GB2518138B

GB2518138B - Ducted fan assembly

Info

Publication number: GB2518138B
Application number: GB1313700.5A
Authority: GB
Inventors: Gatward Lindsay
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-07-05
Filing date: 2013-07-31
Publication date: 2019-08-21
Anticipated expiration: 2033-07-31
Also published as: GB201313700D0; WO2015001290A1; GB2518138A; GB201312139D0

Description

DUCTED FAN ASSEMBLY FIELD OF THE INVENTION

The present invention relates to a ducted fan assembly. More especially, the invention relates to ducted fan assemblies for propelling land and sea going vehicles such as hovercrafts and for providing a flow of air under pressure for venting purposes. These are just a few examples of uses for ducted fan assemblies, in accordance with this invention, can be employed.

BACKGROUND TO THE INVENTION

Ducted fan assemblies general comprise a fan and a duct which directs a flow of pressurised air. In such assemblies the fan sits within the duct itself in an attempt to ensure that as much air is directed through the duct as possible.

There is a constant need to improve performance of ducted fan assemblies to drive as much air through the duct as possible. In hovercrafts this is especially important as increased air flow through the duct contributes to an increase in thrust.

Convention currently dictates that as little gap as possible must be provided between the tips of the fan blades and the inner wall of the duct so as to minimise turbulence around the blade tips causing re-direction from the high pressure at the back of the fan to low pressure at the front.

Convention also currently dictates that increased performance and thrust is achieved by increasing the duct diameter or by having two ducted fan assemblies side-by-side.

The fact that the fan has to sit very accurately within the duct causes tolerances in the manufacture of the fan blade design and length to be minimal. In the event that the blades of the fan become bent or damaged, or that they expand through heat, the fan blades are likely to strike the inside of the duct, causing damage, or potentially blocking the duct thereby restricting the airflow.

Minimum tolerance leads conventional ducted fan assemblies to require precision engineering and manufacture.

Furthermore, manufacturers are often restricted as to the types of material that they may use to make the fan as any material used should be non-expandable in heat and also brittle so as to reduce any damage to the duct should the blades of the fan strike it. This is particularly important in ducted fans used for vehicle tunnels for example.

Through extensive development and testing, the Applicant has found that a surprise affect occurs when the fan is located immediately in front of the entrance of the duct (in this case for a system used on a hovercraft) , the effect being an enhanced performance of the ducted fan assembly resulting in significantly increased thrust.

Contrary to conventional teaching, tests have shown that the air is sucked in to the duct at the region of the outer periphery of the fan blades, rather than, as one would expect, air within that region to directed outwardly away from the duct.

Moreover, tests have shown that noise level is reduced and that noise emitted is smoother and more stable. The Applicant believes that noise reduction is as a result of less turbulent air flow at the blade tips.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a ducted fan assembly comprising an axial flow fan positioned immediately in front of the entrance of a duct whose internal diameter is less than then external diameter of the fan, the duct having formed in its side wall a louvred assembly including an array of slats each having a surface angled towards the entrance of the duct and a plurality of rudders located near to or at the exit of the duct and operable to direct at least part of the air flow through the duct to exit the duct through the louvred assembly.

Preferably the distance between the fan and the entrance to the duct is in the range of 02. cm to 13 cm, and preferably still the distance is 0.6 cm.

Preferably, the rudders are independently controllable.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only with reference to the accompanying drawings in which,

Figure 1 is perspective of a ducted fan assembly constructed in accordance with the present invention for use with a hovercraft;

Figure 2 is a side view of the ducted fan assembly of figure 1;

Figure 3 is a front view of the ducted fan assembly;

Figure 4 is a rear view of the ducted fan assembly shown on a hovercraft body;

Figure 5 is a rear view of the ducted fan assembly with one rudder tilted;

Figure 6 is a rear view of the ducted fan assembly with both rudders tilted;

Figure 7 is a front view of the ducted fan assembly with both rudders tilted;

Figure 8 is a front view of the ducted fan assembly with one rudder tilted;

Figure 9 is a front view of the ducted fan assembly; and

Figure 10 is an exploded view of a section of the ducted fan assembly.

DETAILED DESCRIPTION OF THE INVENTION

Figure 1 illustrates a ducted fan assembly constructed in accordance with the invention. Such an assembly is described hereinafter with reference to use with a hovercraft.

As can be seen in this figure, the invention comprises an first annular duct 1 with an entrance 2 and exit 3. A second annular duct 4 of less length that the first duct 1 is provided immediately in front of the first duct 1.

In an alternative embodiment the first and second ducts 1, 4 are formed integral with one another, in a further embodiment only one duct is provided.

The entrance of the second duct 1 is formed as a bell mouth 5.

The bell mouth of the ducts 1, 4 in the embodiment described is not of constant radius whereby the duct increases in diameter towards the opening of the bell mouth. The ducts though may be formed with a constant radius.

Typically, the duct 1 may have an internal diameter of approximately 81 cm and an outer diameter of approximately 99 cm.

An axial fan 6 is positioned immediately in front of bell mouth 5 of the duct 4. The fan 6 consists of a housing 7, driven to rotate by a motor (not shown) and blades 8 extending laterally from the housing 7. The fact the fan 6 is located outside the duct 4, immediately in front of the bell mouth 5, means that the overall fan diameter may be larger than the duct 4. Consequently, increased performance is no longer limited solely to the duct size. Moreover, the ducted system would not be compromised or otherwise affected by slight expansion or deformation of the blades 8. This would allow for increased tolerances during the manufacture and design of the fan blades 8. It would also allow for a greater selection of material from which the fan blades 8 can be manufactured allowing for materials that would be more suited for the purpose .

Tests have shown that the optimum distance between the fan housing 7 and the duct entrance 2 is in the range of 0.2 cm to approximately 13 cm, and most preferably around 0.6 cm.

Within this range, it has been observed that, contrary to expectations, air flow into the duct increased resulting in an increase in thrust of approximately 20%. In tests, for example, thrust was increased from 851b (38.5kg) 1051b (47.6kg).

Preferably the fan housing 7 is as near to the bell mouth 5 of the duct 4 as possible. The fan and bell mouth may be close to the extent that the tips of the blades 8 of the fan 6 touch or brush the outer rim of the bell mouth 5.

As can be seen in figure 2, the side walls of the duct 1 towards the exit are louvred with each slat 9 having an angled or curved surface 10 so that air flow may be reversed and directed through the slats 8 and out of the duct 1 towards the entrance of the duct 1.

Disposed and moveably fixed at the exit of the annular duct 1, are two rudder members 11, 12 (best seen in figures 5 and 6) .

In use the rudders 11, 12 can be individually controlled to direct part or all of the flow along one side of the duct 1 out of the slats 9.

Figures 3 and 4 show the rudders 11, 12 left open allowing air to pass straight through the exit 3 of the duct.

Figure 5 shows one rudder 11 tilted to close of half the duct 1 (the right hand side in the figure).

Part or full closure of the rudder 11 will cause the hovercraft to turn right.

Figure 6 shows both rudders 11, 12 tilted to close off the entire duct forcing air to flow back through the slats 10 in the reverse direction, causing hovercraft to reverse.

Each rudder 11, 12 is controlled by a controlling means (not shown) , for example a rod or cable extending to a foot pedal or hand lever. Control of the pedal or lever causes the associated rudder to open or close independently of the other. Opening or closing of the rudders forces the airflow to exit via a particular area of the exit portion.

In this way, the ducted fan assembly may be employed, for example, as the propulsion system in a hovercraft to modulate the hovercraft's speed and direction.

Claims

1. A ducted fan assembly comprising an axial flow fan positioned immediately in front of the entrance of a duct whose internal diameter is less than then external diameter of the fan, the duct having formed in its side wall a louvred assembly including an array of slats each having a surface angled towards the entrance of the duct and a plurality of rudders located near to or at the exit of the duct and operable to direct at least part of the air flow through the duct to exit the duct through the louvred assembly.

2. A ducted fan assembly according to claim 1, wherein the distance between the fan and the entrance to the duct is in the range of 0.2 cm to approximately 13 cm.

3. A ducted fan assembly according to claim 2, wherein the distance between the fan and the duct is 0.6 cm.

4. A ducted fan assembly as described in any one of claims 1 to 3, wherein the rudders are independently controllable.