A double sided impeller, which consists of two impellers arranged in a back-to-back configuration with the backdisks eliminated, enables a single centrifugal compressor to have flow capacity similar to two compressors working in parallel but with a smaller packaging size. It reduces inertia of the rotating group and helps improve transient response. The smaller impeller diameter also enhances turbine performance by improving the compressor-turbine matching. These attributes are very attractive for automotive turbocharging applications. As a consequence of a common compressor inlet and diffuser, the two compressor sides interact and two operation modes exist. In the parallel mode, the two compressor sides work under comparable condition and the overall compressor behaves similar to a conventional compressor. As flow rate is reduced below a transition value, the system operates in a single-compressor mode with one compressor side flowing significantly more. The compressor side that flows more operates away from the stability limit and the side with low flow remains stable because of heavy recirculation flow with a ported shroud. Characteristics of the two operation modes are elucidated with test and CFD data.
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