The results also show that the highest pressure gradients are located at the top and sides of the inlet. The pressure decreases and becomes more uniform as the flow approaches the impeller. The uniformity at the inlet was deemed relatively high for this type of design indicating that actual pump efficiency is more likely to be close to the design value. The results also show a flow-recirculation region above the shaft that gradually disappears as the flow approaches the impeller. Flow separation at the inlet is at a minimum, which leads to improved efficiency.
Some separation is observed above the lip as the flow turns toward the impeller.
Minor flow recirculation is also observed above the impeller shaft near the intersection of the shaft and the rear duct wall. This recirculation is more severe when the AAAV is traveling at 25 knots, because the axial momentum of the flow is stronger at higher speeds. Recirculation is an inevitable drawback in this type of design, but the patterns seen here were among the best ever witnessed by the design team. Another critical area of the design is where the shaft driving the pump comes through the inlet. The flow has to go around the pump shaft before it reaches the pump face.