US2208615A - Axial flow type fan or pump - Google Patents

Description

F. L. WATTENDORF 2,208,615

AXIAL FLOW TYPE FAN 0R PUMP Filed July 27, 1939 July 23, 1940.

2 Sheets-Sheet 1 GUIDE VANE RUNNER BLADE v v ,6, v 3 v N3 \i 3 VELOCITY DIAGRAM A L VELOCITY DlAGRAM POINT POINT VELOCITY n AGRAM omr F16. I

R ER 02 (5 euro: VANE V V V v o V M I VELOCITY DIAGRAM 3 POINT 3 k I a.

x VELOCfl'Y mABRAM VELOCITY DIAGRAM POINT POINT FIG. Z

i I v GUIDEVANE RUNNE sum: suma VANE 2 1 *3 3 v v v v /j"s,

I? L T v 3 VELOCITY omen/m #3 a ,iwsmcrrv DIAGRAM POINT a g. i POINT 2 a 0 1. \TY omefiin VE 0c VELOCITY DIAGRAM v POlNT F:s.-3

- lNVENTOR ,E'ranirL. igendoirf' ATTORNEY July 23, 1940. F. WATTENDORF AXIAL FLOW TYPE FAN on PUMP Filed July 27, 1939 2 Sheets-Sheet 2 INVENTOR Ivanifil hfaiz en dorf ATTORNEY Patented July 23, 1940 PATENT OFFICE 2,208,615 mAL'FLow TYPE FAN on rum Frank L. Wattendort, Hull, Man. Application July 27, 1939, Serial No. 286,877

3 Claims. (01. 230-120) (Granted under the act of March amended April 30, 1928; 3'10 0. G. 757) This invention relates to a fan or pump of the axial flow type capable of developing high pressures while maintaining low rotating tip speeds with resulting low noise development in the case of fans and minimum danger of cavitation in the case of pumps.

It is an object of this invention to provide an axial flow type fan or pump having a pressure coefiicient larger than 0.5 with blade spacing ratios larger than 1.

Fan characteristics are preferably expressed in the form of non-dimensional coeflicients for the pressure and capacity. The following notation will be used:

p=total head developed by the fan or pump R=radius of the blade tips w=angular velocity =.=mass density of the fluid (air, water, oil, etc.)

in which the fan is operating A=net area of the fluid passage through the fan proper Q=quantity of fluid delivered per unit time =total efliciency of the unit for each radius =the pressure coefficient 1 A=the volume coeficient C1.=the lift coefiicient r=the radial distance to any blade element p=the mean angle of pitch 'z=the number of blades b=the blade chord so a=the angle of attack S=bz/21rr=the spacing ratio, i. e., the ratio of the blade chord b'to the spacing between two blades 35 1=the circulation w=the average velocity of the fluid relative to each blade element The pressure coefllcient 1/ may be expressed by 0 the following formula:

arm) and the volume coefficient A by:

Axial flow fans described in technical literature are seldom found to exceed a pressure coefiicient '0 of 0.5 for a single stage. The reason for this ship between the pressure coefllcient and the 10 blade characteristics:

' l a h/ (m)n For optimum efliciency of a blade element the best mean angle of pitch ,8 is 45, while the flow coeflicient A, for a given quantity Q, is limited for reasons of efliciency, noises or cavitation. The lift coefficient is limited by the flow separation (stall) phenomenon, and often has to be kept very small for reduction of noise in the case of fans, and for minimizing the danger of cavitation in the case of pumps.

The only means, therefore, to increase the pressure coefficient 0 is by increasing the spacing ratio S. However, when S approaches and exceeds unity the behavior of the fan blades -deviates essentially from that of a single airfoil, so that the usual methods of design do not apply for values of S greater than one.

The present invention provides means for utilizing a spacing ratio greater than 1, and obtaining at the same time a pressure coefllcient ,0 greater than 0.5, with the accompanying advantages of a relatively small fan diameter and low rotating tip speed.

This is accomplished by proper bending of the leading and trailing edges of the blades in the following manner: I

The trailing edge of any blade element is bent at each radius in such a way that the zero lift line of the corresponding element forms with the plane of rotation an angle 52 which is calculated as follows:

Case I-In which guide vanes are mounted in front, i. e., upstream, of the runner:

hind, i. e.,downstream, of the runner:

' 1 Li B l R q r 2 Case III-In which guide vanes are located both upstream and downstream of the runner. In this case the trailing edge of the blade element at each radius is bent in such a direction that the zero lift line of the corresponding element forms with the plane of rotation an angle pr such that:

1 tan fi,-=7\

r i i m-1) where k is a constant depending on the distribution of the rotation added to the fluid by the guide vanes in front and substracted by the guide vanes behind.

In all three cases the leading edge of any blade element has to be bent in such a way that the flow enters the runner sufliciently without shock I that flow separation is avoided over the entire blade, and particularly at the leading edge.

The direction of fiow relative to the blade element at the leading edge forms with the plane of rotation an angle 31 of the following magnitudes:

Case I;

(n 7; 7 '2) Case 11;

tan flu: A

and

Case 111;

(within limits), where B varies with the shape of the profile selected from tested profiles, the term area refers to the area of a blade element or b times unit length in the radial direction, and L refers to the total anodynamic lifting force on the same element, said force acting in a direction perpendicular to the mean flow.

The chord length b and the lift coemcient C1. of each element are selected in such a way that the circulation, I=Cz.bw/2, is approximately independent of the radius 1'.

For the three cases considered, the guide vanes must impart to the fluid a rotational component Cu of the velocity, determined as follows:

Case I l R 2r7 FGR Case Ill-Since the guide vanes are downstream,

. 2,203,015 Case II-in which guide vanes are mounted bethey must remove .from the fluid a rotational.

component of the same magnitude.

, Case lIIThe upstream guide vanes may produce a rotationalcomponent equal to an arbitrary factor times the expression for Case I. The downstream guide vanes then will have to remove the balance of rotational component remaining in the flow leaving the fan.

For all three cases the guide vanes may be located to suit the individual design. They may be used to regulate the flow at operating condi@ tions removed from the design point. The runner blades may be made controllable to obtain a high efiiciency at operating conditions removed from the design point.

In the drawings:

Fig. 1 is a diagrammatic sectional view taken through a runner blade and one of the guide vanes. associated therewith in the arrangement constituting Case I, and showing velocity diagrams for this arrangement.

Fig. 2 is a similar view of the arrangement constituting Case II.

Fig. 3 is a similar view of the arrangement constituting Case III.

Figs. 4 and 5 are side and rear views respectively, of a typical runner blade arranged according to the invention.

Figs. 6 and 7 are sectional views taken along the shortest and longest radii respectively of the runner blade of Figs. 4 and 5.

In each of Figs. 1, 2 and 3 the fluid acted upon enters the fan or pump from the left and the direction of travel of the runner blade is toward the top of the drawing. The velocity diagrams in each figure show the composition of the velocities imparted to the fluid at various points of its travel through the fan. In these figures the runner blade is indicated by reference numeral I, the upstream guide vane by 2 and the downstream guide vane by 3. The relations expressed by the velocity diagrams are as described in the following explanation. When an arrow appears above the plus or minus sign it indicates vectorial addition or subtraction.

At the entrance to the front guide vanes:

V=axial velocity At the exit from the front guide vanes:

V+ (C..), =abso1ute velocity Cu =the rotational velocity component of the absolute velocity, and is counted positive when in the direction of the runner rotation.

(Cu) 1=rotational velocity component imparted by the front guide vanes.

(Cu)! =rotational velocity component imparted by the runner.

(Cu),z=rotational velocity component imparted by the rear guide vanes.

I At the entrance to the runner:

where W1 is the relative velocity at the entrance of the blade element.

At the exit from the runner:

. where W: is the relative velocity at the exit of the blade element.

At the entrance to the rear guide vanes:

+[(Ct) .1+ (C'.)/]=absolute velocity At the exit from the rear guide vanes:

D-r For Case 11 (Fig. 2):

' a)el u)! For Case 111 (Fig. 3)

Figs. 4 and 5 show side and rear views of a typical blade while Figs. 6 and I show the blade profiles along the shortest and longest radii respectively. The plane of rotation is the plane of the paper for Fig. 5, is normal to the plane of the paper in Fig. 4, and lies in the horizontal for Figs. 6 and 7.

The following is a description of the application of the formulas described herein to the development of the typical blade illustrated in Figs. 4 to '7.

Consider that a blade form is to be selected for an axial fan unit to meet the following requirements:

Q=10,000 cu. ft./min. p=3 inches water=15.6 lbs/sq. ft. R=l2% inches wR=125 ft./sec. A=2.33 sq. ft. e=.0024 slugs/cu. ft. R=.57 tI/=.83 1 =83% Calculation of blade angles for Case I, guide vanes upstream.

At blade tip, R=12V inches and the angle of relative flow at blade entrance is given by the formula of page 2 column 1 line B =20.8 At blade root, i=7 inches Tan 131=.393

determined from said curves are 31 for Ca=0.5

- and 6 for Ca=0.8.

The blade exit settings are defined by the formula of page 1 column 2 line 50:

Tan p:=AR/r for the present example the values are:

The corresponding profile shapes and settings are shown in Figs. 4' to 7 inclusive, Fig. 6 representing a typical section at 1:? inches and Fig. 7 showing the corresponding blade section at R=12% inches.

It is to be understood that the invention is limited only by the scope and limitations of the appended claims.

The invention described herein may be manufactured and/or used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

1. An axial flow type fan or pump comprising a multi-bladed runner and guide vanes located upstream of said runner, the elements of said blades being curved in such a manner that the tangent to the zero lift line of any blade element forms at the leading edge of said element an angle (51+a) with the plane of rotation, such that;

1 tan Q R 211 'r and at the trailing edge thereof an angle 52, such that;

tan fig: X? where Q=quantity of fluid delivered per unit time A=net area of the fluid passage through the fan proper w=angular velocity r=radius of any blade element R=radius of the tip of any blade n=total efllciency of the fan p=the mean pitchangle of the blades S=the ratio of the blade chord to the spacing between two blades v p=the mass density of the fluid operated on by the fan C1.=the lift coefficient, and p=the total head developed by the fan or pump,

the angle a being determined by the expression CL=B21r sin a, where B varies with the shape of the selected profile.

2. An axial flow type fan or pump comprising a multi-b1aded runner and guide vanes located downstream of said runner, the elements of said blades being curved in such a manner that the tangent to the zero lift line of any blade element forms at the leading edge of said element an angle (fl1+a) with the plane of rotation, such that;

10 rotation of said runner, such that;

where the meanings of the terms of said equations and at the trailing edge an angle pa, such that:

1 ==M"Tir where the meanings of the terms of said equations are as defined in claim 1, the term It being a constant depending on the distribution of the rotation added to the fluid by said upstream vanes and subtracted by said downstream guide vanes.

FRANK L. WAT'I'ENDORF.

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