VirtuWind proposes the application of Software Defined Networking (SDN) and Network Functions Virtualization (NFV) in critical infrastructure networks. We aim at introducing network programmability, reconfigurability and multi-tenant capability both inside isolated and inter-connected industrial networks. Henceforth, we present the design of the VirtuWind architecture that addresses the requirements of industrial communications: granular Quality of Service (QoS) guarantees, system modularity and secure and isolated per-tenant network access. We present the functional components of our architecture and provide an overview of the appropriate realization mechanisms. Finally, we map two exemplary industrial system use-cases to the designed architecture to showcase its applicability in an exemplary industrial wind park network.