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 an optimal control based linear quadratic regulator. An acceptance region was established in order to decide starting up the control process. Some case studies were carried out to illustrate the effectiveness of the control scheme. The research results present that a simple control method incorporating with an acceptance region enables to avoid the fluid induced instability flexibly in rotary machinery. Moreover, the developed techniques can also be applied in other fluid-induced instability problems such as whip and rub, etc.