Physics Of Airfoil Clocking In A High-Speed Axial Compressor

Abstract

Axial compressors have inherently unsteady flow fields because of relative motion between rotor and stator airfoils. This relative motion leads to viscous and in viscid (potential) interactions between blade rows. As the number of stages increases in a turbomachine, the buildup of converted wakes can lead to progressively more complex wake/wake and wake/airfoil interactions. Variations in the relative circumferential positions of stators or rotors can change these interactions, leading to different unsteady forcing functions on airfoils and different compressor efficiencies. In addition, as the Mach number increases the interaction between blade rows can be intensified due to potential effects. In the current study an unsteady, quasi-three-dimensional Navier-Stokes analysis has been used to investigate the unsteady aerodynamics of stator clocking in a 1-1/2 stage compressor, typical of back stages used in high-pressure compressors of advanced commercial jet engines. The effects of turbulence have been modeled with both algebraic and two-equation models. The results presented include steady and unsteady surface pressures, efficiencies, boundary layer quantities and turbulence quantities.The main contribution of the current work has been to show that airfoil clocking can produce significant performance variations at the Mach numbers associated with an engine operating environment In addition, the growth of turbulence has been quantified to aid in the development of models for the multi-stage steady analyses used in design systems. The effects of airfoil clocking (or indexing) on turbine performance have been investigated byHuber et al. (1995), Griffin et cd. (1995) and Dorney and Sharma (1996). The studies showed changes in efficiency on the order of 0.5\% as the stators were

Effect of clocking on unsteady rotor blade loading in a low-speed axial compressor at design and off-design operating conditions

“…The numerical results in a three-stage low-pressure turbine of Arnone et al [2] show similar trends as reported by Dorney et al [1]. The effect of full-clocking (clocking of both the rotor and stator blade rows) on the maximal efficiency variation was estimated to be 0.7 per cent.…”

“…In the past several decades, many researchers experimentally and numerically investigated the effect of clocking on the efficiency. Dorney et al [1] carried out the investigation of clocking on performance in a 1.5-stage compressor. The numerical results show that the improvement in efficiency with stator clocking is 0.6-0.7 per cent.…”

Effect of Clocking on Compressor Noise Generation

“…That the relation of clocking position and efficiency has a sinusoidal shape with typical variations within the range of 0.2 up to 2.7%, [13][14][15] is nowadays commonly accepted. [16][17][18] However, controversial findings have been reported regarding the optimal impingement location of the upstream stator wake on the downstream stator vane to maximise efficiency. For example, Gundy-Burlet et al 19 and Dorney et al 17 concluded that the optimal combination of high efficiency occurred when the upstream stator wake was convected along the pressure surface of the downstream stator.…”

“…[16][17][18] However, controversial findings have been reported regarding the optimal impingement location of the upstream stator wake on the downstream stator vane to maximise efficiency. For example, Gundy-Burlet et al 19 and Dorney et al 17 concluded that the optimal combination of high efficiency occurred when the upstream stator wake was convected along the pressure surface of the downstream stator. On the contrary, He et al, 20 Hongyan et al, 16 Key et al, 18 and Fruth et al 21 observed maximum efficiency when the first stage/rotor wakes impinge on the leading edges of the second-stage rotor/stator, respectively.…”

Clocking effects on aerodynamics of a gas turbine low pressure axial turbine, part 2: Unsteady simulation

“…5 Quasi 3-D unsteady analyses of a 1.5 stage compressor, executed by Dorney et al, have shown that stator clocking can result in efficiency gain of 0.6-0.7%. 6 They concluded that this advantage is mainly due to the modification of the wake flow trajectory through the optimum clocking, which result in reduction in the existing losses. Cizmas and Dorney through their investigations on a 3-stage axial turbine concluded that clocking of the second stage blades is more efficient than that of the third stage.…”