Liangfeng Wang

The Effect of Wavy Leading Edge on Low Speed Turbine Cascade Aerodynamic and Acoustic Performance

LES and acoustic analogy are performed to investigate the effect of wavy leading edge on a linear low pressure turbine cascade aerodynamic performance and the turbulence cascade interaction noise. One straight leading edge cascade and two different wavy leading edge cascades are studied. In each case a rod with a diameter of 2.05mm is placed upstream of the cascade to produce wake which will then interact with the cascade leading edge. Results show that the wavy leading edge can reduce the turbulence cascade interaction noise peak by up to about 6∼8dB in narrow band and attenuate interaction broadband noise by about 3dB in the frequency range below 4000Hz. However, wavy leading edge can lead to a self noise increase in some frequency and increase cascade total pressure loss. Wavy leading edge can change the flow field near the leading edge while the further downstream flow field is altered only a little. The mechanism of noise reduction is also investigated. It is shown that wavy leading edge can reduce blade surface pressure fluctuation near the leading edge. In addition, the spatial-temporal correlation coefficient of pressure fluctuation near the blade leading edge is also decreased. These factors may work jointly and contribute to the final noise reduction.Copyright

Experimental study on airfoil noise reduction with trailing edge serrations under various incoming flow conditions

An experimental investigation of airfoil trailing edge noise reduction at Reynolds number of 2.76 × 105–4.31 × 105 was conducted within the attack angle of −10°–10° using the trailing edge serrations. An unequally spaced linear microphone array was used to identify the sound source around the airfoil. The results show that trailing edge serrations can effectively reduce airfoil trailing edge noise under various incoming flow conditions. The noise reduction effect varies with incoming flow condition and a maximum noise reduction of about 6 dB is observed. The noise reduction effect is more obvious under negative attack angles. For a specified serration configuration, there is an optimal velocity range for noise reduction.

Numerical Investigation of Wavy Leading Edges on Rod–Airfoil Interaction Noise

A hybrid computational aeroacoustics method is applied to investigate the effect of wavy leading edges on rod–airfoil interaction noise. The flow field is solved by an incompressible large-eddy sim...

Broadband sound power determination with modal decomposition

For the assessment and improvement of noise reduction concepts and the validation of broadband sound power determination in flow ducts, the detailed knowledge of the in-duct acoustic mode spectrum and subsequent broadband noise sources separation is of great interest. A broadband noise mode analysis method was experimentally applied on broadband sound fields at 4 operation points, which were generated by means of a low speed fan test rig. Two axial sensor arrays were mounted wall-flush upstream of the fan. Measurements were made at operating conditions from 40% to 100% rotor design speed. On the whole, broadband mode waves transmitted in the flow direction is 2dB higher than against the flow direction. Mode amplitude results show that the mode decomposition results strongly depend on the chosen reference microphone. Sound power becomes higher as the speed increases. The deviation of results in and against flow directions calculated with different reference microphones is 4dB at all the operation points except for 40% design speed. A deviation of almost 10dB appears in broadband sound power results with different reference microphone in the frequency range, much higher than the results of previous experiment. The method is more accurate if it considers the phenomenon that mode waves in turbo-machinery are partly correlated with each other.© 2015 ASME

Different experimental methods for the measurement of broadband noise sources in ducts

Aeroengine broadband fan noise is a major contributor to the community noise exposure from aircraft. It is currently believed that the dominant broadband noise mechanisms are due to interaction of turbulent wake from the rotor with the stator, and interaction of the turbulent boundary layers on the rotor blades with the trailing edge. Two different methods are presented that enable the separation of different broadband noise sources in turbomachinery ducts, one with respect to modal decomposition developed by DLR, and the other with focused beamformer technique developed in university of Southampton. Different measurement mechanisms are displayed to explain the merits, faults, and requirements.

An Investigation of the Inlet and Exhaust Noise Sources of Turbofan Using Linear Microphone Array

This paper presents noise source location results for a turbofan engine with the bypass ratio of 2.4 obtained from engine static test, in which the engine was installed on aircraft. Source location data from this test was used to develop engine inlet sound absorbing liner and to design the aircraft fuselage sound insulation device. A linear array of 32 microphones was used in this program to determine the jet noise source distribution for the exhaust and the fan noise from inlet. Aeroacoustic beamforming with the delay and sum scheme in time domain was modified using the DAMAS deconvolution algorithm. Data were obtained for the engine power setting which is from 60% to 90% of the design power. It was shown that the noise source was one centralized source from engine inlet, and the location of this centralized source was almost immobile. The multiple sources were also detected in exhaust noise, and the location of distributed source was moving backward with the increase of engine power(that is with the increase of jet velocity). The haymow spectrum was observed for the exhaust noise, and obvious tone noise was observed in the spectrum of inlet noise.