They noted that the final geometry had a higher pressure ratio than the original unit, an improved surge margin, and a lower sensitivity to choke [18]. [PERSON] et al. present a comprehensive experimental and numerical study on the performance of a medium pressure ratio, shrouded, TB centrifugal compressor compared to a conventional compressor used commercially in China for turbocharging applications. They stated that in all tandem design cases, the surge point shifts towards lower mass flow rates. They stated that a maximum increase of 25 percent was observed in the study range. They emphasized that when a 20 percent reduction in inducer thickness was made, it performed better than conventional designs [19]. [PERSON] et al. used the CFD method to examine the specific aerodynamic performance of the TB. They said that compared to a single-row blade, a tandem row has the potential to produce a higher pressure ratio with lower losses over a relatively narrow operating range [20]. [PERSON] studied the effect of TB geometry on rotor and stage characteristics. He performed measurements at nine points all around the rotor, taking into account three different environmental inducer positions. He stated that the improvement achieved by the TB configuration in the rotor and stage characteristics was slight. Still, there were major differences in the flow field at the rear and outlet of the rotor [21]. [PERSON] et al. have mainly investigated experimentally for radial compressor aerodynamic stage optimization. They developed 3D Navier-Stokes calculations in the design to analyze the flow field. They said the inducer setting has a negligible effect on the rotor characteristics. They stated that the maximum rotor efficiency of 93.5% varies within less than 1% depending on different positions of the inducer [22]. [PERSON] et al. improved the compressor performance in highly loaded transonic radial compressors with a TBimpeller configuration with rule-surface inducer and exducer blades. Both the impeller and the diffuser achieved a compressor efficiency of 1.4% by reducing flow loss. They stated that using a forward sweep and negative lean design for the impeller, depending on the tandem impeller configuration, would increase efficiency by 2.11 percent compared to a conventional compressor. They said that diffuser performance can be improved with a negative lean design [23]. [PERSON] et al. first examined the flow characteristics of the conventional impeller to determine the causes of compressor instability. Then, they examined the TB impeller and showed the performance of different impellers. They particularly emphasized the variation in impeller tip leakage flow and impeller leading edge separation flow as the mechanism underlying the compressor operating range [24]. [PERSON] et al. described the mean-line procedure based on isentropic equations for the mixed flow case. They conducted rotor design evaluation studies for 3.5 kg/s mass flow by performing mean-line code and computational analysis based on Bezier curves. They stated that a higher hub load would result in a higher performance of the impeller with a lower tip leakage loss and regular flow at the outlet [25]. [PERSON] et al. computationally evaluated a supersonic mixed-flow compressor stage with a high-pressure ratio of 6:1 and an efficiency of 75.5%. They carried out the analysis by taking into account the effects of three-dimensionality, viscous flow, and compressibility. They described a new tandem design supersonic diffuser. They stated that this new design outperformed previous supersonic diffusion configurations by 20% in terms of efficiency [26]. [PERSON] et al. simulated a two-stage back-to-back radial compressor for refrigerant applications using computational fluid dynamics techniques at operating points close to the surge point. They confirmed the numerical results with experimental results [27]. [PERSON] et al. carried out CFD analysis on the optimization of low- and high-pressure radial compressors in a land-use MW-level gas turbine.