The phenomenon of fluid-induced instability existing in fluid-film bearing systems has been coped with for long time. The study aims to soothe and even eliminate the occurrence of whirl in rotary machinery by increasing the threshold of instability through the anti-swirl injection using the linear quadratic regulator based optimal control. An acceptance region was established in order to decide starting up the control process. Three case studies were carried out to illustrate the effectiveness of the control scheme. The research results demonstrate that the control scheme incorporating with the acceptance region enables to avoid the occurrence of fluid induced instability in rotary machinery. Moreover, the developed techniques can also be applied in other fluid-induced instability problems such as whip and rub, etc.