Conclusions

A third-order-accurate upwind-biased thin-layer Navier-Stokes zonal code (STAGE-2) has been used to study the unsteady flow in a multiple-stage compressor. In particular, the effects of stator clocking and varying axial gaps on the unsteady flow within a 2-1/2 stage compressor have been investigated. Variations in efficiency, force amplitudes and frequencies were found to be functions of the relative position of the clocked airfoil and convected wake groupings. The following general conclusions can be drawn from the simulations:

• Properly clocked compressors can gain almost a point in efficiency under ideal circumstances.
• Higher efficiencies occur when
  • the wake of stator-1 convects along the pressure side of the stator-2 passage
  • the axial gap is increased
  • the unsteadiness is linear in nature (vortical motion of upstream wakes is mixed out)
• Lower efficiencies occur when
  • the wake of stator-1 impacts the leading edge of and/or convects along the suction side of stator-2
  • the axial gap is decreased
  • the unsteadiness is non-linear in nature

Current efforts are focusing on two additional aspects of airfoil clocking:

• The effects of rotor clocking, in combination with stator clocking, on airfoil efficiency.
• The feasibility of clocking airfoils in compressor stages with non-integer blade count ratios