Malavard 



^ ' "' ' '■ - *^ = T^ F-2(0-0„) ,■ .^ (2b) 



dn -^ ■ ■ ■ 



on the lower surface of the foil in the direct problem 



0- = V'o - r , (4b) 



in the inverse problem '^'- -Ji'* '■:■ ~.?ij'5 ^;'...ii. it 



- ^ = CLg(x) + 1+ F-2(^-V^j , (5b) 



at the infinity upstream of the field 



grad 0=0, __ (9b) 



so that the closure cavity condition is now written 



0; = 0^, ,• • - (10b) 



where c and c ' are two points placed at the downstream top of the cavity on 

 both sides of the slit. 



The symbols have the same signification as in the three-dimensional case, 

 except Cl, the global lifting coefficient, and g(x), the function which should now 

 fulfill the conditions g(xj ) = 0, gC^f ) < for xj < .f < x^, and 



I 



g(?) d^ = 1 



8 



RHEOELECTRIC ANALOGIES - PRINCIPLES 



The principles of rheoelectric analogies are classical and various publica- 

 tions on this subject (5,6, 39) give sufficient information on the special technol- 

 ogy required. It may be helpful, however, to recall some of these principles, in 

 a general way. 



An analogy can be made between the Laplacian of the velocities potential (or 

 of the stream function) and the Laplacian of the electric potential, created in a 

 homogeneous and isotropic conductor. The latter is generally comprised of a 

 liquid contained in a rheoelectric tank and confined by boundaries where elec- 

 trodes are placed, of judiciously determined form and disposition. The boimdary 

 conditions are introduced in a generally discontinuous way, by means of suitable 

 electric setups. The two most simple conditions which are very often found in 

 the problem are those of either the constant potential, which is the condition of 

 Eq. (la) for F = co^ or the zero normal derivative, which is the condition of Eq. 

 (8), on one or several boundaries. They are conveyed respectively by conductor 

 or insulating surfaces. 



374 



