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  • 1
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    Hot-film system for transition detection in cryogenic wind tunnels (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: It is well known that the determination of the location of boundary-layer transition is necessary for the correct interpretation of aerodynamic data in transonic wind tunnels. In the late 1970s the Douglas Aircraft Company developed a vapor deposition hot-film system for transition detection in cryogenic wind tunnels. Tests of the hot-films in a low-speed tunnel demonstrated the ability to obtain on-line transition data with an enhanced simultaneous hot-film data acquisition system. The equipment design and specifications are described.
    Keywords: RESEARCH AND SUPPORT FACILITIES (AIR)
    Type: Research in Natural Laminar Flow and Laminar-Flow Control, Part 2; p 358-376
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Advanced measurement techniques, part 1 (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: In modern laminar flow flight and wind tunnel research, it is important to understand the specific cause(s) of laminar to turbulent boundary layer transition. Such information is crucial to the exploration of the limits of practical application of laminar flow for drag reduction on aircraft. The process of transition involves both the possible modes of disturbance growth, and the environmental conditioning of the instabilities by freestream or surface conditions. The possible modes of disturbance growth include viscous, inviscid, and modes which may bypass these natural ones. Theory provides information on the possible modes of disturbance amplification, but experimentation must be relied upon to determine which of those modes actually dominates the transition process in a given environment. The results to date of research on advanced devices and methods used for the study of transition phenomena in the subsonic and transonic flight and wind tunnel environments are presented.
    Keywords: AERODYNAMICS
    Type: Research in Natural Laminar Flow and Laminar-Flow Control, Part 2; p 317-340
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    NASA TECHNICAL REPORTS
  • 3
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    Boundary layer measurements using hot-film sensors (1986)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Measurements in the aerodynamic boundary layer using heat transfer, hot-film sensors are receiving a significant amount of effort at the Langley Research Center. A description of the basic sensor, the signal conditioning employed, and several manifestations of the sensor are given. Results of a flow reversal sensor development are presented, and future work areas are outlined.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Laminar Flow Aircraft Certification; p 141-153
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Convective response of a wall-mounted hot-film sensor in a shock tube (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Shock tube experiments were performed in order to determine the response of a single hot-film element of a sensor array to transiently induced flow behind weak normal shock waves. The experiments attempt to isolate the response due only to the change in convective heat transfer at the hot-film surface mounted on the wall of the shock tube. The experiments are described, the results being correlated with transient boundary layer theory and compared with an independent set of experimental results. One of the findings indicates that the change in the air properties (temperature and pressure) precedes the air mass transport, causing an ambiguity in the sensor response to the development of the velocity boundary layer. Also, a transient, local heat transfer coefficient is formulated to be used as a forcing function in an hot-film instrument model and simulation which remains under investigation.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Old Dominion Univ., New Devices for Flow Measurements: Hot Film and Burial Wire Sensors, Infrared Imagery, Liquid Crystal, and Piezo-Electric Model; 6 p
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  • 5
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    Active thermal isolation for temperature responsive sensors (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The detection of flow transition between laminar and turbulent flow and of shear stress or skin friction of airfoils is important in basic research for validation of airfoil theory and design. These values are conventionally measured using hot film nickel sensors deposited on a polyimide substrate. The substrate electrically insulates the sensor and underlying airfoil but is prevented from thermally isolating the sensor by thickness constraints necessary to avoid flow contamination. Proposed heating of the model surface is difficult to control, requires significant energy expenditures, and may alter the basic flow state of the airfoil. A temperature responsive sensor is located in the airflow over the specified surface of a body and is maintained at a constant temperature. An active thermal isolator is located between this temperature responsive sensor and the specific surface of the body. The total thickness of the isolator and sensor avoid any contamination of the flow. The temperature of this isolator is controlled to reduce conductive heat flow from the temperature responsive sensor to the body. This temperature control includes (1) operating the isolator at the same temperature as the constant temperature of the sensor; and (2) establishing a fixed boundary temperature which is either less than or equal to, or slightly greater than the sensor constant temperature. The present invention accordingly thermally isolates a temperature responsive sensor in an energy efficient, controllable manner while avoiding any contamination of the flow.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
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  • 6
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    Active thermal isolation for temperature responsive sensors (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A temperature responsive sensor is located in the airflow over the specified surface of a body and is maintained at a constant temperature. An active thermal isolator is located between this temperature responsive sensor and the specified surface of the body. The temperature of this isolator is controlled to reduce conductive heat flow from the temperature responsive sensor to the body. This temperature control includes: (1) operating the isolator at the same temperature as the constant temperature of the sensor and (2) establishing a fixed boundary temperature which is either less than or equal to or slightly greater than the sensor constant temperature.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
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  • 7
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    Crossflow vorticity sensor (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A crossflow vorticity sensor for the detection of crossflow vorticity characteristics is described. The sensor is comprised of crossflow sensors which are noninvasively adhered to a swept wing laminar surface either singularly, in multi-element strips, in polar patterns, or in orthogonal patterns. These crossflow sensors are comprised of hot-film sensor elements which operate as a constant temperature anemometer circuit to detect heat transfer rate changes. Accordingly, crossflow vorticity characteristics are determined via cross-correlation. In addition, the crossflow sensors have a thickness which does not exceed a maximum value h in order to avoid contamination of downstream crossflow sensors.
    Keywords: AERODYNAMICS
    Format: application/pdf
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  • 8
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    Use of piezoelectric foil for flow diagnostics (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: A laboratory investigation was conducted to characterize two piezoelectric-film sensor configurations, a rigidly mounted sensor and a sensor mounted over an air cavity. The sensors are evaluated for sensitivity and frequency response, and methods to optimize data are presented. The cavity-mounted sensor exhibited a superior frequency response and was more sensitive to normal pressure fluctuations and less sensitive to vibrations through the structure. Both configurations were sensitive to large-scale structural vibrations. Flight-test data are shown for cavity-mounted sensors, illustrating practical aspects to consider when designing sensors for application in such harsh environments. The relation of the data to skin friction and maximum shear stress, transition detection, and turbulent viscous layers is derived through analysis of the flight data.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: ICIASF ''89; Sept. 18-21, 1989; Goettingen; Germany
    Format: text
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    NASA TECHNICAL REPORTS
  • 9
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    A transition detection study at Mach 1.5, 2.0, and 2.5 using a micro-thin hot-film system (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: A boundary-layer transition detection study was conducted in the NASA Langley unitary plan wind tunnel with an array of microthin hot films on a flat plate at Mach numbers 1.5, 2.0, and 2.5 and Reynolds numbers (1.0-4.5) x 10 to the 6th/ft. Transition locations were obtained online from the variation of normalized rms voltages from an array of hot-film sensors for both natural transition and a grit-induced wedge of turbulence. The effects of Mach number and Reynolds number on the location and length of the transition region for the two types of transition are presented from the online data. Also shown are the unit Reynolds number effects on transition Reynolds number, voltage-versus-time traces, spectra, and the data-acquisition system.
    Keywords: RESEARCH AND SUPPORT FACILITIES (AIR)
    Type: ICIASF ''89; Sept. 18-21, 1989; Goettingen; Germany
    Format: text
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  • 10
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    Transition detection studies in the cryogenic environment (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Boundary-layer transition detection studies were carried out in the 0.3 Meter Transonic Cryogenic Tunnel on a supercritical airfoil, using an infrared imaging system. The purpose of the experiments was to determine the extent of the temperature range in which commercially available IR systems can detect transition in cryogenic environment. The experiment was designed to take advantage of a combination of factors including the wind tunnel operation mode, the model construction materials and the IR system image processing options. During the initial phases of the study, the IR based findings were confirmed by measurements done with a micro-thin hot-film system. Ultimately, free and forced transition could be detected down to 170 K.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: AIAA PAPER 90-3024 , AIAA Applied Aerodynamics Conference; Aug 20, 1990 - Aug 22, 1990; Portland, OR; United States
    Format: text
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