Surface Streamline Research Articles

Wake Closure and Afterbody Heating on a Mars Sample Return Orbiter

Aeroheating wind-tunnel tests were conducted on a 0.028-scale model of an orbiter concept considered for a possible Mars sample return mission. The primary experimental objectives were to characterize hypersonic near-wakeclosure and to determine if shear layer impingement would occur on the proposed orbiter afterbody at incidence angles necessary for a Martian aerocapture maneuver. Global heat transfer mappings, surface streamline patterns, and shock shapes were obtained in the NASA Langley Research Center 20-Inch Mach 6 Air and CF 4 Tunnels for postnormal shock Reynolds numbers (based on forebody diameter) ranging from 1.4 × 10 3 to 4.15 x 105, angles of attack ranging from -5 to 10 deg at 0-, 3-, and 6-deg sideslip, and normal shock density ratios of 5 and 12. Laminar, transitional, and turbulent shear layer impingement on the cylindrical afterbody was inferred from the measurements and resulted in a localized heating maximum that ranged from 40 to 75 % of the reference forebody stagnation point heating.

Inertial levitation

We consider the steady levitation of a rigid plate on a thin air cushion with prescribed injection velocity. This injection velocity is assumed to be much larger than that in a conventional Prandtl boundary layer, so that inertial effects dominate. After applying the classical ‘blowhard’ theory of Cole & Aroesty (1968) to the two-dimensional version of the problem, it is shown that in three dimensions the flow may be foliated into streamline surfaces using Lagrangian variables. An example is given of how this may be exploited to solve the three-dimensional problem when the injection pressure distribution is known.

Building Aerodynamics

Building Aerodynamics

Polyurethane fixtures and masks streamline precision surface treatment operations

Polyurethane fixtures and masks streamline precision surface treatment operations

Steady planar straining flow past a rigid sphere at moderate Reynolds number

This study focuses on the effect of spatial non-uniformity in the ambient flow on the forces acting on a spherical particle at moderate particle Reynolds numbers. A scaling analysis is performed to obtain conditions under which such effects are important. A direct numerical simulation, based on spectral methods, is used to compute the three-dimensional time-dependent flow past a stationary sphere subject to a uniform flow plus a planar straining flow. The particle Reynolds number, Re, in the range 10 to 300 covering different flow regimes, from unseparated flow to unsteady vortex shedding, is considered. A variety of strain magnitudes and orientations are investigated. A systematic comparison with the potential flow results and axisymmetric strain results is given. Under elongational strain, both the planar and axisymmetric cases are found to stabilize the sphere wake and delay the onset of unsteadiness, while compressional strain leads to instability. In terms of separation angles, length of the recirculation eddy and topology of the surface streamlines, planar and axisymmetric strains yield nearly the same results. The drag force appears to have a linear relation with strain magnitude in both cases, as predicted by the potential flow. However, contrary to the potential flow results, the drag in planar strain is higher than that in axisymmetric strain. The generation of higher drag is explained using the surface pressure and vorticity distributions. Planar strain oriented at an angle with the oncoming uniform flow is observed to break the symmetry of the wake and results in a lift or side force. The variation of the drag and lift forces may be quite complex, and unlike the potential flow results they may not be monotonic with strain magnitude. The direction of the lift force may be opposite to that predicted by the inviscid and low Reynolds number (Re [Lt ] 1) theories. This behaviour is dictated by the presence or absence of a recirculation eddy. In the absence of a recirculation region at low Reynolds numbers (Re < 20), or at a very high strain magnitude when the recirculation region is suppressed, the results follow somewhat the pattern observed in potential flow. However, with the presence of a recirculation region, results opposite to those predicted by the potential theory are observed.

Development of a hurricane boundary-layer wind model

Hurricanes cause a variety of damage due to high winds, heavy rains, and storm surges. This study focuses on hurricanes’ high winds. The most devastating effects of sustained high winds occur in the first few hours of landfall. During the short period, hurricanes’ rainfall often increases, while the low-level pressure gradients continue to weaken. Latent heating does not appear to strengthen the surface winds. The indicator is that dry mechanisms such as the boundary layer processes and terrain are responsible for the damaging winds in the coastal areas. In this study, the design of a dry hurricane boundary layer wind model is described. The goal is to develop a forecast tool with near-real time applications in expeditious wind damage assessment and disaster mitigation during a hurricane landfall event. Different surface roughness lengths and topographic features ranging from flat land to the mountainous terrain of Taiwan were used in the model simulation experiments to reveal how the coastal environment affected the hurricane surface winds. The model performed quite well in all cases. The experiments suggested that the downward transfer of high momentum aloft played a significant role in the maintenance of high wind speeds at the surface. The surface wind maximums were observed on the lee sides of high terrain. The surface streamline analyses showed that the high mountains tended to block the relatively weak flow and caused small eddies, while they forced the stronger flow to turn around the mountains. Due to great difficulty in data collection, the hurricane boundary layer over land remains one of the least understood parts of the system. The dry model proves to be an effective way to study many aspects of hurricane boundary layer winds over a wide range of terrain features and landfall sites. The model runs efficiently and can be run on a medium-size personal computer.

Mass conservative fluid flow visualization for CFD velocity fields

Mass conservation is a key issue for accurate streamline and stream surface visualization of flow fields. This paper complements an existing method (Feng et al., 1997) for CFD velocity fields defined at discrete locations in space that uses dual stream functions to generate streamlines and stream surfaces. Conditions for using the method have been examined and its limitations defined. A complete set of dual stream functions for all possible cases of the linear fields on which the method relies are presented. The results in this paper are important for developing new methods for mass conservative streamline visualization from CFD data and using the existing method.

Hypersonic Boundary-Layer Trip Development for Hyper-X

Boundary-layer trip devices for the Hyper-X forebody have been experimentally examined in several wind tunnels.Fivedifferenttripconegurationswerecomparedinthreehypersonicfacilities:theNASALangleyResearch Center 20-Inch Mach 6 Air and 31-Inch Mach 10 Air tunnels and in the HYPULSE Reeected Shock Tunnel at the General Applied Sciences Laboratory. Heat-transfer distributions, utilizing the phosphor thermography and thin-elm techniques, shock system details, and surface streamline patterns were measured on a 0.333-scale model of the Hyper-X forebody. Parametric variations include angles of attack of 0, 2, and 4 deg; Reynolds numbers based on model length of 1.2 ££ 10 6‐15.4 £ 10 6 ; and inlet cowl door simulated in both open and closed positions. Comparisons of boundary-layer transition as a result of discrete roughness elements have led to the selection of a trip coneguration for the Hyper-X Mach 7 eight vehicle.

X-33 Experimental Aeroheating at Mach 6 Using Phosphor Thermography

The goal of the NASA Reusable Launch Vehicle (RLV) technology program is to mature and demonstrate essential, cost effective technologies for next generation launch systems. The X-33 flight vehicle presently being developed by Lockheed Martin is an experimental Single Stage to Orbit (SSTO) demonstrator that seeks to validate critical technologies and insure applicability to a full scale RLV. As with the design of any hypersonic vehicle, the aeroheating environment is an important issue and one of the key technologies being demonstrated on X-33 is an advanced metallic Thermal Protection System (TPS). As part of the development of this TPS system, the X-33 aeroheating environment is being defined through conceptual analysis, ground based testing, and computational fluid dynamics. This report provides an overview of the hypersonic aeroheating wind tunnel program conducted at the NASA Langley Research Center in support of the ground based testing activities. Global surface heat transfer images, surface streamline patterns, and shock shapes were measured on 0.013 scale (10-in.) ceramic models of the proposed X-33 configuration in Mach 6 air. The test parametrics include angles of attack from -5 to 40 degs, unit Reynolds numbers from 1x106 to 8x106/ft, and body flap deflections of 0, 10, and 20 deg. Experimental and computational results indicate the presence of shock/shock interactions that produced localized heating on the deflected flaps and boundary layer transition on the canted fins. Comparisons of the experimental data to laminar and turbulent predictions were performed. Laminar windward heating data from the wind tunnel was extrapolated to flight surface temperatures and generally compared to within 50 deg F of flight prediction along the centerline. When coupled with the phosphor technique, this rapid extrapolation method would serve as an invaluable TPS design tool.

X-33 Hypersonic Boundary-Layer Transition

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.

Flow of non-Newtonian polymeric solutions through fibrous media

The equations of motion (continuity and momentum) describing the steady flow of incompressible power law liquids in a model porous medium consisting of an assemblage of long cylinders have been solved numerically using the finite difference method. The field equations as well as the pertinent boundary conditions have been re-cast in terms of the stream function and vorticity. The inter-cylinder interactions have been simulated using a simple “concentric cylinders” cell model. Extensive information on the detailed structure of the flow field in terms of the surface vorticity distribution, streamlines, and viscosity distribution on the surface of the solid cylinder as well as on the values of the pressure and friction drag coefficients under wide ranges of physical (0.4 ≤ ϵ ≤ 0.95; 1 ≥ n ≥ 0.4) and kinematic (0.01 ≤ Re ≤ 10) conditions have been obtained. The numerical results presented herein have been validated using the experimental results for the flow of Newtonian and power law fluids available in the literature; the match between the present predictions and the experiments was found to be satisfactory. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1171–1185, 2000

Evaluating an Objective Wind Analysis Technique with a Long Record of Routinely Collected Data

Abstract An automated system has collected meteorological data hourly in the San Francisco Bay Area since October 1995. Data from sites operated by the National Weather Service, Federal Aviation Administration, U.S. Navy, U.S. Air Force, the San Francisco Bay Area Air Quality Management District, and others have been integrated into a common database and archived by the U.S. Geological Survey. Data for 0300 and 1500 UTC during 1996 were taken from that archive and used to evaluate the performance of the Winds on Critical Streamline Surfaces objective analysis code in this area of complex terrain, where altitudes range from 0 to over 1000 m above mean sea level. The comparisons of observed and modeled winds are for a longer time period and a wider variety of meteorological conditions than are available from limited-duration field studies. The authors chose 4-, 7-, and 11-station “networks” for analysis; there were 461 h when data were available from all the sites in the 4-station network, 439 h for the 7 s...

Effect of Surface Curvature on Heat Transfer and Hydrodynamics Within a Single Hemispherical Dimple

Turbulent heat transfer and hydrodynamics have been studied in concavely and convexly curved dimples with Reynolds numbers ranging from 1.3×105 to 3.1×105. The large-scale single hemispherical dimple 50 mm in diameter and 25 mm in depth was arranged on the smooth concave or convex wall of a curved rectangular-shaped passage. The fluid flow and heat transfer measurements, and surface streamline observations were performed within the flow curvature parameter δ**/R ranged from 0.002 to 0.007. The “tornado-like” oscillating vortex bursting periodically out of the dimple was registered in the experiments with a “curved” dimple. This vortex structure is similar to that earlier observed in a “flat” dimple. The surface curvature considerably influences the dimple heat transfer rate in both cases. It enhances heat transfer in a “concave” dimple and reduces it in a “convex” one; however, the more remarkable effect occurred in a concavely curved dimple. The correction factors describing the effect of curvature on average heat transfer in a “curved” dimple have been obtained as a result of experimental study.

Free-Surface Shear Layer Instabilities on a High-Speed Liquid Jet

The instabilities of the shear layer beneath the free surface of high-speed liquid jets are investigated. Such instabilities will generate waves on liquid-metal jet targets, affecting adversely the target performance. The most unstable wave number and the spatial growth rate of perturbation are predicted with linear stability theories and are shown to agree fairly well with experimental data for water jets. The effects of fluid surface tension and streamline curvature on the instabilities are analyzed to evaluate the applicability of water data to liquid-metal curved jets. It is shown that the surface tension effects are negligible when the Weber number based on the shear layer thickness is greater than six, and also the streamline curvature effects are negligible when the radius of curvature is more than 30 times greater than the shear layer thickness.

Computer Aided Analysis of Viscous Film Flow along an Inclined Wavy Wall

The steady, laminar flow of a Newtonian liquid along an inclined wavy wall is studied in a two-dimensional numerical experiment using the Galerkin finite element method. The dimensionless Navier–Stokes equations are solved in the whole range of the laminar flow regime. Numerical predictions are compared with available experimental data for very low Reynolds numbers. The emphasis in the discussion of results is given in the presentation of free surface profiles, streamlines, velocity, and pressure distributions along the free surface and the wall. The interaction of the dimensionless numbers of the flow is studied, criteria for flow reversal are established, and a resonance phenomenon at high Reynolds numbers is investigated.

A displacement-based reference frame formulation for steady-state thermo-elasto-plastic material processes

A reference frame formulation for steady state thermo-elasto-plastic processes is presented. The displacement and history dependent response fields appear as the primary variables in this mixed formulation. Unlike displacement based Lagrangian formulations, our formulation does not require a transient analysis to simulate a steady state process and yields results that are free of numerical oscillations and which require considerably less computational effort. And unlike velocity based Eulerian methods, our formulation does not require free surface corrections or streamline integration algorithms. A laser surface treatment process is simulated and our results are in agreement with those obtained from a computationally intensive transient Lagrangian analysis.

Computational Aeroheating Predictions for X-34

Radiative equilibrium surface temperatures, heating rates, streamlines, surface pressures, and flow-field features as predicted by the Langley Aerothermodynamic Upwind Relaxation Algorithm (LAURA) are presented for the X-34 Technology Demonstrator. Results for two trajectory points corresponding to entry peak heating and two control surface deflections are discussed. This data is also discussed in the context of Thermal Protection System (TPS) design issues. The work presented in this report is part of a larger effort to define the X-34 aerothermal environment, including the application of engineering codes and wind-tunnel studies.

Fluid dynamics of flat plates and rectangular prisms in the presence of moving surface boundary-layer control

Abstract Fluid dynamics of a family of two-dimensional flat plates and rectangular prisms (aspect ratio of 0.27, 0.5 and 1.0) with moving surface boundary-layer control (MSBC) was carried out employing three complementary approaches: (i) extensive wind tunnel test program; (ii) finite element-based numerical integration of the complete Navier–Stokes equations; and (iii) flow visualization. A comparison between the drag of rectangular prisms of varying aspect ratios with sharp and rounded corners reveal substantial drag reduction, even in absence of the MSBC. It suggests fundamentally different fluid mechanical processes involved. The surface pressure distribution, resultant forces, streamline patterns and wake characteristics suggest significant increase in the wake pressure, with associated decrease in the drag, in presence of the MSBC. Results show increase in the Strouhal number indicating effective decrease in the bluffness. Both the numerical and flow visualization results show narrowing of the wake with increasing momentum injection and eventual suppression of the vortex shedding. In case of the flat plate, classical quasi-steady analysis suggests significant improvement against galloping type of instability. Implications of the present study to alleviate flow-induced instabilities such as vortex resonance and galloping are apparent.

Capillary waves understood by an elementary method

The central physics of capillary waves (or ripples) can be understood by an elementary method which makes use of the balance of static and dynamic pressure differences along the surface streamline between crest and trough, in the steady reference frame, and conservation of mass through vertical cross-sections beneath crest and trough. Basically Einstein’s (1916) model of surface gravity waves is adapted for the purpose of explaining the existence of capillary waves of infinitesimal amplitude. One product of the physical understanding, the phase speed of capillary waves, is derived as a function of the wave length and surface tension and the result agrees exactly with that obtained by the classical mathematical procedure. In the elementary method it is not necessary to assume irrotational flow, upon which the classical theory is founded, nor are perturbation expansions of the nonlinear fluid equations employed. The extension to capillary-gravity waves, by including the acceleration of gravity in the physical model, is straightforward, and the calculated phase speed of these waves is identical to what is found in the text books as well.

Computational Study of Subsonic Flow over a Delta Canard-Wing-Body Configuration

Subsonic flowfields over a close-coupled, delta canard-wing-body configuration at angles of attack of 20, 24.2, and 30 deg are computed using the OVERFLOW Navier-Stokes solver. Computed flowfields are presented in terms of particle traces, surface streamlines, and leeward-side surface pressure distributions for the canard-on and -off configurations. The interaction between the canard and the wing vortices, wing vortex breakdown, and the influence of the canard on vortex breakdown are identified. The comparison of the pressure data with the available experimental data at Re = 0.32 x 10 6 and Re = 1.4 x 10 6 shows a significant Reynolds-number dependence