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

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At least 541 records · Page 30

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NASA NTRS1991

The aerodynamic characteristics of vortex ingestion for the F/A-18 inlet duct

A Reduced Navier-Stokes (RNS) solution technique was successfully combined with the concept of partitioned geometry and mesh generation to form a very efficient 3D RNS code aimed at the analysis-design engineering environment. Partitioned geometry and mesh generation is a pre-processor to augment existing geometry and grid generation programs which allows the solver to (1) recluster an existing gridlife mesh lattice, and (2) perturb an existing gridfile definition to alter the cross-sectional shape and inlet duct centerline distribution without returning to the external geometry and grid generator. The present results provide a quantitative validation of the initial value space marching 3D RNS procedure and demonstrates accurate predictions of the engine face flow field, with a separation present in the inlet duct as well as when vortex generators are installed to supress flow separation. The present results also demonstrate the ability of the 3D RNS procedure to analyze the flow physics associated with vortex ingestion in general geometry ducts such as the F/A-18 inlet. At the conditions investigated, these interactions are basically inviscid like, i.e., the dominant aerodynamic characteristics have their origin in inviscid flow theory.

Anderson, Bernhard H.↗

NASA NTRS1991

The aerodynamic characteristics of vortex ingestion for the F/A-18 inlet duct

A Reduced Navier-Stokes (RNS) solution technique was successfully combined with the concept of partitioned geometry and mesh generation to form a very efficient 3-D RNS code aimed at the analysis-design engineering environment. Partitioned geometry and mesh generation is a pre-processor to augment existing geometry and grid generation programs which allows the solver to (1) recluster an existing gridlife mesh lattice, and (2) perturb an existing gridfile definition to alter the cross-sectional shape and inlet duct centerline distribution without returning to the external geometry and grid generator. The present results provide a quantitative validation of the initial value space marching 3-D RNS procedure and demonstrates accurate predictions of the engine face flow field, with a separation present in the inlet duct as well as when vortex generators are installed to suppress flow separation. The present results also demonstrate the ability of the 3-D RNS procedure to analyze the flow physics associated with vortex ingestion in general geometry ducts such as the F/A-18 inlet. At the conditions investigated, these interactions are basically inviscid like, i.e., the dominant aerodynamic characteristics have their origin in inviscid flow theory.

Anderson, Bernhard H.↗

NASA NTRS1973

Laboratory vortices in rotating, sheared flow.

By placing a small convective source (electrical heater) in a rotating, vertically sheared, stratified flow in a rotating annulus, a well-organized vortex flow is generated. A qualitative description of the flow is given. The flow is always cyclonic below the heater and anticyclonic above, and is quite persistent in the sheared flow.

Kaiser, J. A. C.↗

NASA NTRS1974

Laser velocimeter measurement of developing and periodic flows

The transmitting-receiving lens system of a two-component backscatter laser-velocimeter optical package currently in operation is discussed. It is basically a Galilean-type telescope which provides for spatial translation of the focal volume along the optical axis, but it also has certain optical constraints which are discussed. This scanning feature of the unit has been used with spectrum analyzer processing for the measurement of (1) trailing vortices in a wind tunnel and (2) a developing (decaying) vortex that was generated by towing a wing model through a water towing tank. The optical system has also been interfaced with period counting electronics and has been applied to the periodic flow generated by a model helicopter rotor. Results are presented and the techniques of data acquisition and the 'strobing' of the processor are discussed.

Orloff, K. L.↗

NASA NTRS1978

Properties of aspect-ratio-4.0 rectangular jets in a subsonic crossflow

A series of wind-tunnel and laboratory tests were conducted at the NASA Langley V/STOL tunnel facility to determine both the detailed structure and the induced effects of aspect-ratio-4.0 rectangular jets both in a subsonic crosswind and in quiescent conditions. Wind-tunnel tests were conducted on both blunt (nozzle major axis normal to free stream) and streamwise (nozzle major axis parallel to free stream) nozzle orientations for jet injection angles ranging from 15 to 90 degrees at jet-to-crossflow velocity ratios of 4, 8, and 10. Results indicate that the blunt nozzle induced effects are more significant than those produced by comparable streamwise-oriented jets and that both the flow-field structure and induced effects of streamwise-oriented rectangular jets are quite similar to those created by round jets. Additionally, it is shown that significant differences exist in the vortex flow fields generated by the same rectangular nozzle mounted in two different test hardware configurations.

Thames, F. C.↗

NASA NTRS1982

Analytical study of vortex flaps on highly swept delta wings

This paper highlights some current results from ongoing analytical studies of vortex flaps on highly swept delta wings. A brief discussion of the vortex flow analysis tools is given along with comparisons of the theories to vortex flap force and pressure data. Theoretical trends in surface pressure distribution for both angle-of-attack variation and flap deflection are correctly predicted by Free Vortex Sheet theory. Also shown are some interesting calculations for attached-flow and vortex-flow flap hinge moments that indicate flaps utilizing vortex flow may generate less hinge moment than attached flow flaps. Finally, trailing-edge flap effects on leading-edge flap thrust potential are investigated and theory-experiment comparisons made.

Frink, N. T.↗

NASA NTRS1982

Control of the forebody vortex orientation by asymmetric air injection. Part A: Application to enhance departure/spin recovery of fighter aircraft. Part B: Details of the flow structure

A novel concept which was developed to provide powerful directional control effectiveness for a fighter aircraft at high angles of attack, where more traditional controls have very limited capability is discussed. The concept utilizes the energy concentrated in the strong forebody vortices (which form on slender bodies at high relative incidence) by controlling the lateral orientation of the vortices with respect to the body. The present concept seeks to utilize the inherent sensitivity of the vortex positioning and its bistable nature to an advantage allowing control of the forces which are developed. As it turns out, the direction or sense of the asymmetric vortex pair is much easier to control than to attenuate. The work which was done to develop the concept for application to an aircraft is described and is directed toward the effects of the concept on aircraft forces and moments and on the flight mechanics of the aircraft during maneuvering at high angles of attack. The objective was to utilize the side force associated with asymmetric vortices, in a controlled manner, to enhance the ability of the fighter to recover from a departure from controlled flight. The results from these water tunnel and wind tunnel experiments show that a small amount of tangential blowing along the forebody near the apex can effectively alter the forebody vortex system and generate large restoring yawing moments.

Skow, A. M.↗

NASA NTRS1984

Status and prospects of computational fluid dynamics for unsteady transonic viscous flows

Applications of computational aerodynamics to aeronautical research, design, and analysis have increased rapidly over the past decade, and these applications offer significant benefits to aeroelasticians. The past developments are traced by means of a number of specific examples, and the trends are projected over the next several years. The crucial factors that limit the present capabilities for unsteady analyses are identified; they include computer speed and memory, algorithm and solution methods, grid generation, turbulence modeling, vortex modeling, data processing, and coupling of the aerodynamic and structural dynamic analyses. The prospects for overcoming these limitations are presented, and many improvements appear to be readily attainable. If so, a complete and reliable numerical simulation of the unsteady, transonic viscous flow around a realistic fighter aircraft configuration could become possible within the next decade. The possibilities of using artificial intelligence concepts to hasten the achievement of this goal are also discussed.

Mccroskey, W. J.↗

NASA NTRS1985

Status and prospects of computational fluid dynamics for unsteady transonic flow

Mccroskey, W. J.↗

NASA NTRS1985

Semiempirical method for predicting vortex-induced rolling moments

A method is described for the prediction of rolling moments on a wing penetrating a vortex velocity field generated by a large aircraft. Rolling moments are determined from lifting pressure coefficients computed with an inviscid-flow linear panel method. Two empirical corrections are included to account for the lifting efficiency of an airfoil section and the local stall on the wing. Predicted rolling moments are compared with those from two windtunnel experiments. Results indicate that experimental rolling moments, for which the Reynolds number of the following wing is low, should be interpreted with caution.

Allison, D. O.↗

NASA NTRS1986

Basic studies on delta wing flow modifications by means of apex fences

The effectiveness of apex fences on a 60-deg delta wing at low speeds was experimentally investigated. Resembling highly swept spoilers in appearance, the fences are designed to fold out of the wing apex region upper surface near the leading edges, where they generate a powerful vortex pair. The intense suction of the fence vortices augments lift in the apex region, the resulting positive pitching moment being utilized to trim trailing edge flaps for lift augmentation during approach and landing at relatively low angles of attack. The fences reduce the apex lift at high angles of attack, leading to a desirable nose-down moment. The above projected functions of the apex fence device were validated and quantified through low speed tunnel tests, comprising upper surface pressure surveys on a semispan model and balance measurements on a geometrically similar fully span wing/body configuration. Fence parameters such as area, shape, hinge position and deflection angle were investigated. Typical results are presented indicating the apex fence potential in controlling the longitudinal characteristics of a tail-less delta.

Hoffler, K. D.↗

NASA NTRS1984

Experimental and analytical studies in fluids

The first objective was to analyze and design a true airspeed sensor which will replace the conventional pitot-static pressure transducer for small commercial aircraft. The second objective was to obtain a numerical solution and predict the frequency response which is generated by the vortex whistle at a certain airspeed. It was concluded flow rate measurements indicate that the vortex tube sound frequency is linearly proportional to the frequency response. The vortex tube whistle frequency is dependent upon geometrical parameters to such an extent that: an increase in vortex tube length produces a decrease in frequency response and that an increase in the exhaust nozzle length produces an increase in the frequency precession. An increase in the vortex tube diameter produces a decrease in frequency precession. An increase in swirler diameter produces a decrease in frequency. An increase in the location distance of the microphone pickup signal point from the inside edge of the exit nozzle produces an increase in frequency response. The experimental results indicate that those parameters most significantly effecting frequency are in descending order of importance microphone location, vortex tube diameter, exit nozzle length, vortex tube length, and swirler diameter.

Goglia, Gene L.↗

NASA NTRS1989

Interaction Of A Helicopter Blade With A Vortex

Measurements in wind tunnel yield data for validation of computations. Report describes experimental investigation of three-dimensional interaction of helicopter rotor blade with vortex like that generated by preceeding rotor blade. Provides theoretical aerodynamicists with data for validation of computer simulations of aerodynamic flow.

Dunagan, Stephen↗

NASA NTRS1992

Turbulence modeling for impinging jet flows

The objective of the present work is to improve the accuracy of the k-epsilon turbulence model for flows involving one or more jets impinging on a plate in a crossflow which generate a horseshoe vortex. The k-epsilon model is modified by adding source terms to the epsilon equation, which enables it to more accurately predict the shear stress in flows subject to streamline curvature and vortex stretching (or lateral divergence). Calculations with the modified model predict the ground vortex core to be about 15 percent upstream of its experimental location. This is a significant improvement over the standard model which yields higher errors for calculation of the vortex-core location.

Childs, Robert E.↗

NASA NTRS2000

Microphysical Modelling of Polar Stratospheric Clouds During the 1999-2000 Winter

The evolution of the 1999-2000 Arctic winter has been examined using a microphysical/photochemical model run along diabatic trajectories. A large number of trajectories have been generated, filling the vortex throughout the region of polar stratospheric cloud (PSC) formation, and extending from November until the vortex breakup, in order to provide representative sampling of the evolution of PSCs and their effect on stratospheric chemistry. The 1999-2000 winter was particularly cold, allowing extensive PSC formation. Many trajectories have ten-day periods continuously below the Type I PSC threshold; significant periods of Type II PSCs are also indicated. The model has been used to test the extent and severity of denitrification and dehydration predicted using a range of different microphysical schemes. Scenarios in which freezing only occurs below the ice frost point (causing explicit coupling of denitrification and dehydration) have been tested, as well as scenarios with partial freezing at warmer temperatures (in which denitrification can occur independently of dehydration). The sensitivity to parameters such as aerosol freezing rates and heterogeneous freezing have been explored. Several scenarios cause sufficient denitrification to affect chlorine partitioning, and in turn, model-predicted ozone depletion, demonstrating that an improved understanding of the microphysics responsible for denitrification is necessary for understanding ozone loss rates.

Drdla, Katja↗

NASA NTRS2014

Analytical Assessment of Simultaneous Parallel Approach Feasibility from Total System Error

In a simultaneous paired approach to closely-spaced parallel runways, a pair of aircraft flies in close proximity on parallel approach paths. The aircraft pair must maintain a longitudinal separation within a range that avoids wake encounters and, if one of the aircraft blunders, avoids collision. Wake avoidance defines the rear gate of the longitudinal separation. The lead aircraft generates a wake vortex that, with the aid of crosswinds, can travel laterally onto the path of the trail aircraft. As runway separation decreases, the wake has less distance to traverse to reach the path of the trail aircraft. The total system error of each aircraft further reduces this distance. The total system error is often modeled as a probability distribution function. Therefore, Monte-Carlo simulations are a favored tool for assessing a "safe" rear-gate. However, safety for paired approaches typically requires that a catastrophic wake encounter be a rare one-in-a-billion event during normal operation. Using a Monte-Carlo simulation to assert this event rarity with confidence requires a massive number of runs. Such large runs do not lend themselves to rapid turn-around during the early stages of investigation when the goal is to eliminate the infeasible regions of the solution space and to perform trades among the independent variables in the operational concept. One can employ statistical analysis using simplified models more efficiently to narrow the solution space and identify promising trades for more in-depth investigation using Monte-Carlo simulations. These simple, analytical models not only have to address the uncertainty of the total system error but also the uncertainty in navigation sources used to alert an abort of the procedure. This paper presents a method for integrating total system error, procedure abort rates, avionics failures, and surveillance errors into a statistical analysis that identifies the likely feasible runway separations for simultaneous paired approaches.

Madden, Michael M.↗

NASA NTRS2016

A Piezoelectric Shear Stress Sensor

In this paper, a piezoelectric sensor with a floating element was developed for shear stress measurement. The piezoelectric sensor was designed to detect the pure shear stress suppressing effects of normal stress generated from the vortex lift-up by applying opposite poling vectors to the: piezoelectric elements. The sensor was first calibrated in the lab by applying shear forces and it showed high sensitivity to shear stress (=91.3 +/- 2.1 pC/Pa) due to the high piezoelectric coefficients of PMN-33%PT (d31=-1330 pC/N). The sensor also showed almost no sensitivity to normal stress (less than 1.2 pC/Pa) because of the electromechanical symmetry of the device. The usable frequency range of the sensor is 0-800 Hz. Keywords: Piezoelectric sensor, shear stress, floating element, electromechanical symmetry

Kim, Taeyang↗

NASA NTRSDate not supplied

Aeroacoustic Analysis using Dynamic Mode Decomposition of Unsteady Pressure-Sensitive Paint Measurements

In this paper, we present a new method for the diagnosis and analysis of aeroacoustic phenomena. Taking advantage of the well-known property that the measurements of the Unsteady Pressure-Sensitive Paint (uPSP) have much higher spatial resolution compared to those of the conventional pressure transducers, the method is based on the visualization and analysis of the outputs of the Dynamic Mode Decomposition (DMD) of the uPSP measurements. The uPSP measurements were collected with four Phantom high-speed cameras in the Ascent Transient Aerodynamics Test (ATAT) of the Space Launch System (SLS) Block 1 cargo vehicle in the 11-by-11-foot transonic test section of the Unitary Plan Wind Tunnel (UPWT) at NASA Ames Research Center in September 2019. The method presented in this paper is demonstrated by investigating an interesting phenomenon observed in the SLS ATAT – the vortex shedding tone generated by the forward attachment of the Solid Rocket Booster (SRB). As examples, the DMD outputs of the uPSP measurements in a subsonic test in the SLS ATAT are presented. It is shown the information retrieved from the DMD outputs of the uPSP measurements can be effectively used in the identification and diagnosis of the aeroacoustic phenomena. The work described in this paper is a part of NASA’s development of a new state-of-the-art uPSP capability in production wind tunnels. Funding was provided by the NASA Aerosciences Evaluation and Test Capabilities Portfolio Office.

acoustics↗