RU2343441C1 - Estimation method of averaged induced rotor speed field in low-speed helicopter flight - Google Patents

Abstract

FIELD: physics, testing.

SUBSTANCE: invention refers to aerodynamic testing, specifically to helicopter rotor aerodynamics, namely to induced rotor (R) speed measurement in low-speed flights and can be used for higher calculation accuracy of helicopter airspeed components. In the course of method implementation, level-flight airspeed is measured; rotor disk area, average induced disk area speed are calculated on the basis of pulse theory. Then average induced disk area speed redistribution is estimated depending on helicopter flight speed and rotor ram effect. Tip eddies are visualised with smoke released by smoke generator from flying helicopter blade ends. Rotor ram effect is recorded by motion picture camera away from rotor rotation axis to cross point of tip eddies and blade taper on azimuth 180°. Preset helicopter speed is estimated for relative area of rotor ram effect. Then average induced disk area speed redistribution is estimated considering relative averaged induced disk area speed.

EFFECT: enhanced aerodynamic rotor calculation in low-speed helicopter flight.

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Description

Technical field

The invention relates to aviation, to the field of aerodynamics of the rotors of a helicopter, and in particular to the measurement of inductive speeds of the rotor (HB) at low speeds, and can be used to improve the accuracy of calculating the components of the airspeed of the helicopter.

State of the art

A known system of helicopter air signals for determining in the region of low flight speeds the bevel angles of the swirl column of the HB helicopter (utility model RU No. 55479 of July 12, 2005).

The system allows the calculation of the components of the airspeed vector and the determination of the altitude-speed parameters of the helicopter; when calculating the components of the airspeed vector, vortex theories are used to calculate inductive velocities at the sensor installation site. However, vortex theories do not correspond to the processes that occur at low helicopter flight speeds, which leads to large errors in determining the components of the helicopter airspeed.

There is a method of calculating the averaged inductive speed over the rotor disk (Mil ML, Nekrasov AV "Helicopters. Calculation and design". Book 1. - M .: Engineering, 1996, p. 108), in which materials of measurements of inductive velocities behind the models of rotors in a wind tunnel (Mil M.L., Speransky M.K. “Investigation of the velocity field around the helicopter rotor during axial and oblique flow around”, Proceedings of TsAGI, 1949, p.32) was taken as the area of air jets through the rotor at low speeds, half the area swept by the rotor blades inta. Although this approach to the refinement of the averaged inductive speed over the HB disk does not improve the aerodynamic calculation, it does not give a complete picture due to the inaccuracy of determining the field of inductive velocities from the HB model disk due to the absence of a cyclic pitch on the blades in model experiments. Given these circumstances, it was assumed that the inductive speed in the front of the disk is zero, and in the back - twice the average value in the entire range of low speeds.

Despite significant improvements to the Glauert-Locke theory, the basic assumption of the stationary field of the inductive velocity field along the NV disk, determined by the impulse theory (Yuryev B.N. “Aerodynamic calculation of helicopters”, Oborongiz, 1956, pp. 356-358), remains intact.

In accordance with the impulse theory, the average inductive speed along the HB disk for a horizontal steady-state helicopter flight at low speeds is determined by the formula

where υ _iср is the average inductive speed along the screw disk;

T - thrust HB equal to the flight weight of the helicopter;

χ is the coefficient of end loss of the blades;

ρ is the density of atmospheric air;

F - swept area of the rotor;

V is the air speed of the horizontal flight of the helicopter.

This assumption significantly limits the possibility of using the impulse theory in calculations.

Thus, the known methods for estimating the field of inductive velocities of HBs at low helicopter flight speeds do not have sufficient reliability of calculating the flywheel motion of the blades, which reduces the reliability of helicopter flight at low speeds.

SUMMARY OF THE INVENTION

The technical solution to the problem is to expand the possibilities of using the claimed method, to clarify the methods for calculating the flywheel movement of the blades, and thereby to improve the aerodynamic calculation of HB at low helicopter flight speeds, by obtaining a closer to reality distribution of inductive speeds on the HB disk, and to clarify the cross-sectional area of the compressed air flow through HB according to the results of visualization of a satellite swirling trail of HB in real helicopter flight conditions.

In accordance with the invention, the technical result is achieved by the fact that in the method for estimating the field of inductive speeds HB at low helicopter flight speeds, including measuring the airspeed of horizontal flight, calculating the swept area HB, the average inductive speed over the screw disk using the impulse theory according to the following ratio:

where υ _iср is the average inductive speed along the screw disk;

T - thrust HB equal to the flight weight of the helicopter;

χ is the coefficient of end loss of the blades;

ρ is the density of atmospheric air;

F - swept area of the rotor;

V - air speed of horizontal flight of a helicopter

<0,2. Фиксируют с помощью кинокамеры величину поджатия воздушной струи через НВ со стороны набегающего потока на расстоянии от оси вращения НВ до точки пересечения концевых вихрей с конусом лопастей на азимуте 180°. Определяют для заданной скорости вертолета относительную площадь поджатого воздушного потока струи через НВ по следующему соотношению:according to the invention, the redistribution of the average values of the inductive velocities over the HB disk is estimated depending on the helicopter flight speed and the amount of air stream compression through the HB from the incoming flow side. The end vortices are visualized with smoke from a smoke generator, which is released from the ends of the helicopter blades when flying at relative speeds

<0.2. Using a movie camera, the amount of air jet preload through the HB from the incoming flow side at a distance from the axis of rotation of the HB to the point of intersection of the end vortices with the cone of the blades at an azimuth of 180 ° is recorded. For a given helicopter speed, the relative area of the compressed air stream of the jet through the HB is determined by the following ratio:

where F _p - the area of the compressed air flow;

F - swept area HB,

then, the redistribution of the average values of the inductive velocities over the HB disk is estimated based on the relative averaged inductive speed over the HB disk from the relation

- относительная осредненная индуктивная скорость по диску НВ;Where

- relative averaged inductive speed over the HB disk;

- относительная средняя индуктивная скорость по диску;

- relative average inductive speed across the disk;

υ _iav - the relative average inductive speed obtained by the impulse theory;

ω is the angular velocity of rotation of the HB;

R is the radius of the rotor.

Thus, knowing the distribution of inductive speeds closer to reality over the HB disk, it is possible to determine the fields of averaged inductive speeds of the HB taking into account the compressed air flow passing through the HB at low helicopter flight speeds and to clarify the methods for calculating the flywheel motion of the blades in order to improve the aerodynamic calculation of the HB at low helicopter flight speeds.

The proposed method is illustrated by drawings, in which:

=0,068, с углом атаки НВ α=2,6°, коэффициентом тяги НВ Ст=0,0108, на высоте полета Н=200 м, гдеFigure 1 is a side view, the trajectory of the visualized end vortices near the HB of the Mi-8 in horizontal flight, at relative air speed

= 0.068, with an angle of attack of HB α = 2.6 °, traction coefficient HB St = 0.0108, at a flight altitude of H = 200 m, where

A-B is the boundary of the area of compressed air flow HB;

B-C is the boundary of the area of preload of the airflow HB;

1 - HB blade;

2 - visualized end vortices.

=0,17, α₃=-5,8°, Ст=0,16, H=200 м.Figure 2 shows a side view, the trajectory of the visualized end vortices near the rotors of the Ka-32 helicopter in horizontal flight at

= 0.17, α ₃ = -5.8 °, St = 0.16, H = 200 m.

), гдеFigure 3 shows the dependence of the magnitude of the compression of the jet through the HB from the side of the incoming air flow from the helicopter flight speed r _x = f (

), where

3 - dependence for the Mi-4;

4 - dependence for the Mi-8;

5 - dependence for the lower propeller of the Ka-32 helicopter;

6 - dependence for the top propeller of the Ka-32 helicopter.

Figure 4 shows a top view, the visualization of smoke end vortices, converging with the blades HB, where

7 - area preload air flow through the HB;

8 - area of compressed air flow;

9 - the point of intersection of the end vortices with the cone of the blades.

Figure 5 shows the results of comparing the dependence of the averaged inductive velocities over the rotor disk for a reduced jet cross-section through the NV from the helicopter flight speed obtained experimentally by visualizing the end vortices by smoke according to the claimed method, with the calculated theoretical values of the average inductive velocities calculated for the Mi-4 helicopter, at St = 0.0079, where

10 - calculated theoretical value of the average inductive speeds;

11 - averaged inductive speeds.

<0,2) как на одновинтовых, так и на соосных вертолетах является сильное поджатие отбрасываемой НВ струи со стороны набегающего воздушного потока (фиг.1 и 2), что приводит к перераспределению средних значений индуктивных скоростей по диску НВ в зависимости от скорости горизонтального полета и величины поджатия воздушной струи через НВ со стороны набегающего потока. Производят визуализацию концевых вихрей дымом от генератора дыма, который выпускают из концов лопастей вертолета при полете с относительными скоростями

<0,2. Фиксируют с помощью кинокамеры величину поджатия воздушной струи через НВ со стороны набегающего потока на расстоянии от оси вращения НВ до точки пересечения концевых вихрей с конусом лопастей на азимуте 180°. При этом впервые зафиксировано, что передние части циклоид концевых вихрей находятся выше лопастей на удалении, соизмеримом с диаметром вихрей, и на определенном удалении от передней кромки диска, смещающихся под НВ, частично размываемых лопастями. Занимаемая ими зона 7 на разных вертолетах заметно отличается друг от друга, существенно изменяется по скорости полета и на одновинтовых вертолетах распространяется даже за ось вращения НВ (фиг.3 и 4).The method is as follows. Flight research was carried out to study the spiral vortex wake of the HB Mi-4, Mi-8 and Ka-32 helicopters of the claimed method by visualizing smoke from the smoke generator of the end vortices, which are released from the end of the helicopter blades. The materials obtained in this work indicate that one of the main previously unknown phenomena at low flight speeds (

<0.2) both on single-rotor and coaxial helicopters there is a strong preload of the discarded HB jet from the side of the incoming air flow (Figs. 1 and 2), which leads to a redistribution of the average values of inductive speeds along the HB disk depending on the speed of horizontal flight and the amount of preload of the air stream through the HB from the side of the incoming flow. The end vortices are visualized with smoke from a smoke generator, which is released from the ends of the helicopter blades when flying at relative speeds

<0.2. Using a movie camera, the amount of air jet preload through the HB from the incoming flow side at a distance from the axis of rotation of the HB to the point of intersection of the end vortices with the cone of the blades at an azimuth of 180 ° is recorded. In this case, it was first recorded that the front parts of the end vortex cycloid are located above the blades at a distance commensurate with the diameter of the vortices, and at a certain distance from the front edge of the disk, which are displaced under the HB, partially washed out by the blades. The occupied by them zone 7 on different helicopters differs markedly from each other, varies significantly in flight speed and on single-rotor helicopters extends even beyond the axis of rotation of the HB (Figures 3 and 4).

The obtained materials on the visualization of the end vortices can be used to calculate the averaged value of the inductive velocity by taking into account the redistribution of the average values of the inductive velocities over the screw disk using the impulse theory according to the following relation:

where υ _iср is the average inductive speed along the screw disk;

T - thrust HB equal to the flight weight of the helicopter;

χ is the coefficient of end loss of the blades;

ρ is the density of atmospheric air;

F - swept area of the rotor;

V is the air speed of the horizontal flight of the helicopter.

The redistribution of the average values of inductive speeds along the screw disk can be based on the dependencies

_x=f(

),

_x = f (

),

- относительный радиус, характеризующий величину поджатия воздушной струи через НВ со стороны набегающего потока (см. фиг.4) на расстоянии от оси вращения НВ до точки 9 пересечения концевых вихрей с конусом лопастей на азимуте 180° - точку встречи концевых вихрей с конусом лопастей при их смещении под НВ;Where

- the relative radius characterizing the amount of preload of the air stream through the HB from the side of the incoming flow (see Fig. 4) at a distance from the axis of rotation of the HB to the point 9 of intersection of the end vortices with the cone of the blades at an azimuth of 180 ° - the meeting point of the end vortices with the cone of the blades at their displacement under the HB;

R is the radius of the HB;

- относительная воздушная скорость горизонтального полета вертолета;

- the relative air speed of the horizontal flight of the helicopter;

ω is the angular velocity of rotation of the HB.

With acceptable accuracy, for the cross-sectional area of the squeezed air stream 8 (zone AB, Fig. 1) flowing through the screw F _p , we can consider the area F = πR ² swept by the blades minus the shaded (see Fig. 4) area of segment 7 with height h = Rr _x characterizing the area occupied by the end vortices under the blades of the HB. Then the relative area of the air stream 8, limited by the end vortices 2 (zone BC, Fig. 1) and flowing through the HB, will be determined by the expression

(2)

(2)

where F _p is the cross-sectional area of the air stream flowing through the HB;

F is the area swept by the blades of the HB.

Using formula (2) and the average value of the inductive speed over the disk, using formula (1), we can obtain the averaged inductive speed for low flight speeds for a reduced value of the jet cross section through the HB. To this end, we turn to the equation of continuity of the jet, whence we will have

- относительная площадь поджатого воздушного потока струи через НВ;Where

- the relative area of the compressed air stream of the jet through the HB;

- относительная осредненная индуктивная скорость;

- relative averaged inductive speed;

- относительная средняя индуктивная скорость, полученная по импульсной теории.

- the relative average inductive speed obtained by the impulse theory.

Obtained in accordance with formula (3), the averaged inductive speed for a reduced cross-section of the jet through HB qualitatively and quantitatively differs from the average values of the inductive speed calculated by formula (1), for example, for the Mi-4 helicopter (Fig. 5).

The practical significance of the invention

≤0,2) позволяет уточнить расчетные средние индуктивные скорости по импульсной теории путем более правильного перераспределения ее по диску НВ. Зная более близкое к действительности распределение индуктивных скоростей по диску, можно уточнить методы расчета махового движения лопастей и усовершенствовать аэродинамический расчет НВ на малых скоростях полета вертолета с целью повышения надежности расчетных характеристик несущих винтов.New information received in flight research during the visualization of end vortices at low helicopter flight speeds (

≤0.2) makes it possible to refine the calculated average inductive velocities by the impulse theory by more correctly redistributing it over the HB disk. Knowing the distribution of inductive velocities across the disk closer to reality, it is possible to clarify the methods for calculating the flywheel motion of the blades and improve the aerodynamic calculation of HB at low helicopter flight speeds in order to increase the reliability of the design characteristics of the main rotors.

Claims (1)

The method of estimating the field of averaged inductive speeds of the main rotor at low helicopter flight speeds, including measuring the air speed of horizontal flight, calculating the swept area of the main rotor (HB), the average inductive speed over the rotor disk using the impulse theory according to the following relation:

where υ _icp is the average inductive speed over the screw disk;
T - thrust HB equal to the flight weight of the helicopter;
χ is the coefficient of end loss of the blades;
ρ is the density of atmospheric air;
F - swept area of the rotor;
V is the air speed of the horizontal flight of the helicopter,
characterized in that the redistribution of the average values of the inductive speeds along the NV disk is estimated depending on the helicopter flight speed and the amount of air stream preload through the NV from the incoming flow side by providing visualization of the end vortices by smoke from the smoke generator, which is released from the ends of the helicopter blades during flight with relative speeds

<0.2, with the help of a movie camera, the amount of air stream preload through the HB from the incoming flow side is equal to the distance between the axis of rotation of the HB and the point of intersection of the end vortices with the cone of the blades at an azimuth of 180 °, the relative area of the compressed air stream of the jet is determined for a given helicopter speed through HB in the following ratio:

where F _p - the area of the compressed air flow;
F - swept area HB;
then, the redistribution of the average values of the inductive velocities over the HB disk is estimated based on the relative averaged inductive speed over the HB disk from the relation

Where

- relative averaged inductive speed over the HB disk;

- relative average inductive speed across the disk;
υ _icp is the average inductive speed obtained by the impulse theory;
ω is the angular velocity of rotation of the HB;
R is the radius of the rotor.

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