Straight vs. Curved Fan Blades - Dispelling the Myth!

24/03/2017 09:00AM

The relative merits and technology of curved vs. straight fan blades have been debated for some time. Davies Craig conducted a thorough research program to formulate the design of fans in which several design types including straight blades and curved blades with and without a ring were considered.

As a result of the extensive research program, Davies Craig were able to ascertain that curved blades generated less noise, however, this was achieved at the expense of a significant loss in performance. The loss in performance is caused by the fact that curved blades stall at a lower static pressure than straight blades. If a fan moves less air, then simply, you can expect less noise. As shown in the performance curves below, Davies Craig Thermatic Fan outperforms a competitor’s curved blade product across the full pressure range: 

Noise Control: Most fan noise is generated from a blade passing a shroud strut. The noise level is higher when the whole length of a blade overlaps/passes a shroud strut and if all the blades pass all the struts of a shroud at the same time, noise is at its worst. Some manufacturers have chosen to curve the blades and keep the struts straight. Since this approach significantly affects performance, Davies Craig has proven it's best to adopt the reverse approach of having straight blades and curving the struts.

Our investigations also found that when air flowed in layers (laminar flow), it breaks up into counter rotating airflow vortices (whirlwinds): 

These vortices consume energy and therefore reduce the airflow. It was found that by inserting triangular protrusions near the leading edge of the blade, the air is tripped into going into vortices earlier. The resulting vortices were much smaller and removed much less energy therefore making the blade more efficient. The idea of a ring around the blade tips was also researched and rejected since the performance suffered due to the increased energy required to propel the blade with extra weight at the tips. While the purpose of a ring is to reduce losses from air passing from the high-pressure side of the blade to the low-pressure side as shown, Davies Craig managed to achieve this by adding winglets to the blade tips without energy loss. 

 

When all aspects of blade design are considered, straight blades with trips, winglets and the correct shroud is the optimum, test-proven combination for efficient fan operation. 

Please visit our buy online section to view our Thermatic Electric Fan range.