mean velocity, turbulence and Reynolds shear stress profiles are presented. The development of the Tollmien-Schlichting waves is clearly shown until the turbulent spots appear. The intermittency phenomenon is studied by conditional sampling of the hotwire signal. The comparison with calculation results obtained by resolution of a set of transport equations shows a good agreement for the mean characteristics of the flow; discrepancies observed for the turbulent quantities evolution are due to the intermittency phenomenon.
NASA Technical Reports Server (NTRS)
Hollis, Brian R.; Liechty, Derek S.
2008-01-01
The influence of cavities (for attachment bolts) on the heat-shield of the proposed Mars Science Laboratory entry vehicle has been investigated experimentally and computationally in order to develop a criterion for assessing whether the boundary layer becomes turbulent downstream of the cavity. Wind tunnel tests were conducted on the 70-deg sphere-cone vehicle geometry with various cavity sizes and locations in order to assess their influence on convective heating and boundary layer transition. Heat-transfer coefficients and boundary-layer states (laminar, transitional, or turbulent) were determined using global phosphor thermography.
NASA Technical Reports Server (NTRS)
Silverstein, Abe; Becker, John V
1938-01-01
For the purpose of studying the transition from laminar to turbulent flow, boundary-layer measurements were made in the NACA full-scale wind tunnel on three symmetrical airfoils of NACA 0009, 0012, and 0018 sections. The effects of variations in lift coefficient, Reynolds number, and airfoil thickness on transition were investigated. Air speed in the boundary layer was measured by total-head tubes and by hot wires; a comparison of transition as indicated by the two techniques was obtained. The results indicate no unique value of Reynolds number for the transition, whether the Reynolds number is based upon the distance along the chord or upon the thickness of the boundary layer at the transition point. In general, the transition is not abrupt and occurs in a region that varies in length as a function of the test conditions.
Some Effects of Leading-Edge Sweep on Boundary-Layer Transition at Supersonic Speeds
NASA Technical Reports Server (NTRS)
Chapman, Gray T.
1961-01-01
The effects of crossflow and shock strength on transition of the laminar boundary layer behind a swept leading edge have been investigated analytically and with the aid of available experimental data. An approximate method of determining the crossflow Reynolds number on a leading edge of circular cross section at supersonic speeds is presented. The applicability of the critical crossflow criterion described by Owen and Randall for transition on swept wings in subsonic flow was examined for the case of supersonic flow over swept circular cylinders. A wide range of applicability of the subsonic critical values is indicated. The corresponding magnitude of crossflow velocity necessary to cause instability on the surface of a swept wing at supersonic speeds was also calculated and found to be small. The effects of shock strength on transition caused by Tollmien-Schlichting type of instability are discussed briefly. Changes in local Reynolds number, due to shock strength, were found analytically to have considerably more effect on transition caused by Tollmien-Schlichting instability than on transition caused by crossflow instability. Changes in the mechanism controlling transition from Tollmien-Schlichting instability to crossflow instability were found to be possible as a wing is swept back and to result in large reductions in the length of laminar flow.
Direct Numerical Simulations of Boundary Layer Transition on a Flat Plate
NASA Technical Reports Server (NTRS)
Rai, Man Mohan
1997-01-01
In recent years the techniques of computational fluid dynamics (CFD) have been used to compute flows associated with geometrically complex configurations. However, success in terms of accuracy and reliability has been limited to cases where the effects of turbulence and transition could be modeled in a straightforward manner. Even in simple flows, the accurate computation of skin friction and heat transfer using existing turbulence models has proved to be a difficult task, one that has required extensive fine-tuning of the turbulence models used. In more complex flows (for example, in turbomachinery flows in which vortices and wakes impinge on airfoil surfaces causing periodic transitions from laminar to turbulent flow) the development of a model that accounts for all scales of turbulence and predicts the onset of transition is an extremely difficult task. Fortunately, current trends in computing suggest that it may be possible to perform direct simulations of turbulence and transition at moderate Reynolds numbers in some complex cases in the near future. This presentation will focus on direct simulations of transition and turbulence using high-order accurate finite-difference methods. The advantage of the finite-difference approach over spectral methods is that complex geometries can be treated in a straightforward manner. Additionally, finite-difference techniques are the prevailing methods in existing application codes. An application of accurate finite-difference methods to direct simulations of transition and turbulence in a spatially evolving boundary layer subjected to high levels of freestream turbulence will be presented.
Direct Numerical Simulations of Boundary Layer Transition on a Flat Plate
NASA Technical Reports Server (NTRS)
Rai, Man Mohan
1998-01-01
In recent years the techniques of computational fluid dynamics (CFD) have been used to compute flows associated with geometrically complex configurations. However, success in terms of accuracy and reliability has been limited to cases where the effects of turbulence and transition could be modeled in a straightforward manner. Even in simple flows, the accurate computation of skin friction and heat transfer using existing turbulence models has proved to be a difficult task, one that has required extensive fine-tuning of the turbulence models used. In more complex flows (for example, in turbomachinery flows in which vortices and wakes impinge on airfoil surfaces causing periodic transitions from laminar to turbulent flow) the development of a model that accounts for all scales of turbulence and predicts the onset of transition is an extremely difficult task. Fortunately, current trends in computing suggest that it may be possible to perform direct simulations of turbulence and transition at moderate Reynolds numbers in some complex cases in the near future. This presentation will focus on direct simulations of transition and turbulence using high-order accurate finite-difference methods. The advantage of the finite-difference approach over spectral methods is that complex geometries can be treated in a straightforward manner. Additionally, finite-difference techniques are the prevailing methods in existing application codes. An application of high-order-accurate finite-difference methods to direct simulations of transition and turbulence in a spatially evolving boundary layer subjected to high levels of freestream turbulence will be presented.
NASA Technical Reports Server (NTRS)
Albers, J. A.; Gregg, J. L.
1974-01-01
A finite-difference program is described for calculating the viscous compressible boundary layer flow over either planar or axisymmetric surfaces. The flow may be initially laminar and progress through a transitional zone to fully turbulent flow, or it may remain laminar, depending on the imposed boundary conditions, laws of viscosity, and numerical solution of the momentum and energy equations. The flow may also be forced into a turbulent flow at a chosen spot by the data input. The input may contain the factors of arbitrary Reynolds number, free-stream Mach number, free-stream turbulence, wall heating or cooling, longitudinal wall curvature, wall suction or blowing, and wall roughness. The solution may start from an initial Falkner-Skan similarity profile, an approximate equilibrium turbulent profile, or an initial arbitrary input profile.
Boundary Layer Transition Flight Experiment Overview and In-Situ Measurements
NASA Technical Reports Server (NTRS)
Anderson, Brian P.; Campbell, Charles H.; Saucedo, Luis A.; Kinder, Gerald R.; Berger, Karen T.
2010-01-01
In support of the Boundary Layer Transition Flight Experiment (BLTFE) Project, a manufactured protuberance tile was installed on the port wing of Space Shuttle Orbiter Discovery for the flights of STS-119 and STS-128. Additional instrumentation was also installed in order to obtain more spatially resolved measurements downstream of the protuberance. This paper provides an overview of the BLTFE Project, including the project history, organizations involved, and motivations for the flight experiment. Significant efforts were made to place the protuberance at an appropriate location on the Orbiter and to design the protuberance to withstand the expected environments. Efforts were also extended to understand the as-fabricated shape of the protuberance and the thermal protection system tile configuration surrounding the protuberance. A high-level overview of the in-situ flight data is presented, along with a summary of the comparisons between pre- and post-flight analysis predictions and flight data. Comparisons show that predictions for boundary layer transition onset time closely match the flight data, while predicted temperatures were significantly higher than observed flight temperatures.
NASA Technical Reports Server (NTRS)
Heineck, James; Schairer, Edward; Ramasamy, Manikandan; Roozeboom, Nettie
2016-01-01
This paper describes simultaneous optical measurements of a sub-scale helicopter rotor in the U.S. Army Hover Chamber at NASA Ames Research Center. The measurements included thermal imaging of the rotor blades to detect boundary layer transition; retro-reflective background-oriented schlieren (RBOS) to visualize vortices; and stereo photogrammetry to measure displacements of the rotor blades, to compute spatial coordinates of the vortices from the RBOS data, and to map the thermal imaging data to a three-dimensional surface grid. The test also included an exploratory effort to measure flow near the rotor tip by tomographic particle image velocimetry (tomo PIV)an effort that yielded valuable experience but little data. The thermal imaging was accomplished using an image-derotation method that allowed long integration times without image blur. By mapping the thermal image data to a surface grid it was possible to accurately locate transition in spatial coordinates along the length of the rotor blade.
Measured and calculated wall temperatures on air-cooled turbine vanes with boundary layer transition
NASA Astrophysics Data System (ADS)
Liebert, C. H.; Gaugler, R. E.; Gladden, H. J.
1982-11-01
Convection cooled turbine vane metal wall temperatures experimentally obtained in a hot cascade for one vane design were compared with wall temperatures calculated with TACT1 and STAN5 computer codes which incorporated various models for predicting laminar-to-turbulent boundary layer transition. Favorable comparisons on both vane surface were obtained at high Reynolds number with only one of these transition models. When other models were used, temperature differences between calculated and experimental data obtained at the high Reynolds number were as much as 14 percent in the separation bubble region of the pressure surface. On the suction surface and at lower Reynolds number, predictions and data unsatisfactorily differed by as much as 22 percent. Temperature differences of this magnitude can represent orders of magnitude error in blade life prediction.
Numerical simulation of boundary layers. Part 2: Ribbon-induced transition in Blasius flow
NASA Technical Reports Server (NTRS)
Spalart, P.; Yang, K. S.
1986-01-01
The early three-dimensional stages of transition in Blasius boundary layers are studied by numerical solution of the Navier-Stokes equations. A finite-amplitude two-dimensional wave and random low-amplitude three-dimensional disturbances are introduced. Rapid amplification of the three-dimensional components is observed and leads to transition. For intermediate amplitudes of the two-dimensional wave the breakdown is of subharmonic type, and the dominant spanwise wave number increases with the amplitude. For high amplitudes the energy of the fundamental mode is comparable to the energy of the subharmonic mode, but never dominates it; the breakdown is of mixed type. Visualizations, energy histories, and spectra are presented. The sensitivity of the results to various physical and numerical parameters is studied. Agreement with experimental and theoretical results is discussed.
Dynamic subgrid-scale modeling for high-speed transitional boundary layers
NASA Technical Reports Server (NTRS)
El-Hady, Nabil M.; Zang, Thomas A.; Piomelli, Ugo
1993-01-01
The subgrid scales are modeled dynamically in a large-eddy simulation of transitional boundary-layer flow along a hollow cylinder at a Mach number of 4.5. The behavior of the dynamic-model coefficients, which is determined from local information in the resolved field, is investigated through both an a priori test with direct numerical simulation data for the same case and a complete large-eddy simulation. Both contractions proposed by Germano et al. (1991) and Lilly (1992) are used for the unique determination of the coefficients of the dynamic model, and their results are compared and assessed. The behavior, as well as the energy cascade of the subgridscale field structure, is investigated at various stages of the transition process.
Transition in a Supersonic Boundary-Layer Due to Roughness and Acoustic Disturbances
NASA Technical Reports Server (NTRS)
Balakumar, P.
2003-01-01
The transition process induced by the interaction of an isolated roughness with acoustic disturbances in the free stream is numerically investigated for a boundary layer over a flat plate with a blunted leading edge at a free stream Mach number of 3.5. The roughness is assumed to be of Gaussian shape and the acoustic disturbances are introduced as boundary condition at the outer field. The governing equations are solved using the 5'h-rder accurate weighted essentially non-oscillatory (WENO) scheme for space discretization and using third- order total-variation-diminishing (TVD) Runge- Kutta scheme for time integration. The steady field induced by the two and three-dimensional roughness is also computed. The flow field induced by two-dimensional roughness exhibits different characteristics depending on the roughness heights. At small roughness heights the flow passes smoothly over the roughness, at moderate heights the flow separates downstream of the roughness and at larger roughness heights the flow separates upstream and downstream of the roughness. Computations also show that disturbances inside the boundary layer is due to the direct interaction of the acoustic waves and isolated roughness plays a minor role in generating instability waves.
Turbulence vertical structure of the boundary layer during the afternoon transition
NASA Astrophysics Data System (ADS)
Darbieu, C.; Lohou, F.; Lothon, M.; Vilà-Guerau de Arellano, J.; Couvreux, F.; Durand, P.; Pino, D.; Patton, E. G.; Nilsson, E.; Blay-Carreras, E.; Gioli, B.
2015-09-01
We investigate the decay of planetary boundary layer (PBL) turbulence in the afternoon, from the time the surface buoyancy flux starts to decrease until sunset. Dense observations of mean and turbulent parameters were acquired during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field experiment by several meteorological surface stations, sounding balloons, radars, lidars and two aircraft during the afternoon transition. We analysed a case study based on some of these observations and large-eddy simulation (LES) data focusing on the turbulent vertical structure throughout the afternoon transition. The decay of turbulence is quantified through the temporal and vertical evolution of (1) the turbulence kinetic energy (TKE), (2) the characteristic length scales of turbulence and (3) the shape of the turbulence spectra. A spectral analysis of LES data, airborne and surface measurements is performed in order to characterize the variation in the turbulent decay with height and study the distribution of turbulence over eddy size. This study highlights the LES ability to reproduce the turbulence evolution throughout the afternoon. LESs and observations agree that the afternoon transition can be divided in two phases: (1) a first phase during which the TKE decays at a low rate, with no significant change in turbulence characteristics, and (2) a second phase characterized by a larger TKE decay rate and a change in spectral shape, implying an evolution of eddy size distribution and energy cascade from low to high wave number. The changes observed either in TKE decay (during the first phase) or in the vertical wind spectra shape (during the second phase of the afternoon transition) occur first in the upper region of the PBL. The higher within the PBL, the stronger the spectra shape changes.
NASA Astrophysics Data System (ADS)
Sayadi, Taraneh; Moin, Parviz
2010-11-01
Large eddy simulation of subharmonic transition of a spatially developing zero pressure gradient boundary layer at Ma = 0.2 is investigated using three different subgrid scale (SGS) models: Dynamic Smagorinsky [1], dynamic model involving the SGS kinetic energy [2] and dynamic scale similarity model. The interest lies in assessing the capability of each model in predicting the location of transition and the overshoot in the skin friction coefficient which is specific to this transition scenario. In the case of dynamic Smagorinsky model results were obtained for four different grid resolutions and it is observed that the location of transition is largely unaffected, indicating robust performance of the dynamic model in this respect. However, after breakdown and in the turbulent region the simulations with coarsest grids produce insufficient eddy viscosity to sustain the correct value of skin friction along the plate. As a result the coarsest resolution is employed to compare the performance of these three models. The point of transition is estimated correctly in each case, but the value of the overshoot and the turbulent statistics are affected by the model. [1] Moin P. et. al. Phys Fluids A, 3(11), 2746-2757, 1991. [2] Ghosal. S. et. al. JFM, 286, 229- 255, 1995.
Distributed-Roughness Effects on Stability and Transition In Swept-Wing Boundary Layers
NASA Technical Reports Server (NTRS)
Carrillo, Ruben B., Jr.; Reibert, Mark S.; Saric, William S.
1997-01-01
Boundary-layer stability experiments are conducted in the Arizona State University Unsteady Wind Tunnel on a 45 deg swept airfoil. The pressure distribution and test conditions are designed to suppress Tollmien-Schlichting disturbances and provide crossflow-dominated transition. The surface of the airfoil is finely polished to a near mirror finish. Under these conditions, submicron surface irregularities cause the naturally occurring stationary crossflow waves to grow to nonuniform amplitudes. Spanwise-uniform stationary crossflow disturbances are generated through careful control of the initial conditions with full-span arrays of micron-high roughness elements near the attachment line. Detailed hot-wire measurements are taken to document the stationary crossflow structure and determine growth rates for the total and individual-mode disturbances. Naphthalene flow visualization provides transition location information. Roughness spacing and roughness height are varied to examine the effects on transition location and all amplified wavelengths. The measurements show that roughness spacings that do not contain harmonics equal to the most unstable wavelength as computed by linear stability theory effectively suppress the most unstable mode. Under certain conditions, subcritical roughness spacing delays transition past that of the corresponding smooth surface.
Boundary Layer Transition on Slender Cones in Conventional and Low Disturbance Mach 6 Wind Tunnels
NASA Technical Reports Server (NTRS)
Horvath, Thomas J.; Berry, Scott A.; Hollis, Brian R.; Chang, Chau-Lyan; Singer, Bart A.
2002-01-01
An experimental investigation was conducted on a 5-degree half-angle cone and a 5-degree half-angle flared cone in a conventional Mach 6 wind tunnel to examine the effects of facility noise on boundary layer transition. The influence of tunnel noise was inferred by comparing transition onset locations determined from the present test to that previously obtained in a Mach 6 low disturbance quiet tunnel. Together, the two sets of experiments are believed to represent the first direct comparison of transition onset between a conventional and a low disturbance wind tunnel using a common test model and transition detection technique. In the present conventional hypersonic tunnel experiment, separate measurements of heat transfer and adiabatic wall temperatures were obtained on the conical models at small angles of attack over a range of Reynolds numbers, which resulted in laminar, transitional, and turbulent flow. Smooth model turbulent heating distributions are compared to that obtained with transition forced via discrete surface roughness. The model nosetip radius was varied to examine the effects of bluntness on transition onset. Despite wall to total temperature differences between the transient heating measurements and the adiabatic wall temperature measurement, the two methods for determining sharp cone transition onset generally yielded equivalent locations. In the 'noisy' mode of the hypersonic low disturbance tunnel, transition onset occurred earlier than that measured in the conventional hypersonic tunnel, suggesting higher levels of freestream acoustic radiation relative to the conventional tunnel. At comparable freestream conditions, the transition onset Reynolds number under low disturbance conditions was a factor of 1.3 greater than that measured on flared cone in the LaRC conventional hypersonic tunnel and a factor of 1.6 greater that the flared cone run in the low disturbance tunnel run 'noisy'. Navier-Stokes mean flow computations and linear stability
Large-Eddy Simulation of Transition to Turbulence in Boundary Layers
NASA Technical Reports Server (NTRS)
Huai, Xiao-Li; Joslin, Ronald D.; Piomelli, Ugo
1997-01-01
Large-eddy simulation results for laminar-to-turbulent transition in a spatially developing boundary layer are presented. The disturbances are ingested into a laminar flow through an unsteady suction-and-blowing strip. The filtered, three-dimensional time- dependent Navier-Stokes equations are integrated numerically using spectral, high-order finite-difference, and three-stage low-storage Runge-Kutta methods. The buffer-domain technique is used for the outflow boundary condition. The localized dynamic model used to parameterize the subgrid-scale stresses begins to have a significant impact at the beginning of the nonlinear transition (or intermittency) region. The flow structures commonly found in experiments are also observed in the present simulation; the computed linear instability modes and secondary instability lambda-vortex structures are in agreement with the experiments, and the streak-like-structures and turbulent statistics compare with both the experiments and the theory. The physics captured in the present LES are consistent with the experiments and the full Navier-Stokes simulation (DNS), at a significant fraction of the DNS cost. A comparison of the results obtained with several SGS models shows that the localized model gives accurate results both in a statistical sense and in terms of predicting the dynamics of the energy-carrying eddies, without ad hoc adjustments.
Multigrid direct numerical simulation of the whole process of flow transition in 3-D boundary layers
NASA Technical Reports Server (NTRS)
Liu, Chaoqun; Liu, Zhining
1993-01-01
A new technology was developed in this study which provides a successful numerical simulation of the whole process of flow transition in 3-D boundary layers, including linear growth, secondary instability, breakdown, and transition at relatively low CPU cost. Most other spatial numerical simulations require high CPU cost and blow up at the stage of flow breakdown. A fourth-order finite difference scheme on stretched and staggered grids, a fully implicit time marching technique, a semi-coarsening multigrid based on the so-called approximate line-box relaxation, and a buffer domain for the outflow boundary conditions were all used for high-order accuracy, good stability, and fast convergence. A new fine-coarse-fine grid mapping technique was developed to keep the code running after the laminar flow breaks down. The computational results are in good agreement with linear stability theory, secondary instability theory, and some experiments. The cost for a typical case with 162 x 34 x 34 grid is around 2 CRAY-YMP CPU hours for 10 T-S periods.
NASA Technical Reports Server (NTRS)
Maestrello, L.; Grosveld, F. W.
1991-01-01
The experiment is aimed at controlling the boundary layer transition location and the plate vibration when excited by a flow and an upstream sound source. Sound has been found to affect the flow at the leading edge and the response of a flexible plate in a boundary layer. Because the sound induces early transition, the panel vibration is acoustically coupled to the turbulent boundary layer by the upstream radiation. Localized surface heating at the leading edge delays the transition location downstream of the flexible plate. The response of the plate excited by a turbulent boundary layer (without sound) shows that the plate is forced to vibrate at different frequencies and with different amplitudes as the flow velocity changes indicating that the plate is driven by the convective waves of the boundary layer. The acoustic disturbances induced by the upstream sound dominate the response of the plate when the boundary layer is either turbulent or laminar. Active vibration control was used to reduce the sound induced displacement amplitude of the plate.
Effect of Compliant Walls on Secondary Instabilities in Boundary-Layer Transition
NASA Technical Reports Server (NTRS)
Joslin, Ronald D.; Morris, Philip J.
1991-01-01
For aerodynamic and hydrodynamic vehicles, it is highly desirable to reduce drag and noise levels. A reduction in drag leads to fuel savings. In particular for submersible vehicles, a decrease in noise levels inhibits detection. A suggested means to obtain these reduction goals is by delaying the transition from laminar to turbulent flow in external boundary layers. For hydrodynamic applications, a passive device which shows promise for transition delays is the compliant coating. In previous studies with a simple mechanical model representing the compliant wall, coatings were found that provided transition delays as predicted from the semi-empirical e(sup n) method. Those studies were concerned with the linear stage of transition where the instability of concern is referred to as the primary instability. For the flat-plate boundary layer, the Tollmien-Schlichting (TS) wave is the primary instability. In one of those studies, it was shown that three-dimensional (3-D) primary instabilities, or oblique waves, could dominate transition over the coatings considered. From the primary instability, the stretching and tilting of vorticity in the shear flow leads to a secondary instability mechanism. This has been theoretical described by Herbert based on Floquet theory. In the present study, Herbert's theory is used to predict the development of secondary instabilities over isotropic and non-isotropic compliant walls. Since oblique waves may be dominant over compliant walls, a secondary theory extention is made to allow for these 3-D primary instabilities. The effect of variations in primary amplitude, spanwise wavenumber, and Reynolds number on the secondary instabilities are examined. As in the rigid wall case, over compliant walls the subharmonic mode of secondary instability dominates for low-amplitude primary disturbances. Both isotropic and non-isotropic compliant walls lead to reduced secondary growth rates compared to the rigid wall results. For high frequencies
NASA Astrophysics Data System (ADS)
Erdem, E.; Kontis, K.; Johnstone, E.; Murray, N.; Steelant, J.
Shock Wave Boundary Layer Interactions (SWBLIs) can induce separation which causes loss of a control surface effectiveness, drop of an air intake efficiency and it may be the origin of large scale fluctuations such as air-intake buzz, buffeting or fluctuating side loads in separated propulsive nozzles. The subsequent reattachment of the separated shear layer on a nearby surface gives rise to local heat transfer rates which can be far in excess of those of an attached boundary layer [1].
NASA Astrophysics Data System (ADS)
Sastre, Mariano; Yagüe, Carlos; Román-Cascón, Carlos; Maqueda, Gregorio
2015-12-01
The planetary boundary-layer (PBL) afternoon and evening transition is investigated with measurements from two-month datasets, gathered at two experimental sites significantly different regarding heterogeneity, the degree of terrain wetness, and proximity to mountains. The period of 4 h prior to and after astronomical sunset is extensively analyzed. We show the mean evolution, average, maximum and minimum values of PBL variables, including wind speed, turbulent kinetic energy and potential temperature vertical gradient. Characteristic events, such as the wind minimum around sunset and a common pattern in the evolution of other variables, are identified. Results suggest that, for the establishment of the nocturnal stable boundary layer, moisture plays a more decisive role than turbulence. We also look into the occurrence of katabatic flows, finding more intense but less frequent events at the driest site. In contrast, at that location the crossover of the sensible heat flux takes place later. Time-scale evolution is investigated through case studies, and air humidity and soil moisture are found to have crucial importance explaining most of the site-to-site differences. Therefore, a humidity sensitivity experiment with the Weather Research and Forecasting model is performed, evaluating the role of moisture during the transition by increasing the soil humidity at the driest site and reducing it at the other location. The simulations reveal that humidity effects are more important until 1 h before sunset, both near the surface and at upper levels in the PBL. Furthermore, the moisture change is more relevant at the less humid and more homogeneous site, with intense and long-lasting effects after sunset.
NASA Astrophysics Data System (ADS)
Sandeep, A.; Rao, T. N.; Rao, S. V. B.
2015-07-01
The transitory nature of the atmospheric boundary layer (ABL) a few hours before and after the time of sunset has been studied comprehensively over a tropical station, Gadanki (13.45° N, 79.18° E), using a suite of in situ and remote sensing devices. This study addresses the following fundamental and important issues related to the afternoon transition (AT): which state variable first identifies the AT? Which variable best identifies the AT? Does the start time of the AT vary with season and height? If so, which physical mechanism is responsible for the observed height variation in the start time of the transition? At the surface, the transition is first seen in temperature (T) and wind variance (σ2WS), ~ 100 min prior to the time of local sunset, then in the vertical temperature gradient and finally in water vapor mixing ratio variations. Aloft, both signal-to-noise ratio (SNR) and spectral width (σ) show the AT nearly at the same time. The T at the surface and SNR aloft are found to be the best indicators of transition. Their distributions for the start time of the AT with reference to time of sunset are narrow and consistent in both total and seasonal plots. The start time of the transition shows some seasonal variation, with delayed transitions occurring mostly in the rainy and humid season of the northeast monsoon. Interestingly, in contrast to the general perception, the signature of the transition is first seen in the profiler data, then in the sodar data, and finally in the surface data. This suggests that the transition follows a top-to-bottom evolution. It indicates that other processes, like entrainment, could also play a role in altering the structure of the ABL during the AT, when the sensible heat flux decreases progressively. These mechanisms are quantified using a unique high-resolution data set to understand their variation in light of the intriguing height dependency of the start time of the AT.
NASA Technical Reports Server (NTRS)
Lysenko, V. I.
1987-01-01
By comparing the calculated results with experimental data, it is demonstrated that the position of the laminar-boundary transition point of a boundary layer can be estimated by using the e-exp-n method. The effect of the Mach number, pressure gradient, and heat transfer on the laminar-turbulent transition is discussed. It is found that under conditions of strong cooling, the effect of the pressure gradient on the position of the transition point is less pronounced than in the absence of heat transfer.
Nonlinear interaction of near-planar TS waves and longitudinal vortices in boundary-layer transition
NASA Technical Reports Server (NTRS)
Smith, F. T.
1988-01-01
The nonlinear interactions that evolve between a planar or nearly planar Tollmien-Schlichting (TS) wave and the associated longitudinal vortices are considered theoretically for a boundary layer at high Reynolds number. The vortex flow is either induced by the TS nonlinear forcing or is input upstream, and similarly for the nonlinear wave development. Three major kinds of nonlinear spatial evolution, Types 1-3, are found. Each can start from secondary instability and then become nonlinear, Type 1 proving to be relatively benign but able to act as a pre-cursor to the Types 2, 3 which turn out to be very powerful nonlinear interactions. Type 2 involves faster stream-wise dependence and leads to a finite-distance blow-up in the amplitudes, which then triggers the full nonlinear 3-D triple-deck response, thus entirely altering the mean-flow profile locally. In contrast, Type 3 involves slower streamwise dependence but a faster spanwise response, with a small TS amplitude thereby causing an enhanced vortex effect which, again, is substantial enough to entirely alter the meanflow profile, on a more global scale. Streak-like formations in which there is localized concentration of streamwise vorticity and/or wave amplitude can appear, and certain of the nonlinear features also suggest by-pass processes for transition and significant changes in the flow structure downstream. The powerful nonlinear 3-D interactions 2, 3 are potentially very relevant to experimental findings in transition.
Transitional regime and laminar-turbulent coexistence in the asymptotic suction boundary layer
NASA Astrophysics Data System (ADS)
Khapko, Taras; Schlatter, Philipp; Duguet, Yohann; Henningson, Dan
2015-11-01
We study numerically the asymptotic suction boundary layer (ASBL) in the transitional regime on the verge of laminarization. Starting from a turbulent state the Reynolds number Re is decreased in small steps until the laminar state is established. This study protocol allows not only to investigate the regime at the onset of turbulence, but also to identify the critical Reynolds number Reg ~ 270 , below which turbulence is not sustained. In other planar shear flows the transitional regime at the onset takes the form of stable laminar-turbulent bands, however in ASBL no regime of sustained laminar-turbulent coexistence has been identified. The flow stays fully turbulent even at the lowest Re before laminarization. During the laminarization process streamwise turbulent and laminar avenues are created with no oblique interfaces between the two. This behavior is connected with the existence of a large-scale vertical transport, the feature that distinguishes ASBL from the other wall-bounded shear flows. After an artificial forcing is added canceling all spanwise and wall-normal fluctuations above y+ = 100 , transient oblique bands are observed similar to the ones in other subcritical shear flows, while the flow later laminarizes or becomes fully turbulent again.
Transition along a finite-length cylinder in the presence of a thin boundary layer
NASA Astrophysics Data System (ADS)
Wang, Hanfeng; Peng, Si; Zhou, Yu; He, Xuhui
2016-05-01
This work aims to investigate experimentally the transition of the aerodynamic forces on a cantilevered circular cylinder immersed in a thin boundary layer whose thickness is comparable to the cylinder diameter d. The aspect ratio H/ d of the cylinder is 5, where H is the cylinder height. The Reynolds number Re, based on the freestream velocity ( U ∞ ) and d, is varied from 0.68 × 105 to 6.12 × 105, covering the subcritical, critical and supercritical regimes. It has been found that the flow transition is non-uniform along the cylinder span, taking place at a smaller Re near the cylinder free end than near the base. Furthermore, the sectional drag coefficient of the cantilevered cylinder is smaller relative to that of a two-dimensional cylinder in the subcritical regime, but larger than the later in the supercritical regime. The sectional lift coefficient is not zero in the critical regime, with its maximum near the free end reaching almost four times of that near the base.
Boundary-layer transition detection with infrared imaging emphasizing cryogenic applications
NASA Technical Reports Server (NTRS)
Gartenberg, Ehud; Wright, Robert E.
1994-01-01
This paper reviews the technique of boundary-layer transition detection using infrared (IR) imaging, emphasizing cryogenic wind-tunnel testing. With the exception of the low-temperature effects on the IR radiation, the discussion is relevant to conventional wind-tunnel and flight testing as well. At low temperatures, IR imaging encounters a reduction in the radiated energy throughout the IR spectrum, combined with a shift to longer wavelengths of the bulk of the radiation. This radiation behavior affects the minimum resolvable temperature difference (MRTD) of the IR imaging system because of its fixed wave band sensitivity. In the absence of commercial long wavelength IR imaging systems, operating at wavelengths longer than 13 micron, some measures can be taken to alleviate the problem caused by the MRTD limitation. The thermal signature of transition can be enhanced by allowing a small and controlled temperature increase of the wind-tunnel flow that induces a transient heat transfer to the model. This action temporarily reveals the model area under the turbulent regime through its higher heating rate compared with the laminar regime. The contrast between the areas exposed to the two regimes can be enhanced by subtraction of thermograms (the equilibrium thermogram from the transient thermogram). Further visual improvement can be obtained through shade stretching or binary shading.
Boundary Layer Transition Protuberance Tests at NASA JSC Arc-Jet Facility
NASA Technical Reports Server (NTRS)
Larin, M. E.; Marichalar, J. J.; Kinder, G. R.; Campbell, C. H.; Riccio, J. R.; Nquyen, T. Q.; DelPapa, S. V.; Pulsonetti, M. V.
2009-01-01
A series of arc-jet tests in support of the Shuttle Orbiter Boundary Layer Transition flight experiment was conducted in the Channel Nozzle of the NASA Johnson Space Center Atmospheric Reentry Materials and Structures Facility. The boundary layer trip was a protrusion of a certain height and geometry fabricated as part of a 6"x6" tile insert, a special test article made of the Boeing Rigid Insulation tile material and coated with the Reaction Cured Glass used for the bottom fuselage tiles of the Space Shuttle Orbiter. A total of five such tile inserts were manufactured: four with the 0.25-in. trip height, and one with the 0.35-in. trip height. The tile inserts were interchangeably installed in the center of the 24"x24" variable configuration tile array mounted in the 24"x24" test section of the channel nozzle. The objectives of the test series were to demonstrate that the boundary layer trip can safely withstand the Space Shuttle Orbiter flight-like re-entry environments and provide temperature data on the protrusion surface, surfaces of the nearby tiles upstream and downstream of the trip, as well as the bond line between the tiles and the structure. The targeted test environments were defined for the tip of the protrusion, away from the nominal surface of the tile array. The arc jet test conditions were approximated in order to produce the levels of the free stream total enthalpy at the protrusion height similar to those expected in flight. The test articles were instrumented with surface, sidewall and bond line thermocouples. Additionally, Tempilaq temperature-indicating paint was applied to the nominal tiles of the tile array in locations not interfering with the protrusion trip. Five different grades of paint were used that disintegrate at different temperatures between 1500 and 2000 deg F. The intent of using the paint was to gauge the RCG-coated tile surface temperature, as well as determine its usefulness for a flight experiment. This paper provides an
The effects of wall surface defects on boundary-layer transition in quiet and noisy supersonic flow
NASA Technical Reports Server (NTRS)
Morrisette, E. Leon; Creel, Theodore R., Jr.
1987-01-01
The design of supersonic vehicles with laminar flow control and vehicles such as the Space Shuttle requires information on allowable transition tolerances to fabrication defects such as discrete surface roughness and waviness. A relatively large data base on the effects of discrete roughness on transition exists for subsonic and supersonic speeds. The existing supersonic wind tunnel transition data are contaminated by wind tunnel noise emanating from the turbulent boundary layers on the nozzle walls. Roughness and waviness transition data obtained in a quiet Mach 3.5 supersonic wind tunnel are compared with those obtained in conventional noisy flows.
Boundary-Layer Transition Results from the F-16XL-2 Supersonic Laminar Flow Control Experiment
NASA Technical Reports Server (NTRS)
Marshall, Laurie A.
1999-01-01
A variable-porosity suction glove has been flown on the F-16XL-2 aircraft to demonstrate the feasibility of this technology for the proposed High-Speed Civil Transport (HSCT). Boundary-layer transition data have been obtained on the titanium glove primarily at Mach 2.0 and altitudes of 53,000-55,000 ft. The objectives of this supersonic laminar flow control flight experiment have been to achieve 50- to 60-percent-chord laminar flow on a highly swept wing at supersonic speeds and to provide data to validate codes and suction design. The most successful laminar flow results have not been obtained at the glove design point (Mach 1.9 at an altitude of 50,000 ft). At Mach 2.0 and an altitude of 53,000 ft, which corresponds to a Reynolds number of 22.7 X 10(exp 6), optimum suction levels have allowed long runs of a minimum of 46-percent-chord laminar flow to be achieved. This paper discusses research variables that directly impact the ability to obtain laminar flow and techniques to correct for these variables.
Role of Detuning in the Final Stage of Subharmonic Mode Transition in Boundary Layers
NASA Technical Reports Server (NTRS)
Corke, Thomas C.
2007-01-01
This work involves mechanisms for transition to turbulence in a Blasius boundary layer through resonant interactions between a plane Tollmien-Schlichting Wave and pairs of oblique waves with equal-but-opposite wave angles. When the frequency of the TS wave is exactly twice that of the oblique waves, we have a "tuned" subharmonic resonance. This leads to the enhanced growth of the oblique modes. Following this, other nonlinear interactions lead to the growth of other 3-D modes which are harmonically based, along with a 3-D mean flow distortion. In the final stage of this process, a gradual spectral filling occurs which we have traced to the growth of fundamental and subharmonic side-band modes. To simulate this with controlled inputs, we introduced the oblique wave pairs at the same conditions, but shifted the frequency of the plane TS mode (by as much as 12 percent) so that it was not exactly twice that of the 3-D modes. These "detuned" conditions also lead to the enhanced growth of the oblique modes, as well as discrete side-band modes which come about through sum and difference interactions. Other interactions quickly lead to a broad band of discrete modes. Of particular importance is the lowest difference frequency which produces a low frequency modulation similar to what has been seen in past experiments with natural 3-D mode input. Cross-bispectral analysis of time series allows us to trace the origin and development of the different modes. Following these leads to a scenario which we believe is more relevant to conditions of "natural" transitions, where low amplitude background disturbances either lead to the gradual detuning of exact fundamental/subharmonic resonance, or in which 3-D mode resonance is detuned from the onset. The results contrast the two conditions, and document the propensity of the 2-D/3-D mode interactions to become detuned.
Analysis of the leading edge effects on the boundary layer transition
NASA Technical Reports Server (NTRS)
Chow, Pao-Liu
1990-01-01
A general theory of boundary layer control by surface heating is presented. Some analytical results for a simplified model, i.e., the optimal control of temperature fluctuations in a shear flow are described. The results may provide a clue to the effectiveness of the active feedback control of a boundary layer flow by wall heating. In a practical situation, the feedback control may not be feasible from the instrumentational point of view. In this case the vibrational control introduced in systems science can provide a useful alternative. This principle is briefly explained and applied to the control of an unstable wavepacket in a parallel shear flow.
Exploratory Investigation of Boundary-Layer Transition on a Hollow Cylinder at a Mach Number of 6.9
NASA Technical Reports Server (NTRS)
Bertram, Mitchel H
1957-01-01
The Reynolds number for transition on the outside of a hollow cylinder with heat transfer from the boundary layer to the wall has been investigated at a Mach number of 6.9 in the Langley 11-inch hypersonic tunnel. The type of boundary layer was determined from impact-pressure surveys and optical viewing. From a correlation of results obtained from various sources at lower Mach numbers (in the range 2.0 to 4.5) and data from the present tests with variable Reynolds number per inch, leading-edge thickness and free-stream Reynolds number per inch appear to be important considerations in flat-plate transition results. At a given Mach number, it appears that the Reynolds number based on leading-edge thickness is an important parameter that must be considered in comparisons of flat-plate transition data from various installations.
Some Recent Contributions to the Study of Transition and Turbulent Boundary Layers
NASA Technical Reports Server (NTRS)
Dryden, Hugh L
1947-01-01
The first part of this paper reviews the present state of the problem of the instability of laminar boundary layers which has formed an important part of the general lectures by von Karman at the first and fourth Congresses and by Taylor at the fifth Congress. This problem may now be considered as essentially solved as the result of work completed since 1938. When the velocity fluctuations of the free-stream flow are less than 0.1 percent of the mean speed, instability occurs as described by the well-known Tollmien-Schlichting theory. The Tollmien-Schlichting waves were first observed experimentally by Schubauer and Skramstad in 1940. They devised methods of introducing controlled small disturbances and obtained measured values of frequency, damping, and wave length at various Reynolds numbers which agreed well with the theoretical results. Their experimental results were confirmed by Liepmann. Much theoretical work was done in Germany in extending the Tol1mien-Schlichting theory to other boundary conditions, in particular to flow along a porous wall to which suction is applied for removing part of the boundary layer. The second part of this paper summarizes the present state of knowledge of the mechanics of turbulent boundary layers, and of the methods now being used for fundamental studies of the turbulent fluctuations in turbulent boundary layers. A brief review is given of the semi-empirical method of approach as developed by Buri, Gruschwitz, Fediaevsky, and Kalikhman. In recent years the National Advisory.Commsittee for Aeronautics has sponsored a detailed study at the National Bureau of Standards of the turbulent fluctuations in a turbulent boundary layer under adverse pressure gradient sufficient to produce separation. The aims of this investigation and its present status are described.
NASA Technical Reports Server (NTRS)
Hunter, W. W., Jr.; Ocheltree, S. L.; Russ, C. E., Jr.
1991-01-01
Laser transit anemometer (LTA) measurements of a 7 degree sharp cone boundary layer were conducted in the Air Force/AEDC Supersonic Tunnel A Mach 4 flow field. These measurements are compared with Pitot probe measurements and tricone theory provided by AEDC staff. Measurements were made both in laminar and turbulent boundary layers of the model. Comparison of LTA measurements with theory showed agreement to better than 1 percent for the laminar boundary layer cases. This level of agreement was obtained after small position corrections, 0.01 to 0.6 mm, were applied to the experimental data sets. Pitot probe data when compared with theory also showed small positioning errors. The Pitot data value was also limited due to probe interference with the flow near the model. The LTA turbulent boundary layer data indicated a power law dependence of 6.3 to 6.9. The LTA data was analyzed in the time (Tau) domain in which it was obtained and in the velocity domain. No significant differences were noted between Tau and velocity domain results except in one turbulent boundary layer case.
NASA Astrophysics Data System (ADS)
Bountin, D. A.; Gromyko, Yu. V.; Maslov, A. A.; Polivanov, P. A.; Sidorenko, A. A.
2015-11-01
As a rule, aerodynamic studies at hypersonic flow velocities are carried out in short-duration wind-tunnel facilities. For such facilities, optical diagnostic methods are most preferable. In the present study, we give for the first time a comparison of two methods for determining the end of laminar-turbulent transition: from the distribution of heat fluxes and from schlieren visualization data for the boundary-layer flow. Parametric data on the position of the transition are obtained. These data can be used in the future as reference ones while calibrating semi-empirical calculation models for the transition.
NASA Technical Reports Server (NTRS)
Spanos, Theodoros A.; Micklos, Ann
2010-01-01
In an effort to better the understanding of high speed aerodynamics, a series of flight experiments were installed on Space Shuttle Discovery during the STS-119 and STS-128 missions. This experiment, known as the Boundary Layer Transition Flight Experiment (BLTFE), provided the technical community with actual entry flight data from a known height protuberance at Mach numbers at and above Mach 15. Any such data above Mach 15 is irreproducible in a laboratory setting. Years of effort have been invested in obtaining this valuable data, and many obstacles had to be overcome in order to ensure the success of implementing an Orbiter modification. Many Space Shuttle systems were involved in the installation of appropriate components that revealed 'concurrent engineering' was a key integration tool. This allowed the coordination of all various parts and pieces which had to be sequenced appropriately and installed at the right time. Several issues encountered include Orbiter configuration and access, design requirements versus current layout, implementing the modification versus typical processing timelines, and optimizing the engineering design cycles and changes. Open lines of communication within the entire modification team were essential to project success as the team was spread out across the United States, from NASA Kennedy Space Center in Florida, to NASA Johnson Space Center in Texas, to Boeing Huntington Beach, California among others. The forum permits the discussion of processing concerns from the design phase to the implementation phase, which eventually saw the successful flights and data acquisition on STS-119 in March 2009 and on STS-128 in September 2009.
NASA Technical Reports Server (NTRS)
Rozendaal, Rodger A.
1986-01-01
The Variable Sweep Transition Flight Experiment (VSTFE) was initiated to establish a boundary-layer transition data base for laminar flow wing design. For this experiment, full-span upper-surface gloves will be fitted to a variable sweep F-14 aircraft. The results of two initial tasks are documented: a parametric pressure distribution/boundary-layer stability study and the design of an upper-surface glove for Mach 0.8. The first task was conducted to provide a data base from which wing-glove pressure distributions could be selected for glove designs. Boundary-layer stability analyses were conducted on a set of pressure distributions for various wing sweep angles, Mach numbers, and Reynolds number in the range of those anticipated for the flight-test program. The design procedure for the Mach 0.8 glove is described, and boundary-layer stability calculations and pressure distributions are presented both at design and off-design conditions. Also included is the analysis of the clean-up glove (smoothed basic wing) that will be flight-tested initially and the analysis of a Mach 0.7 glove designed at the NASA Langley Research Center.
Mislevy, S.P.; Wang, T.
1996-10-01
The effects of adverse pressure gradients on the thermal and momentum characteristics of a heated transitional boundary layer were investigated with free-stream turbulence ranging from 0.3 to 0.6 percent. Boundary layer measurements were conducted for two constant-K cases, K1 = {minus}0.51 {times} 10{sup {minus}6} and K2 = {minus}1.05 {times} 10{sup {minus}6}. The fluctuation quantities, u{prime}, v{prime}, t{prime}, the Reynolds shear stress ({ovr uv}), and the Reynolds heat fluxes ({ovr vt} and {ovr ut}) were measured. In general, u{prime}/U{sub {infinity}}, v{prime}/U{sub {infinity}}, and {ovr vt} have higher values across the boundary layer for the adverse pressure-gradient cases than they do for the baseline case (K = 0). The development of v{prime} for the adverse pressure gradients was more actively involved than that of the baseline. In the early transition region, the Reynolds shear stress distribution for the K2 case showed a near-wall shear developed at Y{sup +} = 70. For the baseline case, however, the maximum turbulent shear in the transition region was generated at Y{sup +} = 70, and no near-wall high-shear region was seen. Stronger adverse pressure gradients appear to produce more uniform and higher t{prime} in the near-wall region (Y{sup +} < 20) in both transitional and turbulent boundary layers. The instantaneous velocity signals did not show any clear turbulent/nonturbulent demarcations in the transition region. Increasingly stronger adverse pressure gradients seemed to produce large nonturbulent unsteadiness (or instability waves) at a similar magnitude as the turbulent spots could not be identified visually or through conventional conditional-sampling schemes. In addition, the streamwise evolution of eddy viscosity, turbulent thermal diffusivity, and Pr{sub t} are also presented.
NASA Astrophysics Data System (ADS)
Cuchiara, Gustavo; Rappenglück, Bernhard
2016-04-01
The transition from the convective boundary layer during the daytime to the stable stratified boundary layer during nighttime after sunset plays an important role in the transport and dispersion of atmospheric pollutants. However, our knowledge regarding this transition and its feedback on the structure of the subsequent nocturnal boundary layer is still restricted. This also prevents forecast models from accurate prediction of the onset and development of the nighttime boundary layer, which determines the redistribution of pollutants within the nocturnal surface layer and the residual layer aloft. In the present study, the well-known case of day 33 of the Wangara experiment is resimulated using the Weather Research and Forecasting (WRF) model in an idealized single-column mode to assess the performance of a frequently used planetary boundary layer (PBL) scheme, the Yonsei University (YSU) PBL scheme. These results are compared with two large eddy simulations (LES) for the same case study imposing different surface fluxes: one using previous surface fluxes calculated for the Wangara experiment and a second one using output from the WRF model. The results show a reasonable agreement of the PBL scheme in WRF with the LES. Overall, all the simulations presented a cold bias of ~3 Kelvin for the potential temperature and underestimation of the wind speed, especially after the transition to nighttime conditions (biases were up to 4 ms-1). Finally, an alternative set of eddy diffusivity equations was tested to represent the transition characteristics of a sunset period, with a stable layer below and a new parameterization for the convective decay regime typically observed in the RL aloft. This set of equations led to a gradual decrease of the eddy diffusivity, which replaces the instantaneous collapse of traditional diagnostics for eddy diffusivities. More appreciable changes were observed in air temperature, wind speed and specific humidity (up to 0.5 K, 0.6 ms-1, and 0
NASA Technical Reports Server (NTRS)
Bathel, Brett F.; Danehy, Paul M.; Jones, Stephen B.; Johansen, Craig T.; Goyne, Christopher P.
2013-01-01
Measurements of mean streamwise velocity, fluctuating streamwise velocity, and instantaneous streamwise velocity profiles in a hypersonic boundary layer were obtained over a 10-degree half-angle wedge model. A laser-induced fluorescence-based molecular tagging velocimetry technique was used to make the measurements. The nominal edge Mach number was 4.2. Velocity profiles were measured both in an untripped boundary layer and in the wake of a 4-mm diameter cylindrical tripping element centered 75.4 mm downstream of the sharp leading edge. Three different trip heights were investigated: k = 0.53 mm, k = 1.0 mm and k = 2.0 mm. The laminar boundary layer thickness at the position of the measurements was approximately 1 mm, though the exact thickness was dependent on Reynolds number and wall temperature. All of the measurements were made starting from a streamwise location approximately 18 mm downstream of the tripping element. This measurement region continued approximately 30 mm in the streamwise direction. Additionally, measurements were made at several spanwise locations. An analysis of flow features show how the magnitude, spatial location, and spatial growth of streamwise velocity instabilities are affected by parameters such as the ratio of trip height to boundary layer thickness and roughness Reynolds number. The fluctuating component of streamwise velocity measured along the centerline of the model increased from approximately 75 m/s with no trip to +/-225 m/s with a 0.53-mm trip, and to +/-240 m/s with a 1-mm trip, while holding the freestream Reynolds number constant. These measurements were performed in the 31-inch Mach 10 Air Tunnel at the NASA Langley Research Center.
Study of Transitions in the Atmospheric Boundary Layer Using Explicit Algebraic Turbulence Models
NASA Astrophysics Data System (ADS)
Lazeroms, W. M. J.; Svensson, G.; Bazile, E.; Brethouwer, G.; Wallin, S.; Johansson, A. V.
2016-08-01
We test a recently developed engineering turbulence model, a so-called explicit algebraic Reynolds-stress (EARS) model, in the context of the atmospheric boundary layer. First of all, we consider a stable boundary layer used as the well-known first test case from the Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study (GABLS1). The model is shown to agree well with data from large-eddy simulations (LES), and this agreement is significantly better than for a standard operational scheme with a prognostic equation for turbulent kinetic energy. Furthermore, we apply the model to a case with a (idealized) diurnal cycle and make a qualitative comparison with a simpler first-order model. Some interesting features of the model are highlighted, pertaining to its stronger foundation on physical principles. In particular, the use of more prognostic equations in the model is shown to give a more realistic dynamical behaviour. This qualitative study is the first step towards a more detailed comparison, for which additional LES data are needed.
The Atmospheric Boundary Layer
ERIC Educational Resources Information Center
Tennekes, Hendrik
1974-01-01
Discusses some important parameters of the boundary layer and effects of turbulence on the circulation and energy dissipation of the atmosphere. Indicates that boundary-layer research plays an important role in long-term forecasting and the study of air-pollution meteorology. (CC)
NASA Technical Reports Server (NTRS)
Malik, M. R.
1982-01-01
A fast computer code COSAL for transition prediction in three dimensional boundary layers using compressible stability analysis is described. The compressible stability eigenvalue problem is solved using a finite difference method, and the code is a black box in the sense that no guess of the eigenvalue is required from the user. Several optimization procedures were incorporated into COSAL to calculate integrated growth rates (N factor) for transition correlation for swept and tapered laminar flow control wings using the well known e to the Nth power method. A user's guide to the program is provided.
Study of Separation and Transition of Boundary Layer For Flow Through Linear Turbine Cascade
NASA Astrophysics Data System (ADS)
Mutnuri, Pavan Kumar; Ayyalasomayajula, Haritha; Ghia, Urmila; "Karman" Ghia, Kirti
2002-11-01
The objective of the present work is to study the boundary-layer separation of unsteady flow in turbomachines. A parallel, Chimera version of FDL3DI is used as the flow solver. The code uses second and fourth-order damping for a stable numerical solution. The use of fourth-order damping terms necessitates a minimum of 4-cell overlap at inter-block boundaries. The extended overlap is also necessary for the later intended use of a higher-order accurate differencing technique. The blocks are extended in such a way that the grid points in the overlap region coincide with the grid points in the neighboring-block (under-lapping) region and hence direct injection may be used for inter-block communication. This maintains the order of accuracy of the difference scheme; otherwise, any interpolation involved in inter-block communication needs to be of the same high-order accuracy as the difference scheme of the flow equations. PEGASUS is used to update the flow variables at the block interfaces. A 12-block structured grid of multiple topologies generated by GRIDPRO is used. Low-Re separated flow results are examined and will be presented for a cascade configuration. Passive control methodology is also planned for application to unsteady boundary-layer flow separation in the cascade.
NASA Technical Reports Server (NTRS)
Kuhn, G. D.
1971-01-01
A computer program was developed to do the calculations for two-dimensional or axisymmetric configurations from low speeds to hypersonic speeds with arbitrary streamwise pressure, temperature, and Mach number distributions. Options are provided for obtaining initial conditions either from experimental information or from a theoretical similarity solution. The transition region can be described either by an arbitrary distribution of intermittency or by a function based on Emmons' probability theory. Correlations were developed for use in estimating the parameters of the theoretical intermittency function. Correlations obtained from other sources are used for estimating the transition point. Comparisons were made between calculated and measured boundary layer quantities for laminar, transitional, and turbulent flows on flat plates, cones, cone flares, and a waisted body of revolution. Excellent agreement was obtained between the present theory and two other theories based on the method of finite differences. The intermittency required to reproduce some experimental heat transfer results in hypersonic flow was found to be quite different from the theoretical function. It is suggested that the simple probability theory of Emmons may not be valid for representing the intermittency of hypersonic transitional boundary layers and that the program could be useful as a tool for detailed study of the intermittency of the transition region.
NASA Astrophysics Data System (ADS)
Zheng, Wenjie; Yang, Yue; Chen, Shiyi
2015-11-01
Evolutionary geometry of flow structures in a compressible transitional boundary layer at Ma = 0 . 7 is investigated from a Lagrangian perspective. The Lagrangian structures in the transition are extracted from the Lagrangian scalar field by a moving window filter, and then their geometry is characterized by the multi-scale and multi-directional geometric analysis (Yang and Pullin, J. Fluid Mech., 674, 2011), including the averaged inclination and sweep angles at different scales ranging from one half of the boundary layer thickness to several viscous length scales δν. The results show that averaged angles are almost unaltered for different scales before the transition. As the transition occurs, averaged inclination angles increase and sweep angles decrease rapidly with increasing reference time. Furthermore, the orientation changes more significantly for structures with small scales than large scales. In the late stage of transition, the averaged inclination angle of small-scale structures with the length scale ~ O (10) δν is 42° , and the averaged sweep angle in the logarithm law region is approximately 30° . This work is supported in part by NSFC (No. 11472015) and the Thousand Young Talent Program of China.
NASA Technical Reports Server (NTRS)
Marek, Lindsay C.
2011-01-01
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
Control of the vortical structure in the early stages of transition in boundary layers
NASA Technical Reports Server (NTRS)
El-Hady, Nabil M.
1990-01-01
The effect of suction and pressure gradient on controlling the production of the three-dimensional vortical structure due to secondary instability is investigated for a boundary layer in the presence of small but finite amplitude Tollmien-Schlichting wave. The subharmonic instability is the focus of the study due to its realistic application in low disturbance flight environment. The spanwise wavelength of the most unstable secondary subharmonic disturbance increases with the increase of control indicating possible alteration of the flow structure from H-type to C-type.
NASA Technical Reports Server (NTRS)
Ahn, Kyung H.
1994-01-01
The RNG-based algebraic turbulence model, with a new method of solving the cubic equation and applying new length scales, is introduced. An analysis is made of the RNG length scale which was previously reported and the resulting eddy viscosity is compared with those from other algebraic turbulence models. Subsequently, a new length scale is introduced which actually uses the two previous RNG length scales in a systematic way to improve the model performance. The performance of the present RNG model is demonstrated by simulating the boundary layer flow over a flat plate and the flow over an airfoil.
NASA Technical Reports Server (NTRS)
Holmes, B. J.; Gall, P. D.; Croom, C. C.; Manuel, G. S.; Kelliher, W. C.
1986-01-01
The visualization of laminar to turbulent boundary layer transition plays an important role in flight and wind-tunnel aerodynamic testing of aircraft wing and body surfaces. Visualization can help provide a more complete understanding of both transition location as well as transition modes; without visualization, the transition process can be very difficult to understand. In the past, the most valuable transition visualization methods for flight applications included sublimating chemicals and oil flows. Each method has advantages and limitations. In particular, sublimating chemicals are impractical to use in subsonic applications much above 20,000 feet because of the greatly reduced rates of sublimation at lower temperatures (less than -4 degrees Farenheit). Both oil flow and sublimating chemicals have the disadvantage of providing only one good data point per flight. Thus, for many important flight conditions, transition visualization has not been readily available. This paper discusses a new method for visualizing transition in flight by the use of liquid crystals. The new method overcomes the limitations of past techniques, and provides transition visualization capability throughout almost the entire altitude and speed ranges of virtually all subsonic aircraft flight envelopes. The method also has wide applicability for supersonic transition visualization in flight and for general use in wind tunnel research over wide subsonic and supersonic speed ranges.
NASA Astrophysics Data System (ADS)
Li, Xinliang; Fu, Dexun; Ma, Yanwen
2010-02-01
The direct numerical simulation of boundary layer transition over a 5° half-cone-angle blunt cone is performed. The free-stream Mach number is 6 and the angle of attack is 1°. Random wall blow-and-suction perturbations are used to trigger the transition. Different from the authors' previous work [Li et al., AIAA J. 46, 2899 (2008)], the whole boundary layer flow over the cone is simulated (while in the author's previous work, only two 45° regions around the leeward and the windward sections are simulated). The transition location on the cone surface is determined through the rapid increase in skin fraction coefficient (Cf). The transition line on the cone surface shows a nonmonotonic curve and the transition is delayed in the range of 20°≤θ≤30° (θ =0° is the leeward section). The mechanism of the delayed transition is studied by using joint frequency spectrum analysis and linear stability theory (LST). It is shown that the growth rates of unstable waves of the second mode are suppressed in the range of 20°≤θ≤30°, which leads to the delayed transition location. Very low frequency waves (VLFWs) are found in the time series recorded just before the transition location, and the periodic times of VLFWs are about one order larger than those of ordinary Mack second mode waves. Band-pass filter is used to analyze the low frequency waves, and they are deemed as the effect of large scale nonlinear perturbations triggered by LST waves when they are strong enough.
NASA Technical Reports Server (NTRS)
Von Doenhoff, Albert E; Horton, Elmer A
1958-01-01
An investigation was made in the Langley low-turbulence pressure tunnel to determine the effect of size and location of a sandpaper type of roughness on the Reynolds number for transition. Transition was observed by means of a hot-wire anemometer located at various chordwise stations for each position of the roughness. These observations indicated that when the roughness is sufficiently submerged in the boundary layer to provide a substantially linear variation of boundary-layer velocity with distance from the surface up to the top of the roughness, turbulent "spots" begin to appear immediately behind the roughness when the Reynolds number based on the velocity at the top of the roughness height exceeds a value of approximately 600. At Reynolds numbers even slightly below the critical value (value for transition), the sandpaper type of roughness introduced no measurable disturbances into the laminar layer downstream of the roughness. The extent of the roughness area does not appear to have an important effect on the critical value of the roughness Reynolds number.
NASA Astrophysics Data System (ADS)
Ryzhov, Olef S.
2000-01-01
Absolute instability of (Gortler vortices on the severely curved concave pressure side of a gas-turbine blade is the main thrust of the third-year work under this grant. For the most part, the Gortler vortices have been investigated in an incompressible boundary layer over thin-wing sections or artificial inserts on an otherwise flat plate. The cascade of modern aircraft engines operate in the high subsonic Mach number regime with velocity fields strongly affected by centrifugal forces maintained by the large curvature of profiles. Unsteady spiral-type vortices developing in these environments provoke the absolute instability in the streamwise direction of the boundary layer leading to earlier transition. An effort undertaken after the meeting in Shalimar (May 29-31, 2002) show that the heat transfer coefficient is even more susceptible to enhancing oscillations in the upstream moving wave packets than the pressure.
Aeschliman, D.P.; Croll, R.H.; Kuntz, D.W.
1997-04-01
The use of shear-stress-sensitive, temperature-insensitive (SSS/TI) liquid crystals (LCs) has been evaluated as a boundary-layer transition detection technique for hypersonic flows. Experiments were conducted at Mach 8 in the Sandia National Laboratories Hypersonic Wind Tunnel using a flat plate model at near zero-degree angle of attack over the freestream unit Reynolds number range 1.2-5.8x10{sup 6}/ft. Standard 35mm color photography and Super VHS color video were used to record LC color changes due to varying surface shear stress during the transition process for a range of commercial SSS liquid crystals. Visual transition data were compared to an established method using calorimetric surface heat-transfer measurements to evaluate the LC technique. It is concluded that the use of SSS/TI LCs can be an inexpensive, safe, and easy to use boundary-layer transition detection method for hypersonic flows. However, a valid interpretation of the visual records requires careful attention to illumination intensity levels and uniformity, lighting and viewing angles, some prior understanding of the general character of the flow, and the selection of the appropriate liquid crystal for the particular flow conditions.
NASA Technical Reports Server (NTRS)
Suzen, Y. B.; Huang, P. G.; Hultgren, Lennart S.; Ashpis, David E.
2003-01-01
A new transport equation for the intermittency factor was proposed to predict separated and transitional boundary layers under low-pressure turbine airfoil conditions. The intermittent behavior of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, t , with the intermittency factor, y. Turbulent quantities are predicted by using Menter s two-equation turbulence model (SST). The intermittency factor is obtained from a transport equation model, which not only can reproduce the experimentally observed streamwise variation of the intermittency in the transition zone, but also can provide a realistic cross-stream variation of the intermittency profile. In this paper, the intermittency model is used to predict a recent separated and transitional boundary layer experiment under low pressure turbine airfoil conditions. The experiment provides detailed measurements of velocity, turbulent kinetic energy and intermittency profiles for a number of Reynolds numbers and freestream turbulent intensity conditions and is suitable for validation purposes. Detailed comparisons of computational results with experimental data are presented and good agreements between the experiments and predictions are obtained.
NASA Technical Reports Server (NTRS)
Suzen, Y. Bora; Huang, P. G.; Hultgren, Lennart S.; Ashpis, David E.
2001-01-01
A new transport equation for the intermittency factor was proposed to predict separated and transitional boundary layers under low-pressure turbine airfoil conditions. The intermittent behavior of the transitional flows is taken into account and incorporated into computations by modifying the eddy viscosity, mu(sub t), with the intermittency factor, gamma. Turbulent quantities are predicted by using Menter's two-equation turbulence model (SST). The intermittency factor is obtained from a transport equation model, which not only can reproduce the experimentally observed streamwise variation of the intermittency in the transition zone, but also can provide a realistic cross-stream variation of the intermittency profile. In this paper, the intermittency model is used to predict a recent separated and transitional boundary layer experiment under low pressure turbine airfoil conditions. The experiment provides detailed measurements of velocity, turbulent kinetic energy and intermittency profiles for a number of Reynolds numbers and freestream turbulent intensity conditions and is suitable for validation purposes. Detailed comparisons of computational results with experimental data are presented and good agreements between the experiments and predictions are obtained.
NASA Astrophysics Data System (ADS)
Tumin, Anatoli
2015-11-01
Zavol'skii and Reutov (1983), Luchini (2008, 2010), Fedorov (2010, 2012, 2014) explored potential role of kinetic fluctuations (KF) in incompressible and calorically perfect gas boundary layer flows. The results indicate that role of KF is comparable with other disturbance sources in flight experiments and in quiet wind tunnels. The analysis is based on the Landau and Lifshitz (1957) concept of fluctuating hydrodynamics representing the dissipative fluxes as an average and fluctuating parts. We are extending analysis of the receptivity problem to the fluctuating dissipative fluxes in chemically reacting nonequilibrium boundary layer flows of binary mixtures. There are new terms in the energy, and the species equations. The species conservation equation includes the dissipative diffusion flux and the species generation due to dissociation. The momentum equation includes fluctuating stress tensor. The energy equation includes fluctuating heat flux, energy flux due to diffusion of the species, and fluctuating dissipative flux due to viscosity. The effects are compared for the cases stemming from constraints of the HTV project (Klentzman and Tumin, AIAA Paper 2013-2882). Supported by AFOSR.
NASA Astrophysics Data System (ADS)
Laurence, S. J.; Wagner, A.; Hannemann, K.
2014-08-01
Three variants of schlieren techniques are employed to investigate the development of second-mode instability waves in the hypersonic boundary layer of a slender cone in a reflected shock tunnel. First, a previously proposed technique using high frame rate (i.e., at least as high as the dominant instability frequency) schlieren visualization with a continuous light source is shown to provide repeatable measurements of the instability propagation speed and frequency. A modified version of the technique is then introduced whereby a pulsed light source allows the use of a higher-resolution camera with a lower frame rate: this provides significant benefits in terms of spatial resolution and total recording time. A detailed picture of the surface-normal intensity distribution for individual wave packets is obtained, and the images provide comprehensive insight into the unsteady flow structures within the boundary layer. Finally, two-point schlieren deflectometry is implemented and shown to be capable of providing second-mode growth information in the challenging shock tunnel environment.