The Effect of Airfoil Clocking on Efficiency and Noise of Low Pressure Turbines

Abstract

The effect of airfoil clocking (stator-stator interaction) on efficiency and noise of low pressure turbines (LPT) was investigated experimentally in a multistage turbine high-speed rig. The rig consisted of three stages of a state-of-the-art LPT. The stages were characterized by a very high wall-slope angle, reverse cut-off design, very high lift, and very high aspect ratio airfoils. The rig had identical blade count for the second and third stators. The circumferential position of the second stator was individually adjusted with respect to the third stator. Eight different circumferential clocking locations over one pitch were back-to-back tested. The rig was heavily instrumented with miniature five hole probes, hot wires, hot films, total pressure and temperature rakes, pressure tappings on the airfoil surface, two array of Kulites in a rotatory module, etc. Every clocking location was tested with the same instrumentation and at the same operating conditions with the intention of determining the impact of the clocking on the overall efficiency and noise. Due to the large amount of data, the results of this test will be reported in several papers. The present paper contains the impact on the overall efficiency, radial traverses, static pressure fields on the airfoils and averaged sound pressure levels in the duct. The comparison of the results suggests that the efficiency is weakly affected by clocking; however the effect on noise is noticeable for some acoustic tones at certain operating conditions.

Turbine Tone Noise Prediction in High Speed Turbines Using a Linearized CFD Solver: Comparison with Measurements

“…Mode 1B1-1V1-V2 is also generated by the interaction of the fourth harmonic (Figure 7b), thus these mechanisms are able to be clocked. Total energy associated to this mode depends on the relative position between vane 1 and vane 2 as argued in Vazquez et al [19]. Figure 7c and d shows the acoustic modes that can be generated by the interaction of the 2 nd and 5 th harmonic with rotor 1 and vane 2.…”

Numerical investigationof clocking effect of impellerson a multistage pump

“…The clocking effect is a phenomenon that the performance of the turbo machinery can be adjusted by changing the circumferential position of rotors or stators. This theory was firstly found in compressors (Walker, 1972), and it then successively improved the performance of gas turbines, both in decreasing noise and increasing working stability (Key et al, 2010;Lu et al, 2011;Vázquez et al, 2013). With the development of technology, this theory came to pumps.…”

Blade stacking and clocking effects in two-stage high-pressure axial turbine

“…Cizmas and Dorney (1998) investigated the effects of full clocking (stator and rotor are simultaneously clocked) in a three-stage steam turbine and noticed that the clocking of the second stage leads to larger efficiency variations than the third stage and the benefit from the rotor blade-row clocking is approximately twice that of stator (vane) clocking. Further works on the clocking effect in axial turbines were produced in the case of 1.5 stage (Reinmöller et al, 2001;Charles et al, 2004;Jongil et al, 2006;Schennach et al, 2006;Billiard et al, 2007), two stage (Dieter et al, 2005;Krysinski et al, 2005;Blaszczak, 2007) and three stage (Arnone et al, 2001;Vázquez et al, 2013). According to the literature larger efficiency benefits can be obtained when the blade count ratio of the clocked rows is close to one (Arnone et al, 2003).…”