CN112098039B - System and method for measuring pulsation density of hypersonic flow field - Google Patents
System and method for measuring pulsation density of hypersonic flow field Download PDFInfo
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- CN112098039B CN112098039B CN202010933814.6A CN202010933814A CN112098039B CN 112098039 B CN112098039 B CN 112098039B CN 202010933814 A CN202010933814 A CN 202010933814A CN 112098039 B CN112098039 B CN 112098039B
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- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M9/00—Aerodynamic testing; Arrangements in or on wind tunnels
- G01M9/06—Measuring arrangements specially adapted for aerodynamic testing
- G01M9/065—Measuring arrangements specially adapted for aerodynamic testing dealing with flow
- G01M9/067—Measuring arrangements specially adapted for aerodynamic testing dealing with flow visualisation
Abstract
The invention discloses a system and a method for measuring the pulse density of a hypersonic flow field, wherein laser is transmitted through Y-shaped optical fibers 1A, 1C, 2A and 2C, the output end aligns the laser to a photoelectric detector b through an optical fiber collimator d, and the intensity of the laser output by the laser is monitored; laser is transmitted through the Y-shaped optical fibers 1A and 1B, and a laser signal at the output end enters a flow field test area; the optical fiber collimator B on the other side collects laser signals and then couples the laser signals again to form an interference measuring light path through the transmission of the Y-shaped optical fibers 3B and 3A; the laser is transmitted through the Y-shaped optical fibers 1A, 1C, 2A, 2B, 3C and 3A to form an interference reference light path, the measurement light and the reference light generate interference after meeting, and the output end of the Y-shaped optical fiber 3A aligns the laser to the photoelectric detector a through the optical fiber collimator C to measure interference signals. The measurement result of the system is directly related to the pulse density; the sensitivity is high; the anti-interference capability is strong; the structure is compact, the adjustment is simple and convenient, and the utilization rate of the laser light source is high; response frequencies of hundreds of megahertz can be achieved.
Description
Technical Field
The invention belongs to the technical field of measuring equipment in a hypersonic wind tunnel, and particularly relates to a system and a method for measuring the pulse density of a hypersonic flow field.
Background
The hypersonic pulsation characteristic is an important parameter for measuring the dynamic quality of a wind tunnel flow field and is a key parameter for researching a turbulence model and a transition mechanism. The pulsation velocity is measured by a hot wire anemometer in a subsonic wind tunnel, and the pulsation velocity cannot be applied to a hypersonic wind tunnel due to the limitation of hot wire strength and interference introduced by a convection field. The hypersonic wind tunnel mainly measures pulsating pressure or pulsating density. The measurement method of the pulsating pressure is limited by the response frequency of the sensor and cannot cover all important frequency bands, and when the total temperature of a flow field is higher, the sensor cannot meet the requirements of heat load and impact load. The existing pulse density measurement methods, such as a schlieren instrument and a laser focusing differential interferometer, have density gradient as a measurement result, and the pulse density change can be obtained only through complicated conversion. Therefore, how to develop a method for measuring the pulsation density of the hypersonic flow field has important practical significance.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a system for measuring the pulse density of a hypersonic flow field aiming at the measurement requirement of the hypersonic flow field, in particular to a pulse density measuring method based on laser interference, wherein the measuring result is directly related to the pulse density, and the system has the characteristics of non-contact measurement, high response frequency, high sensitivity, strong anti-interference capability and the like.
The technical scheme adopted by the invention is as follows:
a hypersonic flow field pulse density measuring system comprises a laser energy monitoring system and an interference measuring system,
more specifically, the system comprises a laser, an optical fiber coupler, a Y-shaped optical fiber, an optical fiber connector, an optical fiber collimator, a photoelectric detector and a signal collector, wherein the laser is connected with the optical fiber coupler,
in the laser energy monitoring system, the optical fiber coupler is connected with an optical fiber connector a through a Y-shaped optical fiber 1A, Y-shaped optical fiber 1C, and the optical fiber connector a is connected with the laser energy monitoring component through a Y-shaped optical fiber 2A, Y-shaped optical fiber 2C in sequence;
the interferometric measuring system comprises an interferometric reference optical path and an interferometric measurement optical path,
in the interference measurement light path, the optical fiber coupler is connected with an optical fiber collimator a through a Y-shaped optical fiber 1A, Y-shaped optical fiber 1B, the optical fiber collimator a and the optical fiber collimator B are placed on two sides of a flow field to be measured, and the optical fiber collimator B is connected with an interference measurement component through a Y-shaped optical fiber 3B, Y-shaped optical fiber 3A;
in the reference optical path of the interference, the optical fiber coupler is connected with an optical fiber connector a through a Y-shaped optical fiber 1A, Y-shaped optical fiber 1C, the optical fiber connector a is connected with an optical fiber connector B through a Y-shaped optical fiber 2A, Y-shaped optical fiber 2B, and the optical fiber connector B is connected with the interference measurement component through a Y-shaped optical fiber 3C, Y-shaped optical fiber 3A;
the laser energy monitoring assembly is a structure formed by an optical fiber collimator d and a photoelectric detector b, the interference measurement assembly is a structure formed by an optical fiber collimator c and a photoelectric detector a, and the photoelectric detector a and the photoelectric detector b are respectively connected with a signal collector to collect signals through the signal collector.
Furthermore, one end of the Y-shaped optical fiber is set to be a conducting optical core, the other end of the Y-shaped optical fiber is set to be two optical cores which are arranged side by side, and optical signals are shunted or compounded through the Y-shaped optical fiber.
Further, the Y-shaped fibers are 3, and are respectively denoted by arabic numerals 1, 2, and 3, and three ports thereof are respectively denoted by A, B, C.
Furthermore, the laser adopts a helium-neon laser, and laser beams are coupled into the Y-shaped optical fiber at the output end through an optical fiber coupler.
Furthermore, a calibration device is arranged between the optical fiber collimator a and the optical fiber collimator b, the pulse density measurement range is calibrated by the calibration device, the calibration device comprises a glass pressure ring, a calibration pipe, quartz glass, a pressure/temperature sensor and a vacuum pump, the glass pressure ring and the quartz glass are respectively arranged at two ends of the calibration pipe, the pressure/temperature sensor and the vacuum pump are respectively arranged at a certain interval position in the middle of the calibration pipe, and the pressure/temperature sensor and the vacuum pump are arranged along the direction perpendicular to the axis of the calibration pipe.
A method for measuring the pulse density of a hypersonic flow field adopts the system for measuring the pulse density of the hypersonic flow field, and specifically comprises the following steps:
laser energy monitoring: the laser is transmitted through the Y-shaped optical fiber 1A, Y-shaped optical fiber 1C, Y-shaped optical fiber 2A, Y-shaped optical fiber 2C, the output end of the laser is connected with an optical fiber collimator d and a photoelectric detector b, the optical fiber collimator d aligns the laser to the photoelectric detector b, and the intensity of the laser output by the laser is monitored;
and (3) interference measurement:
laser is transmitted through a Y-shaped optical fiber 1A, Y-shaped optical fiber 1B, the output end is connected with an optical fiber collimator a, the optical fiber collimator a and the optical fiber collimator B are placed on two sides of a flow field to be measured, and laser signals enter a flow field test area; the optical fiber collimator b on the other side collects laser signals, then couples the laser signals into the Y-shaped optical fiber again, and transmits the laser signals through the Y-shaped optical fiber 3B, Y-shaped optical fiber 3A to form an interference measuring optical path;
laser is transmitted through a Y-shaped optical fiber 1A, Y-shaped optical fiber 1C, Y-shaped optical fiber 2A, Y-shaped optical fiber 2B, Y-shaped optical fiber 3C, Y-shaped optical fiber 3A to form an interference reference optical path;
the output end of the Y-shaped optical fiber 3A is connected with an optical fiber collimator c and a photoelectric detector a, interference is generated after the measurement light meets the reference light, and the optical fiber collimator c aligns the laser to the photoelectric detector a to measure interference signals.
The invention has the beneficial effects that:
(1) the measurement is directly related to the pulse density;
(2) the non-contact measurement does not influence the flow field pulsation characteristic;
(3) based on the interference measurement, the system has high sensitivity and can realize the measurement of the micro-pulse density;
(4) the optical fiber is used for transmitting laser, so that the system has strong anti-interference capability;
(5) the Y-shaped optical fiber is used for realizing the light splitting and the compounding of optical signals, the system has compact structure and simple and convenient adjustment, and the utilization rate of the laser light source is high;
(6) the system measurement pulsation frequency depends on the response frequency of the photoelectric detector, and the current manufacturing level of the photoelectric detector can realize the bandwidth of hundreds of MHz, so the system can realize the response frequency of hundreds of MHz, which is far higher than the 1MHz response frequency of the piezoelectric sensor measurement method.
Drawings
Fig. 1 is a block diagram of the pulse density measurement system of the hypersonic flow field according to the present invention.
Fig. 2 is a schematic structural diagram of the calibration device of the present invention.
FIG. 3 is a graph showing the results of an experiment in which the nozzle jet causes density pulsation in accordance with the present invention.
Wherein, 1, a glass pressure ring; 2. calibrating the tube; 3. quartz glass; 4. a pressure/temperature sensor; 5. a vacuum pump.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
Example 1
As shown in fig. 1, a hypersonic flow field pulse density measuring system comprises a laser energy monitoring system and an interferometry system,
more specifically, the system comprises a laser, an optical fiber coupler, a Y-shaped optical fiber, an optical fiber connector, an optical fiber collimator, a photoelectric detector and a signal collector, wherein the laser is connected with the optical fiber coupler,
in the laser energy monitoring system, the optical fiber coupler is connected with an optical fiber connector a through a Y-shaped optical fiber 1A, Y-shaped optical fiber 1C, and the optical fiber connector a is connected with the laser energy monitoring component through a Y-shaped optical fiber 2A, Y-shaped optical fiber 2C in sequence;
the interferometric measuring system comprises an interferometric reference optical path and an interferometric measurement optical path,
in the interference measurement light path, the optical fiber coupler is connected with an optical fiber collimator a through a Y-shaped optical fiber 1A, Y-shaped optical fiber 1B, the optical fiber collimator a and the optical fiber collimator B are placed on two sides of a flow field to be measured, and the optical fiber collimator B is connected with an interference measurement component through a Y-shaped optical fiber 3B, Y-shaped optical fiber 3A;
in the reference optical path of the interference, the optical fiber coupler is connected with an optical fiber connector a through a Y-shaped optical fiber 1A, Y-shaped optical fiber 1C, the optical fiber connector a is connected with an optical fiber connector B through a Y-shaped optical fiber 2A, Y-shaped optical fiber 2B, and the optical fiber connector B is connected with the interference measurement component through a Y-shaped optical fiber 3C, Y-shaped optical fiber 3A;
the laser energy monitoring assembly is a structure formed by an optical fiber collimator d and a photoelectric detector b, the interference measurement assembly is a structure formed by an optical fiber collimator c and a photoelectric detector a, and the photoelectric detector a and the photoelectric detector b are respectively connected with a signal collector to collect signals through the signal collector.
One end of the Y-shaped optical fiber is set to be a conducting optical core, the other end of the Y-shaped optical fiber is set to be two optical cores which are arranged side by side, and optical signals are shunted or compounded through the Y-shaped optical fiber.
The Y-shaped fibers are 3, and are labeled with arabic numerals 1, 2, and 3, respectively, and their three ports are labeled A, B, C, respectively.
The laser adopts a helium-neon laser, and laser beams are coupled into the Y-shaped optical fiber at the output end through an optical fiber coupler.
Basic principle of measurement:
the pulse density measurement of the present invention is based on the basic principle of laser interference. The relationship between the gas density of the flow field and the refractive index thereof can be given by the Gladstone-Dale formula:
n＝KGDρ+1 (1)
wherein n is refractive index, rho is flow field gas density, and KGDIs the Gladstone-Dale coefficient.
According to the interference principle of light, the intensity of two beams of light after interference is as follows:
in the formula I1、I2The intensities of two beams participating in interference when the two beams do not interfere with each other are respectively defined as λ is the laser wavelength and Δ OPL is the optical path difference of the two beams1For the length of the detection zone, L2For measuring the length of the light path without the probe region, L3For reference optical path length, n2The refractive index of the optical fiber is, the optical path difference between the two beams is:
ΔOPL＝(KGDρ+1)L1+n2(L2-L3) (3)
the substitution formula (2) includes:
the gas density in the visible detection area is directly related to the intensity of the interference signal, and the change of the gas density causes the change of the light intensity.
Homogeneous phase when defined:
in the formula
The average density of the gas in the measurement area is shown. When measuring the system layout
Whereink is an integer to maximize the range of system-measured pulse densities, is
Example 2
On the basis of embodiment 1, different from embodiment 1, as shown in fig. 2, the pulse density measurement range is calibrated by using a calibration device, the calibration device includes a glass pressure ring, a calibration pipe, quartz glass, a pressure/temperature sensor and a vacuum pump, the two ends of the calibration pipe are respectively provided with the glass pressure ring and the quartz glass, the middle part of the calibration pipe is respectively provided with the pressure/temperature sensor and the vacuum pump at certain intervals, and the pressure/temperature sensor and the vacuum pump are arranged along the direction perpendicular to the axis of the calibration pipe.
Quartz glass is additionally arranged on two sides of the calibration pipe and used for simulating a measurement area; the pressure sensor is used for recording the pressure in the calibration pipe; the temperature sensor is used for recording and calibrating the temperature in the pipe; the vacuum pump is used for changing the pressure in the calibration pipe, so that the control of the density is realized.
The calibration process of the calibration device comprises the following steps:
1) placing the calibration device between two optical fiber collimators of the pulse density measurement system, namely between an optical fiber collimator a and an optical fiber collimator b;
2) after debugging equipment, starting a vacuum pump to run, and synchronously recording temperature and pressure information and output signals of a pulse density output device;
3) stopping the vacuum pump after the output signal of the pulse density device presents a complete cosine trigonometric function signal;
4) and determining the actual pulse density measurement range according to the measurement result.
Example 3
On the basis of embodiment 1, it is further, set up calibration device between fiber collimator a and the fiber collimator b, the pulsation density measuring range adopts calibration device to mark, calibration device includes glass clamping ring, calibration pipe, quartz glass, pressure/temperature sensor, vacuum pump, the both ends of calibration pipe are provided with glass clamping ring and quartz glass respectively, and the middle part interval certain position department of calibration pipe is provided with pressure/temperature sensor and vacuum pump respectively, and pressure/temperature sensor and vacuum pump all arrange along the perpendicular to calibration pipe axis direction and set up.
A method for measuring the pulse density of a hypersonic flow field adopts the system for measuring the pulse density of the hypersonic flow field, and specifically comprises the following steps:
laser energy monitoring: the laser is transmitted through the Y-shaped optical fiber 1A, Y-shaped optical fiber 1C, Y-shaped optical fiber 2A, Y-shaped optical fiber 2C, the output end of the laser is connected with an optical fiber collimator d and a photoelectric detector b, the optical fiber collimator d aligns the laser to the photoelectric detector b, and the intensity of the laser output by the laser is monitored;
and (3) interference measurement:
laser is transmitted through a Y-shaped optical fiber 1A, Y-shaped optical fiber 1B, the output end is connected with an optical fiber collimator a, the optical fiber collimator a and the optical fiber collimator B are placed on two sides of a flow field to be measured, and laser signals enter a flow field test area; the optical fiber collimator b on the other side collects laser signals, then couples the laser signals into the Y-shaped optical fiber again, and transmits the laser signals through the Y-shaped optical fiber 3B, Y-shaped optical fiber 3A to form an interference measuring optical path;
laser is transmitted through a Y-shaped optical fiber 1A, Y-shaped optical fiber 1C, Y-shaped optical fiber 2A, Y-shaped optical fiber 2B, Y-shaped optical fiber 3C, Y-shaped optical fiber 3A to form an interference reference optical path;
the output end of the Y-shaped optical fiber 3A is connected with an optical fiber collimator c and a photoelectric detector a, interference is generated after the measurement light meets the reference light, and the optical fiber collimator c aligns the laser to the photoelectric detector a to measure interference signals.
As shown in FIG. 3, the results of the experiments in the present invention are 85-87ms, with time on the horizontal axis and interference signal measurements on the vertical axis. The signal amplitude reflects the size of density pulsation; and Fourier transform is carried out on the interference signal to obtain the frequency spectrum characteristic of the pulse signal.
The above description is not meant to be limiting, it being noted that: it will be apparent to those skilled in the art that various changes, modifications, additions and substitutions can be made without departing from the true scope of the invention, and these improvements and modifications should also be construed as within the scope of the invention.
Claims (5)
1. A hypersonic flow field pulse density measuring system is characterized by comprising a laser energy monitoring system and an interference measuring system,
in the laser energy monitoring system, the optical fiber coupler is connected with an optical fiber connector a through a Y-shaped optical fiber 1A, Y-shaped optical fiber 1C, and the optical fiber connector a is connected with the laser energy monitoring component through a Y-shaped optical fiber 2A, Y-shaped optical fiber 2C in sequence;
the interferometric measuring system comprises an interferometric reference optical path and an interferometric measurement optical path,
in the interference measurement light path, the optical fiber coupler is connected with an optical fiber collimator a through a Y-shaped optical fiber 1A, Y-shaped optical fiber 1B, the optical fiber collimator a and the optical fiber collimator B are placed on two sides of a flow field to be measured, and the optical fiber collimator B is connected with an interference measurement component through a Y-shaped optical fiber 3B, Y-shaped optical fiber 3A;
in the reference optical path of the interference, the optical fiber coupler is connected with an optical fiber connector a through a Y-shaped optical fiber 1A, Y-shaped optical fiber 1C, the optical fiber connector a is connected with an optical fiber connector B through a Y-shaped optical fiber 2A, Y-shaped optical fiber 2B, and the optical fiber connector B is connected with the interference measurement component through a Y-shaped optical fiber 3C, Y-shaped optical fiber 3A;
the laser energy monitoring assembly is a structure consisting of an optical fiber collimator d and a photoelectric detector b, the interference measurement assembly is a structure consisting of an optical fiber collimator c and a photoelectric detector a, and the photoelectric detector a and the photoelectric detector b are respectively connected with a signal collector and collect signals through the signal collector;
the calibration device is arranged between the optical fiber collimator a and the optical fiber collimator b, the pulse density measurement range is calibrated by the calibration device, the calibration device comprises a glass pressure ring, a calibration pipe, quartz glass, a pressure/temperature sensor and a vacuum pump, the glass pressure ring and the quartz glass are respectively arranged at two ends of the calibration pipe, the pressure/temperature sensor and the vacuum pump are respectively arranged at a certain interval position in the middle of the calibration pipe, and the pressure/temperature sensor and the vacuum pump are arranged along the direction perpendicular to the axis of the calibration pipe.
2. The system for measuring the pulsating density of the hypersonic flow field according to claim 1, wherein one end of the Y-shaped optical fiber is provided with a conducting optical core, the other end of the Y-shaped optical fiber is provided with two optical cores which are arranged side by side, and an optical signal is split or compounded through the Y-shaped optical fiber.
3. The system as claimed in claim 1 or 2, wherein the Y-shaped optical fibers are 3, respectively denoted by arabic numerals 1, 2 and 3, and three ports of the Y-shaped optical fibers are respectively denoted by A, B, C.
4. The system of claim 1, wherein the laser is a helium-neon laser, and the laser beam is coupled into the Y-shaped optical fiber at the output end via a fiber coupler.
5. A method for measuring the pulse density of a hypersonic flow field adopts any one of 1 to 4, and is characterized by comprising the following steps:
laser energy monitoring: the laser is transmitted through the Y-shaped optical fiber 1A, Y-shaped optical fiber 1C, Y-shaped optical fiber 2A, Y-shaped optical fiber 2C, the output end of the laser is connected with an optical fiber collimator d and a photoelectric detector b, the optical fiber collimator d aligns the laser to the photoelectric detector b, and the intensity of the laser output by the laser is monitored;
and (3) interference measurement:
laser is transmitted through a Y-shaped optical fiber 1A, Y-shaped optical fiber 1B, the output end is connected with an optical fiber collimator a, the optical fiber collimator a and the optical fiber collimator B are placed on two sides of a flow field to be measured, and laser signals enter a flow field test area; the optical fiber collimator b on the other side collects laser signals, then couples the laser signals into the Y-shaped optical fiber again, and transmits the laser signals through the Y-shaped optical fiber 3B, Y-shaped optical fiber 3A to form an interference measuring optical path;
laser is transmitted through a Y-shaped optical fiber 1A, Y-shaped optical fiber 1C, Y-shaped optical fiber 2A, Y-shaped optical fiber 2B, Y-shaped optical fiber 3C, Y-shaped optical fiber 3A to form an interference reference optical path;
the output end of the Y-shaped optical fiber 3A is connected with an optical fiber collimator c and a photoelectric detector a, interference is generated after the measurement light meets the reference light, and the optical fiber collimator c aligns the laser to the photoelectric detector a to measure interference signals.
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