Abstract
A computational procedure to simulate the bristle tip lift-off mechanism in a brush seal is established. This involves both macroscopic and microscopic modeling of the brush seal. A porous media model is used in the macroscopic view to estimate the average leakage velocity which serves as one of the boundary conditions for the microscopic model. The microscopic model consists of an arbitrary repeating module of 5 bristles arranged in a staggered fashion. The FIDAP program is used to model this flow domain and solve for the fluid forces on the central bristle. These forces are then integrated using Simpson's algorithm to calculate the bristle tip deflection and lift-off using a simple beam deflection formula. The deflection of the bristle tip represents a slight change of geometry of the domain. FIDAP then creates a computational grid for the new geometry and again solves for the fluid forces on the central bristle. Convergence is declared when the new lift-off is within a pre-specified percentage of the previous one. An enhanced understanding of two effects was obtained: (a) bristle angle effect and (b) bristle length effect. The results indicate that the lift-off gap is more sensitive to changes in bristle length than changes in bristle angle, which is in conformity with the theory. Specifically, the lift-off gap is found to increase linearly with bristle angle &-, well as bristle length. A very complex flow pattern was found in the vicinity of the bristle tips. This flow is very sensitive to changes in the bristle geometry. It is seen that the radial lifting force acting on the bristle tip is the dominant force causing the bristle tip lift-off.
Modi, Sandeep Subhash (1995). Simulation of bristle tip lift-off in a brush seal. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1995 -THESIS -M63.