Optics: measuring and testing – Velocity or velocity/height measuring – With light detector
Reexamination Certificate
2002-11-01
2004-07-13
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Velocity or velocity/height measuring
With light detector
C356S028500
Reexamination Certificate
active
06762827
ABSTRACT:
The present invention relates to an optical probe adapted for use in an enclosed space, for example, a cavity to allow measurement of features such as flow rate, particle size and concentration of substances contained in the space. It is especially, but not exclusively, concerned with PIV. It is concerned with planar light sheet anemometers (PLSA), especially with miniature PLSA's.
Conventional cavity inspection devices (or devices for use in confined spaces) have allowed images to be taken/the cavity to be visualised and include endoscopes having a number of prisms and mirrors which conduct white light from a source into a cavity. The prior art endoscopes allow the user to see what is in the cavity with the naked eye or can be used in combination with a camera allowing visualisation of the cavity on a screen or a photograph.
Conventional fluid flow analysis systems such as Laser Doppler Anemometers (LDA), Particle Image Velocimeters (PIV) and Phase Doppler Anemometers (PDA) are large and when it is desired to obtain flow information in a confined space are incapable of obtaining a wide enough range of information sought, and are practically impossible to use due to the lack of optical access available in enclosed cavities (e.g. in the bearing chamber of an aero-engine).
It would therefore be beneficial in a wide variety of fields, including engineering and medicine, to have a probe system which may or may not allow the visualisation of the inside of an enclosed cavity, but more importantly allows measurements to be taken relating to the contents of the cavity, for example for a fluid-containing cavity, the particle velocity, the particle size, and particle concentration, of the fluid in the cavity.
The present invention originated from work in the field of Particle Imaging Velocimetry (PIV). Particle Image Velocimetry (PIV) benefited from the development of LDV (Laser Doppler Velocimetry) and constitutes an answer to the need for Whole Field measurements. It was developed in the late 1970's, was practically implemented in the early 1980's, and its use started to spread in the late 1980's. It is now a developed technique. The advantages of this type of measurement system are found in many domains: when using intermittent facilities flowfields may be measured without assuming perfect repeatability of testing conditions; in many instances testing times are much shorter than with other methods of flow/fluid measurement; and these techniques allow the access to quantities that were otherwise impossible to determine such as instantaneous vorticity fields. The technique typically images a particle at two different times and establishes the velocity of the particle by evaluating the images to establish how far the particle has travelled in a known time.
Particle Image Velocimetry and Laser Induced Fluorescence (LIF) are based, like Laser Doppler Velocimetry, on the measurement of the velocity of tracer particles carried by the fluid. However, rather than concentrating light in a small probe volume (as in LDV), a complete plane of the flow under investigation is illuminated in PIV and LIF. This is performed by creating a narrow light sheet which is spread over the region of interest, the sheet illuminating an isolated 2-D plane of interest. Tracer particles are therefore made visible and images of the illuminated particles are recorded. These recordings will typically either contain successive images of single tracers in time or successive frames of instantaneous images of the whole flowfield. The displacement of the tracer will then be determined through the analysis of these records.
PIV systems are known for providing information on a fluid in a confined space which have a first probe which comprises an emitter optically coupled to a laser and designed to emit a sheet of laser light, and a second probe, spaced apart from the first probe, and comprising a detector/receiver designed to detect scattered laser light and provide signals to a computer. The spacing between the emitter and the detector needs to be accurately controlled, as does their relative angular orientation and relative position.
Laser-induced fluorescence (LIF) imaging is another imaging technique which uses a sheet of light. It relies on the quantum nature of molecules and atoms, whereby energy transitions can only occur between certain quantized energy states. A diatomic molecule can have several modes of quantum energy. The three relevant to LIF Studies are electronic, vibrational and rotational. The first mode, the electronic state, is usually denoted by letter, with X being the lowest (ground) electronic state, A being the first excited state, B the second, etc. The molecule also has vibrational energy, denoted by the vibrational quantum number v, having integer values starting with 0. The third energy state is the rotational energy, denoted by the rotational quantum number J. Only certain energy transitions are allowed by the selection rules of quantum physics. A molecule in a low energy state can only be optically pumped up to a higher energy state by interaction with a photon of energy exactly equal to the energy difference between allowed energy states of the molecule, and an excited molecule can only relax by giving up a quantum of energy equal to the difference between allowed energy states, either by emission of a photon, or by collision with a neighbouring molecule.
Laser-induced fluorescence takes advantage of this phenomenon by optically exciting a species with photons of a frequency matching an allowable level difference of the species being probed. It should be noted that different species tend to have different energy transitions, so it is generally possible to chose a transition for a given species that is well isolated from possible transitions of other species that may be present. The resulting fluorescence caused as excited molecules relax by photon emission can be collected and analysed to determine local species concentration and/or temperature.
Laser-induced fluorescence utilises a sheet of laser light generated by a tunable laser source to illuminate a two dimensional plane through the sample, and uses a sensitive intensified CCD camera arranged at 90° to the sheet of light to image the resulting fluorescence from the illuminated area. The processing of the acquired images is similar to PIV except for the additional filters and detectors for phase separation. There are several variations of the principle; namely LIF, PLIF (Planar Laser Induced Fluorescence), MLIF (Mixing Measurements using Laser Induced Fluorescence) etc.
In some PIV/LIF measurements it is necessary to move the sheet of light, and also move the detector in a corresponding manner so as to ensure optimum detection for the new position of the sheet of light. Careful alignment of the emitter and detector at their second (and subsequent) positions is also important, but critical to the measurement process.
When, for example, measuring lubricant (oil) parameters in a working engine (e.g. a working test-bed aeroplane engine) such as a turbine jet, it is necessary to put two probes (emitter and detector) into the fluid flow.
This disrupts the flow away from what it is in use, without the probes. Of course, the size of the probes is kept small in the prior art, and the tests are performed with the probes in different positions to see how that effects the results.
According to a first aspect of the invention we provide an endoscopic optical fluid measurement probe assembly comprising an endoscope having a user end and a distal end, the distal end having a light emitter and a reflected light acquirer; and the endoscope being provided with transmission means to transmit information away from the distal end.
Thus, a single probe both emits light and detects light reflected by the fluid: both serves as emitter and data acquirer. This reduces the disruption in comparison with traditional two-probe PLSA systems. A single probe can also get into smaller spaces than can two probes and yield minimal intrusion.
Preferably t
Aroussi Abdelwahab
Menacer Mohamed
Baker & Botts L.L.P.
Buczinski Stephen C.
The University of Nottingham
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