It is ascertained that optimization of bladed rows clocking positions is an effective tool for control of bladed rows unsteady interaction in a multistage turbo machine and could be used equally in refinement and in compressor design stages [1–3].
Up to now the clocking effect issue of highly loaded rotors in compressor stages was not investigated due to growing design complexity of the experimental facility. The issue concerning tip clearances value influence on rotor and stator clocking effects was not studied as well.
In the frames of this work a two stage compressor (HPC2 with the designed pressure ratio π* = 3.7 ) with a unique design was developed to investigate influence of tip clearance values on rotor and stator clocking effect. In order to realize the clocking effect the HPC2 compressor has the following parameters: numbers of stator blades are identical for all stators and equal to ZIGV = ZS1 = ZS2 = 68; number of R1 blades is two times less than of R2: ZR2 = 56, ZR1 = 28.
This work studies HPC2 compressor performances at 3 R1 and R2 tip clearances — dtip = 0.5mm – nominal clearance, 0.75mm, and 1.0 mm – increased clearance. Clocking effects of stators and rotors are tested at 0.5mm and 0.75mm tip clearances for two values of corrected rotational speeds — n = 0.7 and 0.88. As shown, variations in max. efficiency from maximum to minimum when changing the clocking position both the stator and the rotor reach Δη*ad≈0.008÷0.012 at dtip = 0.5mm or Δη*ad≈0.007÷0.008 at dtip = 0.75mm.
For more detailed analysis of the tip clearance influence on rotor and stator clocking effect a mathematical model of HPC2 was developed on base of through flow 3D viscous unsteady flow computations in the HPC2 compressor rows [3–4]. In full unsteady statement the calculation domain includes the following number of blade rows: IGV = 2, R1 = 1, S1 = 2, R2 = 2; S2 = 2.