98 IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY, VOL. 20, NO. 1, JANUARY 2012 Design and Control of Hardware-in-the-Loop Simulations for Testing Non-Return-Valve Vibrations in Air Systems Mark Potter and Marko Bacic Abstract—Non-return-valves are commonly used across the range of industries for prevention of reverse flow conditions where they often exhibit premature failure due to self-sustained oscilla- tions that are a result of fluid structure interactions. This paper details the design of a proof of concept hardware-in-the-loop (HWIL) simulator and its controller for simulating fluid-struc- ture interactions of a non-return-valve with an arbitrary air system geometry. A numerical model of an airbitrary air system is coupled to the physical non-return-valve via a purpose built fast acting control valve and associated instrumentation to sim- ulate both stable and unstable vibrations. The vibrations of the non-return-valve in the HWIL simulator are compared against its vibrations in the real air system and are found to have an excellent agreement for a range of massflows and air system volumes. The simulator described in this paper can be used for simulating other types of passive flow control devices with arbitrary air systems thereby offering potential for significantly reducing the cost of full system tests. Index Terms—Aerospace control, fluid systems, hard- ware-in-the-loop (HWIL), non-return-valves (NRVs), simulation. I. INTRODUCTION T HIS paper describes the design of a proof of concept hard- ware-in-the-loop (HWIL) simulator and its controller for testing non-return valves (NRVs) in air systems. Although we consider a specific case of a spring loaded NRV interacting with air in an arbitrary network of pipes, the HWIL simulator de- scribed here is applicable to any other passive component or a multitude of passive components with the appropriate hard- ware modifications. NRVs shown in Fig. 1 are found in both air and hydraulic systems where there is a need to prevent re- verse flow conditions. Our work has been inspired by the appli- cation of such valves in pneumatic cabin-bleed air systems that are present in a majority of modern day aircraft (see Fig. 2). Qualification testing of NRVs and other similar passive compo- nents forms a sizeable non-recurring cost in any valve develop- ment programme for safety critical applications in the aerospace Manuscript received February 16, 2010; revised October 14, 2010; accepted January 11, 2011. Manuscript received in final form February 01, 2011. Date of publication March 17, 2011; date of current version December 14, 2011. Recommended by Associate Editor C. Natale. This work was supported by the EPSRC CNA Award. The authors were with the Department of Engineering Science, Oxford Uni- versity, Oxford, OX1 3PJ, U.K. (e-mail: marko.bacic@rolls-royce.com). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TCST.2011.2112660 Fig. 1. Spring loaded twin flapper NRV. industry. Integrated testing of such components within its in- tended environments is not carried out until very late in the de- velopment cycle. Consequently passive components like NRVs, poppet valves, check valves and others often exhibit failures that are often due to unforseeable interactions with the rest of the system components, both in gaseous and liquid working fluids [1]. This is primarily due to the lack of systems thinking and sys- tems validation of individual components with respect to their operation in an integrated system environment. Hence it is also one of the aims of this paper to argue that a HWIL simulation methodology is a cost effective concept for integrated system qualification testing of such components in order to reduce the likelihood of their failure in service. HWIL simulation was first used in the testing of missile seekers using motion simulators in anechoic chambers [2]. Today, automotive applications account for majority of HWIL testing with varied research into scaled HWIL simulations [3]–[5], load emulation [6], suspension testing [7], and others. However the great majority of HWIL simulators involve inter- actions between physical and numerical solid objects only (e.g., physical suspension system with numerical car mass) [8], [9]. Apart from the authors own efforts towards integrating fluids in the simulation loop [10]–[12], a review of the literature reveals only one recent notable instant of the application of the HWIL concept that includes actual fluid manipulation [13]–[15]. Moskwa et al. [15] describe the development of the single cylinder engine transient system that simulates a four cylinder engine through the use of the intake airflow simulator that and the four cylinder engine model. In this excellent work they demonstrate very good matching of plenum pressures between four cylinder models and the rig. In this paper, we aim to demonstrate the first application of the HWIL concept for simulation of large amplitude fluid-structure interactions. The NRV air system interaction studied here could 1063-6536/$26.00 © 2011 IEEE