A recently installed Victory Energy boiler is supplied with fresh air through custom ductwork supplied by a third party. This custom ductwork was subject to severe space limitations. During the initial startup, vibrations occurred in the ductwork between the fan and the burner windbox. As the load reached 50%, the frequency and strength of these vibrations increased to the point where they threatened the structural integrity of the ductwork. Even though they had not supplied the ductwork, Victory Energy hired BMA to pinpoint and address this problem.
Steady state CFD simulations of the ductwork carried out in STAR-CCM+ showed a strong recirculation zone downstream of an elbow in the ductwork. Subsequent transient CFD simulations showed that eddies were detaching from the recirculation zone at approximately the same frequency as the vibrations measured on site. This translated into a pressure variation throughout the ductwork with an amplitude that was consistent with the observed movement of the ductwork walls.
A solution using guide vanes placed in the elbow to prevent the recirculation was first tested using CFD. Results showed that the pressure variation in the ductwork was, for all practical purposes, absent. These guide vanes were installed on site within two weeks of the first CFD runs and allowed the load to be increased to 100%.