RU2696942C1 - Method for experimental determination of aerodynamic characteristics of a model during quasi-static tests in a wind tunnel - Google Patents

Abstract

FIELD: aviation.

SUBSTANCE: invention relates to experimental aerodynamics of aircraft during experimental research in a wind tunnel. Method consists in that the analyzed model is installed in the working part of the aerodynamic pipe on the supporting device. No flow is measured. After the pipe is set to the operating mode (preset flow rate is set) with the help of the drive, the model is moved along the angle of attack (sliding) from the initial to the specified final angle and back. Indications of aerodynamic scales, an angle of attack (slip) sensor and a pressure sensor with sampling frequency of not less than 1 kHz are recorded simultaneously with the beginning of movement and to its end. Further processing involves taking detrimental aerodynamic loads from measured readings, which are filtered with a Butterworth low-pass filter with cutoff frequency of 2–5 Hz. As a result, obtaining quasi-static aerodynamic dependencies, from which position of "catastrophic" transitions on angles of attack (slip), as well as angles of attack (slip) of the beginning of aerodynamic shaking and its development on angles of attack (slip) are determined.

EFFECT: location of features in the form of "catastrophic transitions" in aerodynamic characteristics, as well as in determination of angles of attack and sliding at which "pre-threshold" aerodynamic shaking and its development with increase of these angles begins to appear.

1 cl, 7 dwg

Description

The invention relates to experimental aerodynamics of aircraft.

In the work (DV Shukhovtsov “Bifurcations and catastrophes in aerodynamic characteristics.” - Journal “Izvestia RAN. Fluid and Gas Mechanics. Moscow, 2013, No. 3, pp. 70-76) it was shown that in tear-off modes flow around can take place abrupt changes in the values of the coefficients of the longitudinal aerodynamic characteristics of aircraft (LA) (Fig. 1 Applications). Hopping transitions, like the sudden response of a system to a smooth effect, are the subject of catastrophe theory, and the transitions themselves are called “disasters” (Tim Poston and Ian Stewart, “Catastrophe Theory and Its Applications.” - Publisher: Mir, Moscow, 1980 , P. 115) or threshold nonlinearities (A.T. Filippov “The Many-Faced Soliton.” - Publisher: Nauka, Moscow, 1990, pp. 74-75). In the same work, some parameters characterizing the "disaster" were given. So, it is shown that a sharp occurrence of a diving moment of a model of a maneuverable aircraft occurs in a narrow range of angles of attack Δα = 0.05 degrees in a time ΔТ = 0.1 sec. It was also found that getting the balancing value of the angle of attack in the vicinity of the "disaster" leads to the emergence of dynamic instability of an airplane with a limit cycle type attractor. In addition, the “subthreshold” state of the object is characterized by an increase in aerodynamic jolting, which then turns into instability in the form of a “catastrophe”, characterized by the transition of the object from one stationary state to another. “Catastrophic” transitions were also found in the lateral aerodynamic characteristics (Fig. 2 of the Appendix). Thus, the identification of “catastrophes” in aerodynamic characteristics is a fundamentally important task, as it enables the pilot and control system to adequately respond to aircraft behavior.

There is a method of studying the aerodynamic characteristics during static testing of objects, which consists in obtaining aerodynamic dependencies with a fixed step of changing the angle of attack (slip) (N.P. Ilyashenko, I.V. Kolin, V.G. Markov, V.L. Sukhanov, TI Trifonova, DV Shukhovtsov “The influence of wind tunnel flow turbulence on hysteresis characteristics in static aerodynamic forces and moments” - TsAGI Uchenye Zapiski Magazine, Moscow, 2008, vol. XXXIX, No. 3, P. 37 )

In static tests, time dependences are obtained on stationary objects at given angles of attack (slip), and then they are averaged (A.Z. Tarasov, T.I. Trifonova, D.V. Shukhovtsov “Study of temporal dependences of aerodynamic forces and moments at large angles attacks. ”-“ Air Fleet Technique ”magazine. Moscow, 2000, volume LXXIV, No. 1-2, P. 64). Thus, each angle of attack (slip) from the selected range corresponds to the mathematical expectation of the time series of aerodynamic coefficients.

This research method has the following disadvantages:

1. The lack of critical information about the behavior of the aerodynamic characteristics within the step of changing the angle of attack (slip); for example, in pipes ADT T-102,

T-103 TsAGI minimum step of changing the angle of attack (slip) is 1 degree.

2. Lack of information about the appearance and dynamics of the development of aerodynamic shaking at the angles of attack (slip).

3. When recording data on a stationary model, various transitional modes from one stationary state to another can be realized (DV Shukhovtsov, “Bifurcations and catastrophes in aerodynamic characteristics.” - Journal of Izvestia RAN. Fluid and Gas Mechanics. Moscow, 2013, No. 3, pp. 70-76), which leads to incorrect results when processing data ("disaster" "AB" in Fig. 3 of the Appendix).

The prototype adopted a method of studying the aerodynamic characteristics of objects with a continuous change in the angle of attack (slip) with a constant angular velocity. The methodology for this kind of testing is given, for example, in (A.N. Zhuk, K.A. Kolinko, O.L. Miatov, A.N. Khrabrov “Investigation of nonlinear aerodynamic characteristics during continuous movement of a delta wing.” - Moscow: The journal “Scientific notes of TsAGI.” No. 1-2, volume XXXV, 2004. P. 32-39). In the work, as a research object, a triangular wing was used, which moved in the flow of the working part of the wind tunnel with a constant angular velocity of 3 deg / s. The experimental data were recorded with a sampling frequency of 100 Hz with a total number of points equal to 3000. Further processing consisted of filtering the obtained experimental data with a 6th order Butterworth filter with a cutoff frequency of 0.5 Hz. In FIG. 4 Appendix shows the results of measurements of the normal force Y of a triangular wing with a sweep of 70 degrees, obtained by continuously changing the angle of attack.

The disadvantages of the prototype are as follows:

1. Given that "catastrophic" transitions occur in a fast timeline, it is necessary to have a high polling frequency, and, consequently, a large number of collected points of temporary realizations. Selected in the prototype values of the polling frequency and the number of points equal to 100 Hz and 3000 points, respectively, are clearly insufficient for quasistatic tests.

2. Filtering the obtained experimental data was carried out with a filter cutoff frequency of 0.5 Hz; at such a low cutoff frequency, all jumps are smoothed if they occur in the aerodynamic characteristics.

The objective of the invention is to develop a method for the experimental determination of aerodynamic characteristics when conducting quasi-static tests in wind tunnels to determine the topology of the dependencies of the aerodynamic characteristics in order to identify "catastrophic transitions", as well as the dynamics of the development of aerodynamic shaking at the angles of attack and slip.

The technical result consists in finding the position of the features in the form of "catastrophic transitions" in the aerodynamic characteristics, as well as in determining the angles of attack and slip, at which the "subthreshold" aerodynamic jolting begins to appear and its development with increasing these angles.

The task and technical result are achieved by the fact that in the method of experimental determination of the aerodynamic characteristics of the model during quasistatic tests in a wind tunnel, including moving the model in the flow of the working part of the wind tunnel by the angle of attack (slip), measuring instantaneous aerodynamic loads, collecting experimental data and their filtering, collecting experimental data is carried out with a sampling frequency of at least 1000 Hz, filtering of experimental data is carried out tvlyayut with a cutoff frequency of 2-5 Hz, and further based on the collected experimental data determine the position of abrupt transitions in aerodynamic characteristics, and the beginning of the development of the aerodynamic angle of attack by shaking and sliding.

In FIG. 1 shows the static aerodynamic characteristics c _y = c _y (α), m _z = m _z (α) of a triangular wing.

In FIG. Figure 2 shows the quasistatic dependences of the aerodynamic coefficients c _y , m _{z of the} triangular wing on the angle of attack.

, полученных для треугольного крыла.In FIG. 3 illustrates a comparison of the results of quasistatic m _z = m _z (α) and dynamic tests

obtained for the delta wing.

, полученных в летных испытаниях магистрального самолета с результатами трубных квазистатических испытаний его модели m_z=m_z(α).In FIG. 4 shows a comparison of dependencies

obtained in flight tests of a main aircraft with the results of quasistatic tube tests of its model m _z = m _z (α).

при больших забросах на углы атаки в режиме «дача» рулей.In FIG. Figure 5 shows a comparison of the quasistatic dependence of the pitch moment coefficient m _z = m _z (α) with the flight characteristic

with large casts on the angles of attack in the “cottage” mode of the rudders.

характеристики коэффициента момента, полученные при трубных испытаниях модели магистрального самолета.In FIG. Figure 6 shows the quasistatic m _z = m _z (α) and non-stationary

torque coefficient characteristics obtained during pipe tests of a model of a main aircraft.

In FIG. Figure 7 shows a comparison of the standard deviations of the pitch moment coefficient σ _Mz from the results of testing a model in a wind tunnel (ADT) and an airplane in flight tests (LI).

The method is as follows. The investigated model is installed in the working part of the wind tunnel on a supporting device. Measure without flow. After the pipe enters the operating mode (set the specified flow rate), the model is moved in the flow of the working part of the wind tunnel along the angle of attack (slip) with a constant angular velocity of 0.5 deg / s from the initial angle to the final one and vice versa using the drive. In this case, simultaneously with the beginning of the model’s movement and until its end, instantaneous aerodynamic loads are measured, experimental data is collected with a sampling frequency of at least 1000 Hz from the readings of the aerodynamic balance, the angle of attack (slip) sensor and the pressure sensor. Further, the collected data is processed. Processing involves obtaining dimensional data from the raw data, aerodynamic loads are un-dimensioned, and then filtered by a 4th-order Butterworth low-pass filter with a cutoff frequency of 2-5 Hz. Additionally, based on the collected experimental data, the position of the jump-like transitions in the aerodynamic characteristics, the beginning and development of the aerodynamic jolting are determined.

The lower limit of the polling frequency (1000 Hz) is selected based on the duration of the hopping transition (ΔT≤0.1 sec). With a jump duration of ΔT = 0.1 sec and a sampling frequency of 1000 Hz, 100 points are generated per threshold nonlinearity, which is sufficient for the correct determination of a “catastrophe” in aerodynamic characteristics. At lower values of the polling frequency, for example, at 100 Hz (as indicated in the prototype), the number of points per jump decreases to 10, which is clearly not enough to build a transition in aerodynamic characteristics. For spasmodic transitions occurring in a faster timeline (in a shorter period of time than 0.1 sec), the polling frequency should be higher (≥1000 Hz).

The choice of the low-pass filter cutoff frequency range specified in the method (2-5 Hz) is determined from the conditions:

1. the lower limit of the cutoff frequency range should be such as not to “cut out” the jump-like transition in the aerodynamic characteristics of the object, in the prototype (Fig. 3 of the Appendix) the selected cut-off frequency of 0.5 Hz led to smoothing of the section in the aerodynamic characteristics, where there are a number of “catastrophic” "Transitions;

2. The upper limit of the cutoff frequency range is chosen in such a way as to leave aeroelastic frequencies in the spectral composition in quasistatic aerodynamic dependences to assess the onset and development of aerodynamic jolting.

As an example, in FIG. 1 and 2 show, respectively, longitudinal static and quasistatic aerodynamic dependences on the angle of attack, obtained for the same triangular wing as in the prototype. The final step of changing the angle of attack does not provide a complete picture of the behavior of the static dependences c _y = c _y (α), m _z = m _z (α) (Fig. 1), whereas in the quasistatic dependences c _y = c _y (α) , m _z = m _z (α) (Fig. 2) a number of “catastrophic” transitions are visible (one jump in the vicinity of α = 47 degrees, two jump-like transitions in the vicinity of α = 48 degrees, then at α = 50 and 51 degrees) . The presence of "catastrophes" is also clearly visible in the dynamic dependences obtained with harmonic oscillations of the triangular wing in the vicinity of the "catastrophic" angles of attack (Fig. 3). It can be seen that at these angles of attack, the dynamic loops have almost vertical lateral boundaries. In FIG. Figure 3 shows three loops, two of which are placed to the right of the "quasistatic", so as not to clutter the graph. Also from the graphs in FIG. 3 it is clearly seen that at the angle of attack α = 38 degrees there is a “subthreshold” aerodynamic jolting, the amplitude of which increases with increasing angle of attack.

The technical result is confirmed by the fact that the threshold non-linearities found in the aerodynamic characteristics during tube tests of the model were also found in the aerodynamic characteristics of real aircraft during flight tests (V.G. Markov, S.V. Svergun, T.I. Trifonova, Yu.F. Shelyukhin, DV Shukhovtsov “Mathematical modeling of longitudinal non-stationary aerodynamic characteristics of a regional aircraft at large angles of attack.” - Materials of the XXVI Scientific and Technical Conference on Aerodynamics February 26-27 2 015 in the village of Volodarsky, S. 162-163). In FIG. Figure 4 shows graphs of the dependence of the pitch moment coefficient on the angle of attack obtained in flight tests of a long-range airplane during the "summer cottage" mode and the quasistatic dependence of the pitch moment coefficient on the angle of attack obtained in tube tests of its model. It can be seen that at the angle of attack α = 13 deg in both dependences there is a “catastrophic" transition from one stationary state to another. In FIG. 5 in the “cottage” mode, “casting” was carried out at a larger angle of attack of 14.5 degrees. It can be seen that in the direct course of the change in the angle of attack, a jump-like transition to the lower branch of the dependence m _z = m _z (α) is realized, with the reverse course, two “catastrophic” transitions are realized. In FIG. Figure 6 shows the quasistatic and dynamic dependences m _z = m _z (α) obtained in a wind tunnel. It can be seen that the dynamic loops obtained in the tube tests repeat the dynamic loops obtained in the flight tests.

The technical result is also confirmed by the fact that the beginning and development of aerodynamic jolting along the angles of attack obtained in the tube tests of the model are consistent with the data obtained in flight of a real aircraft.

In FIG. 7 compares the results of studies of the aerodynamic jolting of the model in a wind tunnel, carried out by assessing the intensity of fluctuation of the coefficient of the aerodynamic moment of pitch m _z relative to the average value (standard deviation σ _Mz ), with the results of airplane flight tests obtained based on the processing of flight records (A. Z. Tarasov, TI Trifonova, DV Shukhovtsov “Investigation of the temporal dependencies of aerodynamic forces and moments at large angles of attack.” - Journal “Technique Air Fleet. ”Moscow, 2000, volume LXXIV, No. 1-2, S. 64-65). From FIG. 7 it is seen that there is a coincidence in the angle of attack of the beginning and development of aerodynamic shaking to the angle of attack α = 15 deg.

The method of experimental determination of aerodynamic characteristics during quasistatic tests will be widely used in wind tunnels for experimental research of nonlinear aerodynamics of objects.

Claims (1)

A method for experimentally determining the aerodynamic characteristics of a model during quasistatic tests in a wind tunnel, including moving the model in the flow of the working part of the wind tunnel by the angle of attack (slip), measuring instant aerodynamic loads, collecting experimental data and filtering them, characterized in that the experimental data are collected with a sampling frequency of at least 1000 Hz, filtering of experimental data is carried out with a cutoff frequency of 2-5 Hz, and will also complement flax based on the collected experimental data determine the position of abrupt transitions in aerodynamic characteristics, and the beginning of the development of the aerodynamic angle of attack by shaking and sliding.

Images