Evaluation of Shelter Ventilation by Model Tests

Scale model tests using a low speed wind tunnel were performed to determine the wind-induced ventilation throughput in an earth-bermed, single- room, above-ground shelter over a wide range of approach wind velocities. Air flow through the wall openings and the interior of the model was traced with neutrally buoyant tracer bubbles and recorded using a movie camera. Volume flow rate through a door or window opening was determined by taking the product of the average bubble velocity, the area of the opening and an experimentally determined area coefficient. Model ventilation throughput values were obtained by adding the air volume flow rates through all the inlet openings and the full- scale values were projected using scaling laws. Air distribution (fresh air mixing) inside the shelter was also analyzed for different approach wind conditions using a temperature-decay method. A simple design of a Flow Enhancement Device (FED) which could significantly improve wind-induced ventilation in a below-ground shelter was concepted. A scale model of a 100- person, key worker type below-ground shelter was fabricated and preliminary runs were made with it.