Simulation of Cabin Air Outlet Flows

Kurzfassung

In particular the thermal comfort of passengers is the essential design objective in the cabin air ventilation layout for modern civil passenger aircraft. Solar radiation, electrical equipment, on-board electronics, high power converters, in-flight entertainment and communication devices and most important the heat release of the passengers are representing thermal loads. This heat loads have to be balanced by cold air coming from the air vents of cabin air outlets of the air ventilation system. In fact, the temperature distribution inside the passenger cabin can only be controlled by the air conditioning system. Besides providing the passengers with the fresh, an essential task is to avoid discomfort for the passengers by ensuring a good mixing of fresh with aged air and by guaranteeing a high air flow exchange rate for each individual passenger according to the requirements defined in. Cabin air outlets are a crucial device for the air flow distribution within the cabin. Although a high air exchange rate is necessary for thermal comfort the incoming fresh air must not exceed a certain flow velocity in order to avoid gust. Therefore, the air should be evenly distributed by an outlet device, i.e. a plenum, an orifice plate or flow straighteners, before it can leave the outlets through the vents forming a homogeneous planar air jet. This optimal precondition facilitates a successive control of the air distribution within the aircraft cabin. In particular, in the early design phase of aircraft cabin layouts numerical flow simulations are undertaken presuming that this precondition is fulfilled. In fact this is not always the case; hence, design work has to be done to improve cabin air outlets. Unfortunately, the space envelope for cabin air outlets is quite limited by stringers, insulation, ducting, wires, cables or lining elements. Not only the outer space envelope is a major constraint when designing air outlets, moreover, internal drag and weight have a negative impact on the power consumption of the Environmental Control System (ECS) and, therefore, on the fuel consumption of the aircraft. Both have to be minimized in order to save power and costs. Not at all, the optimization of cabin air outlets is a major task in the design process of the air ventilation system, in particular when bearing in mind that future cabin interior will be modularly designed and especially customized in order to meet corporate design constraints of the airliners.