EP1306301B1 - Device for counteracting hub vortex cavitation of propellers and/or marine propulsion units - Google Patents

Abstract

The camber on a propeller blade (12) acts in the opposite direction to the camber on the propeller. The propeller blade spreads from a conical transitional part (9) over a cylindrical hub part (10) to again a conical divergent end part (11). The outer end part of the propeller blade is formed by a cylindrical outer casing (13) equaling 10 to 50 percent of the length of the propeller blade's surface area.

Description

The invention relates to a device for counteracting flow vortices generated in the hub region of propellers and / or propeller drives in the surrounding fluid. It is a rotationally symmetric transition part (Hub Vortex Vane) between a propeller and the adjacent fluid in the jet direction (incompressible medium) on the same axis of rotation as the propeller. Depending on the particular design of the propeller drive (shaft system, engine nacelle, gear pod) and possible other attachments (eg rudders or vanes), the device can be carried out co-rotating with the propeller or fixed. Fields of application are primarily possible in shipbuilding and aircraft construction.
Propellers of propellers and propellers form at the hub ends as well as at the outer edges of the propeller blades energetic edge vortex. In contrast to the outer edge vortexes of the individual propeller blades, the inner edge vortexes of all the propeller blades unite to form a hub vortex in the surrounding fluid in the jet direction behind the propeller, whereby the geometric location of the hub vortex coincides well with the rotational axis of the propeller. It is irrelevant for the formation of the hub vortex whether there is still a flow body behind the actual propeller or not. Highly loaded propellers with relatively large hub diameters usually form stronger hub vertebrae than weakly loaded propellers with relatively small hub diameters. In the patents US 4,212,586 [2], 1978, EP 255 136 [3], 1987, EP 758 606, 1996 [4] various variants for the reduction of the hub vortex are presented. In the document [1]: "An investigation into effective boss cap designs to eliminate propeller stroke vortex cavitation" of Atlar, M .; Patience, G. (Osterveld, MWC; Tan, SG editors: Practical Design of Ships and Mobile Units, 1998 Elsevier Science BV)
a detailed overview of the state of the art is given. In [2], a variant of the reduction of the hub vortex is examined, in which the exhaust gases of an internal combustion engine are passed through the hub, and thus an attempt is made to eliminate the negative pressure area formed by the hub vortex. In [3], in interaction with each individual propeller blade on the hub run additional wings are attached, which should have a hub vortex reducing effect.
For noise reduction on naval ships, especially in submarines, the propeller design attempted to counteract the formation of these edge vortices by means of special pitch and vault distributions. However, this could only be achieved with significant efficiency losses.

While only the pressure conditions in the surrounding area of the propeller hub were influenced by the methods used to reduce the adverse influences of the hub vortex based on [2], which are relatively common in the recreational craft sector, neither the true vortex strength of the hub vortex nor a torque reduction can be achieved with this embodiment. Another crucial disadvantage is the strong additional noise emission in the area of the propeller and the maintenance of the hub cavitation. In addition, the environmental compatibility is in question.
In the hub cap fins according to [3] are on the hub cap of the propeller as many additional wings as the propeller leaves has and are in direct interaction with these. They are (essentially) located outside the limit radius considered later (see Fig. 1 to Fig. 3 in [3]) and can develop their optimal effect only for a relatively small degree of progression (load range), since, depending on the degree of progression Change the positions of the inner edge vortex of the individual propellers. Despite their vortex-reducing effect parasitic cavitation phenomena with their adverse effect on the noise emission can occur especially at higher loads.

In [4] the fins for reducing the hub vortex are already attached within the later explained Grenzradiusses after concentration of the edge vortex to a uniform Hub vortex and result in their usually larger number than the Propellerflügelzahl an efficiency-enhancing effect, but can not fully complete the parasitic Kavitationserscheinungen with their suppress the adverse effect on the noise emission.

The invention has for its object to develop a solution for a significant reduction in energy losses through the formation of the hub vortex, for a noise reduction by fluctuating phenomena in the hub vortex in Propellerabstrom and in particular for the noise reduction caused by the hub vortex cavitation phenomena (hub cavitation).
According to the invention, this object is solved by the features of claim 1. Advantageous embodiments of the invention are contained in the accompanying claims 2 and 3.
The invention is based on a device for counteracting flow vortices generated in the hub region of propellers and / or propeller drives in the surrounding fluid, which has at least one blade, the curvature of the blade being directed counter to the curvature of the propeller.
According to the invention, the blade extends from a cone-shaped transition part via a cylindrical hub part to the re-cone-shaped divergent closure part, wherein the outer termination of the blade is effected by a cylindrical shell of 10 to 50% of the length of the blade surface. According to a preferred feature, a plurality of blades are distributed in meridional arrangement regularly on the circumference of the device.
According to a particularly preferred feature, the blades start in their radial extent in the axis of rotation of the propeller and do not exceed a limit radius (R _G ) within which the tangential component (V _T ) of the velocity (V _W ) of the turbulent flow is greater than that by the propeller rotation caused peripheral speed (V _U ).

The invention is based on the finding that by appropriate design or shaping of the device, the formation of vortices by the propeller in the hub environment can be counteracted by the pressure conditions in this environment are selectively changed by the design of the device.
Since the geometric location of the hub vortex (inner peripheral vortex), in contrast to the tip vortex (outer peripheral vortex) is well known (propeller rotational axis) and independent of the propeller speed and ship speed, secondary measures can only counteract the formation of the hub vortex.

As a result of the configuration of the device according to the invention, energy can be recovered from the vortices, at least in the hub region, and the cavitation formation can be largely delayed, whereby the efficiency of a ship propulsion system can be significantly improved and the detection range of a naval vessel can be considerably reduced.
The advantages of the invention are based on the inventively realized for the first time combination of a significant efficiency-enhancing effect and the greatest possible avoidance of any cavitation phenomena (with their adverse effect on the noise emission). In test series showed the highest efficiency gain compared to other types of Nabenkappenflossen for the device according to the invention. An additional benefit arises on the part of the propeller design for cavitation-free designs, that you no longer need to take measures to prevent Hubavigation cavitation. This means that even the designed propeller itself has a higher efficiency which is increased by the energy recovery by the HVV from the hub vortex losses.

Fig.1:

Wirbelbildung hinter einem Propeller entlang der eines Hub Vortex Vane (nachfolgend HVV genannt),

Fig. 2:

eine Applikation 6 einer HVV als Ersatz für einen normalen Nabenablauf bei dem die HVV mit dem Propeller mitrotiert,

Fig. 3:

eine HVV 6 ist am Ruderblatt 7 eines Schiffes fixiert,

Fig. 4:

die HVV ist am Ende einer Motorgondel/Pod/Getriebegehäuse 8 fest montiert,

Fig. 5:

schematische Darstellung einer möglichen Ausführung eines Hub Vortex Vane,

Fig.6:

schematische Darstellung der "Abwind"komponente der Geschwindigkeitsverteilung in der Nähe der Propellerblätter für die Radienverhältnisse 0.1 als Zylinderabwicklungen,

Fig.7:

schematische Darstellung der "Abwind"komponente der Geschwindigkeitsverteilung in der Nähe der Propellerblätter für die Radienverhältnisse 0.15 als Zylinderabwicklungen,

Fig.8:

Darstellung der Abhängigkeit des Gütegrades der Propulsion von der Reynoldszahl.

The invention will be explained below with reference to an embodiment. In the drawings show the

Fig.1:

Vortex formation behind a propeller along a Hub Vortex Vane (hereafter referred to as HVV),

Fig. 2:

an application 6 of a HVV as a replacement for a normal hub run in which the HVV rotates with the propeller,

3:

a HVV 6 is fixed to the rudder blade 7 of a ship,

4:

the HVV is permanently mounted at the end of a motor nacelle / pod / gearbox 8,

Fig. 5:

schematic representation of a possible embodiment of a Hub Vortex Vane,

Figure 6:

schematic representation of the "downwind" component of the velocity distribution in the vicinity of the propeller blades for the radii ratios 0.1 as cylinder developments,

Figure 7:

schematic representation of the "downwind" component of the velocity distribution in the vicinity of the propeller blades for the radii ratios 0.15 as cylinder developments,

Figure 8:

Representation of the dependence of the degree of quality of the Propulsion on the Reynolds number.

According to a production-technically simple embodiment of the device according to the invention, the hub vortex vane contains at least one blade 12 which during operation ensures a reduction of the hub vortex strength and the associated hub vortex cavitation. An HVV can be retrofitted at any time. No other components need to be replaced; all other components of the drive system can be retained unchanged.

Preferably, a plurality of regularly distributed on the circumference of the HVV blades 12 are provided, which are arranged approximately in meridionaler orientation. The number of vanes is independent of the number of vanes and the outer diameter of the HVV is limited to about 0.16 of the propeller diameter (with co-rotating HVV). The inner boundary of the blades is formed by a rotary body of the shape according to the reference numerals 9, 10, 11 and the outer boundary by a ring of the shape 13. The special inner and outer boundaries serve to largely suppress possible secondary cavitation phenomena at the inner and outer ends of the blade (s).

By opposite orientations of the strong curvature of the hub blades and the curvature of the propeller blades, it is possible to redirect the high tangential speeds near the hub so in the beam direction that an additional thrust is generated. The thereby occurring by the deflection torque is rectified to the propeller driving engine torque, which equates to a power saving. In addition, the complete elimination of the hub vortex leads to a reduction of the sound radiation.

The HVV according to the invention is applicable both to helical propellers operating as pressure propellers and to traction propellers.

Particularly suitable is the use of propellers for higher shear load levels, z. As on propellers, which produce a high thrust on a relatively small area and thereby forcibly cause an increased hub vortex formation. Here, the achievable improvement potential is correspondingly large.
FIGS. 2 to 4 show different application possibilities of the HVV.

The screw propeller operating according to FIG. 2 as a pressure propeller 1 with propeller hub 2 has a co-rotating HVV 6 which lies behind the propeller 1 in the jet direction. The vortex forming behind the propeller 1 along the HVV 6 initially consists of several vortices of the various wings, which then very quickly form into a single vortex, leaving its trace in a narrow area along the axis of rotation of the propeller. This behavior is shown in FIG. 1. The direction of rotation of this vortex coincides with the direction of rotation of the propeller and the Tangential velocities of the vortex are greatest inside (in the vortex eye potential-theoretic infinitely large) and decrease to the outside.

(Γ_B Nabenwirbelstärke), bzw. unter Berücksichtigung zähigkeitsbedingter Einflüsse (Oseen-Wirbel) näherungsweise mit einem geeigneten Wert für das Wirbelalter t ${\mathrm{V}}_{\mathrm{T}}=\frac{{\mathrm{\Gamma }}_{\mathit{B}}}{2\cdot \mathrm{\pi }\cdot \mathit{r}}\left(1-{\mathrm{e}}^{-\left(\frac{{\mathrm{r}}^2}{4\cdot \mathrm{\upsilon }\cdot \mathrm{t}}\right)}\right)$

treten innerhalb eines Grenzradiusses ${\mathrm{R}}_{\mathrm{G}}\approx \sqrt{\frac{{\mathrm{\Gamma }}_{\mathit{B}}}{2\cdot \mathrm{\pi }\cdot \mathrm{n}}}$

(∼ 0.16 R_P mit R_P = 1/2 D_P Propellerradius)Because of the increase of the tangential velocities (V _T ) of the fluid to the vortex eye (in the hub vortex identical to the propeller axis of rotation) towards a purely potential theory law V _T = ${\mathrm{V}}_{\mathrm{T}}=\frac{{\mathrm{<figure-callout\; id="2"\; label="\Gamma \; B"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">\Gamma \; </figure-callout>}}_{\mathit{B}}}{2\cdot \mathrm{\pi }\cdot \mathit{r}}$

(N _B hub vortex strength), or taking into account toughness-related influences (Oseen vortex) approximately with a suitable value for the rotation age t ${\mathrm{V}}_{\mathrm{T}}=\frac{{\mathrm{<figure-callout\; id="2"\; label="\Gamma \; B"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">\Gamma \; </figure-callout>}}_{\mathit{B}}}{2\cdot \mathrm{\pi }\cdot \mathit{r}}\left(1-{\mathrm{e}}^{-\left(\frac{{\mathrm{<figure-callout\; id="2"\; label="r"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">r</figure-callout>}}^2}{4\cdot \mathrm{\upsilon }\cdot \mathrm{t}}\right)}\right)$

occur within a border radius ${\mathrm{R}}_{\mathrm{G}}\approx \sqrt{\frac{{\mathrm{<figure-callout\; id="2"\; label="\Gamma \; B"\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">\Gamma \; </figure-callout>}}_{\mathit{B}}}{2\cdot \mathrm{\pi }\cdot \mathrm{n}}}$

(~ 0.16 R _P with R _P = 1/2 D _P propeller radius)

Tangential speeds V _T on, which are significantly higher than the peripheral speed V _{U of} a rotating with the propeller speed n point at a distance r from the axis of rotation. Up to the limit radius R _G energy recovery is possible with a co-rotating HVV. For a permanently mounted HVV (see Fig. 3 and Fig. 4) there is not this limit radius.
For this reason, the blades 12 of the HVV extend from the propeller axis to at most the limit radius R _G in order to optimally utilize the effect of the blades. The curvature of the blade surfaces is opposite to that of the propeller surfaces. In this way, the eddy currents are deflected in the direction of the beam, with an additional thrust being generated. In the illustrated embodiment, eight blades (FIG. 5) distributed on the circumference of the HVV are shown, which extend from the end 9 facing the propeller hub 2 in FIG. 1 to the end of the HVV at 11 of FIG.

Particularly advantageous over known solutions in terms of avoiding hub vortex is the inner and outer termination of the blade surfaces. The inner connection of the blade surfaces takes place from a cone-shaped transition part 9 from the pressure-side propeller hub end 2 via the cylindrical hub part 10 of the HVV to the again cone-shaped divergent closure part 11 of the hub of the HVV. The outer conclusion of the Vane surfaces of the HVV is effected by a cylindrical shell 13 of 10 to 50% of the length of the blade surfaces.

The hydrodynamic benefit of dividing the hub of the HVV into the three sections 9-11 is the concentration of the individual (hub side) edge vortex portions of the propeller blades into a concentrated hub vortex, the diversion of the tangential velocity components throughout the blade 12 and the "defibering" of one possible residual vortex portion in the region of the divergent conical closing part 11. The diameter of the cylindrical intermediate piece 10 should coincide with the diameter of the viscosity-induced vortex core (vortex age). The hydrodynamic benefit of the cylindrical surface 13 around the blades is to prevent possible parasitic cavitation phenomena at the outer end of the blades.

To illustrate the derivation of the shape of the blade surfaces serve Figures 6 and 7. Shown is the "downdraft" component 14 of the velocity distribution in the vicinity of the propeller blades 1 which is the main cause of the occurrence of the tangential speeds behind the propeller. Due to the generally existing increase in the pitch angle of the propeller blades to the axis of rotation and due to the eddy-induced increase in the tangential velocities, the curvatures of the blades 12 must change as a function of the radius, so that the flow lines are deflected as possible in the beam direction 15. In FIGS. 6 and 7, these ratios for different radii ratios are shown as cylinder developments for the radii ratios 0.10 and 0.15.

Possible applications and embodiments of the HVV are shown in FIGS. 2 to 4. For pressurized propeller arrangements in conjunction with normal shaft systems or on gear pods or on pods or other motor nacelles, the co-rotating embodiment according to FIG. 2 is advantageous. For propeller arrangements to follow behind the propeller attachments such as a rudder plate, a fixed embodiment as outlined in Fig. 3, hydrodynamically advantageous. For traction propeller arrangements Transmission gondolas, pods or motor nacelles is a fixed embodiment at the end of the nacelle according to FIG. 4 advantageous.

The use of specially trained HVV is particularly important on propellers for higher shear rates. Such propellers produce a high thrust on a relatively small area and thus forced hub vortex. Due to the high loss, a high improvement can be achieved when using an inventively designed HVV.

For a pressure propeller arrangement according to FIG. 2, the achievable benefit by means of a HVV ("HVV") is illustrated in FIG. 8 by means of measurements. Compared to a normal frequently used hub end ("Normal") by a simple conical hub cap, the efficiency gain increases significantly with the Reynolds number. The hub vertebra cavitation could be completely suppressed by application. If, as usual, divergent hub processes ("divergent") are used to suppress hub cavitation, the efficiency gain still increases significantly when HVV is used.

List of reference numbers used

1.

Propeller, propeller, propeller

Second

propeller hub

Third

Drive shaft of the propeller

4th

Trap cover

5th

hub vortices

6th

Hub Vortex Vane (HVV)

7th

rudder blade

8th.

Gearbox of all-round drive, motor nacelle, pod with motor

9th

Transition part propeller HVV

10th

Cylindrical hub joint of the HVV

11th

Conical end part of the hub of the HVV

12th

Shovels, fins of HVV

13th

Cylinder shell HVV

14th

"Downwind" of the propeller on a wing

15th

Axial beam direction

Claims (3)

1. Device for counteracting flow vortices that are generated in the surrounding fluid in the hub region of propellers and/or propeller drives, the said device including at least one blade, wherein the curvature of the blade is in the opposite direction to the curvature of the propeller, characterised in that the blade (12) extends from a conical transition portion (9) over a cylindrical hub portion (10) to the diverging end portion (11) that is once again conical, wherein the outer end portion of the blade (12) is formed by a cylindrical outer casing (13) that is between 10 and 50% of the length of the blade surface area.
2. Device according to claim 1, characterised in that a plurality of blades (12) are distributed regularly on the periphery of the device disposed in a meridional manner.
3. Device according to one of the abovementioned claims, characterised in that the radial extension of the blades begins in the axis of rotation of the propeller and does not exceed a boundary radius (R_G), inside which the tangential component (V_T) of the speed (V_W) of the vortex is greater than the peripheral speed (V_U) caused by the rotation of the propeller.

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