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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Large-eddy simulation of laminar-turbulent breakdown at high speeds with dynamic subgrid-scale modeling

The laminar-turbulent breakdown of a boundary-layer flow along a hollow cylinder at Mach 4.5 is investigated with large-eddy simulation. The subgrid scales are modeled dynamically, where the model coefficients are determined from the local resolved field. The behavior of the dynamic-model coefficients is investigated through both an a priori test with direct numerical simulation data for the same case and a complete large-eddy simulation. Both formulations proposed by Germano et al. and Lilly are used for the determination of unique coefficients for the dynamic model and their results are compared and assessed. The behavior and the energy cascade of the subgrid-scale field structure are investigated at various stages of the transition process. The investigations are able to duplicate a high-speed transition phenomenon observed in experiments and explained only recently by the direct numerical simulations of Pruett and Zang, which is the appearance of 'rope-like' waves. The nonlinear evolution and breakdown of the laminar boundary layer and the structure of the flow field during the transition process were also investigated.

El-Hady, Nabil M.↗
NASA NTRS1994

Dynamic and Thermal Turbulent Time Scale Modelling for Homogeneous Shear Flows

A new turbulence model, based upon dynamic and thermal turbulent time scale transport equations, is developed and applied to homogeneous shear flows with constant velocity and temperature gradients. The new model comprises transport equations for k, the turbulent kinetic energy; tau, the dynamic time scale; k(sub theta), the fluctuating temperature variance; and tau(sub theta), the thermal time scale. It offers conceptually parallel modeling of the dynamic and thermal turbulence at the two equation level, and eliminates the customary prescription of an empirical turbulent Prandtl number, Pr(sub t), thus permitting a more generalized prediction capability for turbulent heat transfer in complex flows and geometries. The new model also incorporates constitutive relations, based upon invariant theory, that allow the effects of nonequilibrium to modify the primary coefficients for the turbulent shear stress and heat flux. Predictions of the new model, along with those from two other similar models, are compared with experimental data for decaying homogeneous dynamic and thermal turbulence, homogeneous turbulence with constant temperature gradient, and homogeneous turbulence with constant temperature gradient and constant velocity gradient. The new model offers improvement in agreement with the data for most cases considered in this work, although it was no better than the other models for several cases where all the models performed poorly.

Schwab, John R.↗
NASA NTRS1954

Vertical Descent and Landing Tests of a 0.13-Scale Model of the Convair XFY-1 Vertically Rising Airplane in Still Air, TED No. NACA DE 368

An investigation is being conducted to determine the dynamic stability and control characteristics of a 0.13-scale flying model of Convair XFY-1 vertically rising airplane. This paper presents the results of flight and force tests to determine the stability and control characteristics of the model in vertical descent and landings in still air. The tests indicated that landings, including vertical descent from altitudes representing up to 400 feet for the full-scale airplane and at rates of descent up to 15 or 20 feet per second (full scale), can be performed satisfactorily. Sustained vertical descent in still air probably will be more difficult to perform because of large random trim changes that become greater as the descent velocity is increased. A slight steady head wind or cross wind might be sufficient to eliminate the random trim changes.

Smith, Charlee C., Jr.↗
NASA NTRS1976

Wind tunnel and ground static investigation of a large scale model of a lift/cruise fan V/STOL aircraft

An investigation was conducted in a 40 foot by 80 foot wind tunnel to determine the aerodynamic/propulsion characteristics of a large scale powered model of a lift/cruise fan V/STOL aircraft. The model was equipped with three 36 inch diameter turbotip X376B fans powered by three T58 gas generators. The lift fan was located forward of the cockpit area and the two lift/cruise fans were located on top of the wing adjacent to the fuselage. The three fans with associated thrust vectoring systems were used to provide vertical, and short, takeoff and landing capability. For conventional cruise mode operation, only the lift/cruise fans were utilized. The data that were obtained include lift, drag, longitudinal and lateral-directional stability characteristics, and control effectiveness. Data were obtained up to speeds of 120 knots at one model height of 20 feet for the conventional aerodynamic lift configuration and at several thrust vector angles for the powered lift configuration.

Source record↗
NASA NTRS1990

The acoustic results of a United Techologies scale model helicopter rotor tested at DNW

An initial summary is presented of the acoustic measurements acquired for some of the different configurations of a 1/6 geometrically and aeroelastically scaled UTC model helicopter rotor which was tested in the open-jet anechoic test section of the Duits-Nederlandse Windtunnel in the Netherlands. Of particular interest are high-speed impulsive noise and blade-vortex interaction. An analysis is provided of baseline swept tip rotor acoustic characteristics in the regimes of high-speed forward flight, where high-speed impulsive noise dominates, and low-speed descent, where severe blade vortex interaction noise occurs. Also discussed are more recent studies of data which involve the animation of the acoustic field upstream of the rotor to evaluate the detailed radiation patters caused by BVI and HSI noise sources. The trends of these primary noise sources are examined as the first step in validating the data for release and application.

Liu, Sandy R.↗
NASA NTRS1987

A prediction of helicopter rotor discrete frequency noise for three scale models using a new acoustics program

A new computer program which uses Farassat's most advanced subsonic time domain formulation has been written to predict helicopter rotor discrete frequency noise. A brief description of the program, WOPWOP, is followed by a comparison of predicted and experimentally measured acoustic pressure and spectra for a 1/4 scale UH-1 model rotor blade and a 1/7 scale OLS (AH-1G) model rotor blade. The C81 computer program was used to predict the spanwise loading on the rotor for aerodynamic input into the acoustic prediction. Comparisons are made for different flight conditions and microphone locations with good results. In general the acoustic pressure is underpredicted. The acoustic predictions for a tapered rotor blade and predictions for microphones well below the tip path plane show less underprediction. Finally, in-plane motion of the rotor blade is shown to significantly affect the peak-to-peak amplitude of the acoustic pressure for high advancing tip Mach numbers.

Brentner, Kenneth S.↗
NASA NTRS1975

Mated aerodynamic characteristics investigation for 0.04-scale model Boeing 747 CAM/external tank (model AX1284 E-5) combination in the University of Washington Aeronautical Laboratory F. K. Kirsten Wind Tunnel (CA11)

Experimental investigations of the aerodynamic characteristics of a 0.04-scale external tank (ET) force model in combination with a 0.04-scale Boeing 747 force model were conducted. Test purposes were: (1) to determine ET airloads for selected configurations and (2) to determine the effectiveness of ET position, incidence, and support structure and 747 vertical stabilizing surfaces on stability, control, and performance of 747/ET combinations. The 747 was tested alone to establish baseline data and to verify test results. Six-component aerodynamic force and moment data were recorded for the 747 CAM and ET combination. Six-component force and moment data were also recorded for the ET, which was mounted on an internal balance supported by the 747. Data were recorded for angles of attack from -4 deg to +24 deg in 2 deg increments and angles of sideslip of - deg to + or - 20 deg. Testing was conducted at Mach 0.15 with dynamic pressure deg at 36 psf and unit Reynolds number of 1.3 million per foot. Photographs of test configurations are shown.

Source record↗
NASA NTRS1953

Flight Investigation of the Stability and Control Characteristics of a 0.13-Scale Model of the Convair XFY-1 Vertically Rising Airplane During Constant-Altitude Transitions, TED No. NACA DE 368

An investigation is being conducted to determine the dynamic stability and control characteristics of a 0.13-scale flying model of the Convair XFY-1 vertically rising airplane. This paper presents the results of flight tests to determine the stability and control characteristics of the model during constant-altitude slow transitions from hovering to normal unstalled forward flight. The tests indicated that the airplane can be flown through the transition range fairly easily although some difficulty will probably encountered in controlling the yawing motions at angles of attack between about 60 and 40. An increase in the size of the vertical tail will not materially improve the controllability of the yawing motions in this range of angle of attack but the use of a yaw damper will make the yawing motions easy to control throughout the entire transitional flight range. The tests also indicated that the airplane can probably be flown sideways satisfactorily at speeds up to approximately 33 knots (full scale) with the normal control system and up to approximately 37 knots (full scale) with both elevons and rudders rigged to move differentially for roll control. At sideways speeds above these values, the airplane will have a strong tendency to diverge uncontrollably in roll.

Lovell, Powell M., Jr.↗
NASA NTRS1978

Investigation of steady and fluctuating pressures associated with the transonic buffeting and wing rock of a one-seventh scale model of the F-5A aircraft

A wind tunnel test of a 1/7 scale F-5A model is described. The pressure, force, and dynamic response measurements during buffet and wing rock are evaluated. Effects of Mach number, angle of attack, sideslip angle, and control surface settings were investigated. The mean and fluctuating static pressure data are presented and correlated with some corresponding flight test data of a F-5A aircraft. Details of the instrumentation and the specially designed support system which allowed the model to oscillate in roll to simulate wing rock are also described. A limit cycle mechanism causing wing rock was identified from this study, and this mechanism is presented.

Hwang, C.↗
NASA NTRS1999

A New Way of Testing Large Thin Membrane, Optical Modal Testing of the 1/10th Scale Model of the NASA NAGT Sunshield

The Next Generation Space Telescope design includes a deployed sunshield to thermally insulate the telescope, keeping vital detector temperatures below 60 degrees Kelvin. The sunshield consists of four struts supporting four thin film membranes. Since it would be very difficult to test the full-scale sunshield on the ground due to its size and the 1-g environment, it is important to have accurate analytical models of the sunshield to analyze its affect on the observatory. A 1/10th-scale model of the sunshield has been manufactured in order to test the analytical modeling techniques used to predict the dynamic behavior of such large, lightweight structures. A modal survey test of the scale model has been performed in a vacuum environment, using a laser vibrometer to measure the mode shapes of the membranes. The presentation describes the setup and test procedures related to these tests and presents some of the experimental results obtained and the lessons learned.

Ross, Brian↗
NASA NTRS1990

The acoustic results of a United Technologies scale model helicopter rotor tested at DNW

In a major cooperative program between U.S. Government agencies (represented by the U.S. Army Aeroflightdynamics Directorate and NASA Ames and Langley Research Centers) and United Technologies Corp., a 1/6 geometrically and aeroelastically scaled UTC model helicopter rotor was tested in the open-jet anechoic test section of the Duits-Nederlandse Windtunnel in the Netherlands. As the fourth entry under the Aerodynamic and Acoustic Testing of Model Rotors Program, several comprehensive acoustic and aerodynamic databases were obtained relating the important aerodynamic phenomena to both the near- and far-field acoustic radiation. In particular, high speed impulsive noise and blade-vortex interaction are of primary interest. This paper provides an initial summary of the acoustic measurements acquired for some of the different configurations tested. A review of the baseline swept tip rotor acoustic characteristics in the regimes of high speed forward flight, where high speed impulsive noise dominates, and low speed descent, where severe blade vortex interaction noise occurs, is presented. The trends of these primary noise sources are studied as the first step in validating the data for release and application.

Liu, Sandy R.↗
NASA NTRS1998

A Priori Analyses of Three Subgrid-Scale Models for One-Parameter Families of Filters

The decay of isotropic turbulence a compressible flow is examined by direct numerical simulation (DNS). A priori analyses of the DNS data are then performed to evaluate three subgrid-scale (SGS) models for large-eddy simulation (LES): a generalized Smagorinsky model (M1), a stress-similarity model (M2), and a gradient model (M3). The models exploit one-parameter second- or fourth-order filters of Pade type, which permit the cutoff wavenumber k(sub c) to be tuned independently of the grid increment (delta)x. The modeled (M) and exact (E) SGS-stresses are compared component-wise by correlation coefficients of the form C(E,M) computed over the entire three-dimensional fields. In general, M1 correlates poorly against exact stresses (C < 0.2), M3 correlates moderately well (C approx. 0.6), and M2 correlates remarkably well (0.8 < C < 1.0). Specifically, correlations C(E, M2) are high provided the grid and test filters are of the same order. Moreover, the highest correlations (C approx.= 1.0) result whenever the grid and test filters are identical (in both order and cutoff). Finally, present results reveal the exact SGS stresses obtained by grid filters of differing orders to be only moderately well correlated. Thus, in LES the model should not be specified independently of the filter.

Pruett, C. David↗
NASA NTRS1954

Flight Tests of a 0.13-Scale Model of the Convair XFY-1 Vertically Rising Airplane with the Lower Vertical Tail Removed, TED No.DE 368

An experimental investigation has been conducted to determine the dynamic stability and control characteristics in hovering and transition flight of a 0.13-scale flying model of the Convair XFY-1 vertically rising airplane with the lower vertical tail removed. The purpose of the tests was to obtain a general indication of the behavior of a vertically rising airplane of the same general type as the XFY-1 but without a lower vertical tail in order to simplify power-off belly landings in an emergency. The model was flown satisfactorily in hovering flight and in the transition from hovering to normal unstalled forward flight (angle of attack approximately 30deg). From an angle of attack of about 30 down to the lowest angle of attack covered in the flight tests (approximately 15deg) the model became progressively more difficult to control. These control difficulties were attributed partly to a lightly damped Dutch roll oscillation and partly to the fact that the control deflections required for hovering and transition flight were too great for smooth flight at high speeds. In the low-angle-of-attack range not covered in the flight tests, force tests have indicated very low static directional stability which would probably result in poor flight characteristics. It appears, therefore, that the attainment of satisfactory directional stability, at angles of attack less than 10deg, rather than in the hovering and transition ranges of flight is the critical factor in the design of the vertical tail for such a configuration.

Lovell, Powell M., Jr.↗
NASA NTRS1949

Preliminary Results of a Free-Flight Investigation of the Static Stability and Aileron Control Characteristics of 1/6 Scale Models of the Bell MX-776

An investigation of the static longitudinal stability, static directional stability, and aileron control characteristics at transonic and supersonic speeds is being made of 1/6 scale rocket-propelled model of the Bell MX-776. A stability investigation has been made of two symmetrical models with controls undeflected and centers of gravity one-half and one-body diameter, respectively, ahead of the equivalent design center-of-gravity location of the full-scale version. Both models developed large normal-force coefficients in both the subsonic and supersonic ranges which indicated longitudinal instability at low angles of attack. The side-force coefficients were small for both models and indicated that the models were directionally stable. A possible tendency toward dynamic directional instability in the transonic region was indicated by short-period oscillations of the side forces. The results showed a partial-span inboard aileron to be ineffective or to cause negative control in the the transonic region when deflected approximately 5 deg but not when deflected 10 deg. An investigation of drag showed it to increase with a rearward movement of the center of gravity. This indicates an increase in the trim angle of attack as could be caused by a decrease in static stability.

Michal, David H.↗
NASA NTRS2005

Multi-Scale Modeling of a Graphite-Epoxy-Nanotube System

A multi-scale method is utilized to determine some of the constitutive properties of a three component graphite-epoxy-nanotube system. This system is of interest because carbon nanotubes have been proposed as stiffening and toughening agents in the interlaminar regions of carbon fiber/epoxy laminates. The multi-scale method uses molecular dynamics simulation and equivalent-continuum modeling to compute three of the elastic constants of the graphite-epoxy-nanotube system: C11, C22, and C33. The 1-direction is along the nanotube axis, and the graphene sheets lie in the 1-2 plane. It was found that the C11 is only 4% larger than the C22. The nanotube therefore does have a small, but positive effect on the constitutive properties in the interlaminar region.

Frankland, S. J. V.↗
NASA NTRS1996

Evaluation of Subgrid-Scale Models for Large Eddy Simulation of Compressible Flows

The objective of this project was to evaluate and develop subgrid-scale (SGS) turbulence models for large eddy simulations (LES) of compressible flows. During the first phase of the project results from LES using the dynamic SGS model were compared to those of direct numerical simulations (DNS) of compressible homogeneous turbulence. The second phase of the project involved implementing the dynamic SGS model in a NASA code for simulating supersonic flow over a flat-plate. The model has been successfully coded and a series of simulations has been completed. One of the major findings of the work is that numerical errors associated with the finite differencing scheme used in the code can overwhelm the SGS model and adversely affect the LES results. Attached to this overview are three submitted papers: 'Evaluation of the Dynamic Model for Simulations of Compressible Decaying Isotropic Turbulence'; 'The effect of the formulation of nonlinear terms on aliasing errors in spectral methods'; and 'Large-Eddy Simulation of a Spatially Evolving Compressible Boundary Layer Flow'.

Blaisdell, Gregory A.↗