Patent Application
20210356306
The present the invention pertains to measurement of flow, and, more specifically, a technique for measuring high speed particles.
Atomic tagging velocimetry is a measurement technique that enables high-fidelity measurement of fluid flows. Current applications include measurement of supersonic and hypersonic fluid flows.
There are a few known methods of performing atomic tagging velocimetry. Universal to all of these is seeding a base fluid flow with a trace amount of a noble gas so as to not disturb the flow. Methodologies for making velocity measurements in fluid flows include pressure-based measurement, thermal anemometry, and particle-based techniques such as laser-Doppler velocimetry, global-Doppler velocimetry, and particle image velocimetry (M). The measurement of velocity with pressure-based and thermal anemometry methods is refined in that such methods consistently yield data with low uncertainty; however, these techniques are intrusive, which eliminates them as candidates in certain flow regimes. With respect to PIV, in particular, at high Mach number, the particles do not track the flow of the measured fluid, making any associated measurement inaccurate. Pitot probes are another option, which indirectly measure velocity by way of making pressure measurements. However, frequency response, spatial resolution, and the extent of the required assumptions regarding the local temperature constitute limitations. Particle-based methods of velocimetry, especially PIV, can produce high-quality, multi-component velocity data; in addition, PIV can yield field information about vorticity and pressure after further data processing. However, the limitations of implementing particle-based techniques in high-speed facilities include timing issues associated with particle injection and reduced particle response at Knudsen and Reynolds numbers typical of high-speed wind tunnels.
The present invention relates to a methodology and system for making non-contact velocity measurements. The methods of the present invention are particularly well-adapted for velocity measurement in supersonic and hypersonic wind tunnels. Fundamentally, atomic tagging velocimetry addresses the particle lag response problem outlined above, as experienced by particle-based techniques in flows at supersonic and hypersonic Mach number speeds, which tends to result in failure of the seeded particles to properly track the flow.
Atomic tagging velocimetry is different from molecular tagging velocimetry mainly because of the agent being tagged: an atom as opposed to a molecule. The method of the present invention utilizes an atomic tracer as opposed to a molecular tracer. In contrast to previous techniques, the signal-to-noise ratio is higher and the tracer is inert making it safe to handle in the lab. While prior techniques, such as FLEET (i.e., molecular tagging velocimetry) do not require the seeding of a noble gas, the signal tends to be weaker than with the methods of the present invention.
Fundamentally, the present invention represents a promising opportunity for technological advancement. With this process, fluid mechanical phenomena that were previously inaccessible may be explored in depth.
The process to measure fluid velocity, which could be conducted in a wind-tunnel or another enclosed space, involves introducing inert tracer atoms into a fluid, such as atoms of a noble gas (e.g., Krypton, Argon, etc.), exciting a write line of atoms with a laser or other suitable means, imaging the write line (e.g., with a charge-coupled device camera) as a first image, waiting for a predetermined delay period (e.g., from about 500 ns to 2 about μs) such that said write line translates in the enclosed space and becomes a read line, imaging the read line (e.g., via an equivalent CCD camera or through other means) as a second image, and calculating the fluid velocity by comparing the first and second images.
Alternatively the process to measure fluid velocity can involve introducing inert tracer atoms into a fluid, exciting a write line of atoms, imaging the write line as a first image, waiting for a predetermined delay period (e.g., from about 500 ns to 2 about μs) such that the write line translates in space, re-exciting the translated write-line (e.g., with a laser) such that the translated write line becomes a read line, imaging the read line as a second image, and calculating the fluid velocity by comparing the first and second images. The inventive techniques enable the measurement of even supersonic and hypersonic fluid speeds in wind tunnels.
For a better understanding of the present invention, reference is made to the following detailed description of various exemplary embodiments considered in conjunction with the accompanying drawings, in which like structures are referred to by the like reference numerals throughout the several views, and in which:
Reference will now be made to several embodiments of the present invention(s), examples of which are illustrated in the accompanying figures. Wherever practicable similar or like reference numbers may be used in the figures and may indicate similar or like functionality. The figures depict embodiments of the present invention for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the invention described herein.
All terms defined herein should be afforded their broadest possible interpretation, including any implied meanings as dictated by a reading of the specification as well as any words that a person having skill in the art and/or a dictionary, treatise, or similar authority would assign thereto. The term “write line” as used herein refers to a given population of excited atoms. Likewise, the term “read line” refers to the write line atoms translated in space and/or re-excited.
The terms, “for example”, “e.g.”, “optionally”, as used herein, are intended to be used to introduce non-limiting examples. The phrases “in one embodiment” and “in some embodiments” as used herein do not necessarily refer to the same embodiment(s), though they may. Furthermore, the phrases “in another embodiment” and “in some other embodiments” as used herein do not necessarily refer to a different embodiment, although they may. Thus, as described below, various embodiments of the invention may be readily combined, without departing from the scope or spirit of the invention.
In addition, as used herein, the term “or” is an inclusive “or” operator, and is equivalent to the term “and/or,” unless the context clearly dictates otherwise. The term “based on” is not exclusive and allows for being based on additional factors not described, unless the context clearly dictates otherwise. In addition, throughout the specification, the meaning of “a,” “an,” and “the” includes plural references. The meaning of “in” includes “in” and “on.” In addition, the terms “comprises” and “comprising” when used herein specify that certain features are present in that embodiment, however, this phrase should not be interpreted to preclude the presence or addition of additional steps, operations, features, components, and/or groups thereof.
Before describing the aforementioned figures, it should be noted that the use of atomic noble-gas species for diagnostics is unique because such species are nominally thermochemically inactive at atmospheric or typical high-speed, wind-tunnel flow conditions. In addition, such species are safe and able to be implemented in practice, given that they do not distort the mean flow of interest when introduced in dilute concentrations. That is, there is the potential for implementation in flows where the thermochemical state of the gas or fluid is difficult to prescribe or predict.
Turning now to the figures themselves,
In a second exemplary embodiment, the method for velocimetry in a fluid of interest also performs step 12 (i.e., the seeding of noble gas tracer atoms in the fluid). As in the first exemplary embodiment, these atoms are then tagged with laser system 16 to form a “write line” of excited atoms. A camera, which can be the same camera 18 described above, is then used to image the “write line” as a first image. Following a brief time delay (e.g., 500 ns to 2 us), the “write line” will have been translated as a result of motion of the fluid. At this point in time, the atoms of the translated “write line” are re-excited by laser system 16 in order to obtain a “read line.” This “read line” is imaged by the camera 18 to generate a second image. As a result of post-processing performed on the two images, the translation of the “write line” can be calculated and data 20 generated to determine the velocity of the fluid. While the re-excitation step may be more complex in implementation relative to the previous method described above, it is expected that the signal (i.e., “read line”) will be more prominent.
Table 1 (see below) is a table listing various physical properties associated with the energy level transitions depicted in
It will be understood that the embodiments described hereinabove, are merely exemplary and that a person skilled in the art may make many variations and modifications without departing from the spirit and scope of the present invention. For example, it should be noted that the aforementioned methods are not confined to high-speed (e.g., Mach 1 or greater) flows and are also applicable to slow-moving fluids.
This application claims priority to U.S. Provisional Patent Application No. 63/024,344 filed May 13, 2020, the entire disclosure of which is incorporated herein by reference.
This invention was made with government support under Grant Numbers FA9550-16-1-0262, FA9550-15-1-0325, FA9550-18-1-0403, and FA9550-19-1-0182 awarded by the Air Force Office of Scientific Research (USAF/AFOSR); N00014-20-1-2637, N00014-20-1-2682, and N00014-20-1-2549 awarded by the Office of Naval Research; and FA2487-19-C-0013 and FA9101-17-P-0094 awarded by Air Force Small Business Innovation Research. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63024344 | May 2020 | US |
