Parmeterization of the Total Pressure Distribution Along a Low-Pressure Axial Fan Blade According to the Design Requirements

Abstract

In the field of axial flow turbomachines, the two–dimensional cascade model is often used experimentally or numerically to investigate fundamental flow characteristics and overall performance of the impeller. The core of the present work is a design method for axial fan cascades aiming to derive inversely the optimum blade shape based on the requirements of the impeller and not using any predefined airfoil profiles. While most design strategies based on the airfoil theory assume constant total pressure at all streamlines, i.e. free–vortex flow, this paper investigates the possibility of varying the total pressure along the blade and based on that, an analytical expression of the outlet blade angle is determined. When computing the blade profile at specified radius, critical parameters reflecting on the flow characteristics are observed and adjusted, i.e. sufficient lift and controlled deceleration of the flow on the contour so that the resulting profile is derived for minimum losses. The validation of this design strategy is given by the numerical results obtained when employed as an optimization tool for an industrial fan: 10–20% absolute increase in the efficiency of the optimized impeller.