# Influence of the Main Geometrical Parameters on the Design and Performance of Mixed Inflow Turbines
## 4 Conclusions  
The change in the complex of physical, gas-dynamic parameters and the efficiency of a mixed turbine depends on the ratio between the average diameter of the rotor at the inlet and the average diameter of the inlet of the exducer. A mathematical model for controlling the three-dimensional geometric dimensions of the blade was used. It was described by a Bezier polynomial of the fourth degree, with the definition of the meridian plane and the Cumberline profile. An iterative calculation was used to compare the characteristics of a rotor with a given ratio of diameters. The inlet and outlet blade angles were recalculated to keep the blade profile unchanged.  
It was found that--with a change in the exducer average root diameter and a fixed value of the average diameter of the rotor at the inlet--the output work and the total static isentropic efficiency were directly proportional to the ratio between the blade diameters. At the same time, the output work increased by 2.16%, along with a mass flow saving of 3.52%, which ultimately led to an increase in the isentropic efficiency by 2.15%. It should also be noted that the weight of the rotor was reduced by 31.98% while maintaining the size required to fit in the casing.  
In the second scenario, with a change in the average diameter at the inlet and a fixed value of the exducer average root diameter, the work at the exit and the total static isentropic efficiency was also directly proportional to the diameter ratio, but higher than in the first case, since they reached values of 3.31% and 2.34%, respectively. However, this was accompanied by an increase in the mass flow rate by 4.07% and an increase in the dimensions of the rotor by 6.63%.  
An analysis of the static temperature distribution, static pressure, and relative Mach number revealed dangerous low-pressure areas on the blade surface, accompanied by a high relative Mach number. The most rational choice would be to use the diameter ratio (R) in diapason from 1.5 to 1.55. The higher probability of blade surface erosion with a diameter ratio of 1.6 in both cases should be expected.  
In general, a more accurate determination of the economic efficiency of a turbine in the stages of design and while running is a complex multi-parameter problem that requires an optimization solution, which the authors plan to approach in future studies.  
Conceptualization, M.A.C. and Y.B.; methodology, M.A.C.; software, M.A.C., S.D., M.E. and Y.B.; validation, S.D., J.M. and J.Z.; formal analysis, S.D. and B.A.A.; investigation, M.A.C. and Y.B.; resources, Y.B. and M.A.C.; data curation, J.M.; writing--original draft preparation, M.A.C. and Y.B.; writing--review and editing, S.D. and J.M.; visualization, M.A.C., Y.B. and B.A.A.; supervision, M.E. and J.Z; project administration, M.A.C., Y.B. and J.M.; funding acquisition, J.M. All authors have read and agreed to the published version of the manuscript.  
The authors are grateful to FCT--Fundacao para a Ciencia e Tecnologia (Portugal)--who partially financially supported this work through the RD Units Project Scope: UIDP/04077/2020 and UIDB/04077/2020.  
Not applicable.  
The general approach has been partially developed within the research project \"Development of a methodology for optimal design and manufacture highly efficient, highly reliable turbomachines, taking into account various operating modes\" (State reg. No. 0121U107511).  
The authors declare no conflict of interest.