US3168235A

US3168235A - Helicoidal fans

Info

Publication number: US3168235A
Application number: US79849A
Authority: US
Inventors: Valdi Rene Jacques
Original assignee: Societe Lyonnaise de Ventilation Industrielle Solyvent
Current assignee: Howden Solyvent Ventec SAS
Priority date: 1958-12-12
Filing date: 1960-12-30
Publication date: 1965-02-02
Anticipated expiration: 1982-02-02
Also published as: GB913930A; BE585144A; FR1218500A

Description

R. J. VALD1 HELICOIDAL FANS Feb. 2 1965 4 Sheets-Sheet 1 Filed Dec. 30. 1960 INVENTOR. RENE JACQUES VALDI ATTORNEY Feb. 2, 1965 R. J. VALDI 3,168,235

HELICOIDAL FANS Filed Dec. 30, 1960 4 Sheets-Sheet 2 L o t N INVENTOR.

RENE JACQUES VALDI Feb. 2, 1965 R. J. VALDI 3,168,235

HELICOIDAL FANS Filed Dec. 30, 1960 4 Sheets-Sheet 5 INVENTOR. RENE JACQUES VALDI ATTORNEY Feb. 2, 1965 R. J. VALDI 3,168,235

HELICOIDAL FANS Filed Dec. 30, 1960 4 Sheets-Sheet 4 k I I r I p, g N e a e a e, e, 2 a a. 2

- INVENTOR.

RENJACQUES VALDI ATTORNEY United States Patent O 3,168,235 HELHCOIDAL FANS Ren Jacques Valdi, Pars, France, assignor to Societe Lyonnaise de Veutiiatiou Industrielle Solyvent Filed Dec. 30, 1960, Ser. No. 79,849

Claims priority, application France, Dec. 12, 1953,

781,545, Patent 1,218,569

Claims. (Cl. 230-120) It is known that the conventional axial fans are mainly constituted of a fixed exterior oasing coupled to a pipe on the upstream side and (or) a pipe on the downstream side, through which the air flows and of a moving wheel keyed on a driving shaft, the said wheel having for its object to ensure the flow of air in the pipes and to increase the pressure of air which passes through the said wheel. This wheel is constituted of a hub on which are mounted blades, the free ends of which move in the immediate vicinity of the internal face of the exterior cas ing. Frequently a fan of this kind is completed by a non rotating wheel provided with blades and adapted to reduce the gyration of the air issuing from the rotating wheel.

The conventional types of axial fans have a number of disadvantages and in particular the following: the pressure supplied by the fans can only reach substantial values on the condition that the wheel is driven at very high speeds of rotation. Furthermore, the operation of these fans is usually noisy. Lastly, while it is possible to obtain satisfactory efliciency at a given speed of rotation and in respect of a certain work-rating, that is to say, in respect of a certain value of the delivery and of the pressure supplied by the fan, the efficiency falls very rapidly whenever there is any deviation from this optimum work-rating.

In other words, if, at each speed of rotation, there is any departure from the values of delivery and of pressure at which efiiciency and silence are at the maximurn, this efficiency rapidly decreases, whereas the noise increases considerably.

It appears that the primary cause of detective perforniance and noisy running is the separation of the fine streams of air during their passage through the wheel of the fan. In fact, the streams of air which pass through the fan do not flow smoothly along the blades, but have a tendency to detach themselves from the said blades and form eddy currents. This detective performance is also due to the fact that the different streams of air which pass through the fan are not subject to the same increase in pressure depending on whether they flow near the hub or in the vicinity of the periphery.

It is also known that the separation of the streams of air which flow through the wheel of the fan tends to take place at the time of a slowing-down of the airflow, whereas it does not usually occur when the speed of the air-flow is accelerated. It has consequently been already proposed to accelenate the flow of air as it passes through the fan, this being eifected either by giving the hub of the wheel a section which increases from the ntake to the outlet of the said wheel or by giving the exterior casing a decreasing section from the intake to the outlet. The obvious result of these two methods is to reduce the free section through which the air is intended to pass, from the intake up to the delivery end of the wheel, the effect thereof being to increase the average speed of the air as it passos through the said wheel. It is also known, however, that the first method produces its effects mainly on the fine streams of air located in the vicinity of the hub, whereas the second method acts more especially on the fine streams of air which are located in the vicinity of the periphery of the wheel.

In order that the two methods referred to above should produce their effects up to the vicinity of the central zone in which the air flows through the wheel, and also with a view to balancing the pressures along the blades, the idea which then arose Was to construct fans having short blades mounted on a hub having a large diameter. It is obvious that this solution results in fans having large dimensions for a predetermined flow of air and con sequently results in a costly construction.

An object of the present invention is to increase the efficiency of a fan of the type referred to above by reducing the separation of the fine streams of air and at the same time to make the operation of the fan more silent.

A further object of the present invention consists in obtaining higher pressure while using lower speeds of rotation.

Yet another object of the invention is to construct fans which are provided with longer blades than in the case of fans of known types, the said blades being mounted on a smaller hub and consequently to produce fans which are more economical to construct.

Again a further object of the invention is to produce a fan which, for a pre-determined speed of rotation, has a good running efliciency and is silent over a wide range of values of flow and of pressure of air.

In the present specification, it is understood to mean that:

The base of the blade refers to that portion of the blade which is made fast to the hub.

The extremity of the blade refers to the opposite portion of the said blade. V

The transverse section of the blade refers to the cross section which would oe produced in the blade by a cylinder having a radius r and having the same axis as the hub.

Thickness refers to the distance L which separates the two faces of the blade in a transverse section, said distance being taken as shown by FIG. 1, in a direction perpendicular to the longitudinal axis of the fan.

Chord refers to the straight line which, in each transverse section, joins the leading edge of the blades to the trailing edge of this latter.

Chord length refers to the distance between two circles of same radius co-axial With the wheel, perpendicular to the axis of the hub and tangential to the leading and trailing edgcs of the blades.

In order to carry out these dilferent objects, as well as additional objects which will be brought out by the description given below, the present invention consists mainly of a fan of the type described which comprises inside a casing at least two blades mounted on a hub, each blade comprising a zone of maximum thickness located between the first quarter of its chord length and the trailing edge of the said blade.

In accordance with a further characteristic feature of the present invention, which can be employed either alone .or in combination with the preceding feature, the thickness of the blade for each transverse section increases from its base to its extremity.

In accordance with another feature of the invention, which can either be employed alone or can be combined with one or the other of the characteristics referred to above, the transverse section of the blade is given a pro file such that the leading edge and the trailing edge are thinned down and the thickness of the vane increases pro gressively up to a point of maximum thickness located between a quarter and half the chord length of the blade starting from the leading edge of the said blade and then becomes progressively thinner towards the trailing edge.

of these characteristic features or by combining them,

the blades aloneproduce a progressive reduction in the cross section of the passageway which is provided for the air as it passes through the wheel, in suchmanner that a progressive acceleration, followed by a deceleration, is

communicated to the air which fiows through the said wheelj It is thus possible to impart an optimum speed to allthe fine streams of air fiowing through the wheel,

this being the case on the one hand at every point of their progress in the interior of the said wheel, while the same also holds true, on the other hand, irrespective of the distance away from the axis of the wheel at which the air-flow in question takesplace.

It especially follows from the foregoing that, in the case of a fine stream of air passing through the wheel, the speed increases progressively up to the point of maximum thiekness of the blade and subsequently, decreases progressvely up to the outlet of the wheel. carried out have shown, however, that this reduction of speed takes place without any separation of the fine streams of air, by reason of the stabilzaton of the airflow which was eiected in the phase of initial acceleration of the said air-flow.

The increase of the thickness of the blade from the base, that is to say from the hub to the periphery of the blade, in the vicinity of the exterior casing of the tan, ensures a better equilibrium of the pressure of air along the blade in a radial direction.

Further objects and advantages of the present invention will be brought out by the description which follows below, reference being made to the accompanying drawings which illustrate various,embodiments of the present invention, it being understood that the said invention is in no way limited to the embodiments described and comprises any or all the modifications which can come within the scope of the claims 'which follow hereunder.

In these drawings:

FIG. 1 illustrates a transverse section of a blade in accordance with the present invention;

FIG. 2 is a perspective view of a wheel embodying the invention; 7

FIG. 3 is a view in lateral. elevation, partly broken away, of a fan in accordance.with the present invention;

FIGS. 4, 5 and 6 are transverse sections of one blade of the fan, taken along the lines 1VIV, VV, VI'VI respectively of FIG. 3;

FIG. 7 illustrates the development of a cross-section of the fan-wheel produced by a cylinder having a radius r, the said cylinder being co.axial with the hub of the wheel and n being the number of the blades;

FIG. 8 illustrates an elevational view of an embodment of the present invention with a cross-section of the casing through an axial plane;

FIGS. 8a, 8b and Sc are respectively cross-sections through lines aa', b-b' and cc of FIG. S;

FIG. 9 is a similar view of another embodiment of the r in accord-ance with the present invention as compared with a fan of the conventional type.

The two fans, the performances of which are shown of the diameter of the hub to the diameter of the wheel was equal to 0.45. They were identical in all respects, except as follows: In the conventional fan, the maxi mum thickness and the length of the chord decrease from Experiments '70 1n sa1d curves, were provided With s1x blades and the ratio i the base of the extremity of the blade, and the transverse section of the blade has the outline of a planewing; the blade of the fan according to this invention has a thickness and a chord which increase from the base to the extremity, according to FIG. 2. The dot and dash line curves refer to the conventional fan and the curves in plain line to the fan of the invention.

As shown in a somewhat diagrammatic. manner in FIG. 1, the average chord 4 of this blade is substantially identical to that of a conventional'blade, but the blade in question is much thicker in its central portion, while the leading edge 5 and simila'rly thetrailng edge6 of the said blade are both pointed or thinned-down. The figure shows up particularly clearly the differences of charac- .teristics between the blade of the fan in accordance with the present invention and a conventional blade. The

average chord 4, which is also substantially similar to that of the blades of known types, of fans,is defined by known methods based on the principlesof Euler and which 'make it possible to obtain easily the length 5-6 of the blade, the value of the leading ,angle =/3 and the radios of the curve C of the said chord. The. same figureat once shows that the maximum thickness L of the said blade is located at a distance which is comprised between the first quarter and half the'length of the blade starting from the leading edge of this latter.

FIG. 2 shows more clearly the manner in which a plu-' rality of blades 12, in this case six in number, are mounted on a hub 11 having arelatively small diameter, and in which the blades 12 comprise a leading edge a and a trailihg edge f,both these.latter being thinned down,

and a thick intermediate zone.

As is, shown in greater.detail in FIG. 3, a fan in accordance with the present invention comprises an outer casin the drawing, while the blade which is diamctrcally op-,

posite to the blade 13 cannot be seen. It is quite obvious, however, that this wheel could be provided with a greater number of blades, as shown in FIG. 2.

A rectfier 15, the function of which has been described above, is arranged after the wheel and in the same casing 10.:

FIGS. 4, 5 and6 illustrate cross sections of the blade 12, respectively cut by a cylinder having the same axis as the hub in the vicinity of the extremity of the blade,

in the central zone of the blade and in the vicinity ofits As it will be observed in this drawing, themean thickness of -the blade increases from the cross-section of base.

FIG. 6 taken in the vicinity of the hub, up.to the crosssection of FIG. 4 which is taken in the vicinity of, the v internal surface of the associated casing. These drawings also clearly show that the blade comprses a leading edge.

a and a trailing edge f, both of which are thinned down,

and that the thickness of the blade increases up to a maximum value L located between the first quarter and half the length of the blade. In this form of embodiment, the associated hub is cylindrical and the same applies to the exterior casing, which constitutes a cylinder having the same axis as the hub.

As shown in FIG. 7, each of the blades is characterized when seen in profile, by a progressive increase in the thickness of the blade up to a value L which is'reached at a distance X, from the wheel-intake, the increase in thickness being followed by a.progressive reduction in thickness down to a thinned-down trailing edge 17. By desgr nating n as the number of blades, r as the radius of the cylinder which is co-axial with the wheel and by which from the axis of the said wheel, it can be seen that, between the wheel-intake and the point of maximum thickness of the blade, the air-flow is subjected to an increase in speed as a result of the reduction of the free section of the passageway, the increase in speed being in reverse ratio to the free sections of the passageway provided for the flow of air. In other words, it is easy to determine that the increase in the speed of the air is given by the formula: IL/27:1 wherein it will be noted that the expression 2'rr/ n represents the distance Which exists between the leading edges of two successive blades. The studies and experiments conducted have made it possible to determine that the point of maximum thickness, that is to say, the value X shown in the drawings, should be located preferably between the first quarter and the first half of the length of the blade, starting from the leading edge of the said blade.

Preferably, and in accordance with the present invention, a value greater than 0.08 is given to the ratio nL/27rr.

When the radius r which measures the distance at which the blade is considered with respect to the axis of the hub increases in length, the variation in the thickness of the blade must be such that the ratio nL/27rr increases from the base of the said blade to its periphery, that is to say, from the point of attachment of the blade to the hub right up to the free extremity of the said blade mov ing in the vicinity of the casing.

FIG. 8 illustrates an embodiment of the invention as described above, in which the present invention is applied to a hub of known type, the section of which increases from the intake to the output of the wheel. Under these conditions, the reduction of space in the free section of the passageway through which the air flows is therefore the result, not solely of the special configuration of the blade in accordance with the present invention, but also on account of the fact that the hub has an increasing diameter. The ratio nL/27rr can in that case be less than 0.08 in the vicinity of the hub but must increase from the base of the blade up to the extremity of this latter and must have a value greater than 0.08 at least in the vicinity of the peripheral extremity of the said blade.

FIGS. 8a to 80 clearly show this increase in the maximum thickness L as well as the increase in the length of the chord from the base to the extremity of the blade.

In the form of embodiment which is illustrated in FIG. 9 the acceleration of the fine streams of air is produced in the vicinity ot the extremity of the blades such as 16, 17, 18 by giving the exterior fixed casing 19 a decreasng section from the intake to the outlet of the wheel. The ratio nL/2vrr no longer exactly represents the value of the increase in speed at the extremty of the blades, but a lower value, and the ratio in this case can therefore be less than 0.08 at the periphery.

Finally, FIG. shows a form of construction of the present invention in which a hub 20 having an increasing section, for example a frusto-concal hub, is combined with an exterior casing 21 having a decreasing internal section. The ratio which has been considered above, namely the ratio nL/ 27r1 can have a value less than 0.08 both in the vicinity of the hub and in the vicinity of the periphery, but on the other hand, this ratio must have a value greater than 0.08 at a point at least located between the base and the extremity of the blade.

In the three forms of embodiment which have last been described, the transverse section of the blade has the shape previously described, that is to say thinned-down leading and trailing edges and a thicker central portion.

This is a continuation-in-part application of my application Serial No. 809,871 filed April 29, 1959, now abandoned.

What I claim is:

1. An axial fan of the type described comprising at least two blades mounted on a hub, in Which the maximurn thickness of the transverse section of each blade increases from the base to the extremity of said blade, the number n of blades and the maximum thickness L of said blades, for a transverse section taken at a distance r from the axis of the hub, being such that the relation nL/21rr 0.08 is satisfied in the case of at least one transverse section, and an outer casing coaxially surrounding the extremity of said blades the chord of the blade having an increase in length at any given transverse section therethrough from the base to the extremity of the blade.

2. An axial fan of the type described comprising at least two blades mounted on a hub to constitute a wheel and moving in a fixed exterior casing, in which the maximum thickness of each blade increases from the base to the extremty of said blade, the number n of blades and their maximum thickness L for a transverse section taken at a distance r from the axis of the hub being such that the relation nL/27rr 0.08 is satisfied on the case of at least one transverse section of said blade, the chord of the transverse section of the blade having an increasing length from the base to the extermity of said blade.

3. An axial fan of the type described comprising at least two blades mounted on a hub to constitute a wheel and moving in a fixed exterior casing, in which the maxirnum thickness of each blade increases from the base to the extremity of said blade, each of said blades comprising a thinned-down leading edge and a thinned-down trailing edge, a central body having a thickness which increases progressively from said leading edge up to a maximum value which is reached between the first quarter and the center of the chord length of the blade starting from the leading edge of said blade, and subsequently diminishes down to said trailing edge, the number n of blades and their maximum thickness L for a transverse section taken at a distance r from the axis of said hub being such that the relation nL/2rr 0.08 is satisfied in the case of at least one transverse section of said blade and the chord of the transverse section of the blade having an increasing length at any given transverse section from the base to the periphery of said blade.

4. An axial fan of the type described comprising at least two blades mounted on a hub to constitute a wheel and moving in a fixed exterior casing, the maximum thickness of each of said blades increasing from the base to the extremity of said blade, the number n of blades and their thickness L for a transverse section taken at a distance r from the axis of said hub being such that the relation nL/z7rr 0.08 is satisfied in the case of at least one transverse section of each blade, the chord of the transverse section of the blade having an increasing length from the base to the periphery, and said hub having an increasing section from the ntake to the outlet thereof.

5. An axial fan of the type described comprising at least two blades mounted on a hub to constitute a wheel and moving in a fixed exterior casing, the maximum thickness of each of said blades increasing from the base to the extremity of said blade, each blade comprising a thinned-down leading edge and a thinned-down trailing edge, a central body having a thickness which increases progressively from said leading edge up to a maximum value which is reached between the first quarter and the center of the chord length of the blade starting from the leading edge of said blade, and subsequently diminishes down to said trailing edge, the number n of blades and their maximum thickness L for a transverse section taken at a distance r from the axis of the hub being such that the relation nL/Z7rI- O.O8 is satisfied in the case of at least one transverse section of said blade, the chord of the transverse section of the blade having an increasing length from the base to the periphery, and said hub having an increasing section from the intake to the outlet thereof.

Referentes Cited in the file of this patent UNITED STATES PATENTS (Other references on following page) UNITED STATES PATENTS Bergdoll Sept. 11, Gill j Oct. 23, Adamtchk Oct. 10, Petersen Dee. 5, Herrman Jan. 2, Johnson Dec. 18, Sawyer May 5, Slivka June 11, Ault et al. Oct. 29,

Ech May 17, 1960- Kondo Mar. 6, 1962, Ferreira Sept, 11, 1962 FOREIGN PATENTS France Jan. 2.6, 1911 France July 26, 1937 GreatBrtain June 24, 1920 Great Britain June 16, 1941 The Netherlands Sept. 5, 1926 1923 Switzerland Sept. 17,

Claims

1. AN AXIAL FAN OF THE TYPE DESCRIBED COMPRISING AT LEAST TWO BLADES MOUNTED ON A HUB, IN WHICH THE MAXIMUM THICKNESS OF THE TRANSVERSE SECTION OF EACH BLADE INCREASES FROM THE BASE TO THE EXTREMITY OF SAID BLADE, THE NUMBER N OF BLADES AND THE MAXIMUM THICKNESS L OF SAID BLADES, FOR A TRANSVERSE SECTION TAKEN AT A DISTANCE R FROM THE AXIS OF THE HUB, BEING SUCH THAT THE RELATION NL/2$R$0.08 IS SATISFIED IN THE CASE OF AT LEAST ONE TRANSVERSE SECTION, AND AN OUTER CASING COAXIALLY SURROUNDING THE EXTREMITY OF SAID BLADES THE CHORD OF THE BLADE HAVING AN INCREASE IN LENGTH AT ANY GIVEN TRANSVERSE SECTION THERETHROUGH FROM THE BASE TO THE EXTREMITY OF THE BLADE.