Proceedings of COBEM 2005 18th International Congress of Mechanical Engineering Copyright © 2005 by ABCM November 6-11, 2005, Ouro Preto, MG COMPUTATIONAL SIMULATION OF AN AIRCRAFT CABIN PRESSURE CONTROL SYSTEM Francisco Domingues Ramos ITA – Instituto Tecnológico de Aeronáutica Departamento de Energia Praça Mal. Eduardo Gomes, 50 - Vila das Acácias CEP 12228-900 São José dos Campos – SP – Brazil fdramos@hotmail.com Cláudia Regina de Andrade ITA – Instituto Tecnológico de Aeronáutica Departamento de Energia Praça Mal. Eduardo Gomes, 50 - Vila das Acácias CEP 12228-900 São José dos Campos – SP – Brazil claudia@ita.br Edson Luiz Zaparoli ITA – Instituto Tecnológico de Aeronáutica Departamento de Energia Praça Mal. Eduardo Gomes, 50 - Vila das Acácias CEP 12228-900 São José dos Campos – SP – Brazil zaparoli@ita.br Abstract. In the context of aircraft cabin environmental control, the goal of this work is to build a mathematical model of the cabin pressure control system and to simulate it for some important design cases. The developing of the model is based on the recommendation document ARP 1270 (SAE, 2000) with some modifications in order to apply it to a specific aircraft design, developed in academic work. From the model of the cabin pressure control system built for this aircraft, normal flight operation (climb, cruise and descent) and some failure cases are simulated. The first failure event studied is when the outflow valve fails open and the cabin depressurizes. The second one is the failure of the outflow valve in the closed position, with continuous increase of the cabin pressure, and the third failure case is the complete loss of the pneumatic system, another depressurization case. These cases are especially interesting in the initial analysis of the system, allowing the preliminary design of the aircraft's emergency descent profile (depressurizing cases) and safety valve, that prevents great pressure differentials on the cabin (outflow valve fail closed). Keywords: ecs, cabin pressure, control system, simulation 1. Introduction Aircraft environmental control systems provide appropriate cabin environmental conditions for survival and comfort of passengers and crew, comprising the pneumatic (bleed) system, air conditioning, cabin pressurization and supplemental oxygen. This work is dedicated to the study of a cabin pressure control system through computational simulation of its dynamic response. Simulations here presented are based on the concept of a very light jet, a purely academic design developed during the Engineering Specialization Program, a Professional Master Degree course in partnership between ITA and EMBRAER S.A. Ambient pressure decreases rapidly with altitude and it is not satisfactory to human physiological breathing needs at high altitudes, oxygen partial pressure in the air is very low and the body is not able to adequately supply cells and tissues with oxygen. This lack of oxygen in the blood causes some important effects on human bodies varying from a simple headache and discomfort at relatively low altitudes, 3048 to 4572 m (10000 to 15000 ft), to total loss of consciousness, above 7620 m (25000 ft). Other effects of low ambient pressure levels on human body are expansion of gases in cavities (sinus, abdomen) and dissolved in the blood (nitrogen) that may cause more serious problems. Another physiological problem concerns cabin pressure changes, related to the middle ear equalization through the Eustachian tube. The source of these effects fall into two broad categories: pressure transients (bumps) and slower pressure changes. Pressure bumps are short duration cabin pressure changes of sufficient magnitude to cause passenger pain and discomfort. Proper design of the controls and equipment of the air conditioning and pressurization systems can minimize bumps and significantly enhance passenger comfort. Concerning slower steady pressure changes, studies have shown that acceptable rates of cabin climb and descent are typically in the range of 1.524 to 2.54 m/s (300 to 500ft/min). The Equivalent Eardrum Differential Pressure is a well accepted design reference for pressurization systems. This method considers the sensory perception of the average individual on the basis of time integration of the