Weiyang Qiao

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 and numerical study on noise reduction mechanisms of the airfoil with serrated trailing edge

An acoustic experiment is conducted to investigate the noise reduction potential of trailing edge(TE) serrations on SD2030 airfoils in a normal test bed with high interference noise source. The Reynolds number is 3.1×10 5 and the serration geometry λ/h is 0.8. Noise sources located at test region are recognized clearly by use of a microphone array. With the application of serrated TE, trailing edge noise can be reduced efficiently. An average noise reduction of 3.3 dB is obtained. Large-Eddy Simulation and Ffowcs Willams & Hawkings analogy have been used to study noise reduction mechanisms of serrated TE. Serrated TE decreases the airfoil aerodynamic performance significantly. Spiral flows from pressure side to suction side surface have been formed around serrations and the pre-mixing proess influences the boundary layer characteristics on airfoil suction side, such as separation vortices. When ignore the monopole source and quadrupole source terms, spectra of airfoil self-noise are dominated by tones which are strongly related to separation vortices’ shedding process. By investigating pressure fluctuation distributions on airfoil surface, the most important noise source regions have been found. Serrated TE significantly decreases the pressure fluctuations correspond to peak frequencies in noise spectra. As a result, tones are reduced up to 16.3 dB. Although noise increases as mentioned by Gruber are found when fδ > 1.27, the overall noise reduction reaches 14 dB.

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.

An Investigation on the near-field turbulence and radiated sound for an airfoil with trailing edge serrations

This study concerns the mechanisms of the turbulence broadband noise reduction for an airfoil with the trailing edge serrations. An open jet wind tunnel test of a SD2030 airfoil (with 4% camber, 8.0% thickness) with and without the trailing edge serrations was comparatively investigated. The Dantec Dynamics 3D hot wire anemometry was used to measure the development and intensity of turbulence boundary layer and wake of the airfoil. The noise source identifying technique with the microphone array was used to focus on the trailing edge noise radiation. The far-field acoustics DSP and fluctuating turbulence spatiotemporal information around airfoil were compared for the airfoil with standard straight trailing-edge and the airfoil with the serrated trailing-edges. It is shown that trailing edge noise could be effectively reduced with the using of serrated trailing edge, and the magnitude and frequency range of airfoil trailing edge noise reduction are changed with the increase of main flow velocity. In the frequency range of 10 kHz, the largest noise reduction of sound pressure level is about 5 dB with the using of serrated trailing edge in the test flow speed range. The predicted results of Howe’s theoretical model are in a good agreement with the experiment results when St = ωδ/Uc ≈ 1.2. However, Howe’s theoretical model over-predicted noise reduction levels in high frequency while lowly-predicted the noise suppression in low frequency range. Near-field turbulence measurements show that serrated trailing edge could reduce turbulence strength on some directions and on some positions, and could also increase turbulence strength on other directions and on other positions. This result indicates that noise reduction mechanism with the serrated trailing edge is very complicated. Some special point around serrated trailing edge should be noted in the investigation of the noise reduction of airfoil with serrated trailing edge.

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

An experimental investigation on the near-field turbulence for an airfoil with trailing-edge serrations at different angles of attack

The ability to fly silently of most owl species has long been a source of inspiration for finding solutions for quieter aircraft and turbo machinery. This study concerns the mechanisms of the turbulent broadband noise reduction for an airfoil with the trailing edge serrations while the angles of attack varies from + 5° to Ő5°. The turbulence spatio-temporal information are measured with 3D hot-wire. The experiment is carried out in the Northwestern Polytechnical University low speed open jet wind tunnel on the SD2030 airfoil. λ/h = 0.2. It is showed the spreading rate of the wake and the decay rate of the wake centerline velocity deficit increased with serrated edge compared to the straight edge, and the three components of velocity changed differently with serrated trailing edge while the angle of attack was changed. It is also found that the turbulence peak occurs further from the airfoil surface in the presence of the serrations, and the serrations widened the mix area which allowed the flow mixed toge...

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.

An Experimental Investigation on the near-field turbulence for an airfoil with trailing-edge serrations by using 3-D hot-wire

The ability to fly silently of most owl species has long been a source of inspiration for finding solutions for quieter aircraft and turbomachinery. This study concerns the mechanisms of the turbulence for an airfoil with trailing-edge serrations. the turbulence spatio-temporal information are measured with 3D hot-wire. The experiment is carried out in the Northwestern Polytechnical University low speed open jet wind tunnel on the SD2030 airfoil. Mach numbers range up to 0.3,with the Reynolds numbers from 1.9e+4 to 2.6e+5, the angle of attack α at 0o, the sawtooth of λ/h = 0.2.The individual trailing-edge serrations tips and valleys could be seen in the wake region. It is showed the spreading rate of the wake and the decay rate of the wake centerline velocity deficit increased with serrated edge compared to the straight edge. It is also found that the turbulence peak occurs further from the airfoil surface in the presence of the serrations, and the serrations generate additional horseshoe vortices shed in...