DE3145987A1 - "METHOD AND DEVICE FOR MEASURING THE FLOW VECTORS IN GAS FLOWS" - Google Patents

Description

FROM KREISLER SCHÖNWALD EISHOLD FUES FROM KREISLER KELLER SELTING WERNER

German Research and Experimental Institute for Aviation and space travel e.V.

Linder high
5000 Cologne 90

PATENT LAWYERS Dr.-Ing. by Kreislor + 1973

Dr.-Inn. K, Scnönwaid, Cologne Dr.-Im ,. K. W. E. Shold, Bad Soden Dr. J. F. Fu ". Cologne Dipl.-Chem. Alek von Kreisler, Cologne Dlpl.-Chem. Carola Keller, Cologne Dipl.-Ing. G. Soiling, Cologne Dr. H.-K. Werner, Cologne

DFICHMANNIIAUS AT THE MAIN RAILWAY STATION

D-5000 COLOGNE 1

November 19, 1981 Sg-Fe

Method and device for measuring the flow vectors in gas flows

The invention relates to a method for measuring the flow vectors in gas flows by determination the amount of velocity and the direction of optically detectable particles contained in a flow, in which the parallel rays of a first pair of rays at two closely adjacent ones first focusing points focused and the focusing points on two first photoelectric Implementers are mapped.

In a known method of this type (DE-AS 24 4 9 358) two focusing points are arranged closely one behind the other in a flow channel and these focusing points successively passing particles are imaged on photoelectric converters. A particle that passes the first focussing point generates a start pulse and then when passing the second focussing point a stop pulse. From the time interval between the start impulse and the stop impulse,

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the particle speed can be determined. The direction of flow results from the direction in which the two focussing points are arranged one behind the other in the flow channel. This direction can be changed so that flow vectors with different directions can be detected. In principle, however, applies for the known method that only those components of flow vectors are measured which lie in the plane that is perpendicular to the optical axis of the system. The one running in the axial direction Component cannot be determined. Nevertheless, it is with the known ^ experienced only a two-component speed measurement method .

The invention is based on the object of developing the known method in such a way that the determination of the in Axial direction component of the flow vectors is also possible, so that flow vectors can be recorded completely according to amount and direction, without such a three-component measuring method a greater amount of time is required for the measurements than for the two-component method.

To solve this problem, the invention provides that

a) a second pair of beams, also consisting of beams running parallel to one another, under one Angle to the first pair of beams directed to the first focusing points and focused there will,

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b) the focussing points of the second pair of beams be mapped on two second photoelectric converters,

c) the two pairs of beams together around an optical one Axis are pivoted around, which passes through one of the two focus points and in the plane of the associated rays of the two ray pairs runs,

d) those swivel angles are measured at which for each pair of beams at the converters Signals occur that the passage of particles through the two focussing points of the beam pair specify, and

e) from the measured pivot angles for both beam pairs and the measured frequency value of The vector of the particle speed is determined according to direction and magnitude.

The invention is based on the idea that any vector in space can be detected if initially a plane is determined in which the vector lies, and if the angle of the vector is within this Level and the amount of the vector can be determined. This principle is implemented in that two measuring devices of the known type described above and that with each of these measuring devices The direction and magnitude of that component of the velocity vector are measured independently of one another, those in the plane perpendicular to the respective beam direction

lies. In contrast to the structure of the known measuring device, where the rays run in the direction of the optical axis of the system, the two rays * - pairs according to the invention inclined at an angle to the optical axis and they are each on two measuring points, which define the measuring volume, focused. The measuring volume or the focussing points are in reality not point-shaped, but cylindrical. Your extension in The direction of the beam axes corresponds approximately to twice the distance between the beams. The levels created by the individual rays of the respective pair of rays are spanned, intersect along a straight line (intersection line). When the two pairs of beams are pivoted around the optical axis, this straight line becomes the one perpendicular to the optical axis and passes through one of the focusing points, also pivoted. At a Pivoting therefore remains unchanged at the point of the intersection that lies at the one focussing point. This point of the line of intersection through which the optical axis passes can be used as the zero point of the measuring system regard.

Since, as explained above, the focussing points are not point-shaped, but cylindrical or linear, are not only those particles in the evaluation circuit that pass through two points, but practically all particles that are within a given one Longitudinal section through the rays of a pair of rays go through. So those particles are recorded that move in the plane of a pair of rays. By If the beam pairs are pivoted about the optical axis, the planes of the beam pairs are also pivoted. If one of the planes reaches such a pivoting position that the relevant vector is detected by it, then the passage of particles in

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this level signals. "

A particular advantage of the method according to the invention consists in that the flow vector in the area of the measuring volume can be determined with two search measurements.

This is done by pivoting or rotating the pairs of rays around the optical axis until the Converters of one pair of beams signal the passage of particles. Then the pairs of rays continued to rotate until the converters of the other beam pair register a passage of particles.

From the two swivel angles at which the passage of particles has been registered, on the one hand, determine the vector plane in which the optical axis and the searched vector lie together, and on the other hand also the angle that the vector sought with respect to the optical axis within said Occupies level. The amount of the vector can be calculated using the angles mentioned and the measured frequency of passage be determined. For the exact determination of the three components of any vector in space, so only two search measurements are required.

The beams of the two beam pairs which lie in one plane with the optical axis preferably run at equal angles γ to the optical axis. In principle, it is possible to use both pairs of rays with different To provide alignments to the optical axis of the system and, for example, the one pair of beams parallel to the optical axis and to let the other pair of rays run at an angle to this, but is the Resolution accuracy is greater if both pairs of rays are on different sides of the optical axis.

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For the sake of symmetry and ease of calculation are preferably the angles γ for both pairs of beams on opposite sides of the optical Axis are arranged equal to each other.

This has the advantage that the plane (vector plane) in which the optical axis and the wanted Vector lying, through the relationship

φ =

is determined, where Φ is the angle of the vector plane with respect to the optical axis, φ_ the pivot angle at which transit signals occur at the converters of the first pair of beams, and φ, the swivel angle at which an the converters of the second pair of beams occur through signals.

An apparatus for carrying out the invention The method is characterized in that two beam generating systems are provided, each of which is one Ray pair from parallel rays creates that the plane in which the rays of a ray pair lie, runs at an acute angle to the plane in which the rays of the other pair of rays lie, and that a device is provided for simultaneously rotating the pairs of beams about a common axis. By turning of the pairs of rays is achieved that with a complete revolution the plane of each pair of rays once with the searched vector coincides. This determines the vector plane and at the same time the angle of the vector in the vector plane.

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According to a preferred embodiment of the device it is provided that the beam of a laser in a dichroic beam splitter into two beams with different Colors is divided so that these two beams are fed to a polarization beam splitter, which divides each beam into two parallel, differently polarized beams that the a total of four beams at a distance from the optical axis via a rotating image prism and collecting optics in pairs be directed to the two focusing points and that one directed to the focusing points A lens system separating the pairs of rays from one another and guiding them to different evaluation devices Has facility.

In the following, a preferred embodiment of the invention is explained in more detail with reference to the drawings explained.

Show it:

1 shows a schematic representation of the beam path the measuring device for determining flow vectors,

FIG. 2 is a partial view from the direction of arrow II in FIG. 1,

3 shows a perspective illustration of the beam paths in the measuring volume,

Flg. 4 shows an enlarged representation of the measuring volume and

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5 shows a graphic representation of the measurement angle 2φ as a function of the angle β of the vector within the vector plane.

According to FIG. 1, an argon ion laser 10 sends a focused one Light beam from which is expanded in a (not shown) expansion optics and via a lens 11 on a dichroic beam splitter 12 is passed. The beam splitter 12 splits the one consisting of several colors Laser beam in two parallel beams b and g, of which the beam g of green light and the Ray b consists of blue light. About those caused by the other laser lines and the incomplete color separation To exclude the interference radiation caused is a laser line filter 13 in the beam path of the beam g and in the The beam path of the beam b has a laser line filter 14 arranged. These filters 13 and 14 each allow only light of the color in question to pass through.

The initially linearly polarized laser light is transmitted through λ / 4 plate 14 or 15 converted into circularly polarized light. This results in an even distribution of performance of the rays guaranteed by the polarization beam splitter 17., Between the λ / 4 plates 14,15 and the polarization beam splitter 17 is an inclined deflecting mirror 16 with two bores for passage of rays g and b arranged. The different colored rays b and g reach the through the bores Polarization beam splitter 17 which divides the two beams b and g into two mutually perpendicularly polarized beams 1g, 2g or 1b, 2b. DLos is shown in Fig. 2, where the direction of polarization is perpendicular to the plane of the drawing by three small circles and the polarization

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tion direction in the plane of the drawing is indicated by a double arrow. That perpendicular to the plane of the drawing oscillating light passes through the polarization beam splitter unhindered 17, while the part oscillating in parallel according to FIG. 2 in each case from the plane of the drawing is deflected out upwards.

The four laser beams 1g, 2g and 1b, 2b generated in this way, each with different properties, arrive via an image rotation prism 18, e.g. a Pechan prism, to a lens 19, from which you can focus on the Measurement volume are focused. The measurement volume is located inside a flow channel 20, which is in a Side wall has a window 21 through which the four rays pass. The focus points A and B, which will be explained below, characterize the measuring volume.

The green pair of rays 1g, 2g and the blue pair of rays 1b, 2b can each be used independently of one another a speed measurement can be carried out according to the two focus method. The in the flow channel 20 The prevailing gas flow contains small particles that adhere to the focusing points A, B are illuminated and scatter the incident light. The one emanating from the particles Light travels back through lens 19, image rotation prism 18 and polarization beam splitter 17 up to the deflecting mirror 16. Here the scattered light is separated from the laser beams generating the measuring volume and reflected on a dichroic mirror 22. This lets through the blue light component bs and reflects the green light component gs. The blue light

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portion bs is passed through a mirror 23 and a lens onto a microscope objective 25, behind which a Aperture 26 is arranged for spatial filtering of the scattered light. That passing through the aperture 26 Light that contains two different polarization components is passed through a color filter 27, which is only blue Lets light through, passed to a Rochon prism 28, which the perpendicularly polarized light components in divides two rays 29,30. The beam 29 becomes a photoelectric converter 31 and the beam 30 one photoelectric converter 32 supplied. The converter 32 generates a photoelectric pulse each time at the focusing point A (Fig. 3), scattered light is reflected by a particle and the converter 31 generates a pulse when light is reflected by a particle at the focussing point B. The signals from the converters 31, 32 are fed to an evaluation circuit 33 which generates a pulse, the amplitude of which corresponds to the time interval of the two pulses of the converters 32 and 31 is proportional if these pulses are within a predetermined range Successive time. The amplitude at the output of the evaluation circuit 33 is thus the particle speed between the focus points A and B is inversely proportional.

The elements 24 to 33, which have been described above for the beam path of the blue light bs, are contained in the same way in the beam path of the green light gs and are each marked there with a line. These elements 24 'to 33 ^l each correspond to the elements 24 to 33, but with the exception that the color filter 27' only passes through green light.

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lets while the color filter 27 transmits blue light.

In Fig. 3, the beam path between the lens 19 and the focusing points A and B is shown in perspective. You can see the differently polarized green rays 1g, 2g and the differently polarized ones blue rays 1b, 2b. The parallel green rays 1g, 2g go through the upper part of the Lens 19 through it and the parallel blue rays 1b, 2b through the lower part of the lens. The passage parts the rays 1g and 1b lie on a common diameter of the lens 19, while the passage points of the rays 2g and 2b run laterally at the same intervals next to the rays 1g and 1b. By the center of the lens 19 and through the focussing point A of the rays 1g and 1b goes the optical axis 34 of the system. The rays 1g and 1b therefore lie in one plane with the optical axis 34. They each converge at an angle γ to the optical axis and intersect at the focusing point A.

The rays 2g and 2b also form an angle γ to a parallel to the optical axis 34 and they intersect in the focusing point B, those of the focusing point A a distance along the x .. axis Has. The x-axis runs at right angles to the optical axis 34 and with this spans the plane 35 referred to as the “vector plane”. In the following it is assumed that the vector c proceeding from the focusing point A runs in the vector plane 35 and with the x .. axis encloses an angle β. This vector c is

to be measured by amount and direction.

Before further explanation of the mode of operation, the focusing points A and B according to FIG. 4 are considered. A particle that passes the focusing point A in the direction of the arrow 36 is subsequently registered at the focusing point B not only when it moves exactly along the X ₁ axis, but also when there is any component in the X direction at all -Axis. It has already been mentioned that the focussing points A and B are not point-shaped, but linear or cylindrical. The particle that moves according to arrow 36 also generates a light signal at the focusing point B, the time difference of which from the light signal generated at the focusing point A is _{proportional to the movement component in the direction of the X 1} axis. The only requirement is that the particle which has passed through the light beam 1g also passes through the light beam 2g. This means that the particle must move in the plane of the rays 1g, 2g in order to obtain a measurement result.

Any vector c in space in the measurement volume can be detected by the beam pairs 1g, 2g or 1b, 2b when the plane of the relevant beam pair is placed so that the vector c is in it. This is achieved in that the image rotation prism 18 is rotated about the optical axis 34 around. As a result, the entire shown in Fig. 3 rotates Ray system around the optical axis 34. The angle of rotation is denoted by φ. When rotating the rotating prism

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18, the points of passage of the pairs of rays at the edge of the lens 19 move on a circular path. The focus point A remains at rest.

If the pairs of rays are rotated clockwise according to FIG. 3, the line of intersection at which the plane of the pair of rays 1g, 2g intersects the vector plane 35 changes. The line of intersection in which the plane of the pair of rays 1b, 2b intersects the vector plane 35 changes in the same way. The two cutting lines, which still go through the focussing point A, rotate and wander in opposite directions. This results in the state in which the plane of the rays 1b, 2b has such a direction that the vector c runs in it. If this is the case, a continuity signal is displayed on the evaluation circuit 33 of the blue system. If the image rotation prism 18 is rotated further, at some point a state results in which the vector c lies in the plane of the rays 1g, 2g. If this is the case, a continuity signal is displayed on the evaluation circuit 33 'of the green system. The speed vector c can be determined from the relevant angles φ and φ ^ at which a measured value is displayed in the green or blue system, and from the size of the displayed measured values.

The vector is determined as follows:

It is assumed that the vector c at point A is somewhere in space. By rotating the Image rotation prism 18 about the optical axis 34 is during of a full revolution reaches a state in which the vector c is in the plane of the green rays 1g,

2g and a state in which the vector c lies in the plane of the blue rays 1b, 2b. These both angles are with φ and φ, respectively. designated. The zero point of the angle measurement is on the image rotation prism 18 marked as desired. The relevant angles φ and φ, at which the evaluation circuits 33 'and 33 signals occur, are read off and this angle is used according to the relationship

Ψ Ψ ^
Φ ₌

the angle Φ of the reference plane 35 in which the vector c is located is determined.

However, this measurement not only gives the angle Φ, but at the same time the angle B which the vector c _{includes in the reference plane 35 with the X 1} axis. This angle is calculated as

. + g - "b s in —----- -—

[i = ni-c tq '■.

Furthermore applies

| S | _cos ρ ₌

co ;; - ^ cot;

where ο and c, which are connected to the evaluation circuits 33 'and 30 g b ^

read measured values are dependent on the size of the vector c. These measured values c and c. are equal to each other.

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The angle γ which the beam pairs 1g, 2g and 1b, 2b each form to the optical axis 34 is in FIG Practice limited. With spherically ground optics, an angle γ of approximately 6.5 ° can be justified Realize effort. In Fig. 5 is the course of the

Angle φ - φ, as a function of the angle ti for a gb

Angle γ of 6.5 ° is shown. You can see that this The curve is approximately linear, so that angle differences can still be easily measured even at small angles β Φ - Φ ^ can be obtained.

The accuracy of the angle measurement according to the two focus measurement method depends essentially on the number of measurement events measured and the degree of turbulence in the flow. With small turbulence (<5 %) the measurement uncertainty is 0.1 to 0.2 ° and with large turbulence (> 10%) 0.3 to 0.5 °. This results in the uncertainty in determining the angle β in the case of small turbulence 0.4 to 0.7 ° and in the case of large turbulence 1 to 2 °. In the known optical methods, under the same conditions (ie compact measuring device, a common lens, backward scattering), the measurement uncertainties that occur are many times greater.

The method according to the invention can be used in flow studies find diverse application. For example, the possibility is given for the first time with turbo machines the previously undetectable radial components of the flow velocities in the impellers measure up.

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Claims (1)

Expectations 1 .J Method for measuring the flow vectors in gas flows by determining the speed and direction of optically detectable particles contained in a flow, in which the parallel rays of a first pair of rays (1b, 2b) are focused on two closely adjacent first focusing points (A, B) and the focusing points are imaged on two first photoelectric converters (31, 32), characterized in that a) a second pair of beams (1g, 2g) of beams also running parallel to one another below an angle (2γ) to the first pair of beams (1b, 2b) on the focusing points (A, B) is directed and focused there, b) the focussing points (A, B) of the second pair of beams (1g, 2g) on two second ones photoelectric converters (31 ', 32') are mapped, c) the two pairs of beams (1b, 2b; 1g, 2g) are pivoted together around an optical axis (34) which passes through one of the two focusing points (A) and in the plane of the associated beams (1g, 1b) of the two beam pairs runs, 3H5987 - yf- d) those swivel angles (φ,, φ) measured in which signals occur for each pair of beams at the converters (31, 32; 31 ', 32'), the passage of particles through the two focussing points (A, B) of this Specify a pair of rays, and e) from the measured pivot angles (Φκ / Φ _α ) for both pairs of beams and the measured frequency value, the vector Cc) of the particle velocity is determined according to direction and magnitude. 2. The method according to claim 1, characterized in that with the optical axis (34) in one plane lying rays (1g, 1b) extend at the same angles (λ) to the optical axis. 3. The method according to claim 2, characterized in that that plane (vector plane) in which the optical axis (34) and the sought vector (c) lie by the relationship φ - φ,
Φ = is determined, where Φ is the angle of the vector plane (35) with respect to the optical axis (34), φ, the swivel angle at which transmission signals occur at the converters (31, 32) of the first pair of beams, and φ the swivel angle at which the transducers (31 ', 32') of the second pair of beams receive passage signals occur are. 3U5987 yr- 4. The method according to claim 3, characterized in that that the angle β of the vector (c) sought within the vector plane by the relationship sm
P = arc tg is "^<() b tg \ is determined, where γ is the size of half the angle between the beam pairs (1b, 2b; 1g, 2g). 5. The method according to claim 4, characterized in that -> that the amount of the vector (c) by the relation (c _b or c _g ) α b
cos ——τ cosß is determined, where c and c are the sizes of the an the converters (31,32) or (31 ', 32') for the first or the second pair of rays at the pivot angles In φ ^ or φ are measured velocities. Device for measuring the flow vectors in gas flows, in particular for carrying out the method according to one of the preceding claims, characterized in that two beam generation systems (10, 12, 13, 14) are provided, each of which generates a pair of beams (1g, 2g; 1b, 2b) from parallel beams, that the plane in which the rays of a pair of rays (1g, 2g) lie at an acute angle (2γ) to the plane 3U5987 runs in the plane of the other pair of rays (1b, 2b) lie and that a device (18) for simultaneous rotation of the beam pairs (1g, 2g, 1b, 2b) by one common axis (34) is provided. 7. Apparatus according to claim 6, characterized in that the beam of a laser (10) in a dichroic beam splitter (12) is divided into two beams (g, b) with different colors, that these two beams are a polarization beam splitter (17) which splits each beam (g, b) into two parallel, differently polarized beams (1g, 2g; 1b, 2b) so that the total of four beams are spaced from the optical axis (34) via an image rotating prism (18 ) and a collecting optics (19) are directed in pairs to the two focusing points (A, B) and that a lens system directed to the focusing points (A, B) separates and ^{opens the pairs of beams (29,30; 29 ', 3O 1)} has different evaluation devices (31,32,33; 31 ', 32', 33 ') conducting device (22,23; 24 to 28; 24' to 28 '). 8. Apparatus according to claim 6 or 7, characterized in that two beams (1g, 1b), each of which belongs to one of the beam pairs, in the image rotation prism (8) a common diameter of the image rotation prism cut.