RU2561829C2 - Method and device for determination of aircraft aerodynamics - Google Patents

Abstract

FIELD: instrumentation.

SUBSTANCE: invention relates to experimental aerodynamics, particularly, to devices intended for research of aerodynamics of aircraft. Proposed method consists in determination of aircraft aerodynamics in hydrodynamic tunnel with water used as aircraft fluid flow medium. Aircraft mockup is placed in said hydrodynamic tunnel, mockup head being secured at top holder and mockup tail being secured at bottom holder. Note here that resistive-strain sensors are fitted in said holders to measure crosswise and lengthwise forces as well as the moment. Water flow rate meters are arranged in said hydrodynamic tunnel. Then, motor is activated to develop water flow rate therein to set required water flow rate and to measure crosswise and lengthwise forces and moment. Hydrodynamic tunnel top section incorporates the system of supercharging to preset pressure required for simulation by Euler number in tunnel working section. Proposed device comprises working section, motor, revolving impeller machine to develop water head, water rate registration hardware, resistive-strain sensors for measurement of crosswise and lengthwise forces and moment and recording hardware. Blow-over tube is composed of hydrodynamic tunnel while blow-over medium is water.

EFFECT: enhanced performances, higher accuracy and safety of tests.

11 cl, 2 dwg, 1 tbl

Description

The invention relates to the field of experimental aerodynamics, in particular to methods and means for determining the aerodynamic characteristics of aircraft.

The following methods are known in experimental aerodynamics for determining the aerodynamic characteristics of aircraft [1, 2]:

1) experimental determination in wind tunnels of the aerodynamic characteristics of models of aircraft (LA) or individual parts of the aircraft;

2) experimental ground tests of individual parts of the aircraft or the aircraft as a whole under conditions that maximally simulate full-scale operating conditions in order to determine the aerodynamic characteristics of the aircraft;

3) experimental determination of aerodynamic characteristics of aircraft during flight tests.

The disadvantages 2 and 3 of the method for determining the aerodynamic characteristics of an aircraft are large time and material costs, as well as the late identification of the aerodynamic design flaws of the aircraft and its individual elements, the elimination of which requires large material and time costs. Therefore, the main experimental method for determining the aerodynamic characteristics of an aircraft at the initial stages of design is the experimental testing of an aircraft in wind tunnels.

A device is known for measuring the constituent vectors of aerodynamic force and moment — mechanical aerodynamic scales, consisting of a rigid frame and connecting elements, interconnected lever systems that hold it in equilibrium; output links of linkage mechanisms are connected to dynamometers ([3] p.82 - Aerodynamic characteristics).

The frame is a structure located in the flow created by the wind tunnel, which is directed perpendicular to the plane of the frame. The model is installed inside the frame using stretch marks, which are metal strips with a profiled cross section oriented along the flow. The components of the aerodynamic force and moment acting on the tested model and tapes are transmitted to the frame and measured using dynamometers. The main disadvantage of the known solution [3] is the low accuracy of measurements, especially of such an important characteristic as the drag coefficient of an aircraft, for example, a modern passenger plane, which has a value close to or even lower than the drag coefficient of the belts. Therefore, to obtain a result, it is necessary to subtract the force on the tape from the measured force. The drag coefficient of the tapes is determined in the "empty" wind tunnel in the absence of an aircraft model in the same test modes as with the model, which leads to increased material costs. In addition, we are talking about the difference between two close physical quantities obtained in different experiments, which leads to a decrease in the measurement accuracy.

A close analogue is also a device for measuring the components of the aerodynamic force and moment vectors - aerodynamic tensometric scales, consisting of an elastic body, dynamometric elements and strain gauges that convert deformations of sensitive elements into electrical signals. The dynamometric elements here are made together with the body and are oriented so that the deformation of the element caused by the corresponding component of the aerodynamic force or moment is maximum [2].

At the moment, there are a large number of inventions for determining the aerodynamic characteristics of aircraft [4-12], which work well when simulating flow for Reynolds numbers greater than 10 ⁶ . A significant drawback of all these devices is that studies of the aerodynamic characteristics of aircraft at launch positions (when modeling Reynolds numbers less than 10 ⁶ ) do not allow for the accuracy and reliability of determining the aerodynamic forces and moments of the model due to the small values of the measured model parameters.

Known devices for measuring the constituent vectors of aerodynamic force and moment [9, 10]. The disadvantages of the devices according to patents [9, 10] are: determination of ADH at high speeds, at low speeds there are large errors; impossibility of simultaneous modeling by Euler, Reynolds, Froude numbers; the impossibility of modeling ADC aircraft at the launch pad, taking into account the interference of launch facilities.

The closest analogue of the proposed solutions, in our opinion, is the invention [13], which we adopted as a prototype. The disadvantage of the prototype is its working range - the working section is designed for turbulent flows and Reynolds numbers more than critical (Re> 10 ⁶ ). When tested in wind tunnels, the Euler numbers are several times higher than the Euler numbers in kind. The working range of the prototype is due to the fact that the determination of ADH occurs at supersonic and transonic speeds, when the impact on the aircraft model reaches 100 KN, and at low speeds the impact is less than 10N, i.e. the error of the measuring system is comparable to the measured force at low speeds (<10 m / s). Another significant drawback of the prototype [13] is the inability to vary the pressure in the working area over a wide range, which means that it is impossible to conduct experiments for a single model of aircraft in a wide pressure range, and therefore it is impossible to simulate blowing at large ranges of Euler numbers. Also, the prototype does not provide modeling of launch facilities at the launch position, their automatic circular rotation, therefore, the prototype does not allow to solve the problem of determining the interference of launch facilities on the aircraft.

We characterize in more detail the disadvantages of the prototype [13], also inherent in other similar devices [4-12]:

1) Reynolds numbers are not modulated at low blowing speeds (V <5 m / s) and large model scales;

2) Euler numbers are not modulated due to the impossibility of creating necessary pressures in the working section of the blowing pipe *;

3) It is impossible to simultaneously simulate the similarity criteria of Reynolds, Froude and Euler;

4) When conducting experiments for Reynolds numbers less than 10 ^{6 there} is a large level of measurement error.

(*) Hereinafter, by a blowing pipe we mean a specially profiled contour that provides a given flow of blowing the aircraft model.

All these shortcomings are due to the need to comply with the aerodynamic similarity of the flow around the model to natural conditions, which is ensured by the observance of the main similarity criteria: Reynolds Re, Froude Fr and Euler Eu:

, $$Fr=\frac{V_0}{\sqrt{gL}}$$

, $$Eu=\frac{P_o}{\rho V_0^2/2}$$

. $$\mathrm{Re}=\frac{V_0\rho L}{\eta },$$

, $$Fr=\frac{V_0}{\sqrt{gL}}$$

, $$Eu=\frac{P_o}{\rho V_0^2/2}$$

.

Here L is the characteristic linear size, V ₀ is the characteristic speed, P ₀ is the pressure, ρ is the density of the medium, g is the acceleration of gravity, η is the dynamic viscosity coefficient.

, давления $$\lambda =\frac{P_{0H}}{P_{0M}}$$

, скорости $$\mu =\frac{V_{0H}}{V_{0M}}$$

. Из требования подобия вытекает необходимость соблюдения равенств: Re_H=Re_M, Fr_H-Fr_M, St_H=St_M, Eu_H=Eu_M, из которых следуют соответствующие требования к масштабам моделирования:Denoting by the index “n” the quantities in nature and the index “m” on the model, we introduce the scale of modeling the quantities: linear dimensions $$M=\frac{L_H}{L_M}$$

pressure $$\lambda =\frac{P_{0H}}{P_{0M}}$$

, speeds $$\mu =\frac{V_{0H}}{V_{0M}}$$

. The requirement of similarity implies the need to observe the equalities: Re _H = Re _M , Fr _H -Fr _M , St _H = St _M , Eu _H = Eu _M , from which the corresponding requirements for the modeling scale follow:

$$\mu =M^{-\mathrm{one}},\lambda ={\mathrm{<figure-callout\; id="2"\; label="\mu "\; filenames="00000011.png"\; state="\{\{state\}\}">\mu </figure-callout>}}^2,M={\mathrm{<figure-callout\; id="2"\; label="\mu "\; filenames="00000011.png"\; state="\{\{state\}\}">\mu </figure-callout>}}^2.\left(\mathrm{one}\right)$$

(наддув в аэродинамических трубах до нужных величин в отличие от гидродинамических невозможен).The first requirement µ = M ⁻¹ , which follows from the equality Re _H = Re _M , means that the flow rate on the model should be M times greater than on nature. This is almost impossible to accomplish in a model experiment, and also contradicts the second and third requirements (1). As an example, we consider the need for an experiment simulating the flow of aircraft around an air stream with a speed of 10 m / s on a model with a scale of M = 20, then the speed in the wind tunnel should be 200 m / s. This and other examples of simulation parameters are given in the table. To ensure model test parameters that are as close as possible to full-scale tests, it is proposed to investigate the flow around aircraft models in the airflow pipe made in the present invention in the form of a hydrotube, where water is used as the flow medium, then the flow velocities of the medium on the model and nature will be closer to each other at identical Reynolds numbers (see table). To achieve the equalities of Euler numbers in nature and the model, it is proposed to create a pressure in the hydrotube by boosting that satisfies the condition $$E{u}_H=E{u}_M=\frac{P_{0H}}{{\rho }_H{V}_{0\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="00000011.png"\; state="\{\{state\}\}">H</figure-callout>}}^2/2}=\frac{P_{0H}}{{\rho }_M{V}_{0\mathrm{<figure-callout\; id="2"\; label="H"\; filenames="00000011.png"\; state="\{\{state\}\}">H</figure-callout>}}^2/2}$$

(pressurization in wind tunnels to the desired values, unlike hydrodynamic ones, is impossible).

Parameters of nature and model tests in wind tunnels and hydrodynamic tubes Blowing speed V ₀ [m / s] Density
ρ [kg / m ³ ] Dynamic viscosity η [Pa · s] Characteristic size L [m] Re Nature 10 1.3 0,000018 3 2.2 10 ⁶ Model air M = 5 fifty 1.3 0,000018 0.6 2.2-10 ⁶ Model air M = 10 one hundred 1.3 0,000018 0.3 2.2-10 ⁶ Model air M = 20 200 1.3 0,000018 0.15 2.2-10 ⁶ Model water M = 5 3.6 1000 0.001 0.6 2.2-10 ⁶ Model water M = 10 7.2 1000 0.001 0.3 2.2-10 ⁶ Model water M = 20 14,4 1000 0.001 0.15 2.2-10 ⁶

The aim of the invention is to eliminate the disadvantages of analogues and prototype.

The specified goal is achieved by the fact that:

- water is used as the medium flowing around the model of the aircraft, and since the liquid has a high density and dynamic viscosity, this makes it possible to simulate less Reynolds numbers in experiments (Re <10 ⁶ );

- when conducting experiments in a hydraulic pipe due to boost, the pressure in the working section rises to the values necessary for modeling by Euler numbers;

- the use of liquid as a flow medium provides increased accuracy of measurements of forces and moments acting on the aircraft model at low flow velocities;

- the proposed load cell system mounted on the holder allows measurements with increased accuracy of lateral and lateral forces, as well as the moment acting on the aircraft model.

During testing, the following features are provided:

- in one test it is possible to change the flow rate and thereby measure the ADH of the aircraft model in a wide range of Reynolds numbers;

- during one test it is possible to change the pressure in the working section of the hydraulic pipe and thereby measure the ADH of the aircraft model in a wide range of Euler numbers;

- provides for the installation on the desktop in the plane of the lower cut of the aircraft model of launch vehicle models in order to determine their interference with the aircraft model at the starting position;

- a circular rotation of the model is provided along with the starting position relative to its longitudinal axis, thereby creating the possibility of obtaining circular blowing of the model at the starting position and determining the influence of the starting structures on the ADH of the aircraft model (interference) without stopping the flow velocity without removing the model from the hydrodynamic pipe and without reinstalling the models of launch facilities relative to the aircraft model, as well as changing pressures in a wide range during one test;

- replacing the head of the aircraft model with another, without changing the model itself, thereby creating the opportunity to obtain measurements of the ADC model with different warheads and choosing the optimal shape of the aircraft.

The present invention solves the urgent problem of implementing measurements of aerodynamic forces and moments acting on the model of the aircraft in the simulation of flow around Reynolds numbers less than 10 ⁶ . The proposed technical solutions allow:

1) reduce the cost of solving the problems of experimental development of the launch of aircraft and their movement at the surface of the earth;

2) increase the accuracy of the measured forces and moments;

3) increase the safety of testing.

The technical nature of the invention is illustrated by graphic images. The figure 1 shows a General view of a hydrodynamic pipe (GT); figure 2 - working section of the GT.

Impellers create the required high-speed flow in the working area (necessary for modeling according to the Reynolds number), in which the aircraft model is installed, the pressurization system provides hydrostatic pressure (necessary for modeling according to the Euler number), the scale of the model and the speed of blowing are selected from the simulation conditions according to the Froude number. The working section has a system of holders, strain gauges, for measuring the forces and moments acting on the model, a table simulating the surface of the earth with starting facilities, transducers and recording devices.

The numbers in figure 2 are indicated.

1. - Hydrotube

2. - Model

3. - Detachable head

4. - Top mount

5. - Bottom mount

6. - Upper holder

7. - Lower holder

8. - Upper fairing

9. - Lower cowl

10. - Top hole

11. - Bottom hole

12. - The load cell according to the measurement of the transverse force Fy

13. - Strain gauge for measuring lateral force Fz

14. - The load cell according to the measurement of moment Mx

15. - Upper protective cover

16. - The lower protective casing

17. - Table imitating the surface of the earth

18. - Control unit

19. - Converter

20. - Recording device

21. - Sensor for measuring the flow rate of water

22. - Direction of water flow

A device for determining the aerodynamic characteristics of a model in a hydrodynamic pipe 1 comprises a model 2 with a removable head 3 fixed through the upper 4 and lower 5 mounts to the upper 6 and lower 7 holders, respectively. The holders are protected from the flow of water by the fairings 8, 9 and through the upper 10 and lower 11 holes in the working part of the hydraulic pipe are connected to the load cells 12, 13, 14. To prevent water from entering the working section of the hydraulic pipe, the holes 10 and 11 are protected by protective covers 15 and 16, respectively. For experiments on the study of the aircraft’s ADC, at the starting positions on the lower fairing 9, a table 17 can be installed that simulates the surface of the earth with launch facilities to determine the interference between the aircraft and launch facilities. For experiments on the study of the ADC of an aircraft in flight, device 17 is not installed on the lower fairing. At the heart of the device for determining the aerodynamic forces and moments acting on the model, the weight method based on the use of tensile weights is used.

The process of measuring aerodynamic forces and moments in the proposed device is carried out in two stages. The transition from one stage to another is carried out according to the commands of the control unit 18. At the first stage, for each measuring channel, the additive error components are determined for de-energized strain gauge bridge sensors and stored for the entire period of regular measurements, at the second stage, regular measurements are carried out and the results of regular measurements are automatically by subtracting the additive components of the errors.

The device operates as follows. At the stage of determining the systematic additive component of errors by command from the control panel, the readings of the strain gauges are measured, their error at the beginning of the experiment is determined depending on the temperature and hydrostatic pressure in the working section of the pipe. At the second stage, the flow rate in the working part of the pipe is set, the liquid is accelerated to a predetermined speed, and the load cell indicators 12, 13, 14 are mounted on the upper and lower holders 7, 8. The load cells are measured on the transducer 19, and then on the recording device 20. At a command from the control unit 18, the flow rate in the pipe 1 is varied. At different angles of installation, the aerodynamic characteristics of model 2 are determined by the flow sensors of model 2 using strain gauges 12, 13, 14 at the detected sweat speed Single sensor 21. The control unit 18 changing the flow rate, is recorded on the storage devices transverse, lateral forces and moments acting on the model 2. The accumulation results in the memory 20 comes to the end of performing the regular measurement mode. The results are transmitted from the storage device 20 to an external device by command from the control unit 18. At the end of the second stage, the additive error components are automatically excluded from the results of regular measurements by subtracting.

The measured results of the load cells 12, 13, 14 and the forces Fy, Fz and the moment Mx recorded by the storage device 20 are converted into dimensionless aerodynamic characteristics:

$$Cy=\frac{Fy}{S_M\cdot \rho V_0^2/2},Cz=\frac{Fz}{S_M\cdot \rho V_0^2/2},m_x=\frac{Mx}{S_M\cdot L\cdot \rho V_0^2/2}(2)$$

where L is the characteristic linear size, V ₀ is the characteristic speed, ρ is the density of the medium, S _M is the midsection area for which the characteristics are dimensioned, Fy is the measured transverse force, Fz is the measured lateral force, Mx is the measured moment.

Using the proposed invention can significantly improve the accuracy of measuring the aerodynamic characteristics of the model and reduce the time of the experiment in hydrodynamic pipes with a large diameter of the working section.

The technical result of the invention is the accurate determination of the force effect on the aircraft model when modeling Reynolds numbers less than 10 ⁶ by eliminating systematic additive measurement errors and increasing the speed of a multichannel measuring device for tensile weights.

Thus, the proposed method and device can provide the following technical results:

- to simulate in experiments in a hydrotube the flow around an aircraft model at Reynolds numbers less than (Re <10 ⁶ );

- conduct an experimental determination of the aerodynamic characteristics of aircraft while simulating the numbers of Euler, Reynolds and Froude;

- reduce the cost of solving the problems of experimental development of the launch of aircraft and their movement at the surface of the earth;

- carry out an experimental determination of interference from launch facilities on an aircraft located at the starting position with full circular airflow (360 °) in one experiment;

- increase the accuracy of measuring forces and moments;

- increase the safety of testing.

List of sources of information

1. Krasnov N.F. et al. Applied Aerodynamics. - M.: Higher School, 1974.

2. Kholodkov N.V. experimental development of spacecraft. - M .: MAI, 1994.

3. Encyclopedia of Aviation, scientific publishing house "Big Russian Encyclopedia", Moscow, 1994

4. Patent SU 369448 A1, IPC G01M 9/06, G01L 23/18. Device for measuring aerodynamic characteristics. Priority 07.26.1971.

5. Patent SU 378738 A1, IPC G01M 9/06. A device for determining rotational derivative models in aerodynamic. Priority 10/7/1969.

6. Patent SU 390399 A1, IPC G01M 9/06. Aerodynamic tensometric scales. Priority 05/20/1971.

7. Patent SU 409085 A1, IPC G01M 9/06, G01G 19/07. Aerodynamic multicomponent intramodel scales. Priority 11.11.1971.

8. Patent RU 2287783 C1, IPC G01G 3/12, G01G 19/00. Strain gauge scales. Priority 04/27/2005.

9. Patent RU 2287795 C1, IPC G9 / 06, G3 / 12. A device for measuring the component vectors of aerodynamic force and moment. Priority 04/27/2005.

10. Patent RU 2287796 C1, IPC G9 / 06, G3 / 12. A device for measuring the component vectors of aerodynamic force and moment. Priority 04/27/2005.

11. Patent RU 2399895 C2, IPC G01M 9/06. A method and apparatus for improving the accuracy of measurements in a wind tunnel, which provide an account of the influence of the suspension device of the model. Priority 12/22/2005.

12. Patent RU 2469283 C1, IPC GO1L 1/22. Multichannel measuring device of aerodynamic intramodel scales. Priority 05/23/2011.

13. Patent RU 2392601 C1, IPC G01M 15/14. A device for determining the aerodynamic characteristics of a model in a supersonic wind tunnel. Priority December 25, 2008.

Claims (11)

1. The method for determining the aerodynamic characteristics (ADC) of an aircraft (LA), which consists in the fact that the ADC of an aircraft is determined in a hydrodynamic pipe (GT), when water is used as a flow around the aircraft. 2. The method for determining the ADH of an aircraft according to claim 1, which means that the aircraft model is installed in the GT, the model head is fixed in the upper holder and the model tail is mounted in the lower holder, while transverse Fy and lateral Fz force gauges are installed in the holders as well as measuring the moment Mx, sensors for measuring the flow rate of water are installed in the gas turbine, the engine of the impeller unit that creates the liquid flow in the pipe is turned on, the necessary water flow rate is set and the forces Fy, Fz and the moment Mx are measured. 3. The method for determining the ADC of an aircraft according to claim 1, consisting in the fact that the pressure necessary for modeling by the Euler number is set in the GT working section, and then, during the tests, the pressure is changed in the range of the specified Euler numbers. 4. The method according to claim 1, characterized in that after measuring the forces and moments, the head of the aircraft model is replaced with another without changing the model itself, and the tests are repeated. 5. The method according to claim 1, characterized in that during the tests, the aircraft model is rotated around its longitudinal axis to determine the ADH of the aircraft in specified directions. 6. The method according to claim 1, characterized in that during the tests, the model of the aircraft is rotated, in which models of launching structures are installed in the plane of the lower cut to determine the ADH of the aircraft in specified directions. 7. The method according to claim 1, characterized in that during one test produce a change in flow velocity in a wide range and determine the ADH of the aircraft for a given Reynolds number. 8. A device for determining the ADC of an aircraft, comprising a working section, an engine rotating an impeller unit, creating a high-pressure head of the medium for an aircraft model, equipment that controls the high-speed head of the medium, strain gauges for measuring the forces Fy, Fz and moment Мx, recording equipment, characterized in that the blowing pipe is made in the form of a hydrodynamic pipe, and water is used as a blowing medium. 9. The device according to claim 8, characterized in that the strain gauges measuring the forces Fy, Fz and moment MX are equipped with a protective casing to prevent water from entering them. 10. The device according to claim 8, characterized in that the upper part of the GT is equipped with a boost system to change the hydrostatic pressure in the working section of the hydraulic pipe (Euler numbers). 11. The device according to claim 8, characterized in that, in the plane of the lower cut of the aircraft model, models of launch facilities are installed on the desktop.

Images