This optical velocimeter may be installed in an aircraft to measure the true airspeed and the angles of attack and of sideslip of the aircraft. Alternatively, the velocimeter may be mounted in a wind tunnel to measure the velocity of the airstream passing through the wind tunnel. In either case, the points of reference for measurement are the large number of aerosol particles that are entrained in the air and are assumed to have the same velocity as the oxygen and nitrogen molecules of the air itself. The velocimeter comprises a plurality of optical transmitters and optical receivers. Each transmitter includes a laser operated in the continuous-wave mode and a laser operated in the pulsed mode. The laser operated in the continuous-wave mode generates a "precursor light sheet" at some distance from the aircraft whose velocity is to be measured or in the wind-tunnel airstream whose velocity is to be measured. When an aerosol particle intercepts the precursor light sheet, the laser operating in the pulsed mode, after a suitable time delay, generates a "first successor light sheet," which is in turn intercepted by the aerosol particle. The time of such interception is registered and initiates a delay period for passage of the aerosol particle to intercept "a second successor light sheet", also generated by the laser operated in the pulsed mode. The interception by the aerosol particle of the precursor light sheet and then in turn the two successor light sheets causes scintillations which propagate light back to the aforementioned receivers in the velocimeter. The receivers and their associated electronic circuitry record the time of passage of the aerosol particle between the two successor light sheets, as a first measure of the velocity of the aircraft with respect to the particles, or of the particles with respect to some fixed benchmark. By having a plurality of transmitters forming pairs of light sheets, such pairs being neither parallel nor orthogonal to one another, it is possible to resolve the components of motion of the respective aerosol particles and to recombine the resolved components to compute the vector components of the true velocity of the aircraft with respect to its own coordinate system. Certain other computations enable determination of the angle of attack and the angle of sideslip, if any, of the aircraft. Still further, this velocimeter calculates the Mach rate of the aircraft. These calculated outputs are then used as inputs to the control system for the aircraft, which may be inherently unstable and completely dependent upon such control inputs.
The present invention provides a system, including apparatus and method, using a National Bureau of Standards (NBS) traceable laser velocimeter for in situ calibration of a traversing static pressure probe used to determine a velocity distribution in an air metering bellmouth for testing aircraft gas turbine engines. The invention is particularly useful for large fan-jet engines may be used to calibrate rake mounted probes capable of wall-to-wall stream static pressure survey measurements.
A velocimeter measures flow characteristics of a flow travelling through a chamber in a given direction. Tracer particles are entrained in the flow and a source of radiant energy produces an output stream directed transverse the chamber and having a sufficient intensity to vaporize the particles as they pass through the output stream. Each of the vaporized particles exploding to produce a shock wave and a hot core, and a flow visualization system tracks the motion of the hot cores and shock waves to thereby measure velocity of each tracer particle, and temperature of the flow around the tracer.
An optical design for delivering or receiving light from a fluid being measured is disclosed. The optical design is capable of immersion in the fluid being measured, and is capable of operating with fluids that have a different index of refraction. The optical design includes a solid prism of optical material to which a fiber optic attaches by a suitable adhesive. In an optical delivery system, light from the fiber enters the prism and reflects off an internal mirror to a second internal reflective surface. The second internal reflective surface focuses the light to a fixed point through an exit surface of the prism. The second internal reflective surface may in the shape of an ellipse, or may comprise a diffractive surface. The exit surface has a spherical concave shape that is centered on the fixed point where the light is focused, so that light passes through the exit surface at substantially ninety degrees. In an optical collection system, light from a point enters the prism at an entry surface, that is spherically concave so that light passes through the entry surface at substantially ninety degrees. Light then reflects from a first internal reflective surface that may be a diffractive lens or an elliptically shaped lens, to thereby focus the light received from the point. Light reflecting from the first internal reflective surface is received at a second mirrored surface, where the light is reflected to the base of the prism, where the fiber optic attaches.
A PIV system provides a bias velocity component to each flow field speckle pattern recorded on a video array by rastering each corresponding recorded electrical image pattern by a select number of raster lines in the time interval prior to recording a succeeding speckle pattern image, thereby providing a calibrated spatial offset between recorded images.
The present invention provides an optical device for the measurement of flow rates of fluid through a pipe. The device broadly comprises a narrow frequency light source, an optical delivery system, a collector for light scattered from particles in the fluid, and a photo detector. In a preferred embodiment, the optical delivery system and the collector are contained within the pipe.
