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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Swept wing ice accretion modeling

An effort to develop a three-dimensional ice accretion modeling method is initiated. This first step toward creation of a complete aircraft icing simulation code builds on previously developed methods for calculating three-dimensional flowfields and particle trajectories combined with a two-dimensional ice accretion calculation along coordinate locations corresponding to streamlines. This work is intended as a demonstration of the types of calculations necessary to predict a three-dimensional ice accretion. Results of calculations using the 3D method for a MS-317 swept wing geometry are projected onto a 2D plane normal to the wing leading edge and compared to 2D results for the same geometry. These results indicate that the flowfield over the surface and the particle trajectories differed for the two calculations. This led to lower collection efficiencies, convective heat transfer coefficients, freezing fractions, and ultimately ice accumulation for the 3D calculation.

Potapczuk, M. G.↗
NASA NTRS1990

Three-dimensional thermal-structural analysis of a swept cowl leading edge subjected to skewed shock-shock interference heating

A three-dimensional flux-based thermal analysis method has been developed and its capability is demonstrated by predicting the transient nonlinear temperature response of a swept cowl leading edge subjected to intense three-dimensional aerodynamic heating. The predicted temperature response from the transient thermal analysis is used in a linear elastic structural analysis to determine thermal stresses. Predicted thermal stresses are compared with those obtained from a two-dimensional analysis which represents conditions along the chord where maximum heating occurs. Results indicate a need for a three-dimensional analysis to predict accurately the leading edge thermal stress response.

Polesky, Sandra P.↗
NASA NTRS1990

The stability of a three-dimensional laminar boundary layer on a swept flat plate

The linear stability of the laminar boundary layer on a swept flat plate with an imposed favorable pressure gradient was studied utilizing a linear stability model which accounts for streamline curvature for three-dimensional incompressible flows. Calculations were performed for an effective leading-edge sweep angle of 42.5 degrees and freestream velocity of 19 m/s. Computed disturbance amplification rates for the spectrum of amplified frequencies and wavelengths for stationary crossflow vortices were compared with experimental results.

Collier, F. S., Jr.↗
NASA NTRS1990

Experimental investigation of a supersonic swept ramp injector using laser-induced iodine fluorescence

Planar measurements of injectant mole fraction and temperature have been conducted in a nonreacting supersonic combustor configured with underexpanded injection in the base of a swept ramp. The temperature measurements were conducted with a Mach 2 test section inlet in streamwise planes perpendicular to the test section wall on which the ramp was mounted. Injection concentration measurements, conducted in cross flow planes with both Mach 2 and Mach 2.9 free stream conditions, dramatically illustrate the domination of the mixing process by streamwise vorticity generated by the ramp. These measurements, conducted using a nonintrusive optical technique (laser-induced iodine fluorescence), provide an accurate and extensive experimental data base for the validation of computation fluid dynamic codes for the calculation of highly three-dimensional supersonic combustor flow fields.

Hartfield, Roy J.↗
NASA NTRS1990

Parametric analysis of swept-wing geometry with sheared wing tips

A computational parameter study is presented of potential reductions in induced drag and increases in lateral-directional stability due to sheared wing tips attached to an untwisted wing of moderate sweep and aspect ratio. Sheared tips are swept and tapered wing-tip devices mounted in the plane of the wing. The induced-drag results are obtained using an inviscid, incompressible surface-panel method that models the nonlinear effects due to the deflected and rolled-up wake behind the lifting surface. The induced-drag results with planar sheared tips are compared to straight-tapered tip extensions and nonplanar winglet geometries. The lateral-directional static-stability characteristics of the wing with sheared tips are estimated using a quasi-vortex-lattice method. For certain combinations of sheared-tip sweep and taper, both the induced efficiency of the wing and the relevant static-stability derivatives are predicted to increase compared to the wing with a straight-tapered tip modification.

Fremaux, C. M.↗
NASA NTRS1990

Flow visualization studies of blowing from the tip of a swept wing

Flow visualization studies of blowing from the tip of a swept wing were conducted in the Langley 16- by 24-inch water tunnel. Four wing tips, each with two independent blowing slots, were tested. The two slots were located one behind the other in the chordwise direction. The wing tips were designed to vary systematically the jet length, the jet in-plane exhaust direction (sweep), and the jet out-of-plane exhaust direction (anhedral). Each blowing slot was tested separately at two angles of attack and at four ratios of jet to free stream velocity ratios. Limited tests were conducted with blowing from both slots simultaneously. Blowing from the tip inhibited inboard spanwise flow on the upper wing surface near the tip. The jet path moved farther away from the tip with increasing jet to free stream velocity ratio and moved closer to the tip with increasing angle of attack.

Smith, Jeannette W.↗
NASA NTRS1991

Numerical simulation of ice growth on a MS-317 swept wing geometry

An effort to develop a 3-D ice accretion modeling method was initiated. This first step towards creation of a complete aircraft icing simulation code builds on previously developed methods for calculating 3-D flow fields and particle trajectories combined with a 2-D ice accretion calculation along coordinate locations corresponding to streamlines. The types of calculations necessary to predict 3-D ice accretion is demonstrated. Results of calculations using 3-D method for a MS-317 swept wing geometry are projected onto a 2-D plane parallel to the free stream direction and compared to experimental results for the same geometry. It is anticipated that many modifications will be made to this approach, however this effort will lay the groundwork for future modeling efforts. Results indicate that rime ice shapes indicate a difficulty in accurately calculating the ice shape in the runback region.

Potapczuk, M. G.↗
NASA NTRS1990

Detailed flow-field measurements over a 75 deg swept delta wing

Results from an experimental investigation documenting the flowfield over a 75 deg swept delta wing at an angle-of-attack of 20.5 deg are presented. Results obtained include surface flow visualization, off-body flow visualization, and detailed flowfield surveys for various Reynolds numbers. Flowfield surveys at Reynolds numbers of 0.5, 1.0, and 1.5 million based on the root chord were conducted with both a Pitot pressure probe and a 5-hole pressure probe; and 3-component laser velocimeter surveys were conducted at a Reynolds number of 1.0 million. The Pitot pressure surveys were obtained at 5 chordwise stations, the 5-hole probe surveys were obtained at 3 chordwise stations and the laser velocimeter surveys were obtained at one station. The results confirm the classical roll up of the flow into a pair of primary vortices over the delta wing. The velocity measurements indicate that Reynolds number has little effect on the global structure of the flowfield for the Reynolds number range investigated. Measurements of the non-dimensional axial velocity in the core of the vortex indicate a jet like flow with values greater than twice freestream. Comparisons between velocity measurements from the 5-hole pressure probe and the laser velocimeter indicate that the pressure probe does a reasonable job of measuring the flowfield quantities where the velocity gradients in the flowfield are low.

Kjelgaard, Scott O.↗
NASA NTRS1991

The NASA Langley laminar-flow-control experiment on a swept, supercritical airfoil: Suction coefficient analysis

A swept supercritical wing incorporating laminar flow control at transonic flow conditions was designed and tested. The definition of an experimental suction coefficient and a derivation of the compressible and incompressible formulas for the computation of the coefficient from measurable quantities is presented. The suction flow coefficient in the highest velocity nozzles is shown to be overpredicted by as much as 12 percent through the use of an incompressible formula. However, the overprediction on the computed value of suction drag when some of the suction nozzles were operating in the compressible flow regime is evaluated and found to be at most 6 percent at design conditions.

Brooks, Cuyler W., Jr.↗
NASA NTRS1991

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

A database is established on the fluctuating pressure loads produced on aerodynamic surfaces beneath 3-D shock wave/boundary layer interactions. 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. Fin angles from 5 to 25 deg at freestream Mach numbers between 2.5 and 4 produce a variety of interaction strengths from weak to very strong. Miniature Kulite pressure transducers mounted in the flat plate were used to measure interaction-induced wall pressure fluctuations. These data will be correlated with proposed new optical data on the fluctuations of the interaction structure, especially that of the lambda-shock system and its associated high-speed jet impingement.

Settles, Gary S.↗
NASA NTRS1991

Effects of sweep angle and passive relaminarization devices on a supersonic swept-cylinder boundary layer

The effects of passive leading-edge devices on the boundary layer of a swept cylinder in supersonic flow with very low free-stream disturbance levels are investigated. Tests are conducted at Mach 3.5 over a free-stream Reynolds number based on model diameter of 15,000 to 150,000, and sweep angles of 60 deg and 76 deg are used to evaluate possible sweep-angle effects. The devices tested include a sawtoothed leading edge, square device, and a fence. It is observed that at a sweep angle of 76 deg, relaminarization of the supersonic attachment-line flow is achieved by several of the devices, while no devices are successful at a sweep angle of 60 deg.

Creel, T. R.↗
NASA NTRS1991

Numerical simulation of ice growth on a MS-317 swept wing geometry

An effort to develop a 3-D ice accretion modeling method was initiated. This first step towards creation of a complete aircraft icing simulation code builds on previously developed methods for calculating 3-D flow fields and particle trajectories combined with a 2-D ice accretion calculation along coordinate locations corresponding to streamlines. The types of calculations necessary to predict three-dimensional ice accretion is demonstrated. Results of calculations using 3-D method for a MS-317 swept wing geometry are projected onto a 2-D plane parallel to the free stream direction and compared to experimental results for the same geometry. It is anticipated that many modifications will be made to this approach, however, this effort will lay the groundwork for future modeling efforts. Results indicate that rime ice shapes indicate a difficulty in accurately calculating the ice shape in the runback region.

Potapczuk, M. G.↗
NASA NTRS1990

The stability of a three dimensional laminar boundary layer over a swept flat plate

The linear stability of the laminar boundary layer on a swept flat plate with an imposed favorable pressure gradient was studied utilizing a linear stability model which accounts for streamline curvature for three-dimensional incompressible flows. Calculations were performed for a leading-edge sweep angle of 45 degrees and freestream valocity of 19 m/s. Computed disturbance amplification rates and wavelengths for stationary crossflow vortices were compared with available experimental results.

Mueller, B.↗
NASA NTRS1990

On the stability of swept wing laminar boundary layers including curvature effects

A linear stability analysis that encompasses curvature effects has been conducted in wind tunnel experiments on a swept NACA 64(2)-A015 wing, and published transition-onset results have been correlated with computed N-factor values. A strong stabilizing influence is noted upon the growth of the crossflow disturbance, when the flow is accelerated in regions of high body curvature. The maximum amplified crossflow disturbances were in all cases travelling waves; when TS waves reached their maximum, the N-factors at transition lay in the 9.9-13.8 range. Stabilization due to curvature effects was less pronounced in cases where acceleration occurred over a large portion of chord.

Viken, J.↗
NASA NTRS1991

On the quasi-conical flowfield structure of the swept shock wave-turbulent boundary layer interaction

The swept oblique shock-wave/turbulent-boundary-layer interaction generated by a 20-deg sharp fin at Mach 4 and Reynolds number 21,000 is investigated via a series of computations using both conical and three-dimensional Reynolds-averaged Navier-Stokes equations with turbulence incorporated through the algebraic turbulent eddy viscosity model of Baldwin-Lomax. Results are compared with known experimental data, and it is concluded that the computed three-dimensional flowfield is quasi-conical (in agreement with the experimental data), the computed three-dimensional and conical surface pressure and surface flow direction are in good agreement with the experiment, and the three-dimensional and conical flows significantly underpredict the peak experimental skin friction. It is pointed out that most of the features of the conical flowfield model in the experiment are observed in the conical computation which also describes the complete conical streamline pattern not included in the model of the experiment.

Knight, Doyle D.↗
NASA NTRS1992

The NASA Langley laminar-flow-control experiment on a swept, supercritical airfoil: Evaluation of initial perforated configuration

The initial evaluation of a large-chord, swept, supercritical airfoil incorporating an active laminar-flow-control (LFC) suction system with a perforated upper surface is documented in a chronological manner, and the deficiencies in the suction capability of the perforated panels as designed are described. The experiment was conducted in the Langley 8-Foot Transonic Pressure Tunnel. Also included is an evaluation of the influence of the proximity of the tunnel liner to the upper surface of the airfoil pressure distribution.

Harris, Charles D.↗
NASA NTRS1992

Structure of supersonic turbulent flow past a swept compression corner

The structure of the shock wave/turbulent boundary-layer interaction generated by a 3D swept compression corner has been investigated through a combined experimental and theoretical research program. The flowfield geometry is defined by the streamwise compression angle alpha and the sweep angle lambda of the corner. The present study examines two different configurations, namely (alpha, lambda) = (24 deg, 40 deg) and (24 deg, 60 deg) at Mach 3 and Re sigma infinity about 9 x 10 exp 5. The theoretical model is the 3D Reynolds-averaged compressible Navier-Stokes equations with turbulence incorporated using a turbulent eddy viscosity. The calculated flowfields display general agreement with experimental data for surface pressure and good agreement with experimental flowfield profiles of pitot pressure and yaw angle. The principal feature of the flowfield is a large vortical structure approximately aligned with the corner. The entrainment of incoming fluid into the vortical structure is strongly affected by the sweep angle lambda. Viscous (turbulent and molecular) effects appear to be important only in the immediate vicinity of the surface and in an isolated region within the interaction and near the corner.

Knight, Doyle D.↗
NASA NTRS1991

Suppressing interfering scattered signals in swept-frequency radar measurements by using frequency domain Wiener filtering

A novel approach to the reduction of scattered, interfering signals that corrupt measurements of the signal backscattered from radar targets of interest is being developed. It is being explored with sphere measurements in an indoor microwave radar range. This method is based on the concept of Wiener filtering (which minimizes the difference between the signal plus noise and the desired signal in the time domain). In contrast to the traditional Wiener filter, in which the time domain error between two sequences are minimized, the approach reported uses the frequency domain phasor amplitudes of a swept frequency signal. It minimizes the difference (least-mean-square-magnitude) between the signal-plus-noise and the signal complex phasors, across the entire spectrum.

Weissman, David E.↗