IT202000007819A1 - Propulsion device - Google Patents

Description

DESCRIPTION

of a patent application for an Industrial Invention entitled:

? Propulsion device?

FIELD OF INVENTION

The present found? relating to a propulsion device.

In particular, it refers to an aircraft and / or naval propulsion device, therefore capable of processing a fluid such as air or water.

STATE OF THE TECHNIQUE

The propulsion, in particular the aerial one, through free propeller, allows to generate a thrust that can be calculated through the formula of the variation of the quantity? of motion between upstream and downstream of the rotor; in the ideal case, the thrust F?:

<? >

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Being v1 and v2 the components of the speed? respectively of inlet and outlet of the fluid directed according to the axis

?

dell? propeller,? the density? of the fluid and vP the speed? medium (0.5 (v1 + v2)). In the case of helix v1 and v2 they are the same.

In the real case, moreover, a free helix has a tangential component of the velocity in the fluid volume downstream of it. which does not increase thrust, but is dissipated in frictional heat.

SUMMARY OF THE INVENTION

Purpose of the present invention? that of providing a propulsion device which is improved with respect to the prior art.

This and other purposes are achieved by a propulsion device made in accordance with the attached claims.

Advantageously, the device allows to increase the energy efficiency with respect to known systems.

BRIEF DESCRIPTION OF THE FIGURES

Further characteristics and advantages of the innovation will become evident from the description of a preferred but not exclusive form of the device, illustrated by way of example and therefore not limitative in the attached drawings, in which:

figure 1? a simplified and schematic section of a device according to the present invention;

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figure 2? a simplified and schematic section, taken along the line II-II of figure 1;

figure 3? a simplified schematic sectional view of a variant of the device of Figure 1;

Figure 4 schematically shows a characterization of a stator of the device of Figure 1;

figure 5? a simplified schematic representation of the flow field generated by the device of Figure 1, confined to the fluid volume below it;

figure 6? a theoretical graph relating to the device of the present invention; And

figure 7? a comparative theoretical graph between the device of the present invention and a helix.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the aforementioned figures, a propulsion device indicated as a whole with the reference number 1 is shown.

The attached drawings refer to some schematic sections, therefore without section lines, to simplify the reading of the drawings themselves.

The propulsion device 1 can? be used in a context of aerial propulsion, for example in drones, or naval.

?

In the first case, the fluid processed by the device will be? air, while in the second case it will be? water.

It comprises a frame 2 for supporting at least one impeller 3 (with mixed-radial or centrifugal flow) rotating around an axis A perpendicular to a rotation plane P of the impeller 3 itself.

The frame 2 can? be structurally connected to the vehicle on which the propulsion device? installed (for example a drone, a flying vehicle, a boat etc.).

The impeller 3 can? be of the mixed-radial type with curved blades or in any case shaped to optimize the kinematic flow of the processed fluid. Optionally, the impeller 3 can? be of the centrifugal type.

The impeller can? be torsionally integral with a drive shaft 4, preferably rotated by a prime mover 20 at speed? variable.

The prime mover 20 can? advantageously be of the electric type, but other types of engine are also possible, for example reciprocating internal combustion, gas turbine, etc.

It can? be directly associated with the shaft 4, or between the shaft and the motor 20 suitable kinematic mechanisms for rotating drive such as reducers, pulleys, etc. can be provided.

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The device 1 also provides at least one supply duct 5 of the impeller 3 with its own axis B parallel to the axis A of the impeller 3.

Advantageously, the axis B of the supply duct 5 coincides with the rotation axis A of the impeller 3, and therefore the supply duct 5 feeds the impeller in a part of it close to the rotation axis A.

The prime mover 20, or at least part of it, can? be positioned on the opposite side with respect to the rotation plane P of the impeller 3 with respect to the supply duct 5 (as for example shown in Figure 1) or can? be positioned directly inside the supply duct 5.

In this second configuration, not shown, the drive connection (for example the shaft 4) between the prime mover 20 and the impeller will be able to be positioned opposite to the plane P, with respect to what is represented in figure 1, and therefore inside the supply duct 5. In this condition, the fluid that feeds the impeller 3 through the supply duct 5, can? provide for the appropriate cooling of the prime mover 20. This configuration? also extremely compact.

Optionally the drive connection between the prime mover 20? the impeller 3 can? be possible by means of stator electric windings integral with the suction duct (or in

?

generic terms, to frame 2) cooperating with an array of permanent magnets integral with the impeller 3.

In this configuration the impeller 3 forms a whole with the prime mover 20.

As can be seen from Figure 1, the device further comprises an annular exhaust duct 6 which at least partially surrounds the supply duct 5.

The supply duct 5 and the annular exhaust duct 6 are arranged on the same side with respect to the plane P of rotation of the impeller 3.

This arrangement of the supply and exhaust ducts allows the speeds? of entry and exit to have opposite directions; ? therefore it is possible to obtain a thrust proportional to the sum of the two speeds, how will it be? clearly described below.

From Figure 1 it can be seen that at an outlet 3A of the impeller 3? provided a stator 7 configured to at least partially convert the tangential and radial component of velocity? of the fluid leaving the impeller 3 in an axial component parallel to axis A.

Advantageously, the stator 7 (see Figure 2) comprises a greater number of blades than those of the impeller, and this it allows to avoid resonance effects.

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Furthermore, the stator 7 can? structurally connect the two fixed supply and exhaust ducts.

In the device of Figure 1, the supply conduit 5 and the exhaust conduit 6 have at least one wall in common. In fact, the external surface of the supply duct 5 corresponds to the internal surface of the annular exhaust duct 6.

Obviously, the exhaust duct 6 and the supply duct 5 can also be totally independent as shown in Figure 3, in which? a variant of the invention is shown.

In this figure will be used the same numerical references already? previously used to indicate functionally similar parts, which will no longer come? described.

How can you? note, in this configuration, the exhaust duct 6? radially spaced from an external wall 5A of the supply duct 5.

In both configurations, in order to minimize the recirculation of the fluid expelled from the exhaust duct 6 inside the supply duct 5, the length LA of the latter can? be greater than the length LS of the exhaust duct 6.

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Advantageously, the supply duct 5 can? have at least one section converging and / or diverging towards the impeller 3.

In addition, the exhaust duct 6 can? present at least one convergent and / or divergent portion (when viewed from the impeller 3), advantageously downstream of the stator 7.

To complete the description, it is emphasized that the frame 2 can? supporting the exhaust duct 6 and / or the supply duct 5, possibly structurally connected by the stator 7.

In addition, the stator 7 can? be integrated in said discharge duct 6, directly downstream of the impeller 3.

With regard to a possible optimization of the various components of the propulsion device 1, the following general qualitative considerations can be made.

In particular, one can? concentrate on the following aspects, namely the stator, aimed at minimizing the tangential components of velocity? outlet, the supply duct and the area and configuration of the supply and exhaust ducts.

A possible qualitative characterization of the stator? represented in figure 4.

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Based on the initial general considerations about the device, the velocity vector? absolute c1 of the inlet fluid, directed upwards, pu? have the same modulus of the velocity vector? at exit c3 but in the opposite direction.

For simplicity? of two-dimensional drawing, yes? wanted in this scheme to represent a rotor with speed? direct downward (- z); this implies that the inversion of the flow takes place completely inside the rotor.

A configuration considered advantageous? the one in which the inversion of the speed? ? partly delegated to the rotor (impeller 3) and partly to the stator 7.

In figure 4 we observe the triangle of the velocities? at the outlet of the impeller 3; the velocity vector? absolute c2? given by the vector sum between the velocity vector? relative w2 (detectable by an observer integral with the rotor) and the velocity vector? of dragging u2 (whose modulus is the product between the angular speed of rotation and the average radius of the duct, and whose direction is purely tangential).

In the absence of the bladed stator 7, the speed? leaving the device (c2) it would have a strong tangential component (ct2), which is useless for the upward thrust (+ z).

The stator has the task of deflecting the flux by canceling or minimizing the tangential component of velocity, so the

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velocity vector at the output of the device, c3, it mainly has a component in the axial direction (-z).

As previously stated, to avoid fluid-structure resonance phenomena, the stator must have a number of blades different from the rotor, for example greater.

The fluid flow field in the area below the device (see figure 5)? characterized by the presence of an upward current in the part below the supply duct 5 and a downward current in the annular volume below the discharge duct 6.

The interaction between these two currents generates a toroidal motion field with high vorticity. (as always shown in figure 5), whose effect on the operation of device 1 can? be thoroughly investigated through finite difference calculations (CFDs) or experimental analysis.

Can you? affirm, as already? mentioned, that to minimize the interaction effect between the ascending and descending current,? It is possible to create a supply duct 5 that protrudes (by H = LA-LS) with respect to the outlet (or to the outlet plane) of the exhaust duct 6.

Furthermore, to minimize the non-uniformities? of the flow presented at the entrance of the bladed impeller 3,? It is possible to configure the inlet duct in such a way as to make it 'accelerating', i.e. convergent.

?

In the above discussion, yes? assumed to keep the same area of the inlet and outlet ducts of the fluid. There? derives from a consideration of uniformity? of the flow in the meridian channel of the operating machine that moves the fluid inside the device, avoiding as much as possible acceleration or deceleration of the flow.

This hypothesis can? however, be exceeded in the event that further investigations on the device indicate the opportunity? to improve its performance by using interfaces with the external environment of different areas.

Different speeds? input and output would not compromise the effect of increased thrust with respect to the propeller, being however the two speeds? opposite in direction and then add up.

There? could be implemented if, for example, it is observed that a flow entering the inlet duct pi? faster than the output one can give advantages for the efficiency of the bladed impeller.

Pi? above, in the solution of Figure 1, yes? furthermore it is hypothesized to use two coaxial ducts that guarantee the minimum total area (encumbrance) of the device.

In certain applications it could be advantageous to use a device with a larger footprint in plan (as shown in figure 3) to the advantage of an annular duct

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fluid outlet having a greater mean radius than the configuration described above.

? known from the theory of radial operating machines that an increase in the output radius of the impeller determines an increase in the work exchanged with the fluid at par? of range and speed? of rotation. Therefore, it could be advantageous to use a configuration such as that of figure 3. Furthermore, the annular space left free by the ducts could easily accommodate the electric motor for driving the impeller.

Continuing in the discussion, you can? define the propulsion device 1 as a reverse flow propeller (RFP) fluid system that uses the principle according to which the thrust on a body crossed by a fluid? proportional to the flow rate of fluid for the difference in speed? between entrance and exit.

Arranging the inlet and outlet ducts so that the two speeds? have opposite directions,? It is possible to obtain a thrust proportional to the sum of the two speeds.

On the meridian plane of the machine, the fixed and mobile ducts for the passage of the fluid are shaped in such a way as to invert the flow of the fluid, deflecting the current lines on the meridian plane by 180 °.

Is it believed that maximum efficiency develops when? the meridian component of the speed? fluid is constant

?

crossing the meridian channel, so the machine gives energy to the fluid only by varying its tangential component. Therefore, the best device configuration? deemed the one in which the area of the duct entry? equal to that of the outlet duct.

A fluid-dynamic and energetic study in ideal conditions, in the hypothesis that the engine is immersed in air and installed in a vertical position as in figure 1, thus producing a thrust from the bottom upwards, can? be the following.

It is believed that the configuration pi? efficiency of the device may be that in which the areas of the fluid supply duct (A1) and discharge (A2) are the same (A). For the law of conservation of the mass flow, assuming initially density? ? constant of the air,? it is possible to observe that the axial components of the velocity? they are equal in magnitude (as well as opposite in direction).

A1 = A2 = A? v1 = v2 = v (1)

The push F upwards? given by equation 2:

F = m (v1 + v2) = 2 m v = 2? A v <2> (2)

Since the range m =? A v.

?

The ideal fluid dynamic work to be transferred to the fluid to obtain the thrust F is obtained from the Bernoulli equation (equation 3) written between the inlet 1 and outlet 2 sections of the device. Considering the ambient pressure pa for the air:

(3)

Having neglected the potential energy and considering the term of work lost due to friction to be null, given the hypothesis of ideality. above post. Note how the parenthesized terms of equation (3) represent the total pressures of the fluid in the outlet (2) and inlet (1) sections, respectively.

The ideal fluid dynamic power? represented by the product of labor L times the flow rate of fluid m passing through the machine, and d? expressed in equation 4:

(4)

Moving on to a numerical application example, the following applies.

With reference to the dimensions of the ducts similar to those of figure 1, which provide fluid inlet and outlet passage areas equal to and equal to 0.01 m <2>, and supposing to size the rotor so as to produce a speed? of the air in the inlet and outlet sections equal to 20 m / s, replacing

?

these values in the formulas written above are obtained (in the ideal case of absence of fluodynamic friction):

Where the density? of the air in ambient conditions? was set equal to 1.2 kg / m <3> and considered constant for low speeds? at stake.

The effect of friction losses and turbulent motions in the ducts, not considered in the calculation, would increase the energy needed to ensure the circulation of air through the fixed and mobile channels of the device; therefore the calculated power? underestimated. However, an effective fluid dynamic design of the blades could minimize the amount? of the increase.

?

For comparison with a propeller of equal power, we use the equations described in the theory of the actuator disk, assuming a speed? in the upstream section of the disk equal to v1 = 10 m / s and a speed? in the downstream section equal to v2 = 30 m / s:

Where, by the Law of Betz:

The ideal power of the propeller? equal to:

Observe how the theoretical specific power, in W per kg thrust force, is in the two cases respectively:

By demonstrating that the reverse flow propulsion device, even only in the theoretical case, has a necessary power per unit? thrust equal to half? about compared to the traditional propeller.

Yup ? also performed a parametric analysis to quantify, at least in the ideal case, the performance of a possible configuration of the propulsion device 1 (a

?

which, how already? said, it is also referred to in the text with the abbreviation RFP).

In addition, yes? wanted to make a comparison between the RFP and the propeller in ideal conditions, calculating the thrust generated and the absorbed power on the basis of the above equations.

The comparison ? was performed when the speed varies? of crossing of the fluid, indicated as v in the equations of the RFP and as vp in those of the helix. ? in addition, an equal footprint area was imposed for the two engines compared.

For the propeller yes? assumed a difference in speed? between upstream and downstream equal to v2 - v1 = vp / 2.

The analysis resulted in the graphs shown in figures 6 and 7.

In the case of a? Propeller, the thrust per unit? of fluid disc area? the ratio between the thrust generated by the rotating propeller and the surface of the disc swept by the blades. Such greatness? therefore expressed in unit? of kilogram-force measurement per square meter [kgf / m <2>].

To compare the performance of the propulsion device 1 with that of an equal propeller footprint, yes? thought to consider the size? disk area ?, for the RFP, as the sum of the air inlet and outlet surfaces, affected

?

respectively by the upward and downward flows, which in the ideal case amounts to the total active area of the engine.

In figure 6? represented a graph of thrust per unit? of area [kgf / m <2>] (in ordinate) relative to a device 1 with an external diameter equal to 0.64 m, as a function of the speed? flow crossing [m / s] on the abscissa.

Figure 7 represents the comparison between the efficiency of the device 1 (line reference? 300?) And that of the propeller (line reference? 400?), Imposing the same external diameter equal to 0.64 m. The efficiency (in ordinate)? calculated as the ratio between the thrust generated and the power used to produce it, and? therefore expressed in unit? kilograms-force over kiloWatt [kgf / kW].

On the abscissa? instead present the speed? of crossing, having unit? of measurement [m / s].

The comparison ? was carried out on an equal footing? of thrust calculated for device 1 and the propeller. Observe how, on par? of thrust produced, the device 1 has a higher efficiency value.

Various embodiments of the innovation have been described, but others may be conceived by exploiting the same innovative concept.

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Claims (10)

CLAIMS 1. Air or naval propulsion device (1) comprising a frame (2) supporting at least one impeller (3) rotating around an axis (A) perpendicular to a plane (P) of rotation of the impeller (3) itself , the impeller being driven in rotation by a prime mover (20), at least one supply duct (5) of the impeller (3) with its own axis (B) substantially parallel to the axis (A) of the impeller (3) and a annular exhaust duct (6) which at least partially surrounds the supply duct (5), the supply duct (5) and the annular exhaust duct (6) being arranged on the same side with respect to the plane (P) of rotation of the impeller (3). Device according to claim 1, wherein at an outlet (3A) of the impeller (3)? provided a bladed stator (7) configured to at least partially convert the tangential and radial components of velocity? of a fluid leaving the impeller (3) in an axial component parallel to the axis (A). Device according to claim 1, wherein the prime mover (20)? placed on the opposite side of the plane (P) with respect to the one where? positioned the supply duct (6). Device according to claim 1, wherein the prime mover (20)? positioned inside the supply duct (5). Device according to claim 1, wherein the supply duct (5) and the exhaust duct (6) have at least one wall in common. 6. Device according to claim 1, wherein the exhaust duct (6)? radially spaced from an external wall (5A) of the supply duct (5). Device according to claim 1, wherein the supply duct (5) has a length (LA) greater than the length (LS) of the exhaust duct. 8. Device according to claim 1, wherein the supply duct (5) has at least a convergent and / or divergent portion towards the impeller (3). 9. Device according to claim 1, wherein the exhaust duct (6) has at least one portion diverging and / or converging from the impeller (3). Device according to claim 1, in which the frame (2) supports the exhaust duct (6) and / or the supply duct (5) and / or in which the stator (7)? integrated in said exhaust duct (6).