THEORY 
Consider a thin jet sheet, quasi-two-dimensional, flowing 
into an unbounded region. The jet gets deflected towards an 
adjacent wall. When such wall is relatively close to the jet axis, 
the jet gets attached to and flows along the wall enclosing a 
separation bubble as shown in Figure 1. As is evident, the jet 
undergoes considerable curving during its attachment thus generating 
a centrifugal force field on it. This results in a lower pressure 
within the separation bubble. The pressure pp in the separation 
bubble as derived in Appendix A is given by 
38 
Pepe = T/ib ——_-____ (1) 
B e o(1/t4 - 1) 
where 
P = free stream pressure, 
J jet momentum per unit span of the nozzle, 
b = nozzle width, 
8 = angular location of the reattachment point, 
Oo = jet spread parameter, 
e =satamh! [oy /(s4 + So) | 
Ss 
1 
4 = axial distance between the reattachment point and the 
nozzle, 
y; = half width of the jet at the reattachment point, 
Ss = ob /3 = distance of the nozzle exit from a hypothetical 
origin of the jet. 
Using the theory discussed in Appendix A, dimensionless pressure 
(Po - Pp) bo/J was plotted against the plate offset D/b, for 
values of 7.7, 10 and 12 for the jet spread parameter o. Figure 2 
shows the pressure difference between the separation bubble and 
the ambient as a function of D/b,. 
For a jet composed of a mixture of two fluids which do not 
mix such as oil and water, the lighter fluid flowing along the 
plate side of the jet seeks the separation bubble and gets trapped 
by it. If an outlet is provided at the center of the bubble, the 
accumulated oil can be tapped out while the water and rest of the 
oil flows out of the device. This is the principle of operation of 
the Coanda-effect oil-water separator. 
EXPERIMENTAL PROGRAM 
A test program was designed to determine the feasibility of 
