RU2495794C1 - Method of estimating horizontal components of inductive velocities at single-rotor helicopter low flight speeds - Google Patents

Abstract

FIELD: transport.

SUBSTANCE: invention relates to aircraft engineering, particularly, to aerodynamics of single-rotor helicopter rotor. Proposed method comprises preliminary flight tests with visualisation of end vortices by smoke provided by smoke generator at flight speeds lower than 0.2 km/h. Note here that video cameras is used to register airflow ram effects at rotor on the side of approach flow at the distance from rotor rotation axis to intersection of end vortices with blade cone in azimuth of 180 degrees. Rotor angle of attack is defined as well as relative speeds of end vortices sweep form rotor blades for preset helicopter speed. Velocity of approach airflow is defined by standard instruments as well as local air speed nearby rotor by air pressure receiver arranged at rotor blade to define the structure and geometry of rotor vortex trace visualised by end vortex smokes and to determine circulation of lengthwise vortices. Then, horizontal components of horizontal inductive speeds nearby helicopter from rotor vortex trace at positive angles of attack at preset points are calculated.

EFFECT: higher validity of determination.

2 cl, 4 dwg

Description

The invention relates to aviation, and in particular to the field of rotor aerodynamics (HF) of a single-rotor helicopter, in particular, to a method for evaluating the horizontal components of inductive speeds from a vortex trace of a rotor at low flight speeds of a single-rotor helicopter.

The level of technology.

It is known that methods for estimating inductive velocities both near the rotor (HB) and at a distance from it are based on the use of a beveled vortex column spreading over the entire range of helicopter flight speeds as a model of the HB vortex wake. It is believed that the horizontal components of inductive velocities will be small and act towards a slight increase in air flow rate. Taking into account rather complicated calculations of inductive velocities in both disk and vortex vortex theories, in the aerodynamic calculations of helicopters the horizontal components of inductive speeds are not even mentioned (M.L. Mil, A.V. Nekrasov, A.S. Braverman and other "Helicopters", Volume 1, Aerodynamics, Mechanical Engineering, 1966, pp. 212-212, 225-226, 229-230).

A known method of estimating the field of averaged inductive speeds of the main rotor at low helicopter flight speeds, comprising visualizing the end vortices with smoke from a smoke generator, which is released from the ends of the blades of the helicopter in flight with relative speeds of less than 0.2, fixing the magnitude of the compression of the air stream through the camera HB from the side of the incoming flow 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 °, the definition for a given helicopter speed is the rate of demolition of the end vortices descending from the blades of the HB, the determination of the angle of attack of the HB, the air speed of the incoming flow using standard instruments and the local air speed near the HB using an air pressure receiver (LDPE) placed on its blades (see patent RU 2343441 of 18.07 .08).

However, this method does not evaluate the horizontal components of inductive speeds, which reduces the accuracy of the aerodynamic calculations of the helicopter.

The present invention is aimed at achieving a technical result, which consists in increasing the reliability of the assessment of the horizontal components of inductive speeds at low flight speeds of a single-rotor helicopter, by obtaining a closer to reality distribution of inductive speeds across the HB disk.

SUMMARY OF THE INVENTION

To obtain the specified technical result in a method for evaluating the horizontal components of inductive speeds at low flight speeds of a single-rotor helicopter, containing preliminary flight tests with visualization of the end vortices by smoke from a smoke generator, which is released from the ends of the helicopter blades when flying with relative speeds of less than 0.2 km / h , fixing with the help of a movie camera the amount of compressed air stream through the HB from the side of the incoming flow at a distance from the axis of rotation of the HB to the point of intersection of the end Ihrei with a cone of blades at an azimuth of 180 °, determining the angle of attack of HB, determining for a given helicopter speed the relative speed of drift of the end vortices coming from the blades of HB, determining the air speed of the incoming flow using standard instruments and local air speed near the HB using an air pressure receiver ( LDPE) placed on its blades, determine the structure and geometry of the vortex wake of the HB visualized by the end vortices on the blades by smoke, determine the circulation of longitudinal vortices by the formula

$$G\mathrm{about}=\mathrm{FROM}t\omega R^2(\mathrm{one}-{\overline{r}}_x)/2{\overline{V}}_{x}cn,{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="00000014.png,00000015.png"\; state="\{\{state\}\}">m</figure-callout>}}^2/\mathrm{from},\left(\mathrm{one}\right)$$

where St is the thrust coefficient of HB;

ω is the angular velocity of rotation of the HB;

R is the radius of the rotor.

- относительный радиус, характеризующий величину поджатия воздушной струи через НВ со стороны набегающего воздушного потока на расстоянии от оси вращения НВ до точки пересечения концевых вихрей с конусом лопастей на азимуте 180°; $${\overline{r}}_x=r_x/R$$

- the relative radius characterizing the amount of preload of the air stream through the HB from the side of the incoming air flow 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 °;

- относительная скорость сноса концевых вихрей, находящихся над лопастями НВ вдоль оси X; $${\overline{V}}_x\mathrm{from}n=V_{x}cn/\omega R$$

- the relative drift velocity of the end vortices located above the blades of the HB along the X axis;

V _x sn - the drift velocity of the end vortices, m / s;

then determine the circulation of the end vortices by the formula

$$G\mathrm{at}=\mathrm{FROM}\mathrm{<figure-callout\; id="2"\; label="t\; \omega \; R"\; filenames="00000014.png,00000015.png"\; state="\{\{state\}\}">t\; </figure-callout>}\omega R^{}{}^2\pi /K,{\mathrm{<figure-callout\; id="2"\; label="m"\; filenames="00000014.png,00000015.png"\; state="\{\{state\}\}">m</figure-callout>}}^2/\mathrm{from},\left(2\right)$$

where GW is the circulation of the end vortices, m ² / s;

To - the number of blades HB.

An estimated calculation of the horizontal components of the inductive speeds near the helicopter from the HB vortex wake at positive angles of attack at given points using the formula

$$\upsilon *=\frac{G\mathrm{about}}{\mathrm{four}\pi r_o}\cdot \left(\frac{Z_{01}}{\sqrt{{\mathrm{<figure-callout\; id="0"\; label="r"\; filenames="00000015.png,00000016.png"\; state="\{\{state\}\}">r</figure-callout>}}_0^2+Z_{01}^2}}-\frac{Z_{02}}{\sqrt{{\mathrm{<figure-callout\; id="0"\; label="r"\; filenames="00000015.png,00000016.png"\; state="\{\{state\}\}">r</figure-callout>}}_0^2+Z_{02}^2}}\right)\sin {\mathrm{<figure-callout\; id="0"\; label="\phi "\; filenames="00000015.png,00000016.png"\; state="\{\{state\}\}">\phi </figure-callout>}}_0+{\displaystyle \sum _{i=\mathrm{one}}^n\frac{G\mathrm{at}}{\mathrm{four}\pi r_i}}\cdot \left(\frac{Z_{i\mathrm{one}}}{\sqrt{r_i^2+Z_{i\mathrm{one}}^2}}-\frac{Z_{i2}}{\sqrt{r_i^2+Z_{i2}^2}}\right)\sin {\phi }_i\left(3\right)$$

where υ * is the total horizontal component of the inductive velocity from the front of the longitudinal vortices, the front and rear parts of the end vortices, m / s; $$\upsilon *={\upsilon }_o^{*}+{\displaystyle \sum _{i=\mathrm{one}}^n{\upsilon }_i^{*}};$$

n is the number of end vortices taken into account in the calculation;

r ₀ is the shortest distance from the calculation point to the front of the longitudinal vortices, m;

r _i is the shortest distance from the calculation point to the straight vortex end vortex, m;

Z ₀₁ - the distance from the base of the perpendicular, omitted from the calculation point on the axis of the front of the longitudinal vortex, to the first end of the vortex, m;

Z ₀₂ - the distance from the base of the perpendicular, omitted from the calculation point on the axis of the front of the longitudinal vortex, to the second end of the vortex, the value Z ₀₂ is taken with a minus sign when the ends of the vortex lie on opposite sides from the base of the perpendicular;

Z _i1 and Z _i2 are the distances from the base of the perpendicular to the ends of the end vortices, similar to Z ₀₁ and Z ₀₂ , m;

φ ₀ , φ _i are the angles between the perpendicular dropped from the calculation point to the axis of the front of the longitudinal vortex or the axis of the end vortices, and the horizontal, deg.

The local air speed V * is determined taking into account the total horizontal component of the inductive speed υ * at given points along the Z axis according to the formula

$$V*=V\cos \alpha -3.6\upsilon *,\left(\mathrm{four}\right)$$

where V is the air speed of the helicopter, km / h, recorded in flight, α is the angle of attack of the HB.

The horizontal components of inductive velocities calculated at given points are used to calculate the preliminary aerodynamic characteristics of the helicopter and to develop signaling devices for approaching the zone of “vortex ring” modes on preplant helicopter maneuvers.

The proposed method is illustrated in figures 1-4.

Figure 1 shows a model vortex wake model in the braking mode of a single-rotor helicopter (side view), which calculates the horizontal component of the inductive speed near the HB with horizontal braking at a fixed point in time (helicopter air speed V = 49 km / h, angle of attack φ = 5.6 °, St = 0.0108),

where (1) is the front part of the longitudinal U-shaped vortices after approximation, (2) is the end vortex, (3) is the incoming air flow, (4) is the rotor blade, (5) is the horizontal component of the inductive speed from the front of the longitudinal vortices, (6) - slightly blurred front part of the end vortex, (7) - trajectory of partially blurred front end vortices after separation from longitudinal vortices, (8) - rear part of the end vortices.

Figure 2 shows a model diagram of a vortex wake in braking mode (top view) with approximated longitudinal U-shaped vortices (1), where (6) are slightly blurred front parts of the end vortices, (9) are longitudinal U-shaped vortices after approximation .

Figure 3 shows the dependence of the total horizontal components of the inductive velocities along the Z axis along the X axis in the plane of the LDPE of the low speed meter (IMS), where (10) are the calculated values of the total horizontal components of the inductive speeds.

Figure 4 shows the dependence of the calculated values of local air speeds along the Z axis along the X axis in the plane of the location of the LDPE IC,

where (11) is the estimated value of local air speeds V *,

(12) - local airspeed Vims near the NV recorded in flight by the IC device.

The method is as follows.

To evaluate the horizontal components of inductive speeds at low speeds of a single-rotor helicopter in the modes of interest in preliminary flight tests, visualize end vortices with smoke from a smoke generator, which is released from the ends of the helicopter blades during flight with relative speeds of less than 0.2 km / h, and values are recorded using a movie camera preloaded air stream through the HB from the side of the incoming flow 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 °, I determine t is the angle of attack of the airborne forces, the air speed of the free stream over standard devices and the local airspeed near the airwaves using an air pressure detector (LDPE) located on its blades. Based on the visualization data of the end vortices, a simplified vortex model is used in the estimation calculations, at the same time as close as possible to the real vortex wake (Figs. 1 and 2), which can significantly increase the reliability and accuracy of determining the horizontal components of inductive velocities. The basis of this model is composed of two symmetric longitudinal vortices, closed by visible end vortices located above the blades at a considerable distance from them (Figs. 1 and 2). The longitudinal vortices complement the front and rear parts of the end vortices that are not tied to them, which, together with the front part of the longitudinal vortices, create the horizontal component of the inductive velocity along the X axis. The length of the front of the longitudinal U-shaped vortices (Fig. 2) after approximation was taken to be 1, 6 from the diameter of the HB (1.6D). The front parts of the end vortices, somewhat blurred as a result of interaction between themselves after separation from the longitudinal vortices, were assumed to be rectilinear and symmetric about the X axis, as well as the rear parts of the end vortices. Then, to estimate the inductive velocities, the calculation is made in Earth coordinates according to the Bio-Savart formula at given points given in formula (3).

Example.

The phenomenon of the influence of a low-velocity vortex wake at low speeds on local air speeds near its blades, recorded in aerodynamics, is determined by calculating inductive speeds and especially on pre-landing maneuvers. In preliminary flight tests, a low-speed meter (IC) with LDPE on the blades measured local air speeds near the HB. Based on the visualization of the end vortices during horizontal braking of the Mi-8 helicopter, a simplified vortex model was used in the estimation calculations, the basis of which is two symmetric longitudinal vortices, which are closed by visible end vortices located above the blades (Figs. 1 and 2). The longitudinal vortices complement the front and rear parts of the end vortices that are not tied to them, which together with the front part of the longitudinal vortices create the total horizontal component of the inductive velocity along the X axis. The length of the front part of the longitudinal U-shaped vortices after approximation was assumed to be 1.6D of the diameter of the HB (figure 2). The front parts of the end vortices, somewhat blurred as a result of interaction between themselves after separation from the longitudinal vortices, were assumed to be rectilinear and symmetrical with respect to the X axis 2.5 m long, as well as the rear parts of the end vortices.

The total horizontal components of inductive speeds are determined in Earth coordinates using the Bio-Savard formula at given points along the Z axis in the horizontal plane of the LDPE of the low-speed helicopter meter using the formulas (1, 2 and 3). The local air speed V * is determined taking into account the total horizontal component of the inductive speed υ * at given points along the Z axis (Fig. 3), by the formula

$$V*=V\cos \alpha -3.6\upsilon *,\left(\mathrm{four}\right)$$

where V is the air speed of the helicopter recorded in flight, km / h, α is the angle of attack of the HB.

The calculated value of the air velocity at the location of the LDPE on the NV blades along the Z axis is in satisfactory agreement with its value measured by IC Vims in flight tests - (12) (Fig. 4), which indicates the acceptable accuracy of calculating the total horizontal components of inductive speeds.

The proposed method for determining the horizontal components of inductive speeds at low flight speeds of a single-rotor helicopter can significantly improve the accuracy of determining inductive speeds and clarify the method of aerodynamic calculations of helicopters.

Claims (2)

1. A method for evaluating the horizontal components of inductive speeds at low flight speeds of a single-rotor helicopter, comprising preliminary flight tests with visualization of the end vortices by smoke from a smoke generator, which is released from the ends of the helicopter blades when flying with relative speeds of less than 0.2 km / h, fixing using movie cameras of the amount of preload of the air stream through the HB from the side of the incoming flow 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 °, angle of attack of NV, determining for a given helicopter speed the relative speed of drift of the end vortices descending from the blades of the NV, determining the air speed of the incoming flow using standard instruments and local air speed near the NV using an air pressure receiver (LDPE) placed on its blades, characterized in that determine the structure and geometry of the HB vortex wake, visualized by the smoke of the end vortices on the blades, determine the circulation of longitudinal vortices by the formula
$$G\mathrm{about}=\mathrm{FROM}t\omega R^2(\mathrm{one}-{\overline{r}}_x)/2{\overline{V}}_{x}cn,m^2/\mathrm{from},\left(\mathrm{one}\right)$$

where St is the thrust coefficient of HB;
ω is the angular velocity of rotation of the HB;
R is the radius of the rotor;
$${\overline{r}}_x=r_x/R$$

 - the relative radius characterizing the amount of preload of the air stream through the HB from the side of the incoming air flow;
$${\overline{V}}_x\mathrm{from}n=V_{x}cn/\omega R$$

 - the relative speed of the drift of the end vortices located above the blades of the HB along the X axis;
V_xsn - the speed of the drift of the end vortices, m / s,
then determine the circulation of the end vortices by the formula
$$G\mathrm{at}=\mathrm{FROM}t\omega R^2\pi /K,m^2/\mathrm{from},\left(2\right)$$

where GW is the circulation of the end vortices;
K is the number of blades
at a given flight mode, an estimated calculation of the horizontal components of the inductive velocities near the helicopter from the HB vortex wake at positive angles of attack at given points by the formula
$$\upsilon *=\frac{G\mathrm{about}}{\mathrm{four}\pi r_o}\cdot \left(\frac{Z_{01}}{\sqrt{r_0^2+Z_{01}^2}}-\frac{Z_{02}}{\sqrt{r_0^2+Z_{02}^2}}\right)\sin {\varphi }_0+{\displaystyle \sum _{i=\mathrm{one}}^n\frac{G\mathrm{at}}{\mathrm{four}\pi r_i}}\cdot \left(\frac{Z_{i\mathrm{one}}}{\sqrt{r_i^2+Z_{i\mathrm{one}}^2}}-\frac{Z_{i2}}{\sqrt{r_i^2+Z_{i2}^2}}\right)\sin {\varphi }_i\left(3\right)$$

where υ * is the total horizontal component of the inductive velocity from the front of the longitudinal vortices, the front and rear parts of the end vortices, m / s,
$$\upsilon *={\upsilon }_0^{*}+{\displaystyle \sum _{i=\mathrm{one}}^n{\upsilon }_i^{*}},$$

n is the number of end vortices taken into account in the calculation;
r₀ - the shortest distance from the calculation point to the front of the longitudinal vortices, m;
r_i - the shortest distance from the calculation point to the straight vortex end vortex, m;
Z₀₁ - the distance from the base of the perpendicular, omitted from the calculation point on the axis of the front of the longitudinal vortex, to the first end of the vortex, m;
Z₀₂ - the distance from the base of the perpendicular, omitted from the calculation point on the axis of the front of the longitudinal vortex, to the second end of the vortex, value Z₀₂ it is taken with a minus sign when the ends of the vortex lie on different sides from the base of the perpendicular;
Z_i1 and Z_i2 - the distance from the base of the perpendicular to the ends of the end vortices is similar to Z₀₁ and Z₀₂, m;
φ₀, φ_i - the angles between the perpendicular dropped from the calculation point to the axis of the front of the longitudinal vortex or the axis of the end vortices, and the horizontal, deg. 2. The method for evaluating the horizontal components of inductive speeds at low flight speeds of a single-rotor helicopter according to claim 1, characterized in that the local air speed V * is determined taking into account the total horizontal component of the inductive speed υ * at given points along the Z axis according to the formula
$$V*=V\cos \alpha -3.6\upsilon *\left(\mathrm{four}\right)$$

where V is the air speed of the helicopter, km / h, recorded in flight, α is the angle of attack of the HB.

Images