Why are Davies Craig Fan Blades straight rather than curved?
Fans come in many shapes and sizes with the main point of difference coming down to whether the blades are straight or curved. You may be asking why the blades on Davies Craig Thermatic Fans are straight rather than curved. Well at Davies Craig, we conducted a thorough research program to ascertain the benefits of straight over curved blades. Read on for more.
As a result of the extensive research program, Davies Craig were able to conclude 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.