Conventional flow-level simulators use timescales around the round-trip time when numerically solving fluid-flow models for network simulations. In large-scale and high-speed network simulations, only understanding coarser behavior than that achieved with timescales around the round-trip time is sometimes sufficient for performance evaluation. In this paper, we propose a novel method for accelerating flow-level simulations; it omits timescale finer than that required by the performance evaluation. Through experiments, we investigate the effectiveness of the proposed method for accelerating flow-level simulations. Our findings show that the proposed method offers 60 times faster than the conventional flow-level simulator.