The pressure drops and heat transfer coefficients of helical vane inserts of four different pitch-tube diameter ratios were measured over a Reynolds number range of about 30,000 to 300,000. The heat transfer coefficients and the pressure drops increased with increasing mass flew rate and decreasing insert pitch-tube diameter ratio. A momentum analysis, based on solid body rotation, resulted in new expressions for the momentum and frictional pressure drops for fully-developed flow in these inserts. Helical vane friction factors and Stanton numbers, computed from the experimental data in accordance with parameters derived from the analysis, correlated with conventional plain tube expressions.

A variable flow fan aircraft propulsion system offers the potential for achieving a low specific thrust with high flow and low jet velocity requirement as specified for takeoff, side-line noise, initial climb, and a high specific thrust requirement for climb and acceleration to supersonic cruise. These requirements are conflicting. To achieve this, the operating envelope of a variable flow fan has to be expanded over existing turbofan engines. The variable flow fan concept (i.e., the Variable Fan Exit or “VFX”) can efficiently operate beyond the usual fan (or compressor) stall operating line using novel methods of designing and scheduling the fan geometry as a function of flight Mach Number, fan pressure ratio and corrected speed. Fan geometry is altered by using variable inlet guide vanes (IGV’s), variable stators, and variable outlet guide vanes (OGV’s).