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Technical Paper

Transition Research in the Mach 3.5 Low-Disturbance Wind Tunnel and Comparisons of Data with Theory

1989-09-01
892379
Supersonic wind tunnels with much lower stream disturbance levels than in conventional tunnels are required to advance transition research. The ultimate objectives of this research are to provide reliable predictions of transition from laminar to turbulent flow on supersonic flight vehicles and to develop techniques for the control and reduction of viscous drag and heat transfer. The experimental and theoretical methods used at NASA Langley to develop a low-disturbance pilot tunnel are described. Typical transition data obtained in this tunnel are compared with flight and previous wind-tunnel data and with predictions from linear stability theory,
Technical Paper

Computational Results for the Effects of External Disturbances on Transition Location on Bodies of Revolution from Subsonic to Supersonic Speeds and Comparisons with Experimental Data

1989-09-01
892381
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, the present paper presents results of calculations concerning the effects of unit Reynolds numbers on transition. This phenomenon has been observed by a few experimental investigators but has been analyzed in detail for the first time in the present paper with the aid of the theoretical predictions.
Technical Paper

Investigations of Modifications to Improve the Spin Resistance of a High-Wing, Single-Engine, Light Airplane

1989-04-01
891039
Airplane flight tests have been conducted to determine the effects of wing leading-edge modifications and a ventral fin addition on the spin resistance of a typical high-wing, single-engine, general aviation airplane. Drooped wing leading-edge modifications which improve lateral stability at high angles of attack were tested in combination with a ventral fin that improves directional stability. Each modification was evaluated using spin resistance criteria which have been proposed for incorporation into the Federal Aviation Regulations for certification of light aircraft. The best configuration tested, a combination of outboard wing leading-edge droop and a ventral fin, provided a very significant increase in overall airplane spin resistance, but was not sufficient to satisfy all requirements of the spin resistance criteria.
Technical Paper

Theoretical Investigation for the Effects of Sweep, Leading-Edge Geometry, and Spanwise Pressure Gradients on Transition and Wave Drag at Transonic, and Supersonic Speed with Experimental Correlations

1988-10-01
881484
The results of a design study of a Hybrid Laminar Flow Control (HLFC) wing at transonic speed and correlative studies for finite, swept supersonic wings are discussed in this paper. Transonic HLFC wing was designed such as to obtain laminar laminar flow on the the wing upper surface for X/C of 0.6 and with suction applied from the leading edge to 60% of the chord and with suction applied from just aft of the leading edge to twenty-five percent of the chord. New theoretical methods have been recently developed for predicting pressure distributions, supersonic wave drag and transition location for finite swept wings at transonic and supersonic Mach number conditions and are illustrative computations are given. Results for laminar and turbulent boundary-layer parameters consisting of the displacement effects and skin friction drag are also presented.
Technical Paper

Spin-Up Studies of the Space Shuttle Orbiter Main Gear Tire

1988-10-01
881360
One of the factors needed to describe the wear behavior of the Space Shuttle Orbiter main gear tires is their behavior during the spin-up process. An experimental investigation of tire spin-up processes was conducted at the NASA Langley Research Center's Aircraft Landing Dynamics Facility (ALDF). During the investigation, the influence of various parameters such as forward speed and sink speed on tire spin-up forces were evaluated. A mathematical model was developed to estimate drag forces and spin-up times and is presented. The effect of prerotation was explored and is discussed. Also included is a means of determining the sink speed of the orbiter at touchdown based upon the appearance of the rubber deposits left on the runway during spinup.
Technical Paper

Boundary-Layer Control for Drag Reduction

1987-11-13
872434
Although the number of possible applications of boundary-layer control is large, a discussion is given only of those that have received the most attention recently at NASA Langley Research Center to improve airfoil drag characteristics. This research concerns stabilizing the laminar boundary layer through geometric shaping (natural laminar flow, NLF) and active control involving the removal of a portion of the laminar boundary layer (laminar flow control, LFC) either through discrete slots or a perforated surface. At low Reynolds numbers, a combination of shaping and forced transition has been used to achieve the desired run of laminar flow and control of laminar separation. In the design of both natural laminar flow and laminar flow control airfoils and wings, boundary layer stability codes play an important role. A discussion of some recent stability calculations using both incompressible and compressible codes is given.
Technical Paper

Tollmien-Schlschfing Instabilities in Laminar Flow In-Flight Detection of

1987-09-01
871016
The ability of modern airplane surfaces to achieve laminar flow over a wide range of subsonic and transonic cruise flight conditions has been well-documented in recent years. Current laminar flow flight research conducted by NASA explores the limits of practical applications of laminar flow drag reduction technology. Past laminar flow flight research focused on measurements of transition location, without exploring the dominant instability(ies) responsible for initiating the transition process. Today, it is important to understand the specific causes(s) of laminar to turbulent boundary layer transition. This paper presents results of research on advanced devices for measuring the phenomenon of viscous Tollmien-Schlichting (T-S) instability in the flight environment. In previous flight tests, T-S instability could only be inferred from theoretical calculations based on measured pressure distributions.
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