CFD Investigation on the Air Ventilation Characteristics in the U.S. Airlock: International Space Station Flight 7A Configuration

The objectives of this investigation were to verify the air ventilation characteristics of the U. S. Airlock and to ensure the adequacy of inter-module ventilation (IMV) of the International Space Station (ISS) Flight 7A configuration. There are three operating modes for the air ventilation in the U. S. Airlock: (1) Open Hatch configuration, (2) Closed Hatch configuration and (3) Housekeeping mode. In this study, computational fluid dynamics (CFD) models with the geometrical details representing each mode of the Airlock's operation was built. Proper airflow boundary conditions that represent the operation of the Airlock's Common Cabin Air Assembly (CCAA) and the inter-module ventilation were imposed for the subsequent CFD simulations. Based on the results obtained in this study, the performance of the Airlock ventilation system is marginally acceptable at CCAA fan running at 3600 rpm for both Open Hatch and Closed Hatch operations. In the Housekeeping mode, within the Airlock, most of the air velocity magnitude is below 7 ft/min. This indicated that part of the air entering from the U. S. Node 1 is trapped inside of the Airlock. For the Open Hatch case, the majority of the airflow entering the Airlock comes from Node 1 through the hatch and the rest (approximately 35%) is pulled into the Airlock through the IMV jumper duct. In examining the overall ventilation performance of the ISS Flight 7A configuration, air circulation in the Node 1 is improved from the previous ISS flights. For the U. S. Laboratory module, its air ventilation effectiveness is neither improved nor deteriorated, as indicated from the CFD results.