Axial Spacing Effects on Rotor-Rotor Interaction Noise and Vibration in a Contra-Rotating Fan

Abstract

Because of the potential technical advantages, the contra-rotation technology has become a renewed interest in aviation and other applications. Contra-rotation increases efficiency in comparison with the single-rotor design, but this advantage is not fully harnessed. The axial spacing of two-stage contra-rotating blade rows has a significant impact on a contra-rotating fan/compressor. The results show that with a contra-rotation pattern, the strong unsteadiness of two-stage rotors is caused by the rotor-rotor interaction. The unsteadiness of rotor 1 is caused by the potential disturbance, and the upstream wake leads to the strong unsteadiness of rotor 2. With the increase of axial spacing, the rotor-rotor interaction is weakened, while unsteady features of two-stage rotor blades tend to be consistent. The acoustic and vibration effects of axial spacing are studied. It is found that the axial spacing has great influence of aerodynamic noise. The mean value of sound pressure level decreases by 17.2 dB in total when the axial spacing increased to 1.1 chord from 0.3 chord. For the accuracy of calculation, the scattering effect of the casing wall should be considered in the prediction of the noise. The axial spacing does not have obvious effects on the natural frequencies of the two-stage rotor blades but has certain effect on blade deformation.

Psychoacoustic modelling of rotor noise

“…For the specific case of contra-rotating systems, Luan et al (Luan et al, 2019) found a strong relationship between the axial rotor spacing and OASPL, with a general trend indicating that OASPL decreases with increase in axial spacing. suggested an optimal rotor axial separation distance (relative to the blade diameter) between 0.2 and 0.4.…”

Experimental study of the parameter effects on the flow and noise characteristics for a contra-rotating axial fan

“…Ravelet et al [16] designed three contra-rotating stages with different rotational speed ratios, mean stagger angles of blades and repartitions of blade loads between two rotors to study the global characteristics and the unsteady features of the flow. Luan et al [17] studied the acoustic and vibration effects of the axial spacing based on the experimental analysis and numerical calculation. Ai et al [18] performed experimental studies on the rotational speed matching of two rotors and analyzed its impact on the stable margin and efficient working range.…”

The Effect of Load Control on the Performance of Contra-Rotating Fans

“…Following this, they studied the relationship between different axial gaps and the unsteady influence on the CRF blade boundary layers [6], finding that, with the increment of the axial gap, the inhibition for separation in the RR boundary layers was weakened, since the rotor-rotor interaction of the CRF was weakened and the blade deformed. However, this had little effect on the radiation noise [7]. Ravelet et al [8] redistributed the loads of a CRF load by applying three sets of speed ratios.…”