The Digital Mock-Up (DMU), which is a comprehensive numerical model describing the final manufactured product, is today widely used in the industry (like the automotive and aeronautic industries) to support the concurrent engineering organizations and processes. On the other hand, simulation helps in the development of a product for design decision making or validation purposes. It allows to determine, with the appropriate level of accuracy, the behavior of the future product under a specific environment or set of exterior actions. Virtual Reality (VR) applications are simulations where the focus is on immersion and interaction with the product. However, there is still lacks in the integration of simulation within the product development phases. In particular the link between the DMU and the numerical models for simulation in the large is often hardly achieved. For some types of simulation, it is even inexistent. In this paper, we propose a new object, the Downstream Digital Mock-Up (DDMU), based on a polyhedral representation, and we show that it can be a support for the integration of a subset of simulation activities within the product development process by making the link between the DMU and these simulations. In the particular case of VR, we show that this object is particularly adapted. One particularity of the DDMU is to be prepared for a specific target application, defined by its objectives and the context in which it is immersed.