CN108008146A - A kind of method and apparatus for improving gas flow rate measurement accuracy - Google Patents
A kind of method and apparatus for improving gas flow rate measurement accuracy Download PDFInfo
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- CN108008146A CN108008146A CN201711075096.8A CN201711075096A CN108008146A CN 108008146 A CN108008146 A CN 108008146A CN 201711075096 A CN201711075096 A CN 201711075096A CN 108008146 A CN108008146 A CN 108008146A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
- G01P5/26—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the direct influence of the streaming fluid on the properties of a detecting optical wave
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Abstract
The invention belongs to high-speed gas concentration, the field of measuring technique of flow velocity, discloses a kind of method and apparatus for improving gas velocity measurement precision.This method utilizes Wavelength modulation spectroscopy (WMS) technology, two even harmonics signals (nf and mf are demodulated at the same time with lock-in amplifier, n, m=2,4,6 ... and n ＞ m), the narrow and sharp peak-to-peak signal of high s/n ratio is obtained with mf normalization nf (WMS nf/mf), gas flow rate is calculated by the Doppler frequency shift at narrow peak, Measurement Resolution and precision can be improved.The device of the invention is made of tunable laser, photodetector and lock-in amplifier etc..The work step of device is：Two beam laser and airflow direction be angled to intersect and is slanted through airflow field, shoot laser is received and converted to electric signal by two detectors respectively, demodulated to obtain WMS nf/mf signals by lock-in amplifier, the flow velocity of gas is calculated by the Doppler frequency shift of two signals.
Description
Technical field
Flow velocity, measurement of concetration technical field the invention belongs to high-speed gas, are related to tunable diode laser and absorb light
The method and apparatus of spectral technology, by implementing this programme to the spectral line to be measured of object gas, in measurement gas concentration and flow velocity
Meanwhile the Measurement Resolution and precision of flow velocity can be improved.
Background technology
For High Speed Flow Field, as aerospace engine nozzle at, the measurement of gas flow rate is extremely important.It is and traditional
Speed-measuring method such as Pitot tube, hot-wire anemometer etc., belong to contact type measurement, not only easily combustion process interfered, and
And rugged environment can also influence the reliability of its service life and measurement result.Tunable diode laser absorption spectroscopy (Tunable
Diode Laser Absorption Spectroscopy, TDLAS) technology, utilize the narrow linewidth and wavelength of semiconductor laser
The characteristics such as tuning, carry out absorption line quickly scanning, it can be achieved that to being measured while temperature, pressure, constituents ratio.TDLAS
Combined with laser doppler technique, can further realize quick, on-line measurement to high-speed flow flow velocity, be that one kind is suitable for disliking
The contactless flow-speed measurement method of bad environment.
The measurement that TDLAS is used for High Speed Flow Field starts from the nineties in last century.Basic scheme is to be based on direct absorption spectrum
(DAS) technology or Wavelength modulation spectroscopy second harmonic (WMS-2f) Detection Techniques, laser is divided into two-way relative gas velocity is in
Intersect incidence by flow field, flow velocity is determined using the Doppler frequency shift of DAS signals or WMS-2f signals.In both schemes,
Doppler frequency shift is determined that the judgement of the narrower absorption peak position of peak width is more accurate, i.e. flow velocity resolution ratio by the spacing of two absworption peaks
It is related with breadth of spectrum line.Therefore, limited by line width and sample rate, the resolution ratio of speed is not often high, with common aqueous vapor position
Exemplified by Absorption Line at 1398nm, half high half-breadth of its absorption line is about 0.1cm-1, can extrapolate when laser beam and air-flow
During the angle at 45 ° of direction, velocity resolution is about 59.40m/s.If the flow velocity of measurand is less than 59.40m/s, measurement accuracy
It can be reduced with accuracy, it is impossible to meet the needs of low speed measurement and a wide range of flow velocity measurement.
Therefore the present invention is proposed on the theoretical research foundation of forefathers based on the double higher hamonic wave detections of Wavelength modulation spectroscopy
Scheme, improves accuracy of detection to a certain extent, and the concentration of component of gas is measured while flow velocity is measured.
The content of the invention
It is contemplated that overcome the deficiencies of the prior art and provide a kind of method and dress of raising TDLAS flow velocity measurement accuracy
Put.Based on methods and apparatus of the present invention, while two different even harmonics signals of Wavelength modulation spectroscopy are gathered, improved
The measurement gas flow rate precision and detection sensitivity of TDLAS systems, this method and device can be used for high-speed flow it is online, it is in situ,
Monitoring application in real time.
To reach above-mentioned purpose, the technical scheme is that：The method for improving gas flow rate measurement accuracy, its feature exist
In using Wavelength modulation spectroscopy (WMS) technology, passing through lock-in amplifier and demodulate two even higher hamonic wave signal (nf and mf at the same time
Signal, n, m=2,4,6... and n ＞ m), obtain the narrow of two high s/n ratios using mf normalization nf signals (WMS-nf/mf) and
The peak-to-peak signal of point, the Doppler frequency shift by observing the two narrow peaks are finally inversed by high gas flow rate.
Angle theta between gas flow rate and frequency shift (FS) Δ υ, laser transmission direction and air-flow velocity direction and do not occur
The centre frequency υ of gaseous absorption line during frequency displacement0It is related：
Wherein, c is the light velocity, VgasFor air-flow velocity, unit：m·s-1；Δ υ is frequency shift (FS), υ0For no generation frequency displacement
When gaseous absorption line centre frequency, unit：Hz；Angles of the θ between laser transmission direction and air-flow velocity direction, it is single
Position：°.
Since each even-order harmonic component of Wavelength modulation spectroscopy reduces with the increase of overtone order, thus it is common to use
WMS-4f/2f (i.e. n=4, m=2) signal, obtains the narrow and sharp peak-to-peak signal of two high s/n ratios, its usual peak width is than straight
It is more than 5 times narrow to connect absorption spectrum signal, Doppler frequency shift is determined, so as to improve measurement accuracy and resolution ratio.
The device of TDLAS measurement accuracy is improved based on higher hamonic wave detection 4f/2f, including：Laser controller, semiconductor swash
Light device, signal generator, photodetector, digital servo-control module, etalon, A/D converter, computer or embedded processing
Device, collimation lens etc..Laser controller controls semiconductor laser laser, via laser beam splitter one dividing into three, wherein
A branch of to carry out Wavelength calibration by etalon, in addition two beams converge to photodetector by collimation lens after tested air-flow and connect
Row opto-electronic conversion is taken in, the electric signal after conversion enters digital lock-in amplifier, while the higher hamonic wave by frequency for 4f and 2f
It is demodulated, most three road signals are passed to the processing of progress data in computer or processor, analyze, display and save at last.
Compared with prior art, technical characterstic of the invention and effect：
The ratio between double higher hamonic waves that the present invention uses detecting strategy, improve to a certain extent flow velocity measurement resolution ratio and
Precision.
Brief description of the drawings
Fig. 1 is the TDLAS block diagrams using the progress gas detection of the method for the present invention
1 laser controller
2 semiconductor lasers
3 beam splitters
4 etalons
5 A/D converters
6 tested air-flows
7th, 10 photoelectric detection module
8th, 11 digital servo-control amplification module
9 computers or embeded processor
12 signal generating modules
Fig. 2 is the Frequency Shift (embodiment 1) using 4f/2f obtained by this method
Fig. 3 is the Frequency Shift (embodiment 2) using 6f/2f obtained by this method
Embodiment
The present invention is a kind of method and apparatus for improving gas flow rate measurement accuracy, and the theoretical foundation based on forefathers, utilizes
Wavelength modulation spectroscopy (WMS) technology, two even higher hamonic wave signal (nf and mf signals, n, m are demodulated by lock-in amplifier at the same time
=2,4,6... and n ＞ m), the narrow and sharp peak that two high s/n ratios are obtained using mf normalization nf signals (WMS-nf/mf) is believed
Number, the Doppler frequency shift by observing the two narrow peaks can improve the precision and resolution ratio of gas flow rate measurement.
The technical scheme is that：
The method that TDLAS measurement accuracy is improved based on WMS-nf/mf, detection gas are to the absorption line of laser to including dense
The measurement of the parameter of gas including degree, pressure, temperature and flow velocity, it is characterized in that, in gas when passing through high-speed flow due to laser
It is important to flow direction, so Doppler frequency shift can be produced when receiving laser, the Doppler frequency shift size for having two absorption lines, i.e.,
Can at inverting high-speed flow flow velocity.
Angle theta between gas flow rate and frequency shift (FS) Δ υ, laser transmission direction and air-flow velocity direction and do not occur
The centre frequency υ of gaseous absorption line during frequency displacement0It is related：
Wherein, c is the light velocity, VgasFor air-flow velocity, unit：m·s-1；Δ υ is frequency shift (FS), υ0For no generation frequency displacement
When gaseous absorption line centre frequency, unit：Hz；Angles of the θ between laser transmission direction and air-flow velocity direction, unit：°
Below in conjunction with the accompanying drawings with the specific experiment embodiment that the present invention will be described in detail：
By the use of 760nm lasers as light source, with O2For object gas, O is chosen2Spectral line at 760.445nm is to treat
Spectral line is surveyed, tested air-flow is the air stream of flowing, and specific experiment is analyzed below.
Embodiment 1：(760nm lasers, Vgas=100m/s, 4f/2f)
Below exemplified by analyzing oxygen molecule in the absorption line at 760.445nm, explanation calculates gas stream with this programme
The measuring method of speed.The absorption line that our Selection Center wavelength are 760.445nm in this embodiment, with θ1=45 °, θ2=
135 ° intersect oblique incidence into the air flow field that flow velocity is 100m/s, make n=4, m=2, that is, allow two digital lock-in amplifiers at the same time
Demodulation obtains WMS-4f/2f signals.
| λ0, nm | λ1, nm | λ2, nm | θ1 | θ2 |
| 760.445 | 760.44518 | 760.44482 | 45° | 135° |
T=296K, P=1atm.
Air-flow velocity：
Using above-mentioned formula, it is V to obtain air-flow velocitygas=100.44m/s, relative error 0.44%.Compared to only using
WMS-2f measures (relative error about 4.0%), and error reduces an order of magnitude.
Embodiment 2：(760nm lasers, Vgas=100m/s)
Below exemplified by analyzing oxygen molecule in the absorption line at 760.445nm, explanation calculates gas stream with this programme
The measuring method of speed.The absorption line that our Selection Center wavelength are 760.445nm in this embodiment, with θ1=45 °, θ2=
135 ° intersect oblique incidence into the oxygen flow field that flow velocity is 100m/s, make n=6, m=2, that is, allow two digital lock-in amplifiers at the same time
Demodulation obtains WMS-4f/2f signals.
| λ0, nm | λ1, nm | λ2, nm | θ1 | θ2 |
| 760.445 | 760.44518 | 760.44482 | 45° | 135° |
T=296K, P=1atm.
Air-flow velocity：Vgas=λ0Δυ/(Cosθ1-Cosθ2)
Using above-mentioned formula, it is V to obtain air-flow velocitygas=101.24m/s, relative error 1.24%.
The flow velocity of gas in experiment is resulting in, effectively increases Measurement Resolution and precision.
Claims (3)
- A kind of 1. method for improving gas flow rate measurement accuracy, it is characterised in that using Wavelength modulation spectroscopy (WMS) technology, lead to Lock-in amplifier while the even higher hamonic wave signal (nf and mf signals, n, m=2,4,6... and n ＞ m) of demodulation two are crossed, utilizes mf Normalization nf signals (WMS-nf/mf) obtain the narrow and sharp peak-to-peak signal of two high s/n ratios, by observing the two narrow peaks Doppler frequency shift can improve the precision and resolution ratio of gas flow rate measurement.
- 2. a kind of method for improving gas flow rate measurement accuracy as claimed in claim 1, it is characterized in that, since wavelength modulates light Compose each even-order harmonic component with the increase of overtone order to reduce, thus it is common to use WMS-4f/2f (i.e. n=4, m=2) believes Number, the narrow and sharp peak-to-peak signal of two high s/n ratios is obtained, its usual peak width is more than 5 times narrower than direct absorption spectrum signal, Doppler frequency shift is determined, so as to improve measurement accuracy and resolution ratio.
- 3. a kind of detect the device for improving flow velocity measurement accuracy based on higher hamonic wave, it is characterized in that, including：Laser controller, can Tunable semiconductor lasers, signal generator, photodetector, digital servo-control module, etalon, computer or embedded processing Device, light collimating lenses etc..Laser controller control semiconductor laser goes out laser needed for experiment, via laser beam splitter one Be divided into three, wherein a branch of be used for Wavelength calibration by etalon, in addition two beams with airflow direction is angled intersects oblique incidence Inlet flow field, two beam shoot lasers are converted to electric signal by two detectors receptions respectively and enter two digital lock-in amplifiers, Each digital lock-in amplifier demodulates at the same time obtains WMS-nf/mf signals, and most three road signals are passed to computer or embedded at last Processor, carries out the processing, analysis and preservation of data.
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Cited By (6)
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| CN110361359A (en) * | 2019-07-16 | 2019-10-22 | 清华大学 | A kind of absorptivity function reproducing method based on even-order harmonic |
| CN110596040A (en) * | 2019-09-10 | 2019-12-20 | 上海东富龙科技股份有限公司 | Gas detection device, system and method based on TDLAS technology |
| CN111751484A (en) * | 2020-04-13 | 2020-10-09 | 中国科学院力学研究所 | Solid-liquid rocket engine fuel burning rate measuring system |
| CN112378616A (en) * | 2020-11-16 | 2021-02-19 | 中国科学技术大学 | High-speed flow field multi-parameter measurement system and method based on wavelength modulation absorption spectrum |
| CN113280996A (en) * | 2021-04-25 | 2021-08-20 | 中国航天空气动力技术研究院 | Method for measuring speed of free flow of high-enthalpy flow field |
| CN114814286A (en) * | 2022-02-25 | 2022-07-29 | 上海理工大学 | Online low-pressure system flow velocity testing device and method |
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| CN111751484A (en) * | 2020-04-13 | 2020-10-09 | 中国科学院力学研究所 | Solid-liquid rocket engine fuel burning rate measuring system |
| CN112378616A (en) * | 2020-11-16 | 2021-02-19 | 中国科学技术大学 | High-speed flow field multi-parameter measurement system and method based on wavelength modulation absorption spectrum |
| CN112378616B (en) * | 2020-11-16 | 2021-12-10 | 中国科学技术大学 | High-speed flow field multi-parameter measurement system and method based on wavelength modulation absorption spectrum |
| CN113280996A (en) * | 2021-04-25 | 2021-08-20 | 中国航天空气动力技术研究院 | Method for measuring speed of free flow of high-enthalpy flow field |
| CN114814286A (en) * | 2022-02-25 | 2022-07-29 | 上海理工大学 | Online low-pressure system flow velocity testing device and method |
| CN114814286B (en) * | 2022-02-25 | 2023-06-02 | 上海理工大学 | Online low-pressure system flow velocity testing device and method |
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