Mechanics of a thin web wrapped helically about a turn bar

The mechanics of the interactions between a flexible web and an externally pressurized air cushion is modeled. The web is wrapped around the porous cylindrical turn-bar at an oblique angle (helically). The turn-bar supplies pressurized air into the web/turn-bar clearance. The shell model used to represent the mechanics of the web is an extension of a previous model, and it allows the web to be wrapped around the cylinder in a helical fashion. The geometric relations are based on Rongen's work [1] and steady state equilibrium equations are developed based on the work of Muftu and Cole [2]. The fluid mechanics of the air in the web/turn-bar clearance is a two dimensional form of the incompressible Navier-Stokes equations averaged in the clearance direction and augmented by non-linear source terms. Contact between the web and the reverser, which is undesirable in a turn-bar application, is included in the model in order to enable the analysis of the limiting cases. This paper describes the theory. Case studies and design recommendations are presented