Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Flow Visualization”

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

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

At least 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Low-speed, high-lift aerodynamic characteristics of slender, hypersonic accelerator-type configurations

Two investigations were conducted in the Langley 14 by 22 Foot Subsonic Tunnel to determine the low-speed aerodynamic characteristics of a generic hypersonic accelerator-type configuration. The model was a delta wing configuration incorporating a conical forebody, a simulated wrap-around engine package, and a truncated conical aftbody. Six-component force and moment data were obtained over a range of attack from -4 to 30 degrees and for a sideslip range of + or - 20 degrees. In addition to tests of the basic configuration, component build-up tests were conducted; and the effects of power, forebody nose geometry, canard surfaces, fuselage strakes, and engines on the lower surface alone were also determined. Control power available from deflections of wing flaps and aftbody flaps was also investigated and found to be significantly increased during power-on conditions. Large yawing moments resulted from asymmetric flow fields exhibited by the forebody as revealed by both surface pressure data and flow visualization. Increasing nose bluntness reduced the yawing-moment asymmetry, and the addition of a canard eliminated the yawing-moment asymmetry.

Gatlin, Gregory M.↗
NASA NTRS1987

Research in Natural Laminar Flow and Laminar-Flow Control, part 2

Part 2 of the Symposium proceedings includes papers addressing various topics in basic wind tunnel research/techniques and computational transitional research. Specific topics include: advanced measurement techniques; laminar flow control; Tollmien-Schlichting wave characteristics; boundary layer transition; flow visualization; wind tunnel tests; flight tests; boundary layer equations; swept wings; and skin friction.

Hefner, Jerry N.↗
NASA NTRS1987

Nacelle aerodynamic performance

The boundary layer transition location was measured on a nacelle shape using the sublimating chemical flow visualization technique. This technique involves coating the surface with a thin film of volatile chemical solid, which, during exposure to a free stream airflow, rapidly sublimates in the turbulent boundary layer as a result of high shear stress and high mass transfer near the surface. Transition is indicated because the chemical coating remains relatively unaffected in the laminar region due to lower shear and low mass transfer. The slow response time of the chemical in a laminar boundary allowed for two test conditions during the same flight. The aircraft was first flown at the desired airspeed and altitude with the noise source off. Once a pattern had developed, the noise source was turned on to the desired setting and a new chemical pattern was sought. In this fashion a direct comparison of the effect of the noise could be determined.

Obara, Clifford J.↗
NASA NTRS1990

Experimental measurements of the laminar separation bubble on an Eppler 387 airfoil at low Reynolds numbers

An experimental investigation was conducted to measure the flow velocity in the boundary layer of an Eppler 387 airfoil. In particular, the laminar separation bubble that this airfoil exhibits at low Reynolds numbers was the focus. Single component laser Doppler velocimetry data were obtained at a Reynolds number of 100,000 at an angle of attack of 2.0 degree. Static Pressure and flow visualization data for the Eppler 387 airfoil were also obtained. The difficulty in obtaining accurate experimental measurements at low Reynolds numbers is addressed. Laser Doppler velocimetry boundary layer data for the NACA 663-018 airfoil at a Reynolds number of 160,000 and angle of attack of 12 degree is also presented.

Cole, Gregory M.↗
NASA NTRS1990

Viscous effects on the instability of an axisymmetric jet

The stability characteristics of a laminar, axisymmetric jet, issuing from fully developed Poiseuille flow, are investigated. The jet preferred frequency, as inferred from surveys of u'-spectra, is found to yield a Strouhal number (St) that depends on the Reynolds number (R); St and R are based on the jet diameter (D) and the average velocity (U sub av) at the jet origin. The value of St increases with increasing R in the range 400 less than approximately R less than approximately 4000, attaining an asymptotic value of about 0.45. Flow visualization confirms that the instability is primarily in a helical mode, as predicted by stability analyses. Analyses do predict a similar St versus R variation in approximately the correct St-range. However, the R-range where this is predicted is lower than that found experimentally.

Zaman, K. B. M. Q.↗
NASA NTRS1990

Testing of 3-D models in 2-D adaptive wall test sections

Considerable effort was devoted to the development of two-dimensional adaptive wall test sections. The development of fully three-dimensional test sections, however, has not had this same level of effort expended. The limitations on three-dimensional research are the result of the complexity of both the mechanical design and operational aspects. Typical of the mechanical complexities are lack of readily available model and flow visualization access, and problems of sealing between adjacent walls for multi-wall types of test sections. The operational aspects are complicated by the necessity for many measurements of the boundary conditions which can be very time consuming. In three-dimensional testing, it is impossible to remove all of the boundary interference. It will be necessary, therefore, to apply residual corrections to the data. The more complex the test section shape, the more complex the calculation of the residual corrections becomes. From both the viewpoint of test section complexity and of ease of residual corrections, a simplified test section geometry is desirable. To aid in the design of simplified test sections, several researchers investigated the capability of using two-dimensional adaptive wall test sections to perform three-dimensional testing. By use of this type of design, the inherent complications and limitations of the fully three-dimensional design are avoided. Strategies of adaptation used for this application are described, as well as, sample results and a discussion of some limitations of the technique.

Wedemeyer, Erich H.↗
NASA NTRS1990

The Langley 14- by 22-Foot Subsonic Tunnel: Description, Flow Characteristics, and Guide for Users

The Langley 14- by 22-foot Subsonic Tunnel is a closed circuit, single-return atmospheric wind tunnel with a test section that can be operated in a variety of configurations (closed, slotted, partially open, and open). The closed test section configuration is 14.5 ft high by 21.75 ft wide and 50 ft long with a maximum speed of about 338 ft/sec. The open test section configuration has a maximum speed of about 270 ft/sec, and is formed by raising the ceiling and walls, to form a floor-only configuration. The tunnel may be configured with a moving-belt ground plane and a floor boundary-layer removal system at the entrance to the test section for ground effect testing. In addition, the tunnel had a two-component laser velocimeter, a frequency modulated (FM) tape system for dynamic data acquisition, flow visualization equipment, and acoustic testing capabilities. Users of the 14- by 22-foot Subsonic Tunnel are provided with information required for planning of experimental investigations including test hardware and model support systems.

Gentry, Garl L., Jr.↗
NASA NTRS1989

The DELTA MONSTER: An RPV designed to investigate the aerodynamics of a delta wing platform

The mission requirements for the performance of aerodynamic tests on a delta wind planform posed some problems, these include aerodynamic interference; structural support; data acquisition and transmission instrumentation; aircraft stability and control; and propulsion implementation. To eliminate the problems of wall interference, free stream turbulence, and the difficulty of achieving dynamic similarity between the test and actual flight aircraft that are associated with aerodynamic testing in wind tunnels, the concept of the remotely piloted vehicle which can perform a basic aerodynamic study on a delta wing was the main objective for the Green Mission - the Delta Monster. The basic aerodynamic studies were performed on a delta wing with a sweep angle greater than 45 degrees. These tests were performed at various angles of attack and Reynolds numbers. The delta wing was instrumented to determine the primary leading edge vortex formation and location, using pressure measurements and/or flow visualization. A data acquisition system was provided to collect all necessary data.

Connolly, Kristen↗
NASA NTRS1989

A circular combustor configuration with multiple injection ports for mixing enhancement

A circular combustor design by Ghorashi (1988) which resembles a continuously-stirred tank reactor with multiple injection ports is presented with a view to the enhanced control of mixing, NO(x) reduction, and combustion efficiency maximization. Attention is given to the prototype apparatus for this type of circular combustor, which takes the form of a transparent cold-flow reactor for flow visualization studies under 'chemically frozen' conditions.

Ghorashi, B.↗
NASA NTRS1990

Experimental investigation of a new device to control the asymmetric flowfield on forebodies at large angles of attack

An exploratory experimental investigation of a new device to control the asymmetric flowfield on forebodies at large angles of attack has been conducted. The device is a rotatable forebody tip, which varies in cross section from circular at its base to elliptic at its tip. The device itself extends over a small portion of the aircraft or missile forebody. The device provides two important improvements. First, it replaced the normally random behavior of the nose side force as a function of nose tip orientation with a predictable and generally sinusoidal distribution and, second, the device showed promise for use as part of a vehicle control system, to be deflected in a prescribed manner to provide additional directional control for the vehicle. The device was tested on a cone/cylinder model having a 10 deg semiapex angle and on a 3.0 caliber tangent ogive model, each with a base diameter of 3.5 in, for angles of attack from 30 to 60 deg. Data were taken from 3 circumferential rows of pressure taps on each model at a Reynolds number of 84,000 based on cylinder diameter and by a helium-bubble flow visualization technique at a Reynolds number of 24,000.

Moskovitz, Cary A.↗
NASA NTRS1990

Propeller tip vortex interactions

Propeller wakes interacting with aircraft aerodynamic surfaces are a source of noise and vibration. For this reason, flow visualization work on the motion of the helical tip vortex over a wing and through the second stage of a counterrotation propeller (CRP) has been pursued. Initially, work was done on the motion of a propeller helix as it passes over the center of a 9.0 aspect ratio wing. The propeller tip vortex experiences significant spanwise displacements when passing across a lifting wing. A stationary propeller blade or stator was installed behind the rotating propeller to model the blade vortex interaction in a CRP. The resulting vortex interaction was found to depend on the relative vortex strengths and vortex sign.

Johnston, Robert T.↗
NASA NTRS1990

Navier-Stokes predictions of the flowfield around the F-18 (HARV) wing and fuselage at large incidence

In support of the NASA High Alpha Technology Program, Navier-Stokes solutions have been obtained using the Chimera overset grid scheme for flow over the wing, fuselage, and wing leading-edge extension (LEX) of the F/A-18 High Alpha Research Vehicle (HARV) at high incidence. Solutions are also presented for flow over the fuselage forebody at high angles of attack. The solutions are for turbulent flows at high-Reynolds-number flight-test conditions, and are compared with available qualitative and quantitative experimental data. Comparisons of predicted surface flow patterns, off-surface flow visualization, and surface-pressure distributions are in good agreement with flight-test data. The ability of the numerical method to predict the bursting of the LEX vortex as it encounters the adverse pressure gradient field of the wing is demonstrated, and the capability of predicting high-angle-of-attack aerodynamics around realistic aircraft configurations is established.

Cummings, Russell M.↗
NASA NTRS1990

Simulation and analysis of a delta planform with multiple jets in ground effect

The three-dimensional, thin-layer Navier-Stokes equations on a body-conforming, overset, multiple-grid topology are solved in the present numerical simulations of the flow around a 60-deg delta-planform wing equipped with two thrust-reverser jets in ground-effect conditions. Such experimentally flow-visualized features as jet-deformation and ground vertex-formation are captured by these simulations; the loss of wing-borne lift due to the 'suck-down' phenomenon, which arises as the delta planform flies at low speeds in close proximity to the ground, is also well simulated.

Chawla, K.↗
NASA NTRS1990

Development of non-intrusive instrumentation for NASA-Ames Ballistic Range and Shock Tunnel

The use of nonintrusive instrumentation in high-enthalpy facilities offers the opportunity to collect data that has previously been difficult or impossible to obtain. Three such instruments, now under development, are described: an OH absorption system which can measure OH species concentration and temperature, a holographic interferometer for flow visualization and density measurement at low density, and a telemetry system which allows the measurement of surface quantities on model in free-flight at hypervelocity. The challenges and opportunities encountered when employing these advanced diagnostics to high-enthalpy facilities are discussed.

Strawa, A. W.↗
NASA NTRS1990

Effect of leading edge roundness on a delta wing in wing-rock motion

The effect of wing leading-edge roundness on wing rock was investigated using flow visualization in a water tunnel. Eighty degree delta wing models were tested on free-to-roll and forced oscillation rigs. The onset of wing rock was delayed by increasing the roundness of the leading edges. The wing rock amplitude and frequency results suggested that damping was increased at lower angles of attack but reduced at higher angles of attack. Vortex lift-off and vortex breakdown, especially during dynamic situations, were strongly affected by the leading edge roundness. Different forms of wing rock motion could be sustained by combinations of vortex breakdown and vortex lift-off. Behaviors of the wing and vortex motions were explained by the influence of leading edge roundness on the separation location, vortex trajectory, and vortex breakdown.

Ng, T. Terry↗
NASA NTRS1989

Performance measurements of an airfoil at low Reynolds numbers

Performance characteristics of an Eppler 387 airfoil using both direct (force) and indirect (pressure) measurement techniques have been obtained at Reynolds numbers from 60,000 to 460,000 in the Langley Low-Turbulence Pressure Tunnel. Lift, drag, and pitching-moment data were obtained from two internally-mounted strain-gage balances specifically designed for small aerodynamic loads. Comparisons of these results with data from a pressure model of an Eppler 387 airfoil are included. Drag data for both models using the wake traverse method are compared with the balance data. Oil flow visualization and surface mounted hot-film sensors were used to determine laminar-separation and turbulent-reattachment locations. Problems associated with obtaining accurate wind-tunnel data at low Reynolds numbers are discussed.

Mcghee, Robert J.↗
NASA NTRS1990

Design and evaluation of thrust vectored nozzles using a multicomponent thrust stand

Future aircraft with the capability of short takeoff and landing, and improved maneuverability especially in the post-stall flight regime will incorporate exhaust nozzles which can be thrust vectored. In order to conduct thrust vector research in the Mechanical Engineering Department at Cal Poly, a program was planned with two objectives; design and construct a multicomponent thrust stand for the specific purpose of measuring nozzle thrust vectors; and to provide quality low moisture air to the thrust stand for cold flow nozzle tests. The design and fabrication of the six-component thrust stand was completed. Detailed evaluation tests of the thrust stand will continue upon the receipt of one signal conditioning option (-702) for the Fluke Data Acquisition System. Preliminary design of thrust nozzles with air supply plenums were completed. The air supply was analyzed with regard to head loss. Initial flow visualization tests were conducted using dual water jets.

Thomas W. Carpenter↗
NASA NTRS1991

Experimental parametric study of jet vortex generators for flow separation control

A parametric wind-tunnel study was performed with jet vortex generators to determine their effectiveness in controlling flow separation associated with low-speed turbulence flow over a two-dimensional rearward-facing ramp. Results indicate that flow-separation control can be accomplished, with the level of control achieved being a function of jet speed, jet orientation (with respect to the free-stream direction), and orifice pattern (double row of jets vs. single row). Compared to slot blowing, jet vortex generators can provide an equivalent level of flow control over a larger spanwise region (for constant jet flow area and speed). Dye flow visualization tests in a water tunnel indicated that the most effective jet vortex generator configurations produced streamwise co-rotating vortices.

Selby, Gregory↗