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  • Other Sources  (33)
  • 1
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    Laser velocimetry measurement in a transonic tunnel (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Some preliminary velocity measurements were carried out inside the transonic tunnel using the laser velocimeter (LV) system in association with the smoke generator. Pressure measurements were also performed using a pressure tap located on the side wall of the test section slightly upstream of the windows. Though the pressure measurements and the LV measurements were not taken at exactly the same location, extrapolation of the pressure data into the location of the LV measurements indicated a very close agreement between the velocity values obtained using the two different methods. Thus it is believed that the smoke particle is following the air flow with little or no velocity slip. Velocity measurements with airfoil at various angles of attack are now being carried out in conjuction with schlieren flow visualization. In the near future pressure distribution around and on the airfoil will be obtained by putting pressure taps on the side windows and using a pressure tap model (currently under construction) of the airfoil.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA. Langley Research Center Wind Tunnel Seeding Systems for Laser Velocimeters; p 141-148
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  • 2
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    Experimental determination of the laminar separation bubble characteristics on an airfoil at low Reynolds numbers (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An experimental investigation was conducted in order to document the structure and behavior of laminar separation bubbles at low Reynolds numbers. Data of this type is necessary if the currently insufficient analytical and numerical models are to be improved. The laminar separation bubble which forms on a NACA 66(3)-018 airfoil model was surveyed at chord Reynolds numbers ranging from 50,000 to 200,000 at angles of attack from 8 to 12 degrees. The effects of the various testing conditions on the separation bubble were isolated, and the data was analyzed in relation to existing separation bubble correlations in order to test their low Reynolds number applicability. This analysis indicated that the chord Reynolds number and the disturbance environment strongly influence the experimental pressure distributions. These effects must be included in any analytic prediction technique applied to the low Reynolds number flight regime.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 86-1065
    Format: text
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  • 3
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    An analysis of a separation bubble transition criterion at low Reynolds numbers (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Factors which influence the criterion governing the length of the laminar region of a separation bubble on an airfoil at low Re were investigated. The criterion is the onset of separation when a critical Re value is surpassed. Wind tunnel data were gathered for the flow around a NACA 66(3)-018 airfoil at Re from 50,000-200,000. The data were taken with either hot-wire anemometers or pressure taps. The value of the critical Re was influenced by the chord Re, the angle of attack and the level of turbulence in the free stream. However, the turbulence levels examined, up to 0.184 percent, did not greatly affect the critical Re. Further characterizations of the effects of the three factors on the critical Re are necessary before the important features of separation bubbles can be identified with an acceptable level of certainty.
    Keywords: AERODYNAMICS
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  • 4
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    Conference on Low Reynolds Number Airfoil Aerodynamics, Notre Dame, IN, June 16-18, 1985, Proceedings (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Topics of interest in the design, flow modeling and visualization, and turbulence and flow separation effects for low Reynolds number (Re) airfoils are discussed. Design methods are presented for Re from 50,000-500,000, including a viscous-inviscid coupling method and by using a constrained pitching moment. The effects of pressure gradients, unsteady viscous aerodynamics and separation bubbles are investigated, with particular note made of factors which most influence the size and location of separation bubbles and control their effects. Attention is also given to experimentation with low Re airfoils and to numerical models of symmetry breaking and lift hysteresis from separation. Both steady and unsteady flow experiments are reviewed, with the trials having been held in wind tunnels and the free atmosphere. The topics discussed are of interest to designers of RPVs, high altitude aircraft, sailplanes, ultralights and wind turbines.
    Keywords: AERODYNAMICS
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  • 5
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    The structure of separated flow regions occurring near the leading edge of airfoils including transition (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A semi-empirical method for predicting separation bubble characteristics was evaluated using low Reynolds number test data. On the basis of this data, several observations were made. First, a sizable growth in the momentum thickness can occur in the laminar portion of a separation bubble. This is in direct contrast to the theory and is apparently due to low Reynolds number effects. Secondly, the transition Reynolds number (R sub l sub 1) which governs the extent of a bubble's laminar region, was found to be much lower than that used in the method. At present, there does not seem to be any evidence supporting a single value for R sub l sub 1. Apparently, R sub l sub 1 is affected by the freestream disturbance environment, and airfoil's pressure distribution, and possibly the chord Reynolds number as well. Thirdly, the growth in momentum thickness over a bubble's turbulent region was predicted reasonably well by the method, provided that Roberts' suggested value for the mean dissipation coefficient was used. Finally, the present data does not substantiate the universality of the velocity profile at reattachment. However, measurement error may be responsible for this result.
    Keywords: AERODYNAMICS
    Type: NASA-CR-176857 , NAS 1.26:176857
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  • 6
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    The influence of laminar separation and transition on low Reynolds number airfoil hysteresis (1985)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 763-770
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  • 7
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    Experimental studies of the boundary layer on an airfoil at low Reynolds numbers (1983)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: An experimental wind tunnel investigation was carried out to study the effect of laminar separation bubbles on a NACA 66(3)-018 airfoil for Reynolds numbers less than 4.0 x 10 to the 5th. Leading edge laminar separation bubbles formed for angles of attack of approximately 7 to 12 deg. To study the leading edge separation bubble more closely, hotwire anemometer measurements were made in the airfoil a Reynolds number of 8.0 x 10 to the 4th. Velocity and turbulence intensity profiles were obtained and boundary layer parameters were calculated. Frequency spectra were also calculated at key points in the airfoil boundary layer for this case. Correlation of the anemometry data with static pressure distributions, and flow visualization data provided insight into laminar separation bubble behavior at low Reynolds numbers.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 83-1671
    Format: text
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  • 8
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    The influence of free-stream disturbances on low Reynolds number airfoil experiments (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The results of an investigation of the influence of free stream disturbances on the lift and drag performance of the Lissaman 7769 airfoil are presented. The wind tunnel disturbance environment is described using hot-wire anemometer and sound pressure level measurements. The disturbance level is increased by the addition of a 'turbulence screen' upstream of the test section and/or the addition of a flow restrictor downstream of the test section. For the Lissaman airfoil it was found that the problems associated with obtaining accurate wind tunnel data at low chord Reynolds numbers (i.e., below 200,000) are compounded by the extreme sensitivity of the boundary layers to the free stream disturbance environment. The effect of free stream disturbances varies with magnitude, frequency content, and source of the disturbance.
    Keywords: AERODYNAMICS
    Type: Experiments in Fluids (ISSN 0723-4864); 1; 1 19; 1983
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  • 9
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    Visualization of the laminar separation bubble on airfoils at low Reynolds numbers (1987)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The use of the smoke tube and titanium tetrachloride techniques in the study of low Reynolds number flow about two different airfoils is presented. Emphasis is placed on the problems of determining the characteristics of laminar separation bubbles occurring on the Wortmann FX63-137 airfoil and the NACA 66(3)-018 airfoil. Comparisons are made with the hot-wire technique and the use of kerosene vapor.
    Keywords: AERODYNAMICS
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  • 10
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    The influence of laminar separation and transition on low Reynolds number airfoil hysteresis (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: An experimental study of the Lissaman 7769 and Miley MO6-13-128 airfoils at low chord Reynolds numbers is presented. Although both airfoils perform well near their design Reynolds number of about 600,000, they each produce a different type of hysteresis loop in the lift and drag forces when operated below chord Reynolds numbers of 300,000. The type of hysteresis loop was found to depend upon the relative location of laminar separation and transition. The influence of disturbance environment and experimental procedure on the low Reynolds number airfoil boundary layer behavior is also presented. The use of potential flow solutions to help predict how a given airfoil will behave at low Reynolds numbers is also discussed.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 84-1617
    Format: text
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