TAIL FAIRING DESIGN AND ASSOCIATED LOSSES

This chapter discusses the tail fairing design and associated losses. As the boss diameter in normal fan installations constitutes an appreciable proportion of the fan diameter, considerable diffusion occurs in the downstream section of the duct enclosing the tail fairing. The subsequent loss in fan unit efficiency can be very high, particularly when flow separation occurs. To avoid unnecessary losses, the tail fairing should have a streamlined form and should be of sufficient length to ensure a reasonable rate of diffusion. As the tail fairing length governs the rate of diffusion, some design rule concerning length is obviously required. Insufficient data are available to indicate the minimum fairing length that can be used for a given boss ratio without inviting the risk of flow separation. Despite some uncertainty as a result of the lack of extensive test results, sufficient information has been presented to permit confidence in designing efficient tail fairings.