Karachun V.V, Mel’niсk V. N.

National Technical University of Ukraine «KPI»

THE GYROSCOPIC REAKTION IN ROTOR`S SIREN

Efficiency of rotary pneumatic siren work determines mainly by available minimum distance between planes of rotor and stator. For real structures this value is 3·10^-5 – 7·10^-5 m. In these conditions most accurately reproduces the modulation function and, accordingly, the desired spectrum of radiation.

However, as it turned out, static and dynamic balancing of fast-revolving rotor as essential at the work does not prevent the emergence of disparity and smoothing-out of surfaces of disks with inevitable further development of this phenomenon. The implications are obvious - excessive increases of unsustainable consumption of air and bending of form of modulation function.

Let is find out the nature of emerging effect. Rotary pneumatic siren is on rolling basis, ie on the surface of the Earth, which has angular velocity of daily rotation (fig. 1)

rad sec^-1.

Axis of rotation of the rotor, for example, forms with meridian line an angle ψ (yaw angle). Quickly rotating heavy rotor of siren is a system with two degrees of freedom. One realizes with its own rotational movement around its axis of geometry and angular symmetrywith angular velocity , the other – rotation of lead shaft together with planted on him rotor around the axis, perpendicular to the axis of the shaft by the amount proportional to the radial play Δ of bearings.

Availability of vertical component ω₁ of angular velocity of daily rotation of the Earth (|ω₁| = ω_Зsinφ, where φ - latitude of place) results in an gyroscopic moment

,where I - axial moment of inertia of the rotor and the shaft with bearings, which tries to establish axis of its own rotation of rotor of siren parallel to the vector (fig. 1). Therefore, under the influence of gyroscopic moment the rotor will take a new position (dotted line), variations in the vertical plane to an angle α from the original.

Due to the appointed, the rotor bearings will feel extra pressure . According to the third Newton law, bearing reaction to this pressure will make in value and be opposite in direction to gyroscopic pressure. It is absolutely clear the equality of gyroscopic moment and moment of bearing reaction , ie (fig.2).

So, it will occur delay of disc of rotor and stator. In addition, it will decrease cosα times the effective area of windows of siren and thus increase nonproductive expenditure f_min of air flow, resulting in reduce of level of generic aerodynamic noise for value

ΔP = 20lg (1 – f_min/f_max), dB.

It is clear that the modulationfunction will also change.

If the gap between the rotor and stator disks missing, then f=0 at the closed windows. And f=f_max=f₀ with open windows (f₀ - air flow in the absence of gap between discs with open windows).

To improve the quality of reproduction of aerodynamic noise, and thus reduce unproductive expenditures of aur and increase service life of siren, it can be as one of the options, to enter the automatic correction of the initial minimum distance between the ends of the vertical diameters of discs of rotor and stator. When regulating siren, the clearance between the rotor and stator disks is about 0,03-0,07 mm.

Revibration camera, with the siren, is beong installed in the horizontal tilting platform, mechanically connected to the shaft of engine which control winding is connected to a specified latitude and differential amplifier, connected to the sensor of non-destructive testing. Usung signal of latitude setting device, the engine provides the driving motion to the platform around the vertical of a place with angular velocity

ω'₁ = - ω_Зsinφ,

compensating thereby influence of the vertical component of angular velocity of daily rotary motion of the Earth. Using signals of sensors of non-destructive testing through differential amplifier receives additional stress on the control winding of engine which is proportional to existing inequalitie between the ends of the vertical diameters of the rotor and stator. The appearance of additional speed of platform will serve as expression gyroscopic moment

,

thus, the disc of rotor of siren takes the position along the stator disk plane (to appear equal distances between the ends of the vertical diameters).

To avoid cross-impact of angular velocities, a platform should be always horizontal.

Therefore, on the index of work quality of rotor siren influence kinematic excitation of the basics, including speed of daily movement of the Earth. The analysis of phenomena shows that neglecting this influence is unacceptable. Hence appears the need of monitoring and electrodynamic regulatation of some parameters of rotor siren not only in its static state in retrain period (static and dynamic balancing), but always during its work. Offered solution can avoid this drawback.

Summarizing it should be drawn attention on the fact that when axis of own rotation of rotor of siren does not coincide with the meridian line at the angle ψ, component of angular velocity of daily rotation of the Earth

ω″₂ = ω_Зcosφsinψ,

which points to the west, will also serve as the emergence of gyroscopic reaction and forced movement of the rotor (fig. 3). Obviously, the component

ω′₂ = ω_Зcosφcosψ,

which is parallel to the vector of kinetic moment of the rotor will not affect the dynamics of siren (with a small yawn).

Beyond the focus is still the analysis of kinematic effects (oscilation) and power (vibration) excitation of the foundation. Certainly this influence is sufficiently significant, but doesn’t serve the purpose of data research.

So, joining together the rotor axis with meridian line, you can completely eliminate the influence of the horizontal component ω₂ of Earth's rotation on work of rotor siren. If to orient the axis of rotation of rotor parallel to the line WE (West-East), the impact of cross-component of angular velocity of Earth is the maximum.