modified the blade profile of traditional single-arc segment by using double-arc segment for a squirrel cage fan to improve the fan total pressure efficiency. Their results indicated that the airfoil designed blade decreases obviously the flow separations on the suction surface of blade, which benefits the improvement of fan efficiency. To improve impeller flow conditions, Lin and Huang extended the concept of airfoil-like profile into the blade design of a small squirrel cage fan used in laptop computer. On account of the effect of blade profile curvature, Guo and Kim developed an improved impeller slip factor model for accurate prediction of impeller aerodynamic performance of squirrel cage fan. They pointed out that the slip factor is very small and the design criterion based on flow adherence to blade surface is not suitable for the blade design of squirrel cage fan. studied the impeller slip factor by measuring the flow velocity profiles at the impeller outlets of four squirrel cage fans. During the past decades, many studies have been done on the flow physics and design optimization of impeller to obtain an advanced squirrel cage fan with higher aerodynamic performance. Therefore, it is required to improve the flow conditions and aerodynamic performance of squirrel cage fan.Īs the only work component of squirrel cage fan, impeller exerts great impacts on the internal flow fields and fan aerodynamic performance. Such flow phenomena result in the reduction in effective work width of impeller and the increases of flow losses, and eventually deteriorate the aerodynamic performance of squirrel cage fan. These geometrical structures are prone to flow separations, also termed as inactive zone, near the front span and axial non-uniformity of impeller entrance flow due to the sharp turning of flow from the axial to radial direction with no guide devices. Generally, blade is designed into a two-dimensional circular arc profile with a short chord. The impeller of squirrel cage fan is typically composed of dozens of forward-curved blades, a front span and a back span, and is usually featured with a large inlet-outlet diameter ratio as well as width. A better match between impeller and volute tongue is achieved as the decreases of reversed flow coefficients at the impeller inlet and outlet and recirculated flow coefficient in the volute.Īs a special centrifugal fan, squirrel cage fan is extensively used in heating, ventilation and air-conditioning (HVAC) and other household appliances. On the blade pressure surface, the forces are reduced with obvious improvement of gradients near the front span and back span. The dimension of inactive zone near the front span is decreased. With the optimum full trimming of blade, the axial distributions of mass flow at the impeller inlet and outlet become more uniform. The results show that the blade trimming with proper trimming parameter enables the fan to achieve higher fan aerodynamic performance in terms of total pressure efficiency and static pressure rise, between which full trimming is preferable to part trimming. Aerodynamic performance tests and numerical simulations are performed to explore the effect of blade trimming on the fan aerodynamic performance and the related flow mechanisms. On the premise of maintained impeller-volute tongue distance and production cost reduction, this paper proposes a blade trimming method focusing on axial modification of blade inlet in an attempt to improve the impeller flow condition and further the aerodynamic performance of squirrel cage fan, which is divided into blade full trimming and part trimming. The impeller of squirrel cage fan exerts great effects on the internal flow fields and fan aerodynamic performance.
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