JPS6394130A - Flutter stopping device - Google Patents

Abstract

PURPOSE:To stop a test body from fluttering and to prevent the test body from being broken owing to excitation by a panel which has many ventilation holes while stood against an air flow at an upstream position of a test body support position in a wind channel. CONSTITUTION:The panel 1 consisting of the frame 3 and a wire gauge 2 is stood pivotally on the floor 6 of a blade model 7 at the upstream position in the wind channel. The panel 1 is laid face-down on the floor 6 first and the wind velocity in the wind channel is increased gradually. The signal of an accelerometer 8 mounted on the blade model 7 is monitored during this period and when the blade model 7 begins to flutter, a signal is sent out to an unshown panel driving device to raise the panel 1 speedily from the floor 6. An air flow is reduced in speed and rectified by the many ventilation holes of the panel 1 to stop the blade model 7 from fluttering. At this time, the disturbance of the air flow behind the panel 1 is small, so the blade model 7 never flutters owing to excitation after the stop of the fluttering.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to a flutter stopping device for quickly and safely stopping the flutter of a test object in a wind tunnel experiment.

In conventional flutter mounting in wind tunnel testing, once the test specimen flutters, it typically fails within a few seconds.

Therefore, when flutter occurs, it is necessary to quickly stop the flutter to protect the test specimen.

Broadly speaking, there are two methods for stopping the flutter of a test object: a method of physically restraining the test object, and a method of reducing the wind speed to reduce the dynamic pressure acting on the test object.

Conventionally, as a method of physically restraining a test specimen, several threads 31 are attached to a test specimen 30, as shown in FIG.
A method is used in which a person outside the measuring section pulls the string to restrain the test specimen and stop the flutter. Although this method is simple, it has the disadvantage that the airflow near the test specimen is distorted by the threads, and the aeroelastic properties of the test specimen are changed by the aerodynamic force acting on the threads, so the number of threads used must be limited. Must be. For this reason, it is impossible to stop flutter in various modes simply by restraining the large deformation of a portion of the test specimen. To avoid this, it is sometimes done to stop the flutter by pulling the test specimen with a string and simultaneously lowering the wind speed in the wind tunnel, but in this case, it takes 3 to 5 seconds to stop the flutter. During this period, the test specimen was severely damaged.

Furthermore, as a method of reducing dynamic pressure, there is a known method of bypassing the collecting tunnel and the measuring section, but this requires extensive construction work to improve the wind tunnel.

Another method is to move the test specimen into and out of the wind tunnel airflow. This method complicates the structure of the operating part, and in the case of test specimens such as wings that are soft and have a long span, the test specimen may be damaged by the impact caused by starting and stopping the operating part.

Furthermore, as another method, this device was developed for the purpose of stopping the divergence of a model wing, but depending on how it is used, it can also be used to stop flutter. There is a way to stand it diagonally. Looking at this method from the perspective of the flutter stopping effect, as can be seen from the graph in FIG. In this case, there is a range in which the same aerodynamic force that occurs when the advance angle becomes small acts on the wing model, reducing the flutter speed and making flutter more intense. There is a problem that there is no flutter stopping effect.

Further, the degree of turbulence in the wake of the plate 33 has a property of becoming stronger as the Ray-Nozzle number Re increases.

Generally, the Raynozzle number in the Black experiment in a low-speed wind tunnel is Re = 1.0XIO' or more, and as shown in Fig. 17, the
It is also strongly disturbed in the very vicinity after . For this reason, although the upright plate 35 decelerates the wake and stops the flutter of the test specimen, the strong turbulence of the airflow strongly excites the test specimen, and there is a large possibility that the test specimen will be damaged. In the example, the plate 23 is not stood upright but is raised diagonally, and the divergence is stopped using the airflow deflected along the plate. In addition, the structure of the device requires an actuator with a large output in order to quickly push up a plate with high air resistance against the airflow, and the plate needs to be highly rigid and heavy. There must be.

Problems to be Solved by the Invention The present invention has been devised in view of the drawbacks of the conventional flutter stopping device described above, and it is an object of the present invention to securely stop the flutter by removing flutter at the same time as the test specimen generates flutter. A flutter stopping device for wind tunnel experiments that can be used without significantly vibrating the test specimen due to turbulence of the airflow after the flutter stops, has a simple configuration, and can be applied without major modification of conventional wind tunnels. The purpose is to provide the following.

Means for Solving the Problems In order to solve the above problems, the flutter stop device of the present invention can significantly reduce and rectify the wind speed in the mainstream direction by using a panel having a large number of ventilation holes. It was developed based on the principle that it is possible to reduce the dynamic pressure acting on the test specimen.

That is, the present invention is a flutter stopping device for a test specimen in a wind tunnel experiment, which comprises a panel having a large number of ventilation holes installed on a wall at a position upstream of the test specimen support position in the wind tunnel so as to be able to stand upright facing the airflow. The above-mentioned problem was solved by the technical means of employing a panel drive device that raises the panel when flutter occurs in the test specimen.

The panel having a large number of ventilation holes is a panel composed of a frame and a wire mesh stretched over the frame;
A panel made of a perforated plate, a panel with many slits formed in a flat plate, etc. can be used.

In order to install the panel having a large number of ventilation holes so that it can stand up in the wind tunnel, the panel is pivoted to the floor so that it can rise and fall in a direction perpendicular to the airflow, and when flutter occurs on the test specimen, it is made to stand up against the airflow. It is possible to adopt a form in which the device is installed in the wind tunnel, or a form in which it is installed so that it protrudes from the wind tunnel wall surface such as the floor or ceiling of the wind tunnel at right angles to the airflow into the wind tunnel when flutter occurs, but the former form is preferable because the device is simple.

The size of the panel having the large number of ventilation holes does not necessarily have to cover the entire front of the test specimen, and depending on the test specimen, the panel may have a standing height that covers approximately 40% or more of the height of the specimen.

The panel driving device includes a stability discriminator that determines the occurrence of flutter in the test body based on the output of a sensor that detects vibrations of the test body mounted on the test body, and an actuator that is controlled by a signal from the stability discriminator. By adopting a means of driving the robot upright using a drive device, it is possible to automatically and quickly stand up the robot.

By adopting a panel with many ventilation holes,
The airflow in the wind tunnel is divided into those that pass through the edges of the upright panels and those that pass through the ventilation holes, so the vortices generated from the greenery of the panels are weakened, and the airflow that passes through the ventilation holes is affected by the viscosity of the air. to slow down. The rate of this deceleration is
Determined by the aperture ratio of the panel. Incidentally, flutter in a test object does not occur unless there is an airflow pressure higher than the flutter dynamic pressure unique to the test object. And the air flow pressure is 2 of the air flow velocity.
Therefore, by changing the aperture ratio of the panel so that the deceleration rate of the airflow is lower than the flutter dynamic pressure of the test object, it is possible to stop the flutter of the test object. The airflow passing through the vents in the panel is caused by the vents to generate small, uniform, weak turbulence. However, this turbulence is much smaller than the turbulence caused by vortices originating from the edge of the panel.

Since this airflow prevents the damage generated from the edge of the panel 1 from going around behind the panel, the wake of the panel is not disturbed significantly.

Therefore, the test specimen will not be strongly excited and destroyed by the turbulence of the airflow after the flutter has stopped.

Unlike the case where a non-porous panel is used as in the conventional divergence stop device, a panel with ventilation holes changes the air flow pressure acting on the panel and the panel by changing its opening ratio. Since the pressure difference between the front and rear sides can be reduced, the force acting on the panel can be reduced, and the stiffness of the panel can be correspondingly reduced to reduce the weight, thereby reducing the inertial force during operation of the panel body.

By using panels with these characteristics,
An actuator with a small output can be used, and if the panel is installed on the floor so that it can be raised and lowered, it can be easily raised either in the direction of the airflow or in the opposite direction. In addition, even if the panel is placed upright, the wake of the panel is a decelerated flow with little turbulence, so it is possible to stop the flutter of the specimen. There is no need to adjust the rising angle of the panel according to the mounting angle.

Before standing up, the panel does not physically restrain the test specimen and affect the aeroelastic properties of the test specimen or distort the airflow around the test specimen. Furthermore, when the panel is stood up, the airflow is not disturbed and no impact is applied to the test specimen.

The size of the panel does not need to cover the entire cross section of the wind tunnel; depending on the test specimen, it is sufficient to have a size that covers approximately 40% or more of the height of the test specimen, so the device does not become large and Manufacturing and installation are easy.

Example Examples of the present invention will be described in detail below.

First, the characteristics of the panel having a large number of ventilation holes in the present invention will be explained using the apparatus shown in FIG.

FIGS. 6 and 7 show examples of wind tunnel experiments using a panel using a wire mesh as a panel having a large number of ventilation holes.

In the figure, 7 is a test specimen with a semi-span of 200 mm.
is a wing model 7, and is 64 n from the center of the elastic axis of the wing model 7.
A hinge 5 is fixed to the floor 6 upstream of u, and the hinge 5 allows the height of the frame 3 and the wire mesh 2 to be 170 x 80.
A panel 1 having a size of nm was pivotally mounted on a floor 6 so as to be able to rise and fall.

One end of a panel support rod 8 is rotatably attached to the center of the panel 1. The other end of the panel support rod 8 is
As shown in the figure, the microswitch 9 located outside the wind tunnel through the opening in the floor 6 and installed directly below the opening is turned on.
01"F, so that a signal for the start of panel 1's rise can be generated. In this experiment, the panel support rod was operated manually to cause panel 1 to rise toward the leeward. .With panel 1 in the upright position,
It is configured to cover 83% of the film forming mold 7.

In order to detect the vibration state of the film-forming mold, a strain gauge 10 is attached to the wing spar 11, and its output is sent to a pen recorder 13 via a strain meter 12 along with a signal representing the ON/OFF state of the microswitch 9. It is also possible to record on magnetic tape 16.

In addition, in order to investigate the relationship between the wake attenuation ratio of the wire mesh 2 and the aperture ratio of the wire mesh, we installed a hot wire wind velocity at a position corresponding to the center of the girder of the film forming mold instead of the film forming mold 7, as shown in Fig. 8. meter probe 17
The wind speed was measured by sliding the probe 1q on a plane parallel to the upright panel 1 so that the tip of the probe 1q was aligned with the probe 1q. The output signal of the probe at this time was recorded on a magnetic tape.

As a comparative example, a similar experiment was conducted using a panel made of a non-perforated plate.

A flutter stopping experiment using the above-mentioned apparatus was conducted as follows.

At first, panel 1 is placed face down on the floor, and the wind speed in the wind tunnel is gradually increased. When the film-forming mold 7 starts to flutter, manually lift the support rod 8 of the panel 1 a little upward.
Panel 1 receives wind pressure and rises vigorously toward the leeward. At this time, the microswitch 9 issues a signal that the panel support rod 8 has been released and the panel 1 has begun to move.

When the panel 1 rotates 45 degrees downwind around the hinge, that is, when it rises by 50% and the decelerated airflow after the panel 1 covers 42% of the height of the film forming mold 7, the film forming Type 7
I was able to stop the flutter. Furthermore, panel 1
By rotating the mold so that it finally stood up at right angles to the floor and covering 83% of the height of the film forming mold 7 with the decelerated airflow, we were able to stop the flutter with sufficient margin.

The stoppage of flutter in the above experiment is shown by recording the output of the strain gauge 10 attached to the girder of the film-forming mold 7 and the ON/OFF signals of the microswitch 9 indicating the movement of the panel 1, as shown in FIG. 9(a). , it became like (b). Also ratio 1
As an example, the results of a similar experiment conducted using a panel made of a non-perforated plate are shown in FIGS. 10(a) and 10(b). As is clear from these figures, it is possible to stop flutter even if both of the above panels are used, but the vibration amplitude of the film forming mold after stopping flutter is lower than that when gold W4 is used for the panel. It can be seen that this is much smaller than when a non-perforated plate is used.

Figure 11 also shows that the wind speed was 13°5 m in the above experiment.
2 is a graph showing a power spectrum of the fluctuation in the mainstream direction of the wind tunnel in the wake when the panel 1 stands up at the time of / s. FIG. 12 is a graph showing the results when a non-perforated plate was used under similar conditions.

As is clear from these graphs, the wake of the panel using wire mesh is a nearly uniform random wave between 0 and 50 Hz, and the average value of the power spectrum fluctuation is It is about 20 decibels smaller than that of This is reflected in the difference in vibration amplitude after the flutter of the 's'lh model stops.

FIG. 13 shows the relationship between the wind tunnel main flow pressure 0) of the post-panel flow pressure P and the opening ratio of the wire mesh 2. As is clear from the figure,
It can be seen that as the aperture ratio k increases, the dynamic pressure reduction rate ρ decreases. If the aperture ratio is increased, the air flow pressure acting on the panel 1 will be reduced, so if the aperture ratio is increased within a range where the dynamic pressure reduction rate ρ required to stop flutter does not become smaller than approximately 30%, the panel It is possible to reduce the air flow pressure applied to 1 and the differential pressure across the panel. Therefore,
As the force applied to the panel is reduced, the rigidity of the panel is reduced, making it lighter in weight, and the inertial force during panel operation can be reduced. Therefore.

The actuator of the drive device can also use one with a small output, which makes it possible to reduce the weight of the entire flutter stop device, and the panel can be easily raised in either the airflow direction or the counterairflow direction.

Furthermore, as can be seen from Figures 13 and 11, the panel using wire mesh has the ability to reduce the air flow pressure enough to stop the flutter of the test specimen, and the turbulence in the wake of the panel is small. Therefore, with the film-forming type of the test specimen, it is sufficient to stop flutter simply by standing the panel upright, regardless of whether it is in the forward or backward angle.

Since the panel 1 is placed face down on the floor when not in use, the test specimen is not physically restrained and the airflow around the test specimen is not distorted. Furthermore, as shown in FIG. 10, no impact is applied to the test specimen even when the panel 1 is stood up.

Next, Fig. 1 shows the case where an embodiment of the flutter stopping device of the present invention using a panel having the panel characteristics as described above is used in an active flutter suppression test of a high aspect ratio wing model in a large low-speed wind tunnel. This is explained by:

The film forming mold 7 as a test specimen was a cantilevered blade with a semi-span of 1761 m and a cord of 535 nwe at the blade root, and the elastic axis of the film forming mold was fixed to the floor 6 of the wind tunnel.

The flutter stopping device of this embodiment is provided on the floor 217-upstream from the leading edge of the blade root of the film forming mold 7.

Panel 1 is 1750mm long x 70mm wide
It is made of gold w42 with a 25 mesh aperture ratio of 0.53 and a frame 3. The panel 1 is rotatably supported via a rotating shaft 15 on a ball bearing fixed to the floor 217 m upstream from the leading edge of the blade root of the film forming type. 14 is an actuator of the drive device for the panel, and in this embodiment, a pneumatic cylinder is used.

One end of the rod of the cylinder is pin-coupled with the panel 1 using a knuckle and a bracket, and the bottom of the cylinder is connected to the floor 6.
The rods are connected to the base by pins as well.

As shown in FIG. 3, the pneumatic cylinder includes a speed controller 25, 25' for adjusting the rising speed of the panel 1, a 5-port solenoid valve 26 for raising and lowering the panel 1, and a force for operating the panel 1. and a high pressure air source (7 kgf/cm) via a pressure reducing valve circuit 27 that adjusts the speed.
It is connected to the.

A potentiometer (not shown) is attached to the rotation shaft 15 to detect the rotation angle of the panel 1. The maximum rotation angle of the panel 1 in the above embodiment is 6.6 mm due to the cylinder installation conditions resulting from the wind tunnel structure.
It is set at 8.5 degrees. Therefore, the maximum vertical height from the tip of panel 1 to floor 6 is 1480 mm,
This corresponds to 84% of the semi-span of film forming type 7.

The operation of stopping flutter in a flutter experiment using the apparatus of this embodiment having the above configuration will be explained with reference to the control block diagram shown in FIG. 2.

Initially, panel 1 was placed face down on the floor, and the wind speed in the wind tunnel was gradually increased. During this time, the accelerometer 18 (No. 6) installed in the film forming mold 7 is guided to the stability discriminator 21, and
The dynamic stability of the system is monitored.

When the film-forming mold flutters, a signal is sent from the stability discriminator 21 or the manual switch 22 to the panel drive device consisting of the solenoid valve 26 and the pneumatic cylinder, and the panel 1 quickly rises from the floor, decelerating and rectifying the airflow. The flutter of the film forming mold 7 is stopped. At this time, since the turbulence of the airflow behind the panel 1 is weak, the film forming mold 7 after the flutter stop is not excited and destroyed.

Figures 4(a) and 4(b) show that the wind speed was 45% in the above experiment.
The output of the potentiometer that indicates the rotation angle of panel 1 when panel 1 is stood up in an airflow of m/s, and the rear of panel 1 is 420nwn, and the height from floor 6 is 1200a+.
+ indicates a change in airflow.

As is clear from the figure, the rise time of panel 1 is 0.
．． When panel 1 covered the height of the film forming mold by 0°62% in 75 seconds, the wind speed decreased by 11.2 m/s and the dynamic pressure reduction rate was 4.
4%, which indicates that a dynamic pressure reduction rate sufficient to stop flutter has been achieved.

In addition, Fig. 5 (a) and (b) are graphs recording the outputs of the potentiometer and accelerometer 18 when the panel 1 stands up and stops the flutter when flutter occurs at a wind speed of 35 m/s. It is. As a result, it can be seen that the panel 1 started booting 1.28 seconds after the flutter occurred. This time can be freely adjusted by setting the parameters of the stability discriminator 21. In this experiment, since it was a flutter suppression experiment, startup was started with enough time to visually confirm the flutter phenomenon. Panel 1, which started booting,
Start-up is completed in 0.7 seconds, and film forming mold 7 is completed at the same time.
The amplitude of the film is reduced to stop the flutter of the film forming type. During this time, the duration of the large amplitude of the film-forming mold 7 is approximately 1 second or less, thereby preventing damage to the film-forming mold 7. The reduction rate of the vibration amplitude of the film forming mold after the flutter stops is approximately 0°2 of the maximum amplitude.
It has become significantly smaller. Therefore, the film forming type 7 is
Even if it is continuously exposed to the wake of an upright panel, it will not be damaged. In this experiment, the model wing fluttered and stopped 33 times, but the model was not damaged.

Further, from the same graph, it can be seen that even if the panel 1 is operated at a high speed, the air flow behind the panel 1 is not disturbed. Further, while the panel 1 was lying face down on the floor 6, there was nothing physically restraining the film forming mold, and the airflow around the film forming mold was not distorted.

EffectsAs is clear from the above explanation, the flutter stopping device of the present invention can immediately stop the flutter of the test specimen, and the vibration of the test specimen after the flutter stops is small, making it easy to repeat flutter experiments. The test specimen will not be damaged even if the test is carried out. In addition, since the wind pressure applied to the panel and the differential pressure between the front and rear can be reduced, the direction in which the panel undulates is
It can easily be done in the direction of the airflow or in the opposite direction. Furthermore, the weight of the entire device can be reduced and a panel drive device with low output can be used, so the device can be manufactured at low cost.

Additionally, since the panel does not normally protrude from the floor, it does not restrain the test specimen or distort the airflow around the test specimen during that time.

Furthermore, the flutter stopping device of the present invention utilizes the principle of significantly reducing and rectifying the wind speed in the mainstream direction using a panel having a large number of ventilation holes to reduce the dynamic pressure acting on the test specimen and stopping flutter. Therefore, flutter can be stopped for both forward and backward wing test specimens. Furthermore, by using the dynamic stability determination circuit of the test object based on the output signal of the sensor mounted on the test object, it is possible to automatically raise the panel and quickly stop flutter.

Depending on the test specimen, the size of the panel may be sufficient to cover approximately 40% or more of the height of the test specimen to have a sufficient flutter stopping effect, so the device can be made smaller, easy to manufacture and install, and can be used for major modifications to the wind tunnel. is not required either.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an embodiment of the flutter stopping device of the present invention;
Figure 2 is its control block diagram, Figure 3 is its driving pneumatic circuit diagram, Figure 4 is a graph showing changes in air velocity behind the panel, and Figure S is when the panel is upright (the vibration amplitude of the model). Graphs showing changes, Figures 6 to 8 show the state of a wind tunnel experiment to investigate the panel characteristics related to the device of the present invention, Figure 6 is a perspective view thereof, and Figure 7 is a state where the panel is laid down on the floor. 8 is a perspective view of the state in which the airflow velocity behind the panel is measured with a hot wire anemometer, FIG. 9 is a graph showing the change in vibration amplitude of the film-forming mold when a wire mesh panel is used, and FIG. 1
Figure 0 is a graph showing the vibration amplitude change of the film forming mold when a non-porous panel is used, Figure 11 is a graph showing the turbulence of the panel wake when a wire mesh panel is used, and Figure 12 is a graph showing the change in the vibration amplitude of the membrane forming mold when a non-porous panel is used. Fig. 13 is a graph showing the relationship between dynamic pressure reduction rate and aperture ratio, Fig. 14 is a perspective view showing the conventional flutter stopping method, Fig. 15 is a side view of a conventional divergence suppression device, Fig. 16 is a graph showing the relationship between flutter speed and divergence speed with respect to the advancing and receding angles of the wing, and Fig. 17 is a graph showing the relationship between the flutter speed and the divergence speed when the Raynozzle number Re = 105 to 106. It is a state diagram showing turbulence of airflow. 1: Panel 2: Wire mesh 3: Frame 4.14 near actuator S: Hinge 6: Floor 7: Film forming mold
8: Panel support rod 9: Micro switch 10.19
: Strain gauge 11: Wing spar 15: Rotating shaft 18:
Accelerometer 20: Sensor 21: Stability discriminator
22: Manual switch 23: Operation section 25.25'
2 speed controller 26:5 boat solenoid valve 2
7: Pressure reducing valve circuit diagram 1 Seto Science and Technology Agency Aerospace Technology Research Institute Flamecho Hideo Su Figure 2 S Figure 3 1EJ Figure 5 EC Figure 7 Figure 8 Figure 9 Figure 1 Ω Figure SEC0 11 Hz s. Fig. 12 Fig. 13 Aperture ratio k (w) Fig. 14 Fig. 16 Speed ratio Fig. 17

Claims (1)

[Scope of Claims] 1) A flutter stopping device for a test specimen in a wind tunnel experiment, which has a number of ventilation holes installed in a wall at a position upstream of the test specimen support position in the wind tunnel so as to be able to stand upright facing the airflow. A flutter stopping device comprising a panel and a panel driving device that raises the panel when flutter occurs on a test specimen. 2) The flutter stopping device according to claim 1, wherein the panel having a large number of ventilation holes is composed of a frame and a wire mesh stretched over the frame. 3) Claim 1, wherein the panel having a large number of ventilation holes is pivotally attached to the floor so that it can be raised and lowered.
Or the flutter stop device described in item 2. 4) The panel driving device is controlled by a stability discriminator that determines the occurrence of flutter in the test body based on the output of a sensor mounted on the test body that detects vibrations of the test body, and a signal from the stability discriminator and a manual operation signal. 4. A flutter stop device according to claim 1, wherein the flutter stop device comprises an actuator.