Three-Dimensional Flow in a Transonic Axial Flow Fan of a High Bypass Ratio Turbofan Engine

Abstract

The present study deals with the air flow through an axial flow transonic fan blades, found in high bypass turbofan engines. Examples are CF-6, RB211 and GE90 turbofan engines. The fan has a wide chord, highly twisted blades of large span with a mean hubto-tip ratio of about 0.404. The blades are tapered with its maximum chord at the tip radius. Moreover, these twisted blades have slight reduction in its maximum thickness from hub to tip.Consequently, the flow field is a three dimensional viscous compressible. The engine intake together with the fan resemble the case studied here. The computational domain includes two periodic merged sectors at a central angle of 360 degrees divided by the number of blades (38). The first sector is stationary, which represents the intake domain, while the second is rotating, which represents the fan domain that comprehending one blade. This is an effective way of reducing the calculation time and speeding up the iterations. The investigated model (Intake and fan blade) dimensions and configuration are identified by measuring real dimensions of CF-6 engine fan module. The FLUENT solver employing the Spalart-Allmaras turbulence model is used to solve the flow field in both the intake and fan. The program results represent the variation of the flow characteristics (pressure, temperature, Mach number, etc) in the flow field at the design condition (cruise conditions; namely, 11000 m altitude, 0.85 Mach number and 3674 rpm fan speed). The fan performance map was also predicted for a range of percentage fan corrected speed from 60% to 110%. KEY WORDSTransonic flow, Axial fan, High bypass turbofan engine, Intake, swept blades.