To precisely evaluate the sustained performance and scalability of pipelined multiple FPGAs, this paper presents the implementation of a high-speed communication subsystem for a deeply pipelined stream computing platform. Internally, a pipeline of hardware modules for a domain-specific application is implemented in the FPGAs, where they are directly connected through their serial transceiver links. The necessary inter-FPGA communication subsystem with a flow control mechanism is implemented with Intel Arria 10 FPGAs, where the resource consumption and sustained network throughput are obtained, which averages at 7.92 GB/s. Performance estimation of a fluid simulation using the measured inter-FPGA network parameters is shown for a varied pipeline depth with explored temporal and spatial parallel options. Results show that the proposed platform with 16 FPGAs is estimated to achieve a sustained performance of 4.8 TFlops and may be scaled further by deepening the pipeline with even up to 128 FPGAs.