Table 1 - Geometry of Propellers
LIST OF TABLES
Table 2 Forward Open-Water Performance at Design Advance Coefficient
Table 3 - Forward Open-Water Performance at Design Thrust
Loading Coefficient 6
Table 4 - Effect of Skew on Steady Backing Speed at Constant Power 7
Page
3
NOTATION
Disk area of propeller, R2
Power coefficient, C = 2TTnQ/-A0V,1
CT Thrust loading coefficient, CT = T /.... A0 VA2
c Section chord length
D Propeller diameter
Section camber
g Acceleration due to gravity
H Hydrostatic head at shaft centerline minus vapor pressure
IVEV Inception of face vortex cavitation
!VTV Inception of tip vortex cavitation
J
Advance coefficient, J = VA /nDKQ Torque coefficient, KQ = Q/pn2 D5
KT Thrust coefficient, KT = T /pn2D4
n Propeller revolutions per unit time, positive forward p Propeller section pitch
Power delivered to the propeller
Q Propeller torque, positive in direction rotating propeller forward
I? Propeller radius
C07 JV2 +(O.7nV)2
Rno.7 Reynolds number at 0.7 H, R A
0.7 11
r Radial distance from propeller axis
T Propeller thrust, positive in direction propelling ship forward t Maximum thickness of propeller blade section
VA Speed of advance of propeller, positive forward Ship speed
C
x Nondimensional radius, x = r/R
Z Number of blades
Hydrodynarnic pitch angle
Projected skew angle at radius r
Propeller open-water efficiency,
= J/2
KT / KQ v Kinematic viscosity of waterp Density of water
1References are listed on page 34.
A BSTRACT
Cavitation tunnel and open-water results are presented for a series of
skewed propellers that were designed by lifting-surface methods. The four model propellers had maximum projected skew at the blade tip equal to 0, 36, 72, and
108 deg. The results showed that the cavitation-free bucket becomes sub-stantially wider with increasing skew; however, there was some crossover in
the inception of back cavitation and tip vortex cavitation among the three
skew-ed designs near design advance coefficient. Near the self-propulsion condition, the propeller with 36 deg of skew had the highest cavitation inception speed.
Forward open-water propulsion performance including lift effectiveness and per-formance breakdown due to cavitation were substantially the same for the four
propellers. All four propellers developed the design thrust loading coefficient within 1 percent of design rpm in open water. At constant power and thrust
load-ing coefficients, the backload-ing speed decreased slightly with increasload-ing skew (respective reductions of 1.5, 8.0, and 12.5 percent for 36, 72, and 108 deg of
skew).
ADMINISTRATIVE INFORMATION
The work reported herein was conducted in 1968. Financial support was furnished mainly by the Maritime Administration, Pacific Far East Lines, Prudential Lines, Inc., and
Friede and Goldman, Inc. Friede and Goldman, Inc. administered the funding under the de-velopment program for the LASH Cargo vessels. The backing tests were performed under the in-house independent research program of the Naval Ship Research and Development Center
(NSRDC) and funded under Subproject ZRO11-0101. INTRODUCTION
Interest in highly skewed propellers for surface ships was stimulated by a previous NSRDC investigation with a highly skewed research model propeller. That investigation in-dicated appreciable benefits from the use of blade skew, e.g., substantial reductions in
pro-peller force and moment fluctuations1 and improved tolerance to the inception of cavitation
caused by fluctuations in angle of attack due to operation in a wake.2 Since there was no deterioration in propulsion characteristics, i.e., efficiency and thrust and torque breakdown due to cavitation, it appeared feasible to consider the use of propeller blade skew as a
meth-od of improving propeller cavitation erosion and vibration characteristics without
amounts of skew, however, a parametric study was considered necessary prior to making any definite performance and cavitation predictions for skewed propellers.
In this subsequent parametric study, a series of four propellers was designed, built to model scale, and tested. This report presents the design, open-water performance, and
cavita-tion performance of these propellers. In another phase of the systematic study of skew, these model propellers were used to investigate the effect of skew on unsteady propeller bearing
forces and moments due to operation in a nonuniform flow field3 and propeller-induced
pres-sures.4 A summary of all these results was presented by Cox and Boswell.5
Except as previously noted,2 no data were found in the literature on the effect of skew on cavitation. Shiba6 speculated that skew would delay the inception of cavitation, but he presented no data to substantiate his speculation. Delano and Harrison7 experimentally ob-served that large amounts of skew on aircraft propellers delay the onset of adverse compress-ibility effects, which may be analogous to the cavitation effects on marine propellers.
PROPELLER DESIGNS
Four propellers were designed using the lifting-surface procedure of Cheng8 together with thickness corrections of Kerwin and Leopold.9 The conditions for which these
propel-lers were designed are typical of container ships or single-screw destroyer-type ships. The
four propellers had five blades and maximum skew angles (measured in the plane of the
propel-ler disk) of 0, 36, 72, and 108 deg. These angles correspond to 0, 0.5, 1.0, and 1.5 times the blade angular spacing. All parameters except skew (and pitch and camber corrections due to
skew) were held constant for the four designs.
It is emphasized that the pitch correction due to skew is very substantial and that a skewed propeller with the desired radial distribution of loading can be designed only by the use of lifting-surface techniques. To the writer's knowledge, these propellers are the first model marine propellers so designed to methodically investigate the effects of skew.
Blade stress was calculated by beam theory. The effect of skew on the stress due to centrifugal forces was calculated using the method outlined by Schoenherr.'° The calculated stress level increased moderately with skew. The radial thickness distribution and blade out-line (identical for all propellers) was selected such that the geometry and calculated stress of the propellers with 0, 36, and 72 deg of skew complied with requirements specified by the
American Bureau of Shipping," i.e., maximum working stress of 9000 psi for manganese-nickel-aluminum-bronze (superston 40 - grade 5). However, it was not clear whether the beam
theory adequately predicts the stress in highly skewed propellers. Accordingly, the steady stress of a highly skewed propeller blade was investigated experimentally at NSRDC'2(after the designs of the propellers reported herein were completed). These results indicate that
strength from the point of view of steady stress. Flowever the effect of skew on unsteady stress is not known. Since the existing strength data are very limited, NSRDC plans
addi-tional experimental and theoretical work on the effect of skew on blade stress.
The principal design characteristics of the propellers are shown in Table 1 and 'out-line drawings of the propeller blades are given in Figure 1. Figure 2 is a photograph of the
four propellers.
TABLE 1
Geometry of Propellers
Number of Blades 5
Expanded Area Ratio 0.725
Section Meanline NACAa= 0.8
Section Thickness Distribution NACA 66 with NSRDC modified nose and tail
Design J 0.889 DesignCT 0.534 Propeller 4381 (Skew = 0 Dcg) r/R tan3. c/D tIC 0.2 1.8256 0.174 0.2494 0.3 1.3094 0.229 0.1562 0.4 1.0075 0.275 0.1068 0.5 0.8034 0.312 0.0768 0.6 0.6483 0.337 0.0566 0.7 0.5300 0.347 0.0421 0.8 0.4390 0.334 0.0314 0.9 0.3681 0.280 0.0239 ni? O(deg) P/V fM/C 0.3 0.0 1.3448 0.0368 0.4 0.0 1.3580 0.0348 0.5 0.0 1.3361 0.0307 0.6 0.0 1.2797 0.0245 0.7 0.0 1.2099 0.0191 0.8 0.0 1.1366 0.0148 0.9 0.0 1.0660 0.0123
TABLE 1 (Continued) Propeller 4382 (Skew = 36 Deg)
Propeller 4383 (Skew = 72 Deg)
Propeller 4384 (Skew = 108 Deg)
TEST PROCEDURE
Open-water propulsion tests of the four 1-ft-diameter model propellers were conducted in the NSRDC deep-water basin; the propeller boat was instrumented with a gravity dyna-mometer for the forward tests and with a transmission dynamomoter for the backing tests.
The forward tests for all propellers were run at 7.8 rps and at speed of advance VA varying
O(deg) P/D fM/c 0.3 4.655 1.4332 0.0370 0.4 9.363 1.4117 0.0344 0.5 13.948 1.3613 0.0305 0.6 18.378 1.2854 0.0247 0.7 22.747 1.1999 0.0199 0.8 27.145 1.1117 0.0161 0.9 31.575 1.0270 0.0134 r/R O(deg) P/D fM/C 0.3 9.293 1.5124 0.0407 0.4 18.816 1.4588 0.0385 0.5 27.991 1.3860 0.0342 0.6 36.770 1.2958 0.0281 0.7 45.453 1.1976 0.0230 0.8 54.245 1.0959 0.0189 0.9 63.102 0.9955 0.0159 r/P O(deg) P/V fM/c 0.3 13.921 1.5837 0.0479 0.4 28.426 1.4956 0.0453 0.5 42.152 1.4057 0.0401 0.6 55.199 1.3051 0.0334 0.7 68.098 1.1993 0.0278 0.8 81.283 1.0864 0.0232 0.9 94.624 0.9729 0.0193
from 3.0 to 10.0 ft/sec, permitting operation at a Reynolds number R from 6.1 x i05 to
6.9 < The backing tests for all propellers were run at -8.33 rps and at VA varying from -3.0 to -9.5 ft/sec, permitting operation at R from 6.4 x to 7.4 x iO.
The cavitation tests were conducted in the NSRDC 24-in, variable-pressure water
tun-nel in uniform flow using the open-jet test section and a downstream shaft driven bya 150-hp
dynamometer. Each propeller was tested over a range of advance coefficient J and cavitation
number a . For each advance coefficient, the tunnel water speed was calibrated by setting
thrust and rps based on the open-water test for the propeller. At each advance coefficient, the cavitation test was conducted by starting from a noncavitating condition and reducing the tunnel pressure (and thus a) until cavitation appeared and/or until the cavitation pattern chang-ed significantly. The cavitation patterns at these pressures were photographchang-ed and sketchchang-ed, and the propeller thrust and torque recorded. The cavitation tests for all propellers were run
at n = 14 to 20 rps and VA = 10 to 20 ft/see, i.e., R = 1.38 x 106 to 2.44 x 106. The total air content, as measured with a Van-Slyke apparatus, was maintained at 25 to 30 percent of
saturation at atmospheric pressure.
TEST RESULTS
Figure 3 presents the forward open-water propulsion characteristics of the four
propel-lers. The variation of the open-water propulsion characteristics with skew was negligible. Not only was the performance of the four propellers essentially the same at design condition, but the lift effectiveness (slope of the curve of thrust coefficient KT versus advance coeffi-cient J ) was substantially independent of skew. A comparison of experimental performance with design conditions (Tables 2 and 3) revealed that all the propellers operated within 1 per-cent of design rpm. All the variations between design and experimentwere within
manufac-turing tolerance and experimental accuracy. The uniformly good agreement forall values of skew confirmed the design technique for highly skewed propellers.
Figure 4 presents the backing open-water performance of the fourpropellers. Table 4
shows the effect of skew on steady backing speed at constant power and constant thrust load-ing coefficient. These tables were computed by enterload-ing the backload-ing open-water curves at constant values of thrust loading coefficient, CT = SKT / .j2 . At the corresponding ad-vance coefficient], the power coefficient C
= 2 i nQ/
- pV3 A0 = 16KQ /J3 was ob-tained from the open-water curves. Constantpower, D = 2lTnQ, and diameter werespeci-fied; therefore the speed of advance for each propeller
was VA = (P/ pCA0)"3
. These data show that backing speed decreased slightly with increasing skew and that the amount of reduction was insensitive to the thrust loading coefficient in the region CT = 0.2 to 1.6. Thebacking speed with 36, 72, and 108 deg of skew were approximately 1.5, .8.0, and 12.5 percent
TABLE 2
Forward Open-Water Performance at Design Advance Coefficient
(J - 0.889)
TABLE 3
Forward Open-Water Performance at Design Thrust Loading Coefficient
(Design conditions: C. = 0.534 and I = 0.889) h
Propeller Design Open Water Percent Difference
4381 Kr 0.213 0.208
2.3
10KQ 0.447 0.4450.4
0.673 0.6611.8
4382K.
0.213 0.205 3.8 1OKQ 0.447 0.440 1.6 0.673 0.6572.4
4383 Kr 0.213 0.214 +0.5 1OKQ 0.447 0.460 +2.9 0.673 0.658 2.2 4384 Kr 0.213 0.208 2.3 1OKQ 0.447 0.446 0.2 0.673 0.660 - 1.9 Propeller Experimental Jat Design Cr Percent Difference
4381 0.884 0.6
4382 0.881 -.1.0
4383 0.890 +0.1
TABLE 4
Effect of Skew on Steady Backing Speed at Constant Power
Figures 5a-5d show cavitation inception for the four propellers at various radii, and Figure 6 compares the inception on the different propellers. Sketches and photographs of the cavitation at selected advance coefficients and cavitation numbers are given in Figures 7a-7e. In general, the sheet cavitation on both back and face started near the tip and proceeded to
lower radii with decreasing cavitation number. On the two most highly skewed propellers,
back cavitation started near the tip and, at lower cavitation numbers, a separate cavity formed at inner radii.
On Figures 5a - 5d, a curve marked with one radius means that the propeller was
cay-itating from that radius to the tip. Curves showing the inception of the separate inner cavity are marked with the radial extent of the inner cavity.
The leading-edge face cavitation for the skewed propellers appears to be like a
cavi-tating vortex parallel to the leading edge and slightly removed from the blade surface (see Figure 7e). Back bubble cavitation started at essentially the same conditions on the four propellers (same cavitation number at a given advance coefficient), and at nearly the same
cavitation number for all radii not covered by sheet cavitation. For the two most highly skewed
propellers, cavitation occurred along the trailing edge of the back of the blade near the hub. For Propeller 4384 (skew = 108 deg), this was the first cavitation occurring in the range J =
0.95 to J = 1.2.
Comparison of the back and face sheet cavitation inception of the four propellers (see Figure 6) showed a substantial widening of the cavitation-free bucket with increasing skew.
However, some crossover in the inception of the back cavitation and tip vortex cavitation
occurred for the three skewed propellers such that at design advance coefficient, sheet
cavi-tation was delayed most on Propeller 4382 (skew = 36 deg).
Figure 8 presents the thrust and torque breakdown due to cavitaticrn of the four
propel-lers. No systematic variation of thrust and torque breakdown with skew was apparent. T
VA (Skew = 36 deg) VA (Skew = 72 deg) VA (Skew = 108 deg) VA (Skew = 0 deg) VA (Skew = 0 deg) VA (Skew = 0 deg)
0.2 0.983 0.898 0.871
0.4 0.990 0.917 0.884
0.8 0.993 0.921 0.885
1.2 0.987 0.920 0.877
DISCUSSION
The reason for the widening of the cavitation-free bucket with increasing skew is not
clear. It has been suggested2 that this phenomenon may be somewhat analogous to the
well-known swept-wing effect.13 The two-dimensional swept wing reacts only to the component of
velocity normal to the leading edge and thus the leading-edge pressure peak and the lift effec-tiveness decrease proportionally as the cosine of the sweep angle (for sections parallel to the
flow held invariant with sweep). This analogy predicts that the propeller lift effectiveness decreases substantially with increasing skew; however, the open-water tests clearly showed
that the lift effectiveness is essentially independent of skew in the range of advance
coef-ficient where cavitation data are reported. This difference in variation of lift effectiveness suggests that the effect of propeller blade skew on cavitation inception cannot be explained
by the swept-wing analogy.
It is hypothesized that the widening of the cavitation bucket with increasing skew is due to a secondary flow which tends to equalize the pressure on the face and back along the leading edge of highly skewed propellers. It is well-known that such secondary flow takes
place at the blade tip. However, such a secondary flow could also take place along the lead-ing edge, which is not perpendicular to the resultant flow,14 such as for highly skewed pro-pellers. Such a flow could reduce the local suction peak at the leading edge and thus delay
leading-edge cavitation without measurably affecting the propeller thrust and torque.
Another possible explanation could lie in the variation with skew of induced velocities (especially near the leading edge) at off-design advance coefficient J. The variationof
in-duced velocities with skew could produce progressively smaller pressure peaks at the leading
edge with increasing skew. At the same time, the lift (and thus propeller thrust and torque)
could remain essentially invariant with skew due to changes in induced velocities on regions of the blade removed from the leading edge. This hypothesis can be checked when suitable lifting-surface theories become available for accurately calculating detailedoff-design propel-ler performance.
Prior to full-scale trial evaluation, it is not believed that the scaling problem for lead-ing edge cavitation on skewed propellers is different from that for unskewed propellers.
CONCLUSIONS
The following conclusions are drawn from the present study:
The design procedure is very satisfactory for highly skewed propellers. All four
pro-pellers operated within 1 percent of design rpm in open water.
The cavitatioll-free bucket becomes substantially wider with increasing skew. However,
some crossover in the inception of back cavitation and tip vortex cavitation occurred for the three skewed designs near design advance coefficient. Hence, near the self-propulsion
condition, the propeller with 36 deg of skew had the highest cavitation inception speed. Face cavitation inception speed increases monotonically with increasing skew at all advance coefficients.
The forward open-water propulsion characteristics including lift effectiveness and per-formance breakdown due to cavitation are insensitive to skew.
At constant power and thrust loading coefficient, the backing speed decreases slightly with increasing skew. The backing speeds with 36, 72, and 108 degrees of skew were approxi-mately 1.5, 8.0, and 12.5 percent less respectively than the backing speed with zero skew.
ACKNOWLEDGMENTS
The assistance of Friede and Goldman, Inc. in administering the financial support un-der the development program for the LASH cargo vessels is acknowledged. The author is
grateful to Mr. Dennis E. Crown who conducted most of the open-water tests and to Mr. Dusan
Figure 1 - Blade Outlines of the Four Model Propellers
x = 0.7 Section
Figure Ia - Propeller 4381, Skew 0 Degree
x = 0.7 Section
Figure lb - Propeller 4382, Skew 36 Degrees EXPANDKD OUTLINE PROJEC ED OUTLINE EXPANDED OUTLINE PROJECTED OUTLINE
PROJ TED OUTL INE
Figure Ic - Propeller 4383, Skew 72 Degrees
Figure id - Propeller 4384, Skew 108 Degrees
EXPANDED
1. 1 1.0 0.g I-0.8 U-U-I C L) UI
g07
C I.-C 0.6 0.5 C) U-U-i 0. I-UJ C) U-- 0.3 U-i C C) I.-0.1 0Figure 3 - Forward Open-Water Characteristics of the Propellers
ADVANCE COEFFICIENT, J Figure 3a PROPELLER 4381 SKEW 0. 10 KQ R = 7.0 n 0.7 x i05 = 6.5 0.7 x 0.1 02 03 04 0.5 0 0 7 flO 1 11 1fl 11 1
1.1 1.0 0.9 2 'U U-8 'U 0.7 0 C) 'U 0.5 C-) U- -.4 'U u- 0.3 LU 8 0.2 0.1
/
10 KQ KT 0.1 = 7.0 x i0 0.7 PROPELLER 4382 SKEW 36 = 6.5 x 10 13 0 01 02 03 04 0.5 0.6 07 08 0.9 ADVANCE COEFFICIENT, J Figure 3b 12 1.0 111.1 1.0 0.9 0 I.-C-) U-U-i 8 06 >-C.) U-i 0.5 U-U- -U-i U-I C-) 0.3 0.2 0.1 0 ADVANCE COEFFICIENT,. J Figure 3c 1.3 PROPELLER 4383 SKEW = 720 10 KQ = 7.0 x i05
ii
KT-
-II
LI
/
/
-.---01 02 fl fla flc fl n no nn1.0 0.9 I-LU L) U-LU C) LU = C) I-C) 0 0.5 C) LU C) 0.4 I.- I-0.3 C)
U-
- U-LU C) C) F-= I-0.1/
.5 x 10 KT 0 10 KQ R = 6 0.7 7.0 10 PROPELLER 4384 SKEW = 1080 Figure 3d 0.5 0.6 07 0.8 0.9 ADVANCE COEFFICIENT, J 02 10 11 1.2 1.3 14 0 0.1 03 040 Wa
U'
IL LLI-WZ -w 'Li. LiI-0
zo
OF-U LiI->
'Li
>z
4 Uz
.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.IFigur.e 4 - Backing Open-Water Characteristics of the Propellers
PROPELLER 4381 SKEW = 00 _1OKQ R = 6.8 x R no.7
6.4x105Ui
A
b.
-0 0.1 0.2 0.3 0.4 05 0.6 0.7 0.8 0.9 .0ADVANCE COEFFICIENT,.
J =-y
Figure 4aU IL. U 0 U U,
I
U 0 0 U > U z uja>z
U a I.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 PROPELLER 482 SKEW = 36 lOKQ R no.7 = 6.8 x 10 R "0.7 = 6.4 x 1Oii
0 0.I 0.2 0.3 0.4 0.5 0.6 0.7 08 0.9 .0 _VA DV4NCE COEFFICIENL J =rj Figure 4b-1OKQ PROPELLER 4383 SKEW = 720 O.7 = 6.8 x - VA ADVANCE COEFFICIENT,
J
=--Figure 4c 1.0 0.9 0 >- 0.800
lii 0.7 0.6I-u
zo
-ow
0.5 0.4 0.3I-u
wz
0.2 C., LU z 0i 1.0 0.9 0.6 0.7 0.8 0 0.1 0.2 0.3 0.4 0.5I.0 0.9 0.8
U-0.7 U..wz
- w
0.6 . U..zo
wo
LiJ 0.5 ti..000
0.4 I-cn 0.1 PROPELLER 4384 SKEW = 108° -1 OKQ R no.7 = 6.7 x 10 R 6.4 xA4°1.I
____________________ 0 0.I 02 0.3 0.4 05 06 0.7 0.8 09 1.0 VAADVANCE COEFFICIENT) J =_:iU
12.0 11.0 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0
Figure 5 - Cavitation Inception on the Propellers at Various Radii
\
BACK SHEET CAVITATIONI PROPELLER 4381 SKEW = xrl,5 x = 0.4 08 AREA OF NOCAVITATION 0.6 x r 09 FACE 1E ET CAVITATIOpj
1Ik
1,41
= 0.6IDESIGN CONDITION
IV F. xrO.4-'
PROPELLER 4382 SKEW = 36 \ BACK SHEET CAVITATION 0.6 \VTV AREA OF NO CAVITATION x 0.4Ii
"It'
LI'
\"N + DESIGN CONDITION FACE SHEET CAVITATION-CZ0
NATTACHED)x 07 x rO.6 BACK BU 7'---05 06 07 0.8 09 10 12 13 ADVANCE COEFFICIENT, J Figure Sa 05 06 07 08 09 10 11 12 1.3 ADVNCE COEFFICIENT, J FIgure Sb 12.0 11.0 10.0 9.0 8.0 b 7.0 0 6.0 0 5.0 C C-) 4.0 3.0 2.0 1.012.0 14.0 10.0 9.0 8.0 40 3.0 2.0 1.0 12.0 11.0 0 10.0 9.0 8.0 7.0 6.0 5.0 4.0 30 2.0 .0 0
o,o\
PROPELLER 4383SKEW = 72'04 BACK SHEET CAVITATION
\\
\
AREA OF NO CAVITATION \,rv,x 0.9 FACE SHEET CAVITATION BACK BUBBLE +DESIGN CONDITION 0.6 BACK TRAILING\\\
PROPELLER 4384 SKEW = lOB' BACK SHEET CAVITATION C = 0.8 =0.4 100.5 AREA OF NO CAVITATION x =04 IVTV, 08 vv (UNATTACHED1-
FACE SHEET BACK BUBBLE DESICN CONDITION CAVITATION TRUNDGE x = 0.7 p x= 0.6 05 06 01 08 09 10 1.1 1.2 1.3 ADVANCE COEFFICIENT, J Figure Sd 05 06 01 08 0.9 1.0 0.1 12 13 ADVANCE COEFFICIENT, J Figure Sc12.0 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 10 '. SKEW r 720I SKEW r 35
\
SKEW 108' SKEW 0\
. AREA OF NO CAVITATION SKEW 0 \ :. FACE SHEET BACK SHEET CAVITATION \? CAVITATION SKEW 36 BACK ALL PROPE BUBBLE LL E RD ______________________________________.-
SKEW r lOB 0.5 06 07 08 09 10 Li 12 ADVANCE COEFFICIENT. JFigure 7 - Illustrations of Cavitation at Selected Advance Coefficients J
and Cavitation Numbers a
Skew 0 Degrees Skew = 36 Degrees
Figure 7b - J = 0.8, a = 3.5
(sketches show back cavitation)
Figure7c - 1=0.875, ci= 1.4
(sketches show back cavitation)
Skew = 36 Degrees
Figure 7d - J = 1.0, a = 0.9
(sketches show back cavitation)
Figure 7e - J 1.1, a=O.8
Figure 7f - J = 1.2, U= 1.7
(sketches show face cavitation)
Figure 8 - Thrust and Torque Breakdown Due to Cavitation on the Propellers PROPELLER 4381 SKEW r
-K1 I I I I I I 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 ADVANCE COEFFICIENT, J Figure 8a0.70
0.
-0 I-i_ 0.50 8 0 U-8 = 0.20 - 0.10-.0.10 0.5 0.6 0.7 0.8 0.9 1.0 ADVANCE COEFFICIENT, J Figure 8b 1.2 1.3 0.90 I I I I I I I I PROPELLER 4382 SKEW 36 0.80-0.90 0.70 0.60 0 0.50 U.. 8 UJ 0I-. 0.40 I-C.) 0.30 U-UJ 8 I;; 0.10 -0.10 1.1 0.5 0.6 0.7 0.8 0.9 1.0 ADVANCE COEFFICIENT, J Figure 8c 1.2 1.3
0.90 0.80 0.70 0.10 -0.10 I 1 I Figure Sd PROPELLER 4384 SKEW = 108. 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 ADVANCE COEFFICIENT, .3 0.&1 I-. z 0.50 8 0.40 IJ 0.30 I1 w 8 0.20
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NSRDC Report 3247 (Dec 1969).
Thwaites, B. (editor), "Incompressible Aerodynamics," Clarendon Press, Oxford(1960). Pien, P.C., "The Calculation of Marine Propellers Based on Lifting-Surface Theory,"
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D D FORM
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(PAGE 1)DOCUMENT CONTROL DATA - R & D
Security VIes sificationoftitle, bodyofabstract and i,,desirIA% annota tjr,n must be entered when the overall report is classified) ORIGINATING ACTIVITY (Corporate author)
Naval Ship Research and Development Center Washington, D.C. 20034
20. REPORT SECURITY CLASSIFICATION
UNCLASSIFIED
2b. GROUP 3 REPORT TITLE
DESIGN, CAVITATION PERFOI1MANCE, AND OPEN-WATER PERFOR\IANCEOF A SERIES OF RESEARCH SKEWED PROPELLERS
& DESCRIPTIVE NOTES (T.peofreport and irlelusive dates)
5 AU THORISI (Fisst name, middle initial, last name) Robert J. Boswell
5. REPORT DATE March 17l
70. TOTAL NO. OF PAGES 7b. NO. OF REFS
14
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c. Subproject ZRO11.0101
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Report 3339
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Approved for Public Release: Distribution Unlimited
11. SUPPLEMENTARY NOTES
Most of the work reported was supported by:
Maritime Administration, Pacific Far East Lines, Prudential Lines, Inc., & Friede and Goldman, Inc.
12. SPONSORING MILITARY ACTIVITY
NSRDC JR/lED Program Washington D.C. 20034
13, ABSTRACT
Cavitation tunnel and open-water results are presented for a series of skewed pro' pellers that were designed by lifting-surface methods. The four model propellers had
maxi-mum projected skew at the blade tip equal to 0, 36, 72, and 108 deg. The results showed that the cavitation-free bucket becomes substantially wider with increasing skew;however,
there was some crossover in the inception of back cavitation and tip vortex cavitation among
the three skewed designs near design advance coefficient. Near the self-propulsion condition, the propeller with 36 deg of skew had the highest cavitation inception speed. Forward
open-water propulsion performance including lift effectiveness and performance breakdown due to
cavitation were substantially the same for the four propellers. All fourpropellers developed the design thrust loading coefficient within 1 percent of design rpm in open water. At con-stant power and thrust loading coefficients, the backing speed decreased slightlywith
in-creasing skew (respective reductions of 1.5, 8.0, and 12.5 percent for 36, 72, and 108 deg of
UNCLASSIFIED Security Classification
FORM 1473 (BACK) U NC LASSIF lED
14 KEY WORD! LINK A LINK 0 LINK C
ROLE WT ROLE WT ROLE WT
Propellers
Skewed Propellers Cavitation
Cavitation Inception Model Tests
Lifting Surface Design
Subcavitating Propeller Propeller Backing
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