Engineering topics

Harvey, W. D.

Publications and source records attributed to Harvey, W. D..

At least 19 records

NASA NTRS1989

Computational results for the effects of external disturbances on transition location of bodies of revolution from subsonic to supersonic speeds and comparisons with experimental data

Computational experiments have been performed for a few configurations in order to investigate the effects of external flow disturbances on the extent of laminar flow and wake drag. Theoretical results have been compared with experimental data for the AEDC cone, for Mach numbers from subsonic to supersonic, and for both free flight and wind tunnel environments. The comparisons have been found to be very satisfactory, thus establishing the utility of the present method for the design and development of laminar flow configurations and for the assessment of wind tunnel data. In addition, results of calculations concerning the effects of unit Reynolds numbers on transition are presented. In addition to the AEDC cone, computations have been performed for an ogive body of revolution at zero angle of attack and supersonic Mach numbers. Results are presented for transition Reynolds number and wake drag for external disturbances corresponding to free air and the test section of the AEDC-VKF tunnel. These results have been found to compare quite well with wind tunnel data for cases when surface suction is applied as well as when suction is absent.

Goradia, S. H.↗

NASA NTRS1988

Toward lower drag with laminar flow technology

The most promising method of achieving significantly lower skin-friction drag of an aircraft component is through the stabilization and maintenance of a laminar boundary layer over a large fraction of its surface. In a number of applications, however, laminar flow is unfeasible and/or undesirable, and the most efficient turbulent flow design must be provided. The development of both laminar and turbulent airfoil and wing designs over the past decade is reviewed. High, medium, and low-speed airfoil concepts are discussed, and some overall comparisons are made for different Reynolds number ranges.

Harvey, W. D.↗

NASA NTRS1988

Transition prediction in external flows via linear stability theory

Linear stability theory results are presented for flight and low-disturbance wind tunnels, at low and high speeds, and for T-S, Gortler, and cross-flow modes. Results show that, in the absence of Morkovin 'bypasses', transition at low background disturbance levels corresponds to N-factors of the order of 9 to 11, provided that phenomena such as curvature effects are included. The results point to a wider range of applicability for the e exp N method than previously conjectured, and suggest that the e exp N method can be used to parametrize transition predictions as a function of parameters which affect the mean flow profiles for such purposes as LFC and minimum drag design.

Bushnell, D. M.↗

NASA NTRS1988

Flow control in a wing/fuselage-type juncture

The laminar flow around a juncture formed by an unswept wing and a flat plate has been studied using a combination of smoke flow visualization, and velocity and pressure measurements. The effectiveness of swept leading-edge fillets in controlling the juncture flow field has been evaluated. Flow separation upstream of the wing leading edge is confined to a small region near the plate. This separation results in periodic shedding of horseshoe type vortices. The pressure gradient measured upstream of the leading edge in this laminar juncture is steeper than that of the turbulent flow case. The use of fillets eliminates the leading-edge flow separation and reduces the size of juncture wake, as observed from flow visualization. For one of the filleted cases, there is a significant increase in the extent of laminar flow in the juncture region, and a sizable reduction in the juncture drag.

Kubendran, L. R.↗

NASA NTRS1987

Development of wing and tail configurations for low altitude unmanned research aircraft (LAURA)

The Low Altitude/Airspeed Unmanned Research Aircraft (LAURA) is being developed by the U.S. Navy for flight test research using low-Reynolds number airfoils. This vehicle consists of a standard modular fuselage designed to accept the installation of several wings/tails having low Reynolds number airfoils, and various planform shapes. Design constraints include shipboard storage, long flight endurance at very low airspeeds and sea-skimming cruise altitude. The stringent design constraints require the development of high-performance low Reynolds number (LRN) airfoils, suitable lifting surface configuration, and advanced airframe-propulsion systems. The present paper describes ongoing efforts to develop wing and tail configurations for LAURA using airfoils designed at NASA Langley Research Center.

Mangalam, S. M.↗

NASA NTRS1987

Theoretical investigations, and correlative studies for NLF, HLFC, and LFC swept wings at subsonic, transonic and supersonic speeds

Attention is given to the results of theory/experiment-correlation studies for natural laminar flow, LFC, and hybrid-LFC airfoils at subsonic and supersonic Mach numbers. The method of characteristics, integral compressible boundary layer methods for infinitely swept wings, and a method for prediction of separating turbulent boundary layer characteristics. The integral boundary layer methods are found to be successful at predicting both transonic and supersonic transition phenomena. Computations for wings with 0-50 deg sweep angle, Reynolds number range of 1-30 million, and with and without LFC, are in good agreement with experimental data.

Goradia, S. H.↗

NASA NTRS1986

Design and experimental evaluation of a swept supercritical Laminar Flow Control (LFC) airfoil

A large chord swept supercritical laminar flow control (LFC) airfoil was designed, constructed, and tested in the NASA Langley 8-ft Transonic Pressure Tunnel (TPT). The LFC airfoil experiment was established to provide basic information concerning the design and compatibility of high-performance supercritical airfoils with suction boundary layer control achieved through discrete fine slots or porous surface concepts. It was aimed at validating prediction techniques and establishing a technology base for future transport designs and drag reduction. Good agreement was obtained between measured and theoretically designed shockless pressure distributions. Suction laminarization was maintained over an extensive supercritical zone up to high Reynolds numbers before transition gradually moved forward. Full-chord laminar flow was maintained on the upper and lower surfaces at M sub infinity = 0.82 up to R sub c is less than or equal to 12 x 10 to the 6th power. When accounting for both the suction and wake drag, the total drag could be reducted by at least one-half of that for an equivalent turbulent airfoil. Specific objectives for the LFC experiment are given.

Harvey, W. D.↗

NASA NTRS1986

Transition and separation control on a low-Reynolds number airfoil

The major problem associated with the aerodynamic performance of airfoils at low Reynolds numbers is the presence of extensive laminar boundary-layer separation resulting in a large increase in presssure drag and a decrease in lift. The rapid deterioration in airfoil characteristics can be largely eliminated by artificially controlling the flow through the introduction of suitable disturbances in the boundary layer such that transition occurs ahead of the anticipated laminar separation. This paper presents the results of wind-tunnel tests conducted on a 10-cm model of LRN (1)-1007 airfoil with passive (roughness trips) and active (acoustic excitation) controls to trigger transition and suppress separation. Significant improvements in the aerodynamic characteristics of the airfoil were observed. Results of this study for a chord Reynolds number range of 40,000 to 250,000 are presented in this paper.

Mangalam, S. M.↗

NASA NTRS1985

A study of laminar separation bubble in the concave region of an airfoil using laser velocimetry

Laser velocimetry (LV) was used to study the nature of laminar separation bubbles in the concave region of a 1.83-meter airfoil model which was tested in the NASA Langley Low Turbulence Pressure Tunnel. Three component, coincident data from LV measurements including histograms of particle velocity, mean velocity profiles, turbulence intensity, and Reynolds stresses within the shear layer were used to determine the locations of laminar separation, transition, and turbulent reattachment. boundary-layer parameters determined from velocity profiles were used to compare the results with existing empirical relations for describing the laminar separation bubble.

Mangalam, S. M.↗

NASA NTRS1985

Retractable End Plates for Aircraft Lifting Surfaces

End plates and winglets improve aerodynamic characteristics of aircraft wings and other fixed lifting surfaces. Retractable end plates automatically actuated by same shaft that deflects lifting surface and require little or no extra power and absolutely no control input from cockpit. Besides being modular in construction, easily fitted to any existing aircraft design with only minor modifications.

Harvey, W. D.↗

NASA NTRS1985

Juncture flow control using leading-edge fillets

Flow measurements have been made in the wake region of a simulated wing-fuselage juncture, with and without leading-edge fillets, in order to assess the effect of leading-edge modifications on the flow field around the juncture. Preliminary results indicate that there is some reduction in juncture drag at moderate angles of attack with the use of leading-edge fillets. There is also evidence of improvement in the flow characteristics on the surface downstream of the juncture when fillets are used. As the fillet size is increased, flow characteristics start deteriorating at some point, and an optimum fillet size may be required to achieve an overall improvement in the flow field.

Kubendran, L. R.↗

NASA NTRS1985

A faster 'transition' to laminar flow

A discussion is given of the ongoing research related to laminar flow airfoils, nacelles, and wings where the laminar flow is maintained by a favorable pressure gradient, surface suction or a combination of the two. Design methologies for natural laminar flow airfoil sections and wings for both low and high speed applications are outlined. Tests of a 7-foot chord, 23-deg sweep laminar flow-control airfoil at high subsonic Mach numbers are described, along with the associated stability theory used to design the suction system. The state-of-the-art of stability theory is simply stated and a typical calculation illustrated. In addition, recent computer simulations of transition using the time dependent Navier-Stokes equations are briefly described. Advances in wind tunnel capabilities and instrumentation will be reviewed, followed by the presentation of a few results from both wind tunnels and flight. Finally, some suggestions for future work will complete the paper.

Bobbitt, P. J.↗

NASA NTRS1985

Hybrid approach to steady transonic normal shock-compressible laminar boundary layer interactions over airfoils with suction

Transonic airfoil flow is to a large degree affected by viscous-inviscid interactions. Among them a key role is played by the boundary layer interaction with the shock wave embedded in the flow field and the interaction of the boundary layer with the sustained adverse pressure gradients. The effects of these interactions can be controlled or suppressed by introducing surface mass transfer such as suction. This investigation deals strictly with the study of shock-laminar boundary layer interactions including distributed mass transfer. The present calculations agree with experiments on a swept LFC wing at low speeds which indicates that with a suitable choice of the extent of the airfoil surface over which suction is applied and adjustment of the suction velocity, full-chord laminar flow can be maintained and separation can be prevented completely.

Ram, R. B.↗

NASA NTRS1984

Hybrid approach to steady transonic normal-shock compressible laminar boundary-layer interactions over airfoils

A simulation of steady transonic viscous-inviscid interactions through a combination of zonal solution methods (involving different equation sets and numerical regions for various flow regions) is used in an investigation of a fluid mechanics problem in which the pressure distribution is determined by the interaction between transonic inviscid flow and an inner laminar viscous layer. The results obtained are in good agreement with laminar experimental data. Both attached and separated boundary layer flows are considered for either weak or strong interactions.

Ram, R. B.↗

NASA NTRS1984

Experimental Results for a Flapped Natural-laminar-flow Airfoil with High Lift/drag Ratio

Experimental results have been obtained for a flapped natural-laminar-flow airfoil, NLF(1)-0414F, in the Langley Low-Turbulence Pressure Tunnel. The tests were conducted over a Mach number range from 0.05 to 0.40 and a chord Reynolds number range from about 3.0 x 10(6) to 22.0 x 10(6). The airfoil was designed for 0.70 chord laminar flow on both surfaces at a lift coefficient of 0.40, a Reynolds number of 10.0 x 10(6), and a Mach number of 0.40. A 0.125 chord simple flap was incorporated in the design to increase the low-drag, lift-coefficient range. Results were also obtained for a 0.20 chord split-flap deflected 60 deg.

Mcghee, R. J.↗

NASA NTRS1984

An evaluation of factors affecting the flow quality in wind tunnels

Tests were conducted in a number of NASA wind tunnels to measure disturbance levels and spectra in their respective settling chambers, test sections, and diffusers to determine the sources of these disturbances. Results indicate that properly designed and located second minimum in transonic tunnels prevent fluctuation originating at struts and in diffusers from propagating upstream into the test section. The installation in or upstream of the settling chamber of carefully selected screens, honeycomb, and acoustic baffles could further reduce test section turbulence levels and scales without significant pressure losses. The performance of these modifications is strongly influenced by tunnel geometry and their influence on the mean flow around the circuit.

Owen, F. K.↗

NASA NTRS1983

An evaluation and assessment of flow quality in selected NASA wind tunnels

Tests have been conducted in a number of NASA wind tunnels to measure disturbance levels and spectra in their respective settling chambers, test sections, and diffusers to determine the sources of their disturbances. The present data supplements previous results in other NASA tunnels and adds to the ongoing acquisition of a disturbance level data base. The present results also serve to explain flow related sources which cause relatively large disturbance amplitudes at discrete frequencies. The installation of honeycomb, screens, and acoustic baffles in or upstream of the settling chamber can significantly reduce the disturbance levels.

Harvey, W. D.↗

NASA NTRS1982

Influence of surface static-pressure orifices on boundary-layer transition

An investigation of the interaction of a laminar boundary layer and surface static-pressure orifices was conducted on a natural laminar flow airfoil. The effects of both favorable and adverse pressure gradients were studied at Reynolds numbers based on airfoil chord from approximately 500,000 to 6,000,000 with Mach number varying accordingly from about 0.03 to 0.42. The smaller the diameter of the orifice, the less likely it will cause premature transition. Locating the orifices in a chord-wise row aligned with the flow appears to have an additive, adverse effect on transition. Tube length-to-orifice diameter ration does not seem to have a consistent influence on transition.

Somers, D. M.↗