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At least 955 records · Page 53

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NASA NTRS1986

Energetics and optimum motion of oscillating lifting surfaces of finite span

In certain modes of animal propulsion in nature, such as bird flight and fish swimming, the efficiency compared to man-made vehicles is very high. In such cases, wing and tail motions are typically associated with relatively high Reynolds numbers, where viscous effects are confined to a thin boundary layer at the surface and a thin trailing wake. The propulsive forces, which are generated primarily by the inertial forces, can be calculated from potential-flow theory using linearized unsteady-wing theory (for small-amplitude oscillations). In the present study, a recently developed linearized, low-frequency, unsteady lifting-line theory is employed to calculate the (sectional and total) energetic quantities and optimum motion of an oscillating wing of finite span.

Ahmadi, A. R.↗

NASA NTRS1972

Film boiling on vertical surfaces.

Film boiling of a saturated liquid on a vertical surface is analyzed to determine the local heat-transfer rates as a function of height and heater-surface superheat. Experiments show that the laminar-flow model is inadequate. A turbulent-vapor-flow model is used, and the influence of the interfacial oscillations is incorporated on a semiempirical basis. Measurements of local film boiling were obtained with a transient technique using saturated liquid nitrogen.

Suryanarayana, N. V.↗

NASA NTRS1974

Wind-tunnel free-flight investigation of a model of a spin-resistant fighter configuration

An investigation was conducted to provide some insight into the features affecting the high-angle-of-attack characteristics of a high-performance twin-engine fighter airplane which in operation has exhibited excellent stall characteristics with a general resistance to spinning. Various techniques employed in the study included wind-tunnel free-flight tests, flow-visualization tests, static force tests, and dynamic (forced-oscillation) tests. In addition to tests conducted on the basic configuration tests were made with the wing planform and the fuselage nose modified. The results of the study showed that the model exhibited good dynamic stability characteristics at angles of attack well beyond that for wing stall. The directional stability of the model was provided by the vertical tail at low and moderate angles of attack and by the fuselage forebody at high angles of attack. The wing planform was found to have little effect on the stability characteristics at high angles of attack. The tests also showed that although the fuselage forebody produced beneficial contributions to static directional stability at high angles of attack, it also produced unstable values of damping in yaw. Nose strakes located in a position which eliminated the beneficial nose contributions produced a severe directional divergence.

Grafton, S. B.↗

NASA NTRS1982

Hydrodynamic performance of an annular liquid jet: Production of spherical shells

An annular jet flow of liquid surrounding a flow of gas at its core is extremely unstable. Axisymmetric oscillations arise spontaneously, and grow with such rapidity along the axial dimension that a pinch-off of the liquid and an encapsulation of the core gas occurs within as few as four jet diameters. The shells which result thereby may be described as thick-wall bubbles, for which van der Waals forces are unimportant. A description is given of the fluid dynamic processes by which the shells are formed, and of means for preserving and promoting the geometrical of the product. The forming of metallic shells is mentioned.

Kendall, J. M.↗

NASA NTRS1984

Wind-tunnel free-flight investigation of a model of a forward-swept-wing fighter configuration

A wind-tunnel free-flight investigation was conducted to study the dynamic stability characteristics of a model of a forward-swept-wing fighter-airplane configuration at high angles of attack. Various other wind-tunnel techniques employed in the study included static- and dynamic- (forced-oscillation) force tests, free-to-roll tests, and flow-visualization tests. A unique facet of the study was the extreme level of static pitch instability (in excess of negative 32-percent static margin) inherent in the airframe design which precluded free-flight testing without stability augmentation in pitch. Results are presented which emphasize the high-angle-of-attack aerodynamics and the vehicle-component contributions to these characteristics. The effects of these aerodynamic characteristics on the high-angle-of-attack flying qualities of the configuration are discussed in terms of results of the wind-tunnel free-flight tests.

Murri, D. G.↗

NASA NTRS1984

Airfoil computation at high angles of attack, inviscid and viscous phenomena

An implicit central difference code is used to calculate two dimensional inviscid and thin-layer Navier-Stokes solutions for flow about an NACA0012 airfoil at high angles of attack. Among the issues addressed are whether separation can occur in an inviscid calculation and what the causes would be of such separation. Examples are shown of inviscid shocked flow with and without separation and shock-free flow with separation. An Euler solution with self-induced oscillation and separation driven by a strong shock is contrasted with a shock-free solution whose separation is caused by numerical error. Computed solutions to the Euler equations are compared to those of the potential equations. Comparisons are also made between experimental data from wind tunnel tests and viscous calculations at similar conditions.

Barton, J. T.↗

NASA NTRS1985

Recent transonic unsteady pressure measurements at the NASA Langley Research Center

Four semispan wing model configurations were studied in the Transonic Dynamics Tunnel (TDT). The first model had a clipped delta planform with a circular arc airfoil, the second model had a high aspect ratio planform with a supercritical airfoil, the third model has a rectangular planform with a supercritical airfoil and the fourth model had a high aspect ratio planform with a supercritical airfoil. To generate unsteady flow, the first and third models were equipped with pitch oscillation mechanisms and the first, second and fourth models were equipped with control surface oscillation mechanisms. The fourth model was similar in planform and airfoil shape to the second model, but it is the only one of the four models that has an elastic wing structure. The unsteady pressure studies of the four models are described and some typical results for each model are presented. Comparison of selected experimental data with analytical results also are included.

Sandford, M. C.↗

NASA NTRS1985

Recent transonic unsteady pressure measurements at the NASA Langley Research Center

Sandford, M. C.↗

NASA NTRS1987

Transonic airfoil computation using the integral equation with and without embedded Euler domains

Two transonic computational schemes which are based on the Integral Equation Formulation of the full potential equation were presented. The first scheme is a Shock Capturing-Shock Fitting (SCSF) scheme which uses the full potential equation throughout with the exception of the shock wave where the Rankine-Hugoniot relations are used to cross and fit the shock. The second scheme is an Integral Equation with Embedded Euler (IEEE) scheme which uses the full potential equation with an embedded region where the Euler equations are used. The two schemes are applied to several transonic airfoil flows and the results were compared with numerous computational results and experimental domains with fine grids. The SCSF-scheme is restricted to flows with weak shock, while the IEEE-scheme can handle strong shocks. Currently, the IEEE scheme is applied to other transonic flows with strong shocks as well as to unsteady pitching oscillations.

Kandil, Osama A.↗

NASA NTRS1987

Computation of viscous blast wave solutions with an upwind finite volume method

A fully conservative, viscous, implicit, upwind, finite-volume scheme for the thin-layer Navier-Stokes equations is described with application to blast wave flow fields. In this scheme, shocks are captured without the oscillations typical of central differencing techniques and wave speeds are accurately predicted. The finite volume philosophy ensures conservation and since boundary conditions are also treated conservatively, accurate reflections of waves from surfaces are assured. Viscous terms in the governing equations are treated in a manner consistent with the finite volume philosophy, resulting in very accurate prediction of boundary layer quantities. Numerical results are presented for four viscous problems: a steady boundary layer, a shock-induced boundary layer, a blast wave/cylinder interaction and a blast wave/supersonic missile interaction. Comparisons of the results with an established boundary layer code, similarity solution, and experimental data show excellent agreement.

Molvik, Gregory A.↗

NASA NTRS1988

Unsteady transonic aerodynamics and aeroelastic calculations at low-supersonic freestreams

A computational procedure is presented to simulate transonic unsteady flows and corresponding aeroelasticity of wings at low-supersonic freestreams. The flow is modeled by using the transonic small-perturbation theory. The structural equations of motions are modeled using modal equations of motion directly coupled with aerodynamics. Supersonic freestreams are simulated by properly accounting for the boundary conditions based on pressure waves along the flow characteristics in streamwise planes. The flow equations are solved using the time-accurate, alternating-direction implicit finite-difference scheme. The coupled aeroelastic equations of motion are solved by an integration procedure based on the time-accurate, linear-acceleration method. The flow modeling is verified by comparing calculations with experiments for both steady and unsteady flows at supersonic freestreams. The unsteady computations are made for oscillating wings. Comparisons of computed results with experiments show good agreement. Aeroelastic responses are computed for a rectangular wing at Mach numbers ranging from subtransonic to upper-transonic (supersonic) freestreams. The extension of the transonic dip into the upper transonic regime is illustrated.

Guruswamy, Guru P.↗

NASA NTRS1989

Nonlinear twist-kink instability of a coronal loop

Three-dimensional magnetoinductive particle simulations are used to demonstrate that the mechanical twisting motion applied to a magnetized plasma column induces a current aligned to the external magnetic field direction, pinches the plasma and magnetic fields, and stores the energy in poloidal magnetic fields. As the twist motion continues, the field lines locally begin to wrap around the plasma more than one revolution. A strong MHD instability sets in that is a mixture of kink and ballooning modes, releasing the magnetic energy and causing destruction of coherent column structure and flows of turbulent plasma. A similar episode ensues, exhibiting relaxation oscillations. The buildup of poloidal fields and structure and its sudden release driven by the twist motion may be a model for the solar coronal loop dynamics which exhibits a slow energy buildup with some photospheric motion and a sudden energy release by flares.

Zaidman, E. G.↗

NASA NTRS1992

Analysis of cascades using a two dimensional Euler aeroelastic solver

A two-dimensional unsteady aerodynamic Euler solver based on a flux differencing scheme is being developed to analyze oscillating cascades. The cascades can have subsonic, transonic, or supersonic flow with either subsonic or supersonic axial velocity. The aerodynamic solver is coupled with a typical section structural model for each blade of the cascade. Flutter analysis methods both in time and frequency domains are then implemented into the resulting aeroelastic solver. Methods that reduce computational time for calculating the unsteady aerodynamic coefficients, namely the influence coefficient method and the pulse response method, are also implemented and validated. The present solver showed good correlation with published results for all the flow regimes. It is shown that grid coarsening improved the accuracy of the predictions. A representative flutter calculation showed that both the frequency domain and time domain methods are implemented correctly into the aeroelastic solver.

Reddy, T. S. R.↗

NASA NTRS1992

Navier-Stokes dynamics and aeroelastic computations for vortical flows, buffet and aeroelastic applications

The accomplishments achieved during the period include conference and proceedings publications, journal papers, and abstracts which are either published, accepted for publication or under review. Conference presentations and NASA highlight publications are also included. Two of the conference proceedings publications are attached along with a Ph.D. dissertation abstract and table of contents. In the first publication, computational simulation of three-dimensional flows around a delta wing undergoing rock and roll-divergence motions is presented. In the second publication, the unsteady Euler equations and the Euler equations of rigid body motion, both written in the moving frame of reference, are sequetially solved to simulate the limit-cycle rock motion of slender delta wings. In the dissertation abstract, unsteady flows around rigid or flexible delta wings with and without oscillating leading-edge flaps are considered.

Kandil, Osama A.↗

NASA NTRS1992

Quasi-periodic climate change on Mars

The paper examines evidence that the Martian climate undergoes quasi-periodic variations, including the polar layered terrain, differences between the residual polar caps, and the current net southward flow of H2O. The driving functions for these variations are oscillations in the elements of the Martian orbit coupled with precession of the Martian spin axis. These 'astronomic variations' control the distribution of the insolation, which in turn influences the partition of volatiles between atmospheric and surface reservoirs. The major effects anticipated at low obliquity are growth of the polar caps, substantial decrease in surface pressure, cessation of duststorms, release of CO2 from the regolith, and poleward migration of H2O ground ice. At high obliquity, the mass of the perennial polar caps decreases and permanent CO2 frost disappears, CO2 desorbs from the regolith at high latitudes, the surface pressure may increase to several times its current value, and the atmospheric dust load increases.

Kieffer, Hugh H.↗

NASA NTRS2013

NASA Tech Briefs, Februrary 2013

Topics covered include: Measurements of Ultra-Stable Oscillator (USO) Allan Deviations in Space; Gaseous Nitrogen Orifice Mass Flow Calculator; Validation of Proposed Metrics for Two-Body Abrasion Scratch Test Analysis Standards; Rover Low Gain Antenna Qualification for Deep Space Thermal Environments; Automated, Ultra-Sterile Solid Sample Handling and Analysis on a Chip; Measuring and Estimating Normalized Contrast in Infrared Flash Thermography; Spectrally and Radiometrically Stable, Wideband, Onboard Calibration Source; High-Reliability Waveguide Vacuum/Pressure Window; Methods of Fabricating Scintillators With Radioisotopes for Beta Battery Applications; Magnetic Shield for Adiabatic Demagnetization Refrigerators (ADR); CMOS-Compatible SOI MESFETS for Radiation-Hardened DC-to-DC Converters; Silicon Heat Pipe Array; Adaptive Phase Delay Generator; High-Temperature, Lightweight, Self-Healing Ceramic Composites for Aircraft Engine Applications; Treatment to Control Adhesion of Silicone-Based Elastomers; High-Temperature Adhesives for Thermally Stable Aero-Assist Technologies; Rockballer Sample Acquisition Tool; Rock Gripper for Sampling, Mobility, Anchoring, and Manipulation; Advanced Magnetic Materials Methods and Numerical Models for Fluidization in Microgravity and Hypogravity; Data Transfer for Multiple Sensor Networks Over a Broad Temperature Range; Using Combustion Synthesis to Reinforce Berms and Other Regolith Structures; Visible-Infrared Hyperspectral Image Projector; Three-Axis Attitude Estimation With a High-Bandwidth Angular Rate Sensor Change_Detection.m; AGATE: Adversarial Game Analysis for Tactical Evaluation; Ionospheric Simulation System for Satellite Observations and Global Assimilative; Modeling Experiments (ISOGAME); An Extensible, User- Modifiable Framework for Planning Activities; Mission Operations Center (MOC) - Precipitation Processing System (PPS) Interface Software System (MPISS); Automated 3D Damaged Cavity Model Builder for Lower Surface Acreage Tile on Orbiter; Mixed Linear/Square-Root Encoded Single-Slope Ramp Provides Low-Noise ADC with High Linearity for Focal Plane Arrays; RUSHMAPS: Real-Time Uploadable Spherical Harmonic Moment Analysis for Particle Spectrometers; Powered Descent Guidance with General Thrust-Pointing Constraints; X-Ray Detection and Processing Models for Spacecraft Navigation and Timing; and Extreme Ionizing-Radiation-Resistant Bacterium

Source record↗

NASA NTRS2014

Numerical Simulation of a High-Lift Configuration with Embedded Fluidic Actuators

Numerical simulations have been performed for a vertical tail configuration with deflected rudder. The suction surface of the main element of this configuration is embedded with an array of 32 fluidic actuators that produce oscillating sweeping jets. Such oscillating jets have been found to be very effective for flow control applications in the past. In the current paper, a high-fidelity computational fluid dynamics (CFD) code known as the PowerFLOW(Registered TradeMark) code is used to simulate the entire flow field associated with this configuration, including the flow inside the actuators. The computed results for the surface pressure and integrated forces compare favorably with measured data. In addition, numerical solutions predict the correct trends in forces with active flow control compared to the no control case. Effect of varying yaw and rudder deflection angles are also presented. In addition, computations have been performed at a higher Reynolds number to assess the performance of fluidic actuators at flight conditions.

Vatsa, Veer N.↗

NASA NTRS2016

Numerical Simulation of a High-Lift Configuration Embedded with High Momentum Fluidic Actuators

Numerical simulations have been performed for a vertical tail configuration with deflected rudder. The suction surface of the main element of this configuration, just upstream of the hinge line, is embedded with an array of 32 fluidic actuators that produce oscillating sweeping jets. Such oscillating jets have been found to be very effective for flow control applications in the past. In the current paper, a high-fidelity computational fluid dynamics (CFD) code known as the PowerFLOW R code is used to simulate the entire flow field associated with this configuration, including the flow inside the actuators. A fully compressible version of the PowerFLOW R code valid for high speed flows is used for the present simulations to accurately represent the transonic flow regimes encountered in the flow field due to the actuators operating at higher mass flow (momentum) rates required to mitigate reverse flow regions on a highly-deflected rudder surface. The computed results for the surface pressure and integrated forces compare favorably with measured data. In addition, numerical solutions predict the correct trends in forces with active flow control compared to the no control case. The effect of varying the rudder deflection angle on integrated forces and surface pressures is also presented.

Vatsa, Veer N.↗