JPH11237278A - Sound pressure measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a device that can accurately measure a sound pressure being generated by a high-temperature gas that flows in a duct and can use a general, inexpensive microphone even if a gas temperature is high. SOLUTION: A sound pressure measuring device is provided with a casing 7 where a microphone 4 is provided in a tip part and an opening is provided on a rear end face, a signal cable protection pipe 10 where a tip being provided in the casing 7 is connected to the rear edge of the microphone 4 and a rear edge is connected to the above opening, a cooling water room 21 that is formed between the protection pipe 10/the microphone 4 and the casing 7, and a water- supply pipe 8 and a drain pipe 9 for supplying/draining cooling water 13 into/ from the inside of the cooling water room 21. The tip is mounted to a measurement seat 3 and a sound pressure that is generated by a high-temperature gas that flows inside the duct is measured while the microphone at the tip part is being cooled by the cooling water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sound pressure measuring device applied to measurement of gas turbine exhaust noise in a gas turbine exhaust duct.

[0002]

2. Description of the Related Art The sound power level of exhaust gas from a gas turbine or the like can be determined with high accuracy, thereby making it possible to optimize exhaust noise silencing equipment and reduce costs, thereby reducing the cost of the entire plant. Can contribute to improving the competitiveness of products. However, high-temperature gas flows in the exhaust duct, and it is not easy to measure the exhaust noise in the exhaust duct.

In conventional sound pressure measurement of gas turbine exhaust noise, as shown in FIG. 3, a waveguide 24 is used to measure the distance from the surface of a heat insulating material 2 provided inside a duct wall 1 to a microphone 4. By taking L, the sound pressure was measured assuming that the high-temperature gas did not directly touch the microphone 4. In the middle of the waveguide 24, the elastic tube 2 is used.
5 is provided so that the vibration of the duct 1 does not propagate to the microphone 4.

[0004]

In the conventional sound pressure measurement of gas turbine exhaust sound, as described above, one end of the waveguide is inserted into the exhaust passage, and a microphone is attached to the other end. Was.

However, in the case of a conventional sound pressure measuring device using a waveguide, an air column resonance phenomenon corresponding to the length L of the waveguide occurs. Will change.

[0006] The resonance frequency f _o of the above waveguide of length L is
It can be expressed by the following equation. f _o = (2n−1) C / 4L [Hz] where n: order, C; sound velocity in duct = (g · K · R)
・ T) ^1/2 where g: gravitational acceleration, K: specific heat ratio, R: gas constant,
T: gas absolute temperature In the above equation, if L = 1 m, g = 9.8 m /
Since s, K = 1.4, R = 29.27, and T = 873K (when the gas temperature is 600 ° C.), f _o = 148.
Hz.

[0007] This case, since the range in which a certain sound pressure is obtained for the frequency change (range flat frequency characteristic is obtained) is generally f _o / 3 or less, only up to about 50Hz accurate measurement You can't. It is not impossible to test the sound pressure change with respect to the frequency change in advance and correct the measured data, but the accuracy is considerably reduced.

Although it is conceivable to perform measurement by flush mounting a high-temperature microphone in a duct without using a waveguide, such a microphone is very expensive and the usable temperature is up to 600 ° C. However, under the current situation where the exhaust gas temperature is extremely high due to the high temperature accompanying the high efficiency of the gas turbine, the temperature exceeds the measurable limit temperature, and it is becoming impossible to respond.

As described above, the conventional apparatus has the following problems. (1) In the waveguide method, flat frequency characteristics cannot be obtained in a range up to a high frequency due to a resonance phenomenon of the waveguide, and measurement can be performed only at a very low frequency.

(2) In the method of mounting the high-temperature microphone by flash mounting, the cost of the microphone is extremely high and the measurable temperature is limited, so that it is impossible to cope with the high temperature of the gas turbine. The present invention seeks to solve the above problems.

[0011]

According to a first aspect of the present invention, there is provided a sound pressure measuring apparatus, comprising: a cylindrical casing having a microphone provided at a front end thereof and a circular opening formed at a center of a rear end face; And a signal cable connected to a rear end of the microphone is disposed inside the rear end of the casing, and a signal cable connected to a rear end of the microphone is disposed therein. A cooling water chamber formed between the pipe, the protection tube, the microphone, and the casing, and a water supply pipe and a drain pipe connected to the cooling water chamber, in which a high-temperature gas that generates sound pressure flows. The tip is attached to a measurement seat provided in the duct, and the sound pressure is measured.

In the present invention, when the tip of the sound pressure measuring device is attached to the measuring seat and the sound pressure at which the high-temperature gas flowing in the duct is measured is measured, the cooling water is supplied by the water supply pipe and the drain pipe. The measurement is performed while circulating in the room and cooling the microphone.

[0013] Therefore, the position of the microphone can be adjusted so that the tip end surface forms the same plane as the inner surface of the duct.
Since air column resonance does not occur unlike the conventional device using a waveguide, it is possible to obtain a frequency characteristic with a flat sound pressure level up to the high frequency range where measurement is required, and to obtain high-precision sound. Pressure measurement becomes possible.

Further, even when the temperature of the gas flowing in the duct becomes high, an inexpensive general-purpose microphone can be used. For example, when the microphone is used in a gas turbine exhaust duct, the exhaust gas temperature rises. The accompanying increase in measurement cost can be suppressed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A sound pressure measuring device according to one embodiment of the present invention will be described with reference to FIGS. In this embodiment, the heat insulating material 2 of the exhaust duct of the gas turbine is provided on the duct wall 1.

1 and 2, reference numeral 3 denotes a cylindrical measuring seat, which is provided in the exhaust duct and has an opening communicating with the inside thereof. Reference numeral 4 denotes a microphone to which a signal cable 5 is connected at a rear end. Reference numeral 6 denotes a ring-shaped tip cap, on which the microphone 4 is disposed via an O-ring 11a and a sheet 12a.

Reference numeral 7 denotes a cylindrical casing.
a, 7b, and 7c are formed by welding, the tip member 7a is screwed to the tip cap 6, and the rear member 7c has a circular opening at the center thereof. Forming a wall.

Reference numeral 20 denotes a ring-shaped microphone fixing bracket, the front end of which is joined to the rear end of the microphone 4 via an O-ring 11b and a sheet 12b. Reference numeral 10 denotes a signal cable protection tube in which the signal cable 5 is disposed. The signal cable protection tube 10 has a front end connected to the microphone fixing bracket 20 and a rear end connected to an opening of a member 7c forming the casing 7. Have been.

Reference numeral 8 denotes a water supply pipe inserted and connected from the rear end of the member 7c, and 9 denotes a drain pipe connected to the rear end of the member 7c. Reference numeral 21 denotes a cooling water chamber formed between the tip cap 6 and the casing 7 and the microphone 4, the microphone fixing bracket 20, and the signal cable protection tube 10,
It communicates with the water supply pipe 8 and the drain pipe 9.

Reference numerals 14a and 14b denote loose flanges, respectively, and an O-ring 1 is provided between each and the casing.
1c, and each loose flange 14a, 14
The casing is fixed to the measuring seat 3 by tightening b to the measuring seat 3 with a bolt 15.

The microphone 4, the signal cable 5, the tip cap 6, the casing 7, the water supply pipe 8, the drain pipe 9, the signal cable protection pipe 10, the O-rings 11a, 11
b, the sheets 12a and 12b and the microphone fixing bracket 20 form a sound pressure measuring device.

In the above description, when measuring the exhaust noise of the gas turbine in the exhaust duct, the tip of the sound pressure measuring device provided with the microphone 4 is inserted into the opening of the measuring seat 3, and the O-ring 11c is attached. After the sound pressure measuring device is disposed on the outer periphery of the casing 7 of the sound pressure measuring device sandwiched between the loose flanges 14a and 14b, the loose flanges 14a and 14b are tightened to the measuring seat 3 with bolts 15, so that the sound pressure measuring device can be mounted on the measuring seat. Fix to 3.

After the sound pressure measuring device is fixed to the measuring seat 3, the cooling water 13 is supplied into the cooling water chamber 21 through the water supply pipe 8, circulated therein, and discharged through the drain pipe 9. The sound of the exhaust gas of the gas turbine is measured by the microphone 4.

In this embodiment, since the microphone 4 is cooled by the cooling water 13, the position of the microphone 4 is adjusted so that the front end surface thereof forms the same surface as the surface of the heat insulating material 2, and the microphone 4 is placed inside the duct. Flush mounted.

Therefore, unlike the conventional apparatus using a waveguide, air column resonance does not occur, and a flat frequency characteristic of a sound pressure level can be obtained up to a high frequency range where measurement is required. Highly accurate sound pressure measurement becomes possible. Also,
Since water cooling is performed constantly, even when the exhaust gas temperature becomes high, an inexpensive general microphone can be used, and the measurement cost can be reduced.

The temperature around the microphone 4 can always be kept at an appropriate temperature by checking the water temperature of the drain pipe 9 and controlling the amount of cooling water by operating a valve. Further, the cooling water 13 is supplied to the O-rings 11a and 11b.
Therefore, there is no leakage into the tip of the microphone 4 and the signal cable protection tube 10.

Further, the sheets 12a and 12b provided before and after the microphone 4 are insulating materials made of, for example, polytetrafluoroethylene. Since the microphone 4 is electrically insulated from the casing 7, a power supply nozzle and the like are provided. Not affected by

[0028]

According to the sound pressure measuring device of the present invention, there is provided a casing provided with a microphone in the front end and an opening in the rear end face, and a casing provided in the casing and having the front end joined to the rear end of the microphone. A signal cable protection tube having an end coupled to the opening, a cooling water chamber formed between the protection tube and the microphone and the casing, a water supply pipe for supplying and discharging cooling water to and from the cooling water chamber, and a drainage water With a tube, the tip of which is attached to the measuring seat, and the microphone at the tip is cooled by cooling water, and the sound pressure generated by the hot gas flowing through the duct is measured. Since air column resonance does not occur in this way, it is possible to obtain a frequency characteristic with a flat sound pressure level up to the high frequency range where measurement is required, which enables high-precision sound pressure measurement. , Even when the gas temperature is increased can use microphones inexpensive general use,
It is possible to suppress an increase in measurement cost.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a sound pressure measuring device according to an embodiment of the present invention.

FIG. 2 is a view taken in the direction of the arrow in FIG. 1, wherein FIG.
(B) is a view taken along the arrow BB, (c) is a view taken along the arrow CC, and (d).
FIG. 4 is a view as seen from the direction of the arrow D-D.

FIG. 3 is an explanatory view of a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Duct wall 2 Heat insulation material 3 Measurement seat 4 Microphone 5 Signal cable 6 Tip cap 7 Casing 7a, 7b, 7c Member 8 Water supply pipe 9 Drain pipe 10 Signal cable protection pipe 11a, 11b, 11c O-ring 12a, 12b Sheet 13 Cooling water 14a, 14b Loose flange 15 Bolt 20 Microphone fixing bracket 21 Cooling water chamber

Claims (1)

[Claims] 1. A cylindrical casing having a microphone provided at a front end thereof and a circular opening provided at the center of a rear end face, and disposed in the casing and having a front end joined to a rear end of the microphone and a rear end. A signal cable protection tube in which a signal cable connected to the rear end of the microphone is connected to an opening in the rear end surface of the casing, and the signal cable protection tube is formed between the microphone and the casing. A cooling water chamber, and a water supply pipe and a drain pipe connected to the cooling water chamber. A sound pressure measuring device for measuring pressure.