Finite Element Application for Velocity Characteristics of Local Exhaust Inlets

Abstract

The purpose of this study was to develop a means of representing velocity characteristics for local exhaust inlets by application of the Finite Element Method (FEM). Several inlet configurations were investigated, including four different shapes of free-standing inlets and situations involving a plain exhaust inlet with one and two nearby external boundary surfaces. Values of the velocity potential were determined at nodal points, which divided a domain surrounding the exhaust inlet into numerous finite elements. FEM was used to obtain approximate solutions to the governing equation for airflow in the domain, in this case Laplace's equation for two-dimensional, incompressible and irrotational flow, subject to specified conditions at the boundaries of the domain. Velocity was approximated for each finite element as the gradient of the velocity potential. Approximate, two-dimensional, constant velocity contours were obtained by plotting curves through elements having nearly equal velocity magnitude. Results from using FEM to determine velocity characteristics are promising, need to be validated experimentally and may benefit from empirical “calibration”. If the method can be confirmed to provide reasonably accurate representations of airflow characteristics, then it should be developed further for application in a comprehensive computer design model. FEM offers a means to represent relatively complex inlet configurations. For example, further development of this approach could provide useful data for many different inlet shapes, external boundary surfaces, multiple inlets, crossdrafts and obstructions in proximity to local exhaust openings.