RU2060503C1 - Method for measuring gas current velocity - Google Patents

Abstract

FIELD: instrumentation engineering; development of true-velocity meters for aviation and meteorology. SUBSTANCE: method involves crosswise flow of gas about circular cylinder continuously rotated about its longitudinal axis, mounting of part sensible to gas current velocity on cylinder surface, recording of two points on cylinder surface where local velocity equals zero upon arrival of signal from sensing element, maintenance of permanent annular interval between these points by regulating angular velocity of rotating cylinder; gas current velocity of interest is determined by angular velocity of rotation drive. EFFECT: facilitated procedure. 4 dwg

Description

 The invention relates to measuring equipment and can be used in instrumentation when creating true speed meters for aviation, as well as in meteorology.

 The known effect of the occurrence of lifting force during the rotation of a circular cylinder in a transverse flow of liquid or gas, the so-called Magnus effect. This effect has been widely used in measurement technology.

 A device [1] is known for measuring the flow velocity, in which the lifting force arising on each of the two rotating cylinders mounted on the rotary frame is converted into torque and is perceived by an elastic element rigidly connected to the rotary frame and the meter body. The magnitude of the angular deviation of the frame from the initial position is judged on the value of the measured speed.

 The known device has several disadvantages. Firstly, the presence of an elastic element having the disadvantages inherent in all elastic elements in principle reduces the accuracy of measuring the flow rate as a whole. Secondly, the frame on which the rotating cylinders are located must necessarily be rotatable, this complicates the design and, accordingly, reduces reliability. Thirdly, the known device when installed on an aircraft (LA) measures the airspeed, an important parameter for piloting. But it is necessary to have a true speed meter on board the aircraft, the readings of which are needed for air navigation, aiming during shooting and bombing, and some other tasks.

 The closest in technical essence and coinciding in principle with the claimed invention is a flowmeter based on the Magnus effect [2] In the measuring chamber of the flowmeter, a horizontal cylinder is rotated at a constant angular velocity perpendicular to its longitudinal axis. The flow of liquid (gas) flows around the cylinder in two gaps between the cylinder and the walls of the chamber, the pressure in which is different. The magnitude of the pressure difference, measured at diametrically opposite points of the cross section of the chamber, is directly proportional to the mass flow rate, i.e., the magnitude of the absolute error is the same in the entire measurement range.

 The purpose of the invention to improve the accuracy of speed measurement.

The goal is achieved by the fact that when flowing around a circular cylinder rotating around its longitudinal axis, the radius of the cylinder and its minimum rotation speed are chosen from the condition that the velocity circulation does not exceed 4πRV _{∞ min} , an element sensitive to the flow velocity is placed on the surface of the cylinder, according to the signal two critical points on the surface of the cylinder, at which the local speed is zero, are sequentially recorded from the sensor element, and a constant angle between these points is maintained by adjusting soon ti rotation of the cylinder, and the largest of the cylinder rotation speed is judged on the gas flow rate.

In FIG. 1 shows a picture of the transverse flow around a potential flow of a rotatable cylinder for the case Г <4πRV _∞ , where Г is the velocity circulation; R is the radius of the cylinder; V _∞ true flow rate; in FIG. 2 diagram of speeds along the cross section of a circular cylinder; in FIG. 3 block diagram of the device; in FIG. 4 stress diagram.

The proposed method is based on a specific velocity distribution over a circular cross-section of a cylinder continuously rotating in a transverse quasi-potential liquid or gas flow for the case Г <4πRV _∞ (condition for two critical flow points to be realized, see Fig. 1).

(1) где θ угол между радиусом, проведенным из центра сечения цилиндра в данную точку на поверхности, и направлением истинной скорости V_∞.It is known that in the case of a transverse potential flow around a cross section, the velocity is determined by the expression
V 2V _∞ • sinθ +

(1) where θ is the angle between the radius drawn from the center section of the cylinder to a given point on the surface and the direction of the true velocity V _∞ .

0 или Г -4πRV_∞•sinθ_кр (2)
Из (2) следует, что при постоянной величине θ _кр циркуляция скорости Г прямо пропорциональна истинной скорости потока V_∞.At critical points, the velocity V 0, therefore, (1) has the form:
2V _∞ • sinθ _cr +

0 or Г -4πRV _∞ • sinθ _cr (2)
It follows from (2) that, at a constant value of θ _{cr, the} circulation of the velocity Г is directly proportional to the true flow velocity V _∞ .

•ω (4)
Из (4) следует, что если величина θ _кр поддерживается постоянной, то измеряемая скорость V_∞ прямо пропорциональна угловой скорости вращения ω
Если обозначить K

const, то (4) примет вид
V_∞= K•ω (5)
Практическую реализацию предложенного способа проиллюстрируем возможным вариантом устройства для измерения скорости потока.The magnitude of the circulation depends on the angular velocity of rotation of the cylinder ω and the radius R of the cylinder and is expressed by the dependence
G 2π R ² ω (3)
Equating the right-hand sides of (2) and (3), we obtain:
2πR ² ω -4πRV _∞ • sinθ _cr , hence
V _∞ =

• ω (4)
It follows from (4) that if θ _{cr is} kept constant, then the measured velocity V _{∞ is} directly proportional to the angular velocity of rotation ω
By K

const, then (4) takes the form
V _∞ = K • ω (5)
The practical implementation of the proposed method is illustrated by a possible embodiment of a device for measuring flow velocity.

 The device has a circular cylinder 1 with a hot-wire anemometer 2 located on its surface, driven by a drive 3, a current collector 4, a voltage resistance transducer 5, a differentiator 6, a comparator 7, a trigger 8, a serial count converter 9, a comparison device 10, a speed controller 11, a sensor 12 angular rotation speeds.

 The device operates as follows.

 A circular cylinder 1 with a hot-wire anemometer 2 located on its surface is driven by a drive 3 and is blown by a gas stream, the speed of which is measured.

 Since the resistance of the hot-wire anemometer will depend on the velocity of the flow V washing it, and the velocity plot along the cylinder section is given in FIG. 2, the resistance of the hot-wire anemometer will change, and the nature of the change is shown in FIG. 4a.

 The signal of the hot-wire anemometer through a current collector 4 is supplied to the resistance converter voltage 5, the output of which will be a voltage, the type of change of which is shown in FIG. 4b.

 Differentiator 6, receiving a signal from converter 5 at the input, creates an output voltage proportional to the rate of change of the input. At the output of the differentiator 6 there will be a signal, the form of which is shown in FIG. 4c.

At the first input of the comparator 7, a signal is supplied from the differentiator 6, and at the second input, the reference voltage is U _op , the value of which is 0, i.e., U _op 0.

 Thus, the output of the comparator 7 will have a signal at the same time when the output signal of the differentiator 6 is positive. A view of the output signal from the comparator 7 is shown in FIG. 4g The output signal from the comparator 7 is fed to the input of the trigger 8.

 Depending on the execution scheme, dynamically controlled triggers react to voltage drops from zero to one (active front) or from one to zero (active slice of the control pulse), i.e., signals arriving at a dynamic input are perceived only at those moments time when their state changes in a certain way.

 Trigger 8, receiving a signal from comparator 7 at the input (signal type, see Fig. 4d), sets the signal at the front of the first pulse, and removes it at the front of the second pulse.

 Thus, the output of flip-flop 8 is a sequence of rectangular pulses depicted in FIG. 4d

 The output signal from the hot-wire anemometer 2 (Fig. 4a) is a sequence of alternating pairs of half-cycles, the first half-period having a longer duration than the second. This form of the output signal of the hot-wire anemometer is easily explained when referring to FIG. 2, which shows a plot of speed in the transverse flow around a rotatable cylinder. At point A, the speed is zero, and when moving in the direction indicated in FIG. 2 by an arrow from t. A to t. B, the speed first increases, and then decreases and in t. B it is again zero.

 When moving from t. In speed again first increases, and then decreases in t. A is equal to zero.

 Since the hot-wire anemometer reacts to the value of the airspeed, a change in the output signal of the hot-wire anemometer is similar to a change in the speed.

Thus, the duration of the short half-period of the output signal of the hot-wire anemometer corresponds to the time it takes for the arc to travel between t. B and t. A, limited by the angle γ _cr (see Fig. 2).

 As seen in FIG. 4, the rectangular pulses at the output of the trigger 8 have a duration equal to the transit time of the hot-wire anemometer 2 of the arc between critical points (arc VA in Fig. 2). The output signal from trigger 8 is fed to the input of the serial count converter 9.

The transducer 9 measures the duration of the rectangular pulses generated by the trigger 9, that is, based on the foregoing, the time during which the hot-wire anemometer 2 passes the distance between two critical points (arc VA in Fig. 2), we denote it by the symbol τ _meas .

Comparison device 10 receives a signal τ _ism at one of its input (the time it takes for the hot-wire anemometer to pass the distance between critical points, arc VA in Fig. 2) from the transducer 9 and to another input a signal about the value of the angular velocity ω of the circular cylinder 1 from the angle sensor 12 speed.

Maintaining a constant value of θ _cr (see formula (4)) is equivalent to maintaining a constant value of γ _cr , since according to FIG. 2 values of θ _cr and γ _cr related linearly.

γ _cr 180-2 · θ _cr (6)
On the other hand, the value of γ _cr is defined as the product of the angular velocity of rotation of a circular cylinder 2 with a hot-wire anemometer 2 located on it and the travel time between the critical points of the hot-wire anemometer τ _meas.
γ _cr ω · τ _ISM (7)
Thus, the comparison device 10, receiving the input signals ω and τ _ISM , multiplies them and compares the result with the value of γ _{cr. ass}
The numerical value of γ _{cr. the backside is} determined by the formula (6) when substituting the specified into it, based on the design features determined during the design of the device, the value of θ _cr, which must be kept constant.

If the obtained value of γ _{cr is} greater than γ _{cr. ass} , then the device 10 sends to the regulator 11 revolutions command "Reduce revolutions" if γ _cr <γ _{cr. ass} , then the device 10 sends to the controller 11 command "Increase speed".

If γ γ _{cr cr. ass,} then at the output of the device 10 there is no signal (zero signal) and the measuring system is in a state of dynamic balance, thereby providing a zero measurement method.

 The speed controller 11 carries out increases or decreases in the speed of the rotation drive 3 in accordance with the command that is currently being received at its input from the device 10. If there is no signal from the device 10 at the input of the controller 11, the controller provides constant rotation speeds of the rotation drive 3 corresponding to the value that they had at the moment when the previous command of the device 10 was changed to a zero signal.

The sensor 12 of the angular velocity of rotation changes the angular speed of the actuator 3 and provides a signal (as described above) to the input of the comparison device 10, and at the same time, the sensor 12 generates a signal ω to the output of the device, and this signal, as follows from (5), is proportional to the measured speeds V _∞
Thus, when the device is in operation, stabilization (maintaining a constant value) of the angle θ _cr (or γ _cr , which is the same thing) occurs due to a change in the angular velocity of rotation of cylinder 1 by drive 3, and the output signal of the device, angular velocity ω is generated by sensor 12. Moreover, the value is directly proportional to the value of the measured gas flow velocity V _∞ and, therefore, the magnitude of the absolute error in the entire range will be the same.

Claims (1)

A method of measuring the gas flow velocity by transverse quasi-potential flow around a circular cylinder rotating around its longitudinal axis, characterized in that the cylinder radius R and the minimum rotation speed V _{m i n of} its rotation are selected from the condition that the velocity circulation does not exceed 4πRV _{∞ min} a surface sensitive to the flow velocity is placed on the cylinder surface; two critical points on the surface of the cylinder at which the local speed is equal to n Liu, maintain a constant angle between these points by adjusting the speed of rotation of the cylinder, and the largest of the cylinder rotation speed is judged on the gas flow rate.

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