Installed sheet metal baffle to form new upper wall of the diffuser as shown in the photo. The idea was to assist in maintaining attached flow, and to block leakage through the gap at the top. The baffle was done in 3 pieces in order to insert past the divider/supports in the scoop; each piece is about 7 ½ wide. There are gaps between pieces of about 3/8 ½ inch. The inlet pressure probe was placed at point D.
Test flight showed no noticeable difference in delta T on the oil. The pressure measured at D was 3 H2O. Pressure behind the exit fairing was again -3/4. The pressures at C and D (measured at different times) are at about 6 from the inboard end of the 22 long cooler. There may be some variation axially. Because of the gaps in the baffle, and fitting around the end tanks, there is still some air bypassing the cooler; but I dont know how significant. Given the 9+ H2O dynamic pressure out in front of the scoop still indicates not good pressure recovery.
Nonetheless; it is certainly disappointing that there was no change (within the accuracy of the temp measurements) in the effective cooling. This suggests that the wall shape and the air leakage are not the problem.
Calculating back from the temp changes in oil and air suggest there is only about 1000 cfm going through the cooler core. The extrapolation of my measured data on air flow vs pressure drop across the core suggests that at 3 H2O there should be about 2000 cfm through the core. Because of the centrifugal blower I was using for flow tests I was only able to get data up to about 0.6 H2O and 700 cfm. I fit the data to Y=ax+bx2 using regression analysis, which gave a very good fit up to that point; but extrapolating out to 3 may be stretching it. If I assume the pressure drop goes as the cube of the flow velocity, the extrapolation is considerable different about 1330 cfm at 3 H2O.
Al