Optics: measuring and testing – By light interference – Using fiber or waveguide interferometer
Reexamination Certificate
2000-10-18
2003-10-21
Rosenberger, Richard A. (Department: 2877)
Optics: measuring and testing
By light interference
Using fiber or waveguide interferometer
C385S013000, C250S227140, C244S203000
Reexamination Certificate
active
06636320
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to flow separation detectors and, more particularly relates to feedback sensor arrangements adapted to provide for the measurement of surface aerodynamic flow phenomena, and especially with regard to aerodynamic flow separation which is encountered over a surface. Moreover, the invention is also directed to aspects which facilitate the detection of aerodynamic flow separation with a concurrent detection of encountered mechanical strain and stresses in the surface structure being monitored.
Currently, various types of detection or sensor systems are being investigated for their applicability to the technology concerning problems which are being encountered as a consequence of aerodynamic flow separation; for instance, such as during airflow over the wing surfaces of an aircraft, and which may have a important bearing on and potentially adversely influence the performance of the aircraft. For example, some of the systems being investigated provide for a so-called closed-loop control of aerodynamic flow separation, which necessitate the provision of feedback sensors which are sensitive to flow separation, and whereby such sensors are typically required to be surface-mounted on the surface or wall which is subject to aerodynamic flow separation. At this time essentially fully developed and commercially available sensors employed for this purpose are pressure transducers which are capable of measuring surface aerodynamic phenomena and flow separation parameters.
In particular, types of sensors which are adapted for the investigation or measurement of aerodynamic flow separation which takes place on a surface or wall may be so-called electronic “thermal tuft” sensors. Thus, in essence, thermal tuft sensors may be generally constituted of one or more electrical heating elements with temperature sensors being mounted spaced upstream and downstream thereof along the presumed directions of aerodynamic flows passing over a surface. Generally, the flow separation, encountered in at least a two-dimensional flow, is defined by a location wherein the flow proximate a wall over a surface tends to oppose a primary flow direction; pursuant to a phenomenon referred to as a backflow. Thus, the thermal tuft sensors are spacedly mounted in the presumed flow direction. The electrical heating elements are normally pulsed on and off, thereby heating a local packet of fluid providing the aerodynamic flow. Depending upon the local instantaneous direction of the flow, either the upstream or downstream located temperature sensor will detect a rise in temperature as the heated packet of fluid is convected there past. Generally, the pulses are counted as a measure of the percentage of the time during which the flow is either upstream or downstream in its direction. Alternatively, the time internal between the heater element actuation and sensor detection can be recorded as a measure of near-wall upstream or downstream velocity magnitude.
Such electronic “thermal tuft” sensors are extensively described, in an article by Shivaprasad and Simpson entitled “Evaluation of a Wall-Flow Direction Probe for Measurements in Separated Flows”, published in the Journal of Fluid Engineering, 1981. In that instance, a pair of thermal sensors are spaced along a surface whereby a free stream of a fluidic or airflow may have a flow direction extending across the locations of the sensors. A plurality of heaters are interposed between the sensors, and further heaters are arranged offset aside the directional flow so as to be able to determine aerodynamic separation or, in essence, a breakdown of a boundary-layer flow of fluid passing across the surface which may pass either directly across the sensors or at an angle relative thereto. These sensors are electronically connected to the electrical or electronic circuitry of a device which; for example, may be a part of an aircraft electrical operating system.
Although the foregoing thermal tuft sensors are generally satisfactory in operation in detecting flow separation phenomena, they require the input of electrical energy from the electrical components of various devices, or in connection with aircraft from the electrical aircraft system network, thereby representing a source for electrical energy drain and consumption.
More recently, in order to obviate or ameliorate the electrical energy requirements in the provision of feedback sensor arrangements, particularly such which are employed for a closed-loop control of aerodynamic flow separation; for instance, that on the wing of an aircraft wherein there can be encountered a breakdown of a boundary-layer flow which may adversely affect the performance of the aircraft, there has been developed a system of flow separation sensors which are based on fiber optics and which may be employed for separation feedback control. In that connection, reference may be had to the copending Wetzel, et al. U.S. patent application Ser. No. 09/396,472, now U.S. Pat. No. 6,380,535, entitled “Optical Tuft for Flow Separation Detection”; commonly assigned to the assignee of the present application, the disclosure of which is incorporated herein by reference. In particular, the sensors which are based on fiber optics may employ an optical tuft arrangement based on the thermal/fluidic principles of the electrical thermal tuft, but with the employing of fiber optics signal and energy transmission instead of electronics. To that effect, the light transmitted through the fiber optics is adapted to be converted into heat enabling a packed of heated fluid to be convected in the direction of a predominant aerodynamic flow, and to impact or contact one of the temperature sensors which are based on fiber optics at a small following time interval, so as to provide the required information concerning aerodynamic flow separation.
Although various other types of sensors have been developed which are based on fiber optics, these are primarily employed for the measurement of strain, acceleration and temperature, and currently there is also known the development of new pressure transducers in the technology. However, none of these sensors in themselves are designed for flow separation detection, particularly for use in the closed-loop control of aerodynamic flow separation, or for investigations of breakdown phenomena in boundary layer flow situations.
SUMMARY OF THE INVENTION
Accordingly, in order to substantially improve upon the current state of the technology, the present invention utilizes the end of an optical fiber as a tuft in itself, and optically transduces the movement of the fiber into a useable signal for flow separation detection.
The invention contemplates for a multitude of tufts to be placed on the surface (e.g., the surface of awing), with the tufts made out of an appropriate optical fiber material. The length of the optical fiber exposed to the airstream should be short, on the order of 0.1 to 1 inches, and the optical fiber should be very fine so as to be flexible, with diameters on the order of 0.001 to 0.01 inches. One embodiment calls for the fibers to be flexible enough to bend 90° or more (thus longer, with a smaller diameter), in which case the large flow fluctuations of a separated flow will result in dramatic tuft motion. Another embodiment calls for the tuft to be relatively stiff (thus shorter, with a larger diameter), in which case the large flow fluctuations of a separation flow will result in large optical fiber stresses.
The length of fiber that is not exposed to the aerodynamic flow can be packaged numerous ways. One embodiment calls for the fibers to be embedded in the skin material of the surface (especially when the skin is made of a cured composite material). Alternatively, the fibers can run inside the structure of the device (e.g., along the internal structure of a wing), and exit the wing surface through holes. Also, the fibers could be embedded in a low-profile tape, which can be applied to the surface, and can thus be easily replaced if damaged i
Furlong Edward R.
Wetzel Todd G.
Barth Vincent P.
Katz Erik R.
Kilpatrick & Stockton LLP
Lockheed Martin Corporation
Rosenberger Richard A.
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