A cam-driven sinusoidal gust generator and its design method

Abstract

The present invention discloses a cam-driven sinusoidal gust generator, comprising a fixed-axis oscillating blade grid, a cam, a drive device for rotating the cam, and a cam follower in contact with the cam's working surface. The blade grid is used to generate gusts by swinging in wind experiments. The blade grid is fixedly connected to a rocker arm, which is sleeved with a slider. The slider and the cam follower are hingedly connected via a push rod. The rotation of the cam drives the cam follower to move, thereby driving the blade grid to swing via the push rod, slider, and rocker arm, generating sinusoidal gusts in a wind tunnel. The parameters for generating target sinusoidal gusts are obtained by designing the cam profile. The cam converts continuous rotational motion into reciprocating linear motion, enabling complex motion patterns to be achieved. By designing the cam's profile curve, the push rod is moved in anticipation, generating target sinusoidal gusts. Since the aerodynamic force in a low-speed wind tunnel is relatively small, the power required to drive the blades and the force transmitted by the cam are very small, meeting the requirements for long-term reciprocating operation.

Description

Technical Field

[0001] The present invention relates to a gust generator, in particular to a cam-driven sinusoidal gust generator and a design method thereof. Background Art

[0002] The study of unsteady aerodynamics has always been a crucial area of ​​aircraft design. Aircraft flight safety is highly susceptible to meteorological conditions. Gusts, the most common weather condition, can alter an aircraft's airspeed and aerodynamic angle, causing changes in the aerodynamic forces and moments acting on the aircraft, which in turn can affect its flight characteristics.

[0003] Gust response wind tunnel tests mainly use model test methods to test the impact of gusts, as well as to verify gust response analysis and gust mitigation control technology. Driven by the demand for aircraft gust load prediction and gust load testing, gust wind tunnel test technology has developed rapidly. Models such as the B-52 and C-5A have conducted gust mitigation test research in wind tunnels, and related wind tunnel tests have also been conducted in China. In order to carry out relevant gust flow field simulation experiments, it is often necessary to install certain mechanical devices in the wind tunnel to achieve disturbance of the flow field. The gust generator that generates gusts based on blade oscillation is an indispensable component of relevant wind tunnel experiments. It is used to achieve controllable and adjustable gust disturbances and realize the reasonable simulation of gust disturbances in the atmosphere.

[0004] Traditional blade oscillation gust generators have disadvantages such as obvious high-frequency vibration, large and complex mechanical control, and large motor power requirements. Due to their complex control structure, the wind tunnel size must be very large, making it impossible to generate gusts in small wind tunnels. Summary of the Invention

[0005] Purpose of the invention: In view of the above shortcomings, the present invention provides a cam-driven sinusoidal gust generator with simple mechanical control, high reliability and small size.

[0006] The invention also provides a design method for a sinusoidal gust generator.

[0007] Technical solution: To solve the above problems, the present invention adopts a cam-driven sinusoidal gust generator, comprising a fixed-axis swinging blade, a cam, a driving device for driving the cam to rotate, and a cam follower in contact with the cam working surface. The blade is used to generate gusts by swinging in wind experiments. The blade is fixedly connected to a rocker rod, and a slider is provided on the rocker rod. The slider and the cam follower are hinged through a push rod. The driving device drives the cam to rotate, driving the cam follower to move along the cam working surface, thereby driving the blade to swing through the push rod, slider, and rocker rod to generate sinusoidal gusts in the wind tunnel. The parameters for generating target sinusoidal gusts are obtained by designing the cam profile.

[0008] Furthermore, the cam is a concentric disc cam, with the cam's rotation center aligned with the push rod's motion line, and the push rod reciprocating in a vertical direction. The cascade blades and the rocker arm are connected by a stepped shaft, swinging synchronously, with the rocker arm's swing angle corresponding to the cascade blade's swing angle. The drive device is a motor, and the cascade blade swing frequency, the rocker arm's swing frequency, and the push rod's reciprocating frequency are all identical, equal to the cam's rotation frequency.

[0009] The present invention also provides a design method for a sinusoidal gust generator, comprising the following steps:

[0010] (1) Determine the parameters of the target sinusoidal gust;

[0011] (2) Determine the angular velocity and maximum swing angle of the cascade according to the sinusoidal gust parameters;

[0012] (3) Obtain the distance between the push rod motion line and the blade axis, and determine the maximum stroke of the push rod based on the maximum swing angle of the blade and the obtained distance;

[0013] (4) Determine the push rod motion law based on the maximum stroke of the push rod and the angular velocity of the blade swing;

[0014] (5) Design the cam profile based on the obtained push rod motion law.

[0015] Furthermore, the parameters of the target sinusoidal gust include amplitude, frequency, and gust angle. At a given gust frequency, the ratio of the gust angle to the blade swing angle is a constant, calculated through numerical simulation. The blade swing angle is then calculated based on the target gust angle. The pushrod stroke h is calculated as h = 2d * tanθ, where d is the distance between the pushrod's motion line and the blade axis, and θ is the blade swing angle. The pushrod's velocity ν is calculated as ν = ω * d, where ω is the angular velocity of the blade swing.

[0016] Furthermore, the cam is a concentric disc cam, the cam's rotation center and the push rod's motion line are aligned, and the push rod reciprocates in a vertical direction. Based on the push rod's motion pattern, a push rod displacement-time curve for one cycle is plotted. Then, a suitable base circle radius is selected based on a calculation chart for the cam base circle radius. The push rod stroke curve and the cam base circle radius are superimposed to obtain the cam profile.

[0017] The cam mechanism is a common motion mechanism consisting of a cam, a follower, and a frame. When the displacement, velocity, and acceleration of the follower must vary strictly according to a predetermined pattern, especially when the driver moves continuously and the follower must move intermittently, a cam mechanism is the most convenient choice. The motion pattern of the cam follower is determined by the shape of the cam profile. Cam mechanisms are widely used in various automatic machines, instruments, and control devices. Their simple and compact structure allows them to accurately implement the required complex motion patterns.

[0018] Beneficial Effects: Compared to existing technologies, this invention offers a significant advantage in that the cam can convert continuous rotational motion into reciprocating linear motion, enabling the realization of complex motion patterns. By appropriately designing the cam profile, the pushrod can achieve a variety of desired motion patterns. Given the relatively low aerodynamic forces in low-speed wind tunnels, the power required to drive the blades and the force transmitted by the cam are minimal, enabling the pushrod to maintain long-term reciprocating operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Shown is a schematic structural diagram of the gust generator of the present invention;

[0020] Figure 2 It is a schematic diagram of a connection method of the push rod, the rocker arm and the cascade in the present invention;

[0021] Figure 3 Shown is a schematic diagram of the mechanism of the gust generator of the present invention;

[0022] Figure 4 Shown is a schematic diagram of the mechanism movement mode of the gust generator in the present invention;

[0023] Figure 5 Shown is the calculation principle of the push rod speed in the present invention;

[0024] Figure 6 Shown is a schematic diagram of the stroke relationship of the cam follower in the present invention. DETAILED DESCRIPTION

[0025] Example 1

[0026] like Figure 1 As shown in FIG. 1 , a cam-driven sinusoidal gust generator in this embodiment includes a fixed-axis swinging blade 1, a cam 6, a driving device for driving the cam 6 to rotate, and a cam follower 5 in contact with the working surface of the cam 6. The blade 1 is used to generate gusts by swinging in a wind experiment, as shown in FIG. Figure 2 As shown, the blade 1 and the rocker 2 are connected by a stepped shaft 7. A keyway is provided on the stepped shaft 7 to enable the blade 1, the rocker 2 and the stepped shaft 7 to move in a fixed axis. The blade 1 is positioned by the two stepped shafts 7 on both sides. The stepped shaft on one side of the blade is fixedly connected to the rocker 2. A slider 3 is provided on the rocker 2. The slider 3 slides along the rocker 2. The slider 3 and the cam follower 5 are hinged through the push rod 4. The movement line of the push rod 4 extends vertically. The push rod 4 moves back and forth in the vertical direction. The upper end of the push rod is hinged to the slider 3 through the driven bearing II8, and the lower end is hinged to the cam follower 5 through the driven bearing I. The cam is a concentric disc cam. The rotation center of the cam is on the same straight line as the movement line of the push rod. The driving device is a motor, as shown in FIG. Figure 3As shown in the figure, a motor drives the cam to rotate, driving the cam follower to move along the cam working surface. This, in turn, drives the cascade vanes to oscillate via the push rod, slider, and rocker, generating sinusoidal gusts in the wind tunnel. The parameters for generating the target sinusoidal gusts are determined by designing the cam profile. The cascade vane oscillation frequency, the rocker arm oscillation frequency, and the push rod reciprocating frequency are all equal to the cam rotation frequency.

[0027] Example 2

[0028] In this embodiment, a design method for a sinusoidal gust generator includes the following steps:

[0029] (1) Determine the parameters of the target sinusoidal gust required; the necessary parameters of a sinusoidal gust include amplitude, frequency, and gust intensity (gust angle). The amplitude of the expected sinusoidal gust is half the difference between the maximum and minimum values ​​in a cycle. The frequency is the number of times a periodic change is completed per unit time and is the inverse of the time difference between two adjacent amplitudes.

[0030] (2) Determine the angular velocity and maximum swing angle of the blade cascade according to the sinusoidal gust parameters; according to formula 15, Figure 6 The numerical simulation results presented show that, at a given gust frequency, the ratio of the gust angle to the cascade blade swing angle is a constant. This constant can be calculated through numerical simulation, and then the cascade blade swing angle can be calculated based on the desired gust angle. The cascade blades and the swing arm are connected by a stepped shaft, allowing them to swing synchronously. The swing arm's swing angle is the same as the cascade blade swing angle.

[0031] (3) Obtain the distance between the push rod motion line and the blade axis, and determine the maximum stroke of the push rod based on the maximum swing angle of the blade and the obtained distance. Figure 4 As shown in the figure, the distance d between the straight line where the push rod reciprocates and the swing rod rotation axis O is fixed. In order to convert the swing into linear motion, the contact point A between the push rod and the swing rod should move along the swing rod during the movement. Figure 4 As shown, at a constant swing angular velocity ω, the velocity ν at the point of contact between the pendulum and the push rod along the push rod's direction is constant, equal to the product of the angular velocity and the distance (ν = ω * d). Therefore, at a set angular velocity, the push rod performs a linear reciprocating motion with a constant velocity. Given the maximum swing angle of the pendulum at θmax, the maximum push rod travel h is h = 2d * tanθmax.

[0032] (4) Determine the push rod motion law based on the maximum stroke of the push rod and the angular velocity of the blade swing;

[0033] (5) Based on the obtained push rod motion law, the cam profile is designed. The cam selected is a concentric disc cam, that is, the rotation center of the disc cam and the push rod motion line are on the same straight line. The cam profile is determined according to the push rod stroke. First, draw the following according to the push rod motion form: Figure 5 The push rod displacement-time curve for one cycle is shown. The appropriate base circle radius is then selected based on the cam base circle radius calculation chart. Based on the push rod displacement-time curve, the cam's lift and return strokes are symmetrical, and the motion is constant velocity. By superimposing the push rod stroke curve and the cam base circle radius, the cam profile is generated, completing the design of the sinusoidal gust generator.

Claims

1. A cam-driven sinusoidal gust generator, characterized in that: The invention comprises a blade cascade (1) with a fixed axis swing, a cam (6), a driving device for driving the cam to rotate, and a cam follower (5) in contact with the cam working surface. The blade cascade (1) is used to generate gusts of wind by swinging in a wind experiment. The blade cascade (1) is fixedly connected to a rocker (2), a slider (3) is sleeved on the rocker (2), and the slider (3) and the cam follower (5) are hinged via a push rod (4). The driving device drives the cam to rotate, driving the cam follower to move along the cam working surface, thereby driving the blade cascade to swing via the push rod, the slider, and the rocker, generating sinusoidal gusts of wind in a wind tunnel. The parameters for generating the target sinusoidal gusts of wind are obtained by designing the cam profile.

2. The sinusoidal gust generator according to claim 1, characterized in that: The cam (6) is a concentric disc cam, the cam rotation center and the push rod movement line are on the same straight line, and the push rod moves back and forth in the vertical direction.

3. The sinusoidal gust generator according to claim 1, characterized in that: The blade cascade (1) and the swing rod (2) are connected via a stepped shaft and swing synchronously, and the swing angle of the swing rod is the blade cascade swing angle.

4. The sinusoidal gust generator according to claim 1, characterized in that: The driving device is a motor, and the blade cascade swing frequency, the rocker swing frequency and the push rod reciprocating frequency are the same, which are all equal to the cam rotation frequency.

5. A design method for a sinusoidal gust generator according to claim 1, characterized in that: The following steps are involved: (1) Determine the parameters of the target sinusoidal gust; (2) Determine the angular velocity and maximum swing angle of the cascade according to the sinusoidal gust parameters; (3) Obtain the distance between the push rod motion line and the blade axis, and determine the maximum stroke of the push rod based on the maximum swing angle of the blade and the obtained distance; (4) Determine the push rod motion law based on the maximum stroke of the push rod and the angular velocity of the blade swing; (5) Design the cam profile based on the obtained push rod motion law.

6. The design method according to claim 5, characterized in that: The parameters of the target sinusoidal gust include amplitude, frequency and gust angle.

7. The design method according to claim 6, characterized in that: Under a certain gust frequency, the ratio of the gust angle to the blade swing angle is a constant. The constant is obtained through numerical simulation, and the blade swing angle is obtained according to the target gust angle.

8. The design method according to claim 6, characterized in that: The stroke h of the push rod is h = 2d*tanθ, where d is the distance between the push rod motion line and the blade axis, and θ is the blade swing angle; the movement speed ν of the push rod is ν = ω*d, and ω is the angular velocity of the blade swing.

9. The design method according to claim 6, characterized in that: The cam is a concentric disc cam, the rotation center of the cam and the movement line of the push rod are on the same straight line, and the push rod moves back and forth in the vertical direction.

10. The design method according to claim 9, characterized in that: According to the push rod motion law, draw the push rod displacement-time curve within a cycle, and then select the appropriate base circle radius according to the calculation chart of the cam base circle radius; superimpose the push rod stroke curve and the cam base circle radius to obtain the cam profile line.

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