SUPPRESSION OF BLADE PASSING FREQUENCY TONE IN AUTOMOTIVE AIR HANDLING SYSTEM

A noise tone occurring at a blade passing frequency in a blower for an automotive HVAC system is suppressed. The blower includes a centrifugal fan and a scroll body disposed around the fan. An outlet extends from the scroll body to conduct an air flow from a cutoff point of the scroll body. An inlet is coupled to the scroll body defining an inlet throat comprising an arcuate ring extending between a base and an annular end coaxially disposed over the fan. A partial-perimeter wall extends upstream from the arcuate ring having a height between about 4% and about 6.5% of an inner diameter of the annular end. The wall spans a perimeter portion of the circumference of the throat between about 120 degrees and about 180 degrees. As a result, noise at the blade passing frequency is suppressed without any significant reduction in air flow.