Evaluation of Models for Local Exhaust Velocity Characteristics— Part One: Velocity Contours for Freestanding and Bounded Inlets

Abstract

Constant velocity contours are two-dimensional (2-D) representations of velocity characteristics for airflow into exhaust inlets and are more useful for inlet design than conventional (one-dimensional) centerline velocity gradients. Two computer modeling approaches, finite-element method (FEM) and graphical approximation (GA), have been developed recently as means to provide velocity contours for inlet airflow. This study provides comparison and evaluation of these models against each other and against experimental data. Additional experimental results were obtained in this study by using high velocity/low volume exhaust inlets. The FEM and GA models provide velocity contours having similar basic shapes for most inlet configurations, and these shapes generally are consistent with experimental findings. The GA model alters the size of specific contours for changes in inlet end shape (circular, rectangular), thereby approximating three-dimensional (3-D) effects. The FEM model is strictly 2-D and approximates velocity contours for slot-shaped inlets reasonably well. Possibilities exist for using FEM to represent 3-D characteristics by “calibrating” 2-D results empirically or by developing 3-D models. The FEM approach is more versatile than GA, providing substantial opportunities for further model development. Limitations of available data, especially for inlets near a boundary surface, prevent conclusive validation of the models and support the need for further experimental study.