Lehman and Kaplan 



(the number of blades of the propeller times the propeller rotational speed) and 

 higher harmonic frequencies. Specifically, the propeller- induced appendage 

 forces were examined as a function of propeller- appendage spacing for varia- 

 tions in the propeller blade thickness, number of blades comprising the propel- 

 ler, appendage asymmetry, appendage attack angle, and appendage location 

 (downstream or upstream of the propeller). 



An associated theoretical analysis that predicts the influence of the various 

 physical parameters on the magnitudes of the induced forces was also developed, 

 based on two-dimensional flow characteristics. Limited comparisons between 

 this theory and the experimental data are also presented in this paper. 



TEST FACILITIES v :^ i a ' .: .^^-U:'^ 



All of the testing was performed in the Oceanics Water Tunnel. This tunnel 

 is a recirculating, closed- jet- type tunnel having both the water velocity and the 

 test section static pressure as controllable variables. The test section is ap- 

 proximately 20 in. on a side (with rounded corners) and about 7 ft long. The 

 water velocity is controllable to about 40 ft/sec, and the static pressure can be 

 independently controlled from about 0.1 to 2 atmospheres absolute. For the 

 majority of these tests the water velocity in the tunnel was 5.23 ft/sec. This 

 rather low free- stream velocity was required for low speeds of propeller rota- 

 tion along with acceptable levels of thrust while still allowing the frequencies of 

 interest to be in a range adequately covered by the dynamic response of the 

 balance- appendage system. 



An external dynamometer can be placed at either end of the upper horizontal 

 leg of the tunnel; thus propellers can be driven from either their upstream or 

 downstream side. For these tests, the propellers were driven from their down- 

 stream side. The axial position of the propeller in the test section can be easily 

 changed, as the dynamometer and propeller drive shaft are connected as a unit 

 which rests on a bed similar to that employed on lathes. The propeller is posi- 

 tioned axially by a lead screw which is independently powered. 



In the settling section just ahead of the nozzle there is a honeycomb to im- 

 prove the flow conditions before the water enters the nozzle and passes through 

 the test section. At the entrance to the test section, screens can be inserted to 

 create the desired profile of a particular wake (axial components only). For the 

 investigations discussed here, no screenswere used, and a uniform flow approached 

 the appendage-propeller system. A drawing of the tunnel circuit is shown in 

 Fig. 1. 



PROPELLERS 



The two propeller designs used in most of these tests were selected from a 

 series with eight variations of blade thickness which received extensive study at 

 the National Physical Laboratory (8). The propellers selected are identified in 

 Ref. 8 as BT-1 and BT-2. The same identification nomenclature is used in this 

 report. The propellers were manufactured as individual blades fastened to a 

 common hub. This permitted testing as one-, two-, three-, and four-bladed units. 



170 



J 



