Tham khảo tài liệu 'gas turbines part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 14 Gas Turbines rotation 2 3 Fig. 9. Estimation of the number of compressor stages based on stage loading and mean circumpherential speed. - Choice of the stage degree of reaction possibly around work and flow coefficients and subsequent determination of the velocity triangles Fig. 9 - Mean radius basic cascade characteristics based in the Howell s method or Mellor charts see Emery et al. 1957 Horlock 1958 Mellor 1956 - Estimation of the diffusion performance based on acceptable Lieblein diffusion factors or De Haller numbers Fig. 10 see Lieblein 1960 - Calculation of the blade height at the stage exit based on acceptable blade aspect ratios - Stage stacking - Iteration - 2D approach. Result of stage stacking consists in the flowpath definition from which the distribution of stage parameters along the mean radii can be obtained. Because the stacking procedure is intrinsically iterative a loop is required to satisfy all the design objectives and constraints. As a first check the axial Mach distribution along the stages must be calculated and a value not exceeding is tolerated for both subsonic and transonic stages. By imposing such a constraint the values of stage area passage can be derived from the continuity equation Fig. 11 . Next the values of the hub-to-tip ratios must be defined. To this purpose it is worth recalling that such value comes from a trade-off between aerodynamic technological and economic constraints. For inlet stages values between and can be assigned while outlet stages often are given a higher value say from to in order not to increase the exit Mach number a condition which is detrimental for pneumatic combustor losses . Advances in Aerodynamic Design of Gas Turbines Compressors 15 Fig. 10. Lieblein s Diffusion Factor DLi level versus solidity for given flow and work coefficient left . Iso De Haller number in the q diagram right . Fig. 11. Corrected mass flow over stage area passage as function of the axial Mach .