JP2002082014A - Device and method of accurately measuring non- stationary aerodynamic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure non-stationary aerodynamic force in a wind tunnel test of a model of a various construction member or the like, by removing influence of extremely large inertial forces acting simultaneously. SOLUTION: This measuring device comprises a support bar of the model, an exciting part for vibrating the model through the support bar, and a counter weight mounted on the support bar opposite against a model of a connecting point with the exciting part, and a measuring part using a strain gauge mounted near the connecting point as a sensor. In this measuring method, strain near the connecting point is detected while the model is vibrated through the support bar, and one or both of a mass and a mounting position of the counter weight is adjusted so as to balance a moment acting on the connecting point with the inertial force of the counter weight generated by the vibration with a moment acting on the connecting point with the inertial force of the model generated by the vibration. A hinge structure is introduced into the support bar to remove influence of rigidity of the model.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-precision unsteady aerodynamic force measuring device and a method of measuring unsteady aerodynamic force using the device, and particularly to a wind tunnel test of a model such as various structural members.
The present invention relates to a technique for measuring unsteady aerodynamic forces acting on a model with high accuracy by a forced vibration method.

[0002]

2. Description of the Related Art A representative method for measuring unsteady aerodynamic force, which is a dynamic aerodynamic force acting on a model, includes a forced vibration method and a free vibration method. These methods are described on pages 99 and 587 of “Wind Engineering of Structures” (edited by the Japan Steel Structure Association, published by Tokyo Denki University Press). The forced vibration method is a method of measuring a non-stationary aerodynamic force by forcibly exciting a model at the time of blowing air and measuring a force acting on the model.

FIG. 8 shows an example of a conventional unsteady aerodynamic force measuring device using the forced vibration method. FIG. 9 shows the principle diagram. As shown in FIG. 8, the model 4 to be measured is placed in the wind tunnel 1, and the support rods 5 connected to the supports 14 provided on both sides outside the wind tunnel are projected from the holes of the wind tunnel wall 2 into the wind tunnel. Model 4
I support. The support table 14 is connected to the vibrator 12 by the arm 11 to forcibly vibrate. The vibration is performed by, for example, a method in which the rotation of the electric motor is transmitted to the eccentric plate by a V-belt to change the rotational motion into a vertical motion.

[0004] In the wind tunnel 1, as shown in FIG.
While the model 4 is vibrated at a constant amplitude and a constant frequency by the vibrator 12, the unsteady aerodynamic force Fa acting as a dynamic aerodynamic force acting on the model 4 is applied to the strain gauge 9 via the support rod 5. Was detected. The strain gauge 9 is attached to the base of the support rod 5 protruding from the support base 14 as shown in FIG.
The signal is converted into an electric signal and detected.

However, the force detected here includes not only the unsteady aerodynamic force Fa but also the inertial force Fi acting on the model 4 during vibration. For this reason, conventionally a dummy model was used,
Excitation under the same conditions was performed outside the wind tunnel under no wind, only the inertial force Fi was measured, and the unsteady aerodynamic force Fa was calculated from the difference between the two. The dummy model has the same mass as the model to be measured and is formed so that unsteady aerodynamic force does not work. The model 4 to be measured repeatedly measures Fa + Fi while changing the wind speed in the wind tunnel, and subtracts Fi measured by the dummy model to calculate the unsteady aerodynamic force Fa for each wind speed.

[0006]

As shown in FIG. 9, an inertial force Fi much larger than the unsteady aerodynamic force Fa acts on the model 4, and Fa is usually one order of magnitude smaller than Fi.
Therefore, in order to increase the measurement accuracy of the unsteady aerodynamic force Fa detected by the strain gauge, the electric signal at the time of detection is amplified, but the ratio of the unsteady aerodynamic force Fa to the inertial force Fi is changed no matter how much amplification is performed. Therefore, there is naturally a limit in the measurement accuracy.

The unsteady aerodynamic force F with respect to the inertial force Fi
The ratio of a also depends on the phase difference. For example, if Fa is F
At 10% of i, if the phase difference between Fa and Fi is 0 °, Fa remains 10% of Fi, but the phase difference is 90%.
°, Fa becomes about 1% of Fi. That is, in some cases, there is a possibility that an error will be measured.

The problem to be solved by the present invention is
In the wind tunnel test of models such as various structural members, when measuring the unsteady aerodynamic force acting on the model by the forced vibration method, it eliminates the effect of the extremely large inertia force acting simultaneously and measures with high accuracy And a method for measuring unsteady aerodynamic force using the device.

[0009]

According to an embodiment of the present invention, there is provided an apparatus for supporting a model to be measured, which is installed in a wind tunnel, and a vibrating unit for vibrating the model via the supporting rod. A counterweight attached to a support bar on the opposite side of the model at the connection point with the vibrating section, and a measurement section having a strain gauge attached near the connection point as a sensor. It is a highly accurate unsteady aerodynamic force measurement device. In the above-described device of the present invention, it is preferable that a hinge structure is introduced to the support rod on the model side of the connection point with the vibration unit.

According to the method of the present invention for solving the above-mentioned problems, a supporting rod for supporting a model to be measured, which is installed in a wind tunnel, is connected to a vibrating part, and a connecting point with the vibrating part is opposite to the model. A counterweight is attached to the support rod on the side, the model is vibrated through the support rod, the moment acting on the connection point by the inertia force of the counterweight generated by the vibration, and the inertia force of the model generated by the vibration. A high-precision unsteady aerodynamic force characterized by detecting distortion near the connection point in a state where one or both of the mass and the mounting position of the counterweight is adjusted so that the moment acting on the connection point is balanced. It is a measuring method. In the method of the present invention, it is preferable that a hinge structure is introduced to the support rod on the model side from the connection point with the vibrating section to eliminate the influence of the rigidity of the model.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The apparatus according to the present invention measures unsteady aerodynamic force acting on a model 4 installed in a measuring tunnel of a wind tunnel 1 as shown in FIG. It is composed of a vibrating section, a counterweight 8 and a measuring section. The support rod 5 supports the model 4 from both sides through a hole in the wind tunnel wall 2,
In this example, both sides are bifurcated outside the wind tunnel. Each of the divided support rods 5 is connected to a strain detection column 7 held by a sensor frame 6, and a counter weight 8 is attached outside the strain detection column 7, that is, on the opposite side of the model 4.

The sensor frame 6 is attached to an arm 11 at a mounting portion 10.
The mounting portion 10, the arm 11, and the vibrator 12 form a vibrating portion. A strain gauge 9 is attached to the strain detection column 7 as in the example of FIG. 4, and a measurement unit is configured by the sensor frame 6, the strain detection column 7, the strain gauge 9, a connection (not shown), an instrument, and the like.

FIG. 2 shows the principle of measurement by the apparatus according to the present invention.
The model 4 is supported by the support bar 5 at two points on both sides, but FIG. 2 shows only one side. When the model 4 is vibrated through the strain detecting column 7 and the support rod 5, the unsteady aerodynamic force Fa and the inertia force Fi act on the model 4, but the inertia force Fi also acts on the counterweight 8. At the connection point between the support rod 5 and the strain detecting column 7, a moment due to the inertia force Fi _M of the model and a moment due to the inertia force Fi _C of the counterweight are generated in the opposite direction, as indicated by arrows, and the unsteady air A moment is generated by the force Fa.

The principle of the device of the present invention is as shown in FIG. 2 by balancing the moment due to the inertial force Fi _M of the model 4 and the moment due to the inertial force Fi _C of the counterweight 8 to obtain the moment due to the unsteady aerodynamic force Fa. Is detected and Fa, which is orders of magnitude smaller than the inertial force Fi, is measured with high accuracy.

The procedure is as follows. (1) First, a dummy model having the same mass as that of the model 4 and having no air force acting thereon is mounted. (2) to vibrate in a Model 4 the same conditions to be measured in this state, the inertia force Fi _M and same inertia of the model 4 is the dummy model is applied, the moment due to the inertial force Fi _M and counterweight 8 moment by the inertial force Fi _C is in balance, as distortion due bending moment from the strain gauges 9 is a state of not being detected, the counterweight 8
Adjust one or both of the mass and mounting position.

(3) Next, the dummy model is removed and the model 4 to be measured is mounted. (4) In this state, vibration is performed under the same conditions. Then model 4
Inertia force Fi _M is canceled by the inertia force Fi _C of the counterweight 8, and the unsteady aerodynamic force Fa is obtained from the strain gauge 9.
Is detected, and is amplified and converted into unsteady aerodynamic force Fa. In this state, the wind speed is changed, and the unsteady aerodynamic force Fa with respect to the wind speed can be measured.

The details of the sensor frame 6 are shown in FIG. 3. As shown in FIG. 3, on both sides of a center of rotation 13 opened in the center, strain detecting columns 7 are attached with their upper and lower ends connected to the frame 6. The support bar 5 is connected to the strain detecting column 7, and a strain gauge 9 is attached to the upper end and the lower end of the strain detecting column 7 as shown in FIG. At both ends of the sensor frame 6, mounting portions 1 for the vibrating portion are provided.
0 is provided.

When vertically vibrating the model 4, the mounting portions 10 at both ends are connected to a vibrator 12 by arms 11. When applying rotational vibration, the mounting portion 10 at one end is connected to a vibrator 12 by an arm 11 and the center of rotation 13 is rotatably fitted to a fixed shaft (not shown).

As shown in FIG. 4, a strain gauge 9a and a strain gauge 9b are attached to the strain detecting column 7, and an aerodynamic force (lift) acting in a vertical direction is measured by the strain gauge 9a. The aerodynamic force (air moment) to be rotated about the axis 5 can be measured. In this example, in consideration of the case of canceling the polar moment of inertia during rotation, two strain detection columns 7 are provided on one side, and a counter weight 8 is attached to each of them.

FIG. 5 shows an image of the principle of measurement by the apparatus of the present invention using a Yajirobei doll. In the state of (a),
The doll stands upright with the inertial force Fi _M of the model 4 acting on both arms and the inertial force Fi _{C of the} counterweight 8 being balanced.
When the unsteady aerodynamic force Fa acts on the model 4, even if the Fa is minute, the doll senses this and loses its balance as shown in FIG. Since the degree of inclination of the doll changes depending on the magnitude of the unsteady aerodynamic force Fa, the unsteady aerodynamic force Fa can be measured by detecting the strain at the tip of the strain detecting column 7 supporting the doll.

Further, in the apparatus of the present invention, it is preferable that a hinge structure is introduced into the support rod on the model side with respect to the connection part with the vibration part. An example is shown in FIG. In this example, the support rod 5 is bifurcated outside the wind tunnel in a horizontal plane, and each of the divided support rods 5 is bent into an L-shape in the support direction in the horizontal plane, and is connected to the strain detection column 7. The hinge structure 15 is provided at the portion where the hinge structure is located. The strain detecting column 7 is connected via a sensor frame 6 to a mounting section 10 constituting a vibrating section.

As described above, by introducing the hinge structure 15 to the support rod 5 on the model 4 side from the connection with the vibrating section, the effect of the rigidity of the model 4, that is, the moment due to the deformation of the model 4 during the measurement is obtained. Ingredients are removed. Therefore, the strain gauges 9a and 9b attached to the strain detecting column 7 make it possible to more accurately extract the moment due to the unsteady aerodynamic force.

Next, the method of the present invention is a method for measuring unsteady aerodynamic force by the above-mentioned apparatus of the present invention. As shown in FIG. 1, a support rod 5 for supporting a model 4 installed in a wind tunnel 1 is used as a vibrating part. The counterweight 8 is attached to the support bar 5 on the opposite side of the model 4 at the connection point with the vibration unit. Then, the model 4 is vibrated through the support rod 5, and as shown in FIG. 2, the moment acting on the connection point by the inertia force Fi _C of the counterweight 8 generated by the vibration, and the inertia force of the model 4 generated by the vibration
One or both of the mass and the mounting position of the counterweight 8 is adjusted so that the moment acting on the connection point by Fi _M is balanced. As described above, in a state where the inertia force Fi _M of the model 4 is canceled by the inertia force Fi _{C of the} counterweight 8, distortion near the connection point due to only the moment due to the unsteady aerodynamic force Fa is detected, and the unsteady aerodynamic force is detected. Measure Fa.

In the method of the present invention, it is preferable to remove the influence of the rigidity of the model by introducing a hinge structure to the support rod on the model side of the connection point with the vibrating section. It is possible to more accurately extract the moment due to the unsteady aerodynamic force.

FIG. 6 is a block diagram showing a measurement example according to the method of the present invention. When the model is vibrated at a constant amplitude and a constant frequency by a forced shaker at the time of no wind and at the time of blowing, the unsteady aerodynamic force acting on the model can be detected as strain by the strain gauge. The detected strain is electrically amplified by a dynamic strain meter. Since the unsteady aerodynamic force has a phase difference with the vibration displacement of the model, the vibration displacement of the model is simultaneously measured by the laser displacement meter.

Since the measured vibration displacement and the amplified distortion are both analog signals, they are converted into digital signals by an AD conversion board and input to a personal computer. The personal computer converts the distortion into unsteady aerodynamic force and records the unsteady aerodynamic force and vibration displacement on the MO disk as digitized time-series data. On the other hand, the time series data was analyzed using fast Fourier transform software, and the absolute value and the phase difference of the unsteady aerodynamic force were the same for the excitation frequency component corresponding to the vibration displacement of the model subjected to forced excitation. To be stored. Using this MO disk, various subsequent processes such as data analysis can be performed.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The cross section of a measuring cavity is 1.1 m wide and 1.8 m high.
The experiment was conducted by installing a flat plate model in the wind tunnel. FIG. 7 shows the measurement result of the unsteady aerodynamic force Fa. The amplitude of the forced vibration is 1 mm, the half amplitude (A when the vibration is expressed as A sinωt) is 2 mm.
mm, 3 mm, and 4 mm, and the frequency was 4 Hz. It should be noted that almost the same tendency was exhibited when the frequency was changed. The present invention example was measured by the present invention apparatus as shown in FIG. Conventional example 1
In the wind tunnel, the flat plate was suspended horizontally by a spring, freely vibrated in still air, and measured from the obtained free-damping vibration waveform. Conventional Example 2 was measured by a conventional apparatus as shown in FIG.

The measurement results of the present invention example and the conventional example 2 measured by the forced vibration method are greatly different, and the conventional example 2 is about five times higher than the present invention example. The value of the example of the present invention is almost equal to that of the conventional example 1 measured by the free vibration method. From this, it can be seen that the apparatus and the method of the present invention for measuring the unsteady aerodynamic force, which is indispensable for grasping the dynamic behavior of a structure or the like, with high accuracy are extremely excellent.

In the measurement by the free vibration method, the damping state of the vibration is obtained from the vibration displacement, and the vibration velocity proportional component of the vibrating aerodynamic force is accurately measured. However, since it is difficult to measure a small change in response frequency due to aerodynamic force by the free vibration method, it is very difficult to measure a displacement proportional component of the oscillating aerodynamic force. Therefore, among the unsteady aerodynamic forces measured by the method of the present invention, the fact that the measured value of the vibration velocity proportional component is close to the measured value by the free vibration method means that the accuracy of the method of the present invention is high. .

In particular, the point of the method of the present invention is that the measurement method does not sense the inertial force of the model, so that it is possible to amplify and measure only the aerodynamic force itself, thereby increasing the measurement accuracy of the phase difference from the vibration displacement. It is that you are. In particular, knowing the behavior of the phase difference is important in knowing the mechanism of aerodynamic force generation, so that measurement of unsteady aerodynamic force by the forced vibration method is necessary.

[0031]

According to the present invention, models of various structural members such as girder cross sections of long bridges, wing cross sections of aircraft, cross sections of high-rise buildings, cross sections of slender structural members, and the like, in which vibration in the air flow is a problem. In the wind tunnel test, when measuring the unsteady aerodynamic force acting on the model by the forced vibration method, the effect of the unusually large inertia force acting simultaneously is eliminated, and the unsteady aerodynamic force is measured with high accuracy. As a result, the dynamic behavior of the various structural members and the like in the airflow can be grasped with high accuracy.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration example of a device of the present invention.

FIG. 2 is an explanatory diagram showing the principle of the present invention.

FIG. 3 is a detailed explanatory diagram of an example of a sensor in the device of the present invention.

FIG. 4 is an explanatory diagram illustrating an example of a distortion detection unit in the device of the present invention.

FIGS. 5A and 5B are explanatory views conceptually showing the principle of the present invention.

FIG. 6 is a block diagram showing an example of the method of the present invention.

FIG. 7 is a graph of an example.

FIG. 8 is an explanatory diagram showing a configuration example of a conventional device.

FIG. 9 is an explanatory view showing the principle of a conventional device.

FIG. 10 is an explanatory diagram showing another example of the present invention.

[Explanation of symbols]

1: Wind tunnel 2: Wind tunnel wall 3: Wind 4: Model 5: Support bar 6: Sensor frame 7: Strain detection column 8: Counter weight 9: Strain gauge 10: Mounting part 11: Arm 12: Exciter 13: Rotation center 14: support base 15: hinge structure Fa: unsteady aerodynamic force Fi: inertia force Fi _M : model inertia force Fi _C : counterweight inertia force

Claims (4)

[Claims] 1. A support bar for supporting a model to be measured, which is installed in a wind tunnel, a vibrating unit for vibrating the model via the support bar, and a support of a connection point with the vibrating unit on a side opposite to the model. A high-precision unsteady aerodynamic force measuring device, comprising: a counterweight attached to a rod; and a measuring unit using a strain gauge attached as a sensor near the connection point. 2. The high-precision unsteady aerodynamic force measuring device according to claim 1, wherein a hinge structure is introduced into a support rod on a model side of a connection point with a vibration unit. 3. A supporting rod for supporting a model to be measured, which is installed in a wind tunnel, is connected to the vibrating section, and a counterweight is attached to the supporting rod opposite to the model at a connection point with the vibrating section. The model is vibrated through the support rod, and the moment acting on the connection point by the inertia force of the counterweight generated by the vibration and the moment acting on the connection point by the inertia force of the model generated by the vibration are balanced. And detecting a strain near the connection point while adjusting one or both of the mass and the mounting position of the counterweight. 4. A high-precision unsteady aerodynamic force measurement according to claim 3, wherein a hinge structure is introduced to the support rod on the model side from the connection point with the vibrating part to remove the influence of the rigidity of the model. Method.