Spring device for oscillating movements of models and wind tunnel test device with spring device

Abstract

Spring device (1) for oscillating movements of models, preferably wind tunnel models, comprising a first connection device (3) for connecting to a test device (110) and a second connection device (5) for connecting to a model (120), a central axis (11) and at least one spring assembly (13) with two bending-stressed spring elements (15) which are connected at first ends (15a) to the first connection device and at second ends to the second connection device, wherein the first ends (15a) are spaced apart from each other on the first connection device (3) and the second ends (15b) are connected to a rotation axis element (17) of the second connection device (5), wherein the rotation axis element (17) forms a rotation axis (21) for a relative movement between the first and the second connection device (3, 5), wherein the rotation axis (21) is eccentric to the central axis (11).

Description

The present invention relates to a spring device for oscillatory movements of models and to a wind tunnel test device with spring device.For the aerodynamic characterization of aircraft and spacecraft, experimental investigations are carried out in wind tunnel ducts and static and later dynamic coefficients are determined as far as possible for the entire flight area. The static coefficients are dimensionless forces and moments which act on the vehicle on account of the flow around in flight. The dynamic coefficients, on the other hand, describe the reaction of the vehicle to a fault that occurs, for example, due to a wind gust.Frequently, for the examinations on aircraft and spacecraft, measurement systems are used which are installed in the wind tunnel models and form the connection between model and holder. For the determination of static coefficients, there are internal force measurement balances which can be used in wind tunnel models.For the experimental determination of dynamic coefficients, there are different measurement methods, including the free oscillation / oscillation method. Usually, a rotary spring with only a single degree of freedom of the model movement (rotation about a predetermined axis) is used for this purpose. Depending on the application, different types of springs are used.Dynamic contributions cannot be converted to another reference point, but must be determined from an oscillation about a reference point which in the previously known models lies on the central axis. Therefore, the spring is positioned in the model such that its axis of rotation passes through the reference point.The systems described above are of common knowledge of the applicant, but do not necessarily relate to a prepublished prior art.In the above-described dynamic measurement, individual solutions are prepared for each wind tunnel model. Frequently, different wind tunnel models have to be used for the determination of static and dynamic coefficients or for the determination of dynamic coefficients about different rotational axes, whereby the comparativeability of measurement results is possibly influenced.It has also been found that, in particular in the area of hypersonic currents, the conventional wind tunnel test devices with the corresponding spring devices are inadequate during dynamic measurements during pitch or roll movements, owing to the geometries which are in some cases quite slender.It is therefore the object of the present invention to provide an improved spring device for oscillating movements of models and a wind tunnel test device with spring device for determining dynamic coefficients on a wind tunnel model, wherein the determination of dynamic coefficients is improved.The spring device according to the invention is defined by the features of claim 1.The spring device according to the invention for oscillating movements of models, preferably wind tunnel models, has a first connection device for connection to a test device and a second connection device for connection to a model, a central axis and at least one spring device having two spring elements which are subject to bending stress. The spring elements are connected with first ends to the first connection device and with second ends to the second connection device, wherein the first ends are attached to the first connection device in a manner spaced apart from one another and the second ends are connected to a rotational axis element of the second connection device. The rotational axis element forms a rotational axis for a relative movement between the first and the second connection device, wherein the rotational axis formed by the rotational axis element runs eccentrically with respect to the central axis.In the context of the invention, it has been found that dynamic coefficients for models whose center of gravity lies on the center axis can be readily determined using conventional test methods and using conventional rotary springs with a central axis of rotation.In particular in the field of hypersonic currents, however, there are applications in which the center of gravity of a specific model geometry is eccentric and, for example, very close to a model side wall. Use of the conventional rotary springs with a central axis of rotation is therefore not possible or only possible to a limited extent during pitch and roll movements, since the center of gravity cannot be used as a desired reference point through which the axis of rotation runs.In the spring device according to the invention, however, the axis of rotation extends eccentrically with respect to the central axis, so that the spring device according to the invention is advantageously suitable for such applications, since, for example, when the spring device is arranged with its central axis concentrically with respect to the central axis of the wind tunnel model, the axis of rotation about which a vibration takes place can be arranged by the eccentric center of gravity or close to the eccentric center of gravity.Thus, by means of the spring device according to the invention, the determination of dynamic coefficients in such applications can be significantly improved.The spring device can be used in particular in standardized test devices and models in which the spring device can be connected to the test device by means of the first connection device, wherein the spring device can be arranged with the central axis coaxial to the central axis of the test device. Thus, with the same test apparatus and model, both the spring device according to the invention and a conventional spring device with a central axis of rotation can be used. Because the same test device with different spring devices can be used for different applications, the test results are relatively well comparable. Both in the determination of static and dynamic coefficients and in the determination of dynamic coefficients about different axes of rotation, it is thus possible to achieve measurement results that are well comparable and can thus be evaluated well.In the spring device according to the invention, it can also be provided in principle that the first connection device can be connected to the model and the second connection device can be connected to the test device, that is to say the spring device is arranged rotated by 180°.Preferably, it is provided that the spring elements subject to bending are leaf spring elements. Such spring elements are particularly advantageous for the desired oscillatory movements, since they can be deflected essentially elastically in only one direction.The first terminal device may include a terminal plate for connecting to the test device. The first connection device can be connected to the test device in a simple manner, for example by screwing, via the connection plate. In addition, fits for positive force transmission can also be provided.The second connection device can have a connection plate or a connection element for connecting to the model; for example, the spring device according to the invention can likewise be connected to a connection device of the model by screwing by means of the connection plate of the second connection device. Alternatively, a connection element, for example a cone insertable into a connection device of the model, can also be provided. Such a connection element can be advantageous in particular in the case of pitch movements, since on the one hand the necessary forces and movements are advantageously transmitted and on the other hand a quick connection between spring device and model can be achieved by simply fitting one inside the other.Preferably, it is provided that the second connection device has a projection which extends in the direction of the central axis on an outer edge of the connection plate or of the connection element and forms the rotational element. In other words, the second connection device has on its outer edge an axially extending projection which forms the rotation element, so that the latter can advantageously have an axis of rotation running eccentrically with respect to the central axis. By virtue of such a configuration of the connection device, it is furthermore possible in a simple manner to provide a rotational axis for the oscillation which runs through a center of gravity lying close to a model side wall.The axis of rotation can run, for example, parallel to the central axis. Such a configuration is suitable for measurement during rolling movements. In the measurement during rolling movements, the configuration of the second connection device with a connection plate, which is screwed to the model, for example, is advantageous. In principle, the provision of a connection element is also possible, wherein in this case a force transmission in the circumferential direction must be ensured, for example by a corresponding engagement of connection element and model.Alternatively, the axis of rotation extends orthogonally to the central axis. In other words, the axis of rotation runs transversely to the central axis at a distance therefrom. Such a configuration of the spring device according to the invention is suitable for dynamic measurements during pitch movements.In a preferred exemplary embodiment of the invention, it is provided that at least one strain gauge is arranged on the spring elements subject to bending. The deflection and thus the oscillating movement can be advantageously measured via the strain gauges. In principle, a plurality of strain gages can also be arranged on each of the spring elements subjected to bending stress.The spring device according to the invention can furthermore have two spring devices each with two spring elements subject to bending, wherein the spring devices are spaced apart from one another in the direction of the axis of rotation. In other words, the spring device according to the invention can have two spring devices of identical construction which are spaced apart from one another, wherein in each case the first ends of the spring elements subject to bending are connected to the first connection device and the in each case second ends are connected to the second connection device. By providing two spring devices, the oscillating movement can be stabilized, so that it is ensured that the oscillating movement takes place exclusively or almost exclusively about the axis of rotation.The invention further provides a wind tunnel test device for determining dynamic contributions to a wind tunnel model, which has a wind tunnel model and a test device with a triggering device, wherein the wind tunnel model has a connection recess on a side facing away from an inflow side, in which connection recess a connection device is arranged, wherein the triggering device is connected to the connection device via a spring device according to the invention, wherein the test device further has a deflection device, via which the wind tunnel model can be moved relative to the test device from a holding position in a deflection direction counter to a spring force of the spring device into a deflection position, wherein in the deflection position the triggering device releases the wind tunnel model for oscillation about the spring device.The wind tunnel test device according to the invention for determining dynamic coefficients advantageously enables the wind tunnel model to be released into a vibration about the axis of rotation of the spring device, so that the dynamic coefficients can be determined. By providing a connection recess in which the connection device is arranged and to which the triggering device is connected via the spring device, the wind tunnel model can be used advantageously flexibly, since spring devices of different configurations can be connected to the connection device, or else a force measurement scale for determining static coefficients. For this purpose, it can be provided in particular that the connection recess is adapted to the dimensions on the force measurement balance for determining static coefficients.As a result, the wind tunnel test device according to the invention can be used to determine different coefficients using a wind tunnel model. Furthermore, by using the wind tunnel test device with the spring device according to the invention, the dynamic coefficients can be advantageously determined even in application cases in which an eccentric center of gravity is present in the wind tunnel model.The invention is explained in more detail below with reference to the following figures.The following are shown: FIG. 1 shows a schematic illustration of a first exemplary embodiment of a spring device according to the invention, FIG. 2 shows a schematic illustration of a wind tunnel test device according to the invention with the spring device illustrated in FIG. 1, and FIG. 3 shows a second exemplary embodiment of a spring device according to the invention.FIG. 1 schematically shows a spring device 1 according to the invention for oscillating movements of models.The spring device 1 has a first connection device 3 and a second connection device 5. As can best be seen from FIG. 2, in which a wind tunnel test device 100 according to the invention is schematically illustrated, the spring device 1 according to the invention can be connected by means of the first connection device 3 to a test device 110 of the wind tunnel test device 100 and second connection device 5 to a model 120.For this purpose, the first connection device 3 has a connection plate 7, via which the spring device 1 can be screwed to the test device 110.The second connection device 5 has a connection element 9, which can be inserted into the model 120.The spring device 1 further has a central axis 11 and a spring device 13. The spring device 13 has two spring elements 15 which are subjected to bending stress and by means of which the first connection device 3 is connected to the second connection device 5.The second connection device 5 has, at its outer end in the radial direction, a projection 19 which extends parallel to the central axis 11. On the projection 19, a rotation axis member 17 is formed. The first ends 15 aof the flexurally stressed spring elements 15 are attached to the first connection device 3 at a distance from one another in the axial direction. The second ends 15 bof the flexurally stressed spring elements are connected to the rotational axis element 17 of the second connection device 5. The rotational axis element 17 forms a rotational axis 21, about which a relative movement between the first and the second connection device 3, 5 can take place.The axis of rotation 21 runs transversely to the central axis 11 and eccentrically therefrom. The spring device 1 shown in FIG. 1 can thus be used in an advantageous manner for measurements during pitch movements and eccentric position of the center of gravity.The spring elements 15 subject to bending are designed as leaf spring elements, to which expansion strips, not shown, are attached, by means of which the bending of the spring elements 15 subject to bending can be measuredFIG. 2 shows the spring device 1 according to the invention shown in FIG. 1 in the installed state in a wind tunnel test device 100. The spring device 1 is connected to the first connection device 3 with a test device 110. The connection element 9 of the second connection device 5 is connected to a connection device 130 of the wind tunnel model 120. The connection device 130 is arranged in a connection recess 140 of the wind tunnel model. In the connection recess 140, in the state connected to the wind tunnel model 120, the spring device 1 is also arranged.The test apparatus 110 also has a deflection device 150 and a triggering device 160. By means of the deflection device 150, the wind tunnel model 120 can be moved relative to the test device 110 from a holding position into a deflection position, wherein the movement takes place counter to the spring force of the spring device 1. In the deflection position now present, the wind tunnel model 120 can be released via the triggering device 160 for swinging about the spring device 1 according to the invention. The wind tunnel model 120 is oscillated about the rotation axis 21.FIG. 3 schematically shows a second exemplary embodiment of the spring device according to the invention.In the exemplary embodiment shown in FIG. 3, the axis of rotation 21 runs eccentrically to the central axis 11 and parallel thereto. Thus, the spring device 1 according to the invention is suitable for rolling movements. Furthermore, the spring device 1 according to the invention illustrated in FIG. 3 has two spring devices 13 which each comprise two spring elements 15 which are subject to bending stress. The spring devices 13 are arranged spaced apart from one another in the axial direction and have the same structure.The spring device 1 according to the invention illustrated in FIG. 3 also has a connection plate 7 on the second connection device 5 instead of the connection element 9 of the exemplary embodiment of FIG. 1. The spring device 1 according to the invention illustrated in FIG. 3 can be used in a wind tunnel test device in various ways. For example, the spring device 1 can be connected to the model via the connection plate 7 of the second connection device 5 and can be connected to the test device via the connection plate 7 of the first connection device 3 or to the test device via the connection plate 7 of the second connection device 5 and to the model via the connection plate 7 of the first connection device 3. The connection plates 7 of the first and second connection devices 3, 5 can be configured identically, so that the spring device 1 can be used in any direction. Recesses and, in the model and test device, corresponding projections for forming fits can be provided in the connection plates. The spring device 1 can also be connected to the model and the test device, for example, via screws. As a result, the forces occurring during the rolling movement in the circumferential direction can be advantageously transmitted in a form-fit and force-fit manner.The connection plates 7 can be connected to the model 120 and the test device 110 via intermediate elements, wherein an angle is produced between the central axis of the model and the test device and the rotational axis. This makes it possible to carry out dynamic tests about axes of rotation oriented as desired within certain limits, although the test device remains oriented centrally in the model. For some applications, this makes it possible to carry out the dynamic tests at all.List of reference characters1 Spring device 3 First connection device 5 Second connection device 7 Connection plate 9 Connection element 11 Central axis 13 Spring device 15 Spring elements 15 aFirst ends 15 bSecond ends 17 Axis of rotation element 19 Projection 21 Axis of rotation 100 Wind tunnel test device 110 Test device 120 Model 130 Connection device 140 Connection recess 150 Deflection device 160 Triggering device

Claims

Spring device (1) for oscillating movements of models, preferably wind tunnel models, having a first connection device (3) for connection to a test device (110) and a second connection device (5) for connection to a model (120), having a central axis (11), and having at least one spring device (13) having two spring elements (15) which are subjected to bending stress and are connected to the first connection device by first ends (15a) and to the second connection device by second ends, wherein the first ends (15a) are attached to the first connection device (3) at a distance from one another and the second ends (15b) are connected to an axis of rotation element (17) of the second connection device (5), wherein the axis of rotation element (17) forms an axis of rotation (21) for a relative movement between the first and the second connection device (3, 5), wherein the axis of rotation (21) extends eccentrically to the central axis (11).Spring device according to Claim 1, characterized in that the spring elements (15) subject to bending are leaf spring elements.Spring device according to claim 1 or 2, characterised in that the first connection device (3) has a connection plate (7) for connection to the test device (110).Spring device according to one of Claims 1 to 3, characterized in that the second connection device (5) has a connection plate (7) or a connection element (9) for connection to the model (120).Spring device according to Claim 4, characterized in that the second connection device (5) has a projection (19) which extends on an outer edge of the connection plate (7) or of the connection element (9) in the direction of the central axis (11) and forms the rotational axis element (17).Spring device according to one of Claims 1 to 5, characterized in that the axis of rotation (21) runs parallel to the central axis (11).Spring device according to one of Claims 1 to 5, characterized in that the axis of rotation (21) runs orthogonally to the central axis (11).Spring device according to one of Claims 1 to 7, characterized in that in each case at least one strain gauge is arranged on the spring elements (15) subject to bending.Spring device according to one of Claims 1 to 8, characterized bytwo spring devices (13) each having two spring elements (15) subject to bending, wherein the spring devices (13) are spaced apart from one another in the direction of the axis of rotation (21).Wind tunnel test device (100) for determining dynamic contributions to a wind tunnel model (120), having a wind tunnel model (120) and having a test device (110) having a triggering device (160), wherein the wind tunnel model (120) has a connection recess (140) on a side facing away from an inflow side, in which connection recess a connection device (130) is arranged, wherein the triggering device (160) is connected to the connection device (130) via a spring device (1) according to one of Claims 1 to 9, wherein the test device (110) further has a deflection device (150), via which the wind tunnel model (120) can be moved relative to the test device (110) from a holding position into a deflection direction and counter to a spring force of the spring device (1) into a deflection position, wherein, in the deflected position, the triggering device (160) releases the wind tunnel model (120) for swinging about the spring device (1).

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