Experimental Study of a Novel Centrifugal Compressor With Two Successive and Independent Rotors

This study deals with a low pressure-ratio centrifugal compressor consisting of two counter-rotating rotors called a counter-rotating centrifugal compressor (CRCC). The design method based on the loss model was presented to determine the geometric parameters of the two counter-rotating rotors. According to this method, the rotor of a selected single rotor centrifugal compressor (SRCC) has been redesigned into two counter-rotating rotors (upstream and downstream rotors) by choosing the value of meridional length ratio (LR). The meridional view, the volute shape, and the operating parameters of SRCC are preserved during the design process. In a first step, the counter-rotating mode at a constant rotor speed of 11k rpm has been carried out. The overall characteristics of CRCC are compared to those of SRCC. In a second step, the map characteristic of CRCC is established for seven speed ratios. The results show that CRCC increases up to 4.6% for the pressure ratio and 3.5% for the efficiency compared to SRCC at the same tip-speed. In addition, CRCC can operate at a lower tip-speed by about $2k rpm$ to produce the same characteristics as SRCC, with better efficiency over a wide range of flow rates. However, the surge margin of the CRCC is shifted to higher flow rates. This disadvantage of the CRCC was solved by choosing the adequate pair of the rotational speeds of the two rotors that will be presented in other publication.