STATOR ANALYSIS AND OVERALL FAN UNIT PERFORMANCE

This chapter discusses the stator analysis and overall fan unit. The problem of analyzing stators is a relatively simple one as there is only one major variable, the swirl coefficient. When the aerodynamic design data are known, a prerotator analysis is unnecessary owing to constancy in the nondimensional outlet conditions while ⊼ is changing. The two main occasions on which an analysis is required are when design information is not available and when variable pitch prerotators are installed. When the swirl is removed by the straighteners, there is no radial static pressure gradient; owing to a gradient in total head, however, there must be a span wise axial velocity gradient. The inlet conditions to the straighteners are dictated by the rotor and hence, the main concern in analyzing these stators is associated with predicting the onset of stator stalling. Knowledge of the aerodynamic design data is very helpful in this connection. As the designer accumulates practical experience, it should eventually become possible to achieve a very high order of accuracy in all cases.