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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

The development of crossflow vortices on a 45 degree swept wing

Three-dimensional boundary-layer experiments are currently being conducted on a 45 deg swept wing in the Arizona State University Unsteady Wind Tunnel. Crossflow-dominated transition is produced via a model with contoured end liners to simulate infinite swept-wing flow. Fixed-wavelength stationary and traveling crossflow vortex are observed. The stationary vortex wavelengths vary with Reynolds number as predicted by linear-stability theory, but with observed wavelengths which are about 25 percent smaller than theoretically predicted. The frequencies of the most-amplified moving waves are in agreement with linear-stability theory; traveling waves at higher frequencies than predicted are also observed. These higher-frequency waves may be harmonics of the primary crossflow waves generated by a parametric resonance phenomena. Boundary-layer profiles measured at several spanwise locations show streamwise disturbance profiles characteristic of the crossflow instability. Near the transition location, severe distortions of the laminar boundary-layer profiles are observed. Mean-profile measurements are compared to theoretical predictions.

Mousseux, Marc C.↗
NASA NTRS1991

Icing characteristics of a natural-laminar-flow, a medium-speed, and a swept, medium-speed airfoil

Tests were conducted at the Icing Research Tunnel at the NASA Lewis Research Center to determine the icing characteristics of three modern airfoils, a natural laminar flow, a medium speed and a swept medium speed airfoil. Tests measured the impingement characteristics and drag degradation for angles of attack typifying cruise and climb for cloud conditions typifying the range that might be encountered in flight. The maximum degradation occurred for the cruise angle of attack for the long glaze ice condition for all three airfoils with increases over baseline drag being 486 percent, 510 percent, and 465 percent for the natural laminar flow, the medium speed and the swept medium speed airfoil respectively. For the climb angle of attack, the maximum drag degradation (and extent of impingement) observed were also for the long glaze ice condition, and were 261 percent, 181 percent and 331 percent respectively. The minimum drag degradation (and extent of impingement) occurred for the cruise condition and for the short, rime spray which increases over baseline drag values of 47 percent, 28 percent and 46 percent respectively.

Bidwell, Colin S.↗
NASA NTRS1991

Numerical simulation of swept-wing flows

The transition process characteristics of flows over swept wings were computationally modelled. The crossflow instability and crossflow/T-S wave interaction are analyzed through the numerical solution of the full three dimensional Navier-Stokes equations including unsteadiness, curvature, and sweep. The leading-edge region of a swept wing is considered in a three-dimensional spatial simulation with random disturbances as the initial conditions.

Reed, Helen L.↗
NASA NTRS1991

Effect of a simulated ice accretion on the aerodynamics of a swept wing

The effect of a simulated glaze ice accretion on the aerodynamic performance of a three-dimensional swept wing is studied experimentally. A semispan wing of effective aspect ratio four was mounted from the sidewall of the UIUC subsonic wind tunnel. The model uses a NACA 0012 airfoil section on a rectangular planform with interchangeable tip and root sections to allow for 0- and 30-degree sweep. A sidewall suction system is used to minmize the tunnel boundary-layer interaction with the model. Surface pressure data from five spanwise stations are compared to earlier data from a similar tunnel. A three-component sidewall balance has been designed, built and used to measure lift, drag and pitching moment on the clean and iced model. The data compare well to the integrated pressure data and to theory on the clean model. In addition, helium-bubble flow visualization has been performed on the iced model and reveals extensive spanwise flow in the separation bubble aft of the upper surface horn. This compares well to the computational results of other researchers. Sidewall suction was found to have no effect on the aerodynamics of the swept wing.

Bragg, M. B.↗
NASA NTRS1990

Design aspects of long range supersonic LFC airplanes with highly swept wings

Studies on supersonic long-range LFC (laminar flow control) aircraft were performed with the aim of maximizing L/D and alleviating sonic boom during supersonic cruise. It is found that configurations with highly swept LFC wings of very high structural aspect ratio, with the sweep increasing toward the wing root and braced externally by wide chord laminarized struts, appear especially promising. In the supersonic cruise design condition the wing upper surface isobars are swept such that the flow in the direction normal to them is transonic with embedded supersonic zones and practically shock-free over most of the span, with M-perpendicular equal to the two-dimensional design values of advanced SC LFC airfoils, e.g., of the X-787 or X-6 type.

Pfenninger, W.↗
NASA NTRS1991

Icing characteristics of a natural-laminar-flow, a medium-speed, and a swept, medium-speed airfoil

Tests were conducted in the Icing Research Tunnel at the NASA Lewis Research Center to determine the icing characteristics of three modern airfoils: a natural-laminar-flow, a medium-speed, and a swept medium-speed airfoil. The tests measured the impingement characteristics and drag degradation for angles-of-attack typifying cruise and climb for cloud conditions typifying the range that might be encountered in flight. The maximum degradation occurred at the cruise angle-of-attack for the long, glaze ice condition for all three airfoils with increases over baseline drag being 486 percent, 510 percent, and 465 percent for the natural-laminar-flow, the medium-speed, and the swept, medium-speed airfoils, respectively. For the climb angle-of-attack, the maximum drag degradation (and total extent of impingement) observed were also for the long, glaze ice condition and were 261 percent, 181 percent, and 331 percent, respectively. The minimum drag degradation (and extent of impingement) occurred for the cruise condition and for the short, rime spray with increases over baseline drag values being 47 percent, 28 percent, 46 percent, respectively.

Bidwell, Colin S.↗
NASA NTRS1990

Experiments on swept-wing boundary layers

Three-dimensional boundary-layer experiments are currently being conducted on a 45-deg swept wing in the Arizona State University Unsteady Wind Tunnel. Crossflow-dominated transition is produced via a model with contoured end liners to simulate infinite swept-wing flow. Fixed-wavelength stationary and traveling crossflow vortices are observed. The stationary vortex wavelengths vary with Reynolds number as predicted by linear-stability theory, but with observed wavelengths which are about 25 percent smaller than theoretically predicted. The frequencies of the most amplified moving waves are in agreement with linear stability theory; however, traveling waves at higher frequencies than predicted are also observed. These higher-frequency waves may be harmonics of the primary crossflow waves generated by a parametric resonance phenomena. Boundary-layer profiles measured at several spanwise locations show streamwise disturbance profiles characteristic of the crossflow instability.

Dagenhart, J. R.↗
NASA NTRS1990

Blunt-nosed swept supercritical LFC wings without nose flaps

To simplify the design of swept supercritical (SC) Laminar Flow Control (LFC) wings and maintain satisfactory low speed characteristics, blunt-nosed swept SC LFC wings without nose flaps and lower wing loadings were studied. Their boundary layer crossflow in the leading edge area is optimally controlled (1) by compensating the boundary layer crossflow of the front acceleration zone by an opposite crossflow in a downstream pressure rise area, (2) by maintaining a neutrally stable boundary layer crossflow by suction within a narrow spanwise suction strip located close to the wing attachment line in the front acceleration zone. The required suction massflow and power are then very small, especially considering the strongly stabilizing effect of surface and streamline curvature on crossflow stability.

Pfenninger, W.↗
NASA NTRS1991

Comments on Frequency Swept Rotating Input Perturbation Techniques and Identification of the Fluid Force Models in Rotor/bearing/seal Systems and Fluid Handling Machines

Perturbation techniques used for identification of rotating system dynamic characteristics are described. A comparison between two periodic frequency-swept perturbation methods applied in identification of fluid forces of rotating machines is presented. The description of the fluid force model identified by inputting circular periodic frequency-swept force is given. This model is based on the existence and strength of the circumferential flow, most often generated by the shaft rotation. The application of the fluid force model in rotor dynamic analysis is presented. It is shown that the rotor stability is an entire rotating system property. Some areas for further research are discussed.

Muszynska, Agnes↗
NASA NTRS1991

Numerical simulation of swept-wing flows

Efforts of the last six months to computationally model the transition process characteristics of flow over swept wings are described. Specifically, the crossflow instability and crossflow/Tollmien-Schlichting wave interactions are analyzed through the numerical solution of the full 3D Navier-Stokes equations including unsteadiness, curvature, and sweep. This approach is chosen because of the complexity of the problem and because it appears that linear stability theory is insufficient to explain the discrepancies between different experiments and between theory and experiment. The leading edge region of a swept wing is considered in a 3D spatial simulation with random disturbances as the initial conditions.

Reed, Helen L.↗
NASA NTRS1992

Prediction of ice accretion on a swept NACA 0012 airfoil and comparisons to flight test results

In the winter of 1989-90, an icing research flight project was conducted to obtain swept wing ice accretion data. Utilizing the NASA Lewis Research Center's DHC-6 DeHavilland Twin Otter aircraft, research flights were made into known icing conditions in Northeastern Ohio. The icing cloud environment and aircraft flight data were measured and recorded by an onboard data acquisition system. Upon entry into the icing environment, a 24 inch span, 15 inch chord NACA 0012 airfoil was extended from the aircraft and set to the desired sweep angle. After the growth of a well defined ice shape, the airfoil was retracted into the aircraft cabin for ice shape documentation. The ice accretions were recorded by ice tracings and photographs. Ice accretions were mostly of the glaze type and exhibited scalloping. The ice was accreted at sweep angles of 0, 30, and 45 degrees. A 3-D ice accretion prediction code was used to predict ice profiles for five selected flight test runs, which include sweep angle of zero, 30, and 45 degrees. The code's roughness input parameter was adjusted for best agreement. A simple procedure was added to the code to account for 3-D ice scalloping effects. The predicted ice profiles are compared to their respective flight test counterparts. This is the first attempt to predict ice profiles on swept wings with significant scalloped ice formations.

Reehorst, Andrew L.↗
NASA NTRS1992

Swept shock/boundary layer interaction experiments in support of CFD code validation

Research on the topic of shock wave/turbulent boundary-layer interaction was carried out during the past three years at the Penn State Gas Dynamics Laboratory. This report describes the experimental research program which provides basic knowledge and establishes new data on heat transfer in swept shock wave/boundary-layer interactions. An equilibrium turbulent boundary-layer on a flat plate is subjected to impingement by swept planar shock waves generated by a sharp fin. Five different interactions with fin angle ranging from 10 deg to 20 deg at freestream Mach numbers of 3.0 and 4.0 produce a variety of interaction strengths from weak to very strong. A foil heater generates a uniform heat flux over the flat plate surface, and miniature thin-film-resistance sensors mounted on it are used to measure the local surface temperature. The heat convection equation is then solved for the heat transfer distribution within an interaction, yielding a total uncertainty of about +/- 10 percent. These experimental data are compared with the results of numerical Navier-Stokes solutions which employ a k-epsilon turbulence model. Finally, a simplified form of the peak heat transfer correlation for fin interactions is suggested.

Settles, G. S.↗
NASA NTRS1992

Prediction of ice accretion on a swept NACA 0012 airfoil and comparisons to flight test results

In the winter of 1989-90, an icing research flight project was conducted to obtain swept wing ice accretion data. Utilizing the NASA Lewis Research Center's DHC-6 DeHavilland Twin Otter aircraft, research flights were made into known icing conditions in Northeastern Ohio. The icing cloud environment and aircraft flight data were measured and recorded by an onboard data acquisition system. Upon entry into the icing environment, a 24 inch span, 15 inch chord NACA 0012 airfoil was extended from the aircraft and set to the desired sweep angle. After the growth of a well defined ice shape, the airfoil was retracted into the aircraft cabin for ice shape documentation. The ice accretions were recorded by ice tracings and photographs. Ice accretions were mostly of the glaze type and exhibited scalloping. The ice was accreted at sweep angles of 0, 30, and 45 degrees. A 3-D ice accretion prediction code was used to predict ice profiles for five selected flight test runs, which include sweep angle of zero, 30, and 45 degrees. The code's roughness input parameter was adjusted for best agreement. A simple procedure was added to the code to account for 3-D ice scalloping effects. The predicted ice profiles are compared to their respective flight test counterparts. This is the first attempt to predict ice profiles on swept wings with significant scalloped ice formations.

Reehorst, Andrew L.↗
NASA NTRS1992

A new aeroelastic model for composite rotor blades with straight and swept tips

An analytical model for predicting the aeroelastic behavior of composite rotor blades with straight and swept tips is presented. The blade is modeled by beam type finite elements along the elastic axis. A single finite element is used to model the swept tip. The nonlinear equations of motion for the finite element model are derived using Hamilton's principle and based on a moderate deflection theory and accounts for: arbitrary cross-sectional shape, pretwist, generally anisotropic material behavior, transverse shears and out-of-plane warping. Numerical results illustrating the effects of tip sweep, anhedral and composite ply orientation on blade aeroelastic behavior are presented. Tip sweep can induce aeroelastic instability by flap-twist coupling. Tip anhedral causes lag-torsion and flap-axial couplings, however, its effects on blade stability is less pronounced than the effect due to sweep. Composite ply orientation has a substantial effect on blade stability.

Yuan, Kuo-An↗
NASA NTRS1992

Extending a transonic small disturbance code to treat swept vertical surfaces

A flexible-swept vertical surface capability has been developed and implemented within the CAP-TSD transonic small disturbance (TSD) code. The new capability required a modification to the TSD equation and a grid transformation for swept vertical surfaces. Modifications to the vertical surface boundary conditions allow it to be treated as a flexible surface. The new capability extends the range of problems which the code can treat. In order to assess the accuracy of the modifications, calculations were performed for a rectangular T-tail configuration and an AGARD T-tail configuration. Unsteady forces and moments are presented for the rectangular T-tail oscillating in yaw for a range of reduced frequencies. Comparisons are presented with linear theory and experiment. Steady and unsteady surface pressures are presented for the AGARD T-tail along with generalized aerodynamic forces. Comparisons are made with linear theory. The comparisons demonstrate the accuracy of the vertical surface modifications.

Gibbons, Michael D.↗
NASA NTRS1992

Operating characteristics at Mach 4 of an inlet having forward-swept, sidewall-compression surfaces

A three-dimensional, forward-swept sidewall-compression inlet has been tested in the Mach 4 Blowdown Facility at the NASA Langley Research Center to examine parameters that affect inlet starting, operability, and performance. The inlet was designed to simultaneously provide good starting and mass capture characteristics through the combination of forward-swept sidewalls and the aft placement of the downstream cowl. Parametrics examined included top surface compression, geometric contraction ratio, sidewall compression angle, boundary-layer thickness on the vehicle undersurface, and cowl position. To simulate combustion effects on inlet operation, the inlet was mechanically back pressured to determine maximum achievable combustor-to-inlet pressure ratio prior to inlet unstart. Inlet operability and performance are shown in terms of inlet starting (pulsed and self-starting) and unstarting characteristics, inlet static pressure distributions, combustor back pressure limits, mass capture, and flow uniformity.

Hudgens, Julie A.↗
NASA NTRS1992

Heat transfer measurements and CFD comparison of swept shock wave/boundary-layer interactions

An experimental research program providing basic knowledge and establishing new data on the heat transfer in swept shock wave/boundary-layer interactions is described. An equilibrium turbulent boundary-layer on a flat plate is subjected to impingement by swept planar shock waves generated by a sharp fin. Five different interactions with fin angles ranging from 10 to 20 deg at freestream Mach numbers of 3.0 and 4.0 produce a variety of interaction strengths from weak to very strong. A foil heater generates a uniform heat flux over the flat plate surface and miniature thin-film-resistance sensors mounted on it are used to measure the local surface temperature. The heat convection equation is then solved for the heat transfer distribution within an interaction, yielding a total uncertainty of about +/- 10 percent. These experimental data are compared with the results of numerical Navier-Stokes solutions which employ a kappa-epsilon turbulence model. Finally, a simplified form of the peak heat transfer correlation for fin interactions is suggested.

Lee, Y.↗
NASA NTRS1993

An experimental study of the sources of fluctuating pressure loads beneath swept shock/boundary-layer interactions

An experimental research program providing basic knowledge and establishing a database on the fluctuating pressure loads produced on aerodynamic surfaces beneath three dimensional shock wave/boundary layer interactions is described. Such loads constitute a fundamental problem of critical concern to future supersonic and hypersonic flight vehicles. A turbulent boundary layer on a flat plate is subjected to interactions with swept planar shock waves generated by sharp fins at angle of attack. Fin angles from 10 to 20 deg at freestream Mach numbers of 3 and 4 produce a variety of interaction strengths from weak to very strong. Miniature Kulite pressure transducers flush-mounted in the flat plate are used to measure interaction-induced wall pressure fluctuations. The distributions of properties of the pressure fluctuations, such as their ring levels, amplitude distributions, and power spectra, are also determined. Measurements were made for the first time in the aft regions of these interactions, revealing fluctuating pressure levels as high as 160 dB. These fluctuations are dominated by low frequency (0-5 kHz) signals. The maximum ring levels in the interactions show an increasing trend with increasing interaction strength. On the other hand, the maximum ring levels in the forward portion of the interactions decrease linearly with increasing interaction sweep back. These ring pressure distributions and spectra are correlated with the features of the interaction flowfield. The unsteadiness of the off-surface flowfield is studied using a new, non-intrusive technique based on the shadow graph method. The results indicate that the entire lambda-shock structure generated by the interaction undergoes relatively low-frequency oscillations. Some regions where particularly strong fluctuations are generated were identified. Fluctuating pressure measurements are also made along the line of symmetry of an axisymmetric jet impinging upon a flat plate at an angle. This flow was chosen as a simple analog to the impinging jet region found in the rear portion of the shock wave/boundary layer interactions under study. It is found that a sharp peak in ring pressure level exists at or near the mean stagnation point. It is suggested that the phenomena responsible for this peak may be active in the swept interactions as well, and may cause the extremely high fluctuating pressures observed in the impinging jet region in the present experimental program.

Settles, G. S.↗