Cavity Noise Reduction Research Articles

Cavity noise reduction of a high-speed train pantograph through jet parameter optimization

The effect of aerodynamic noise from high-speed trains on residents living near railway lines is a critical issue. The pantograph cavity is considered to be a major source of aerodynamic noise. To address this problem, this study proposes the application of jetting at the leading edge of the cavity, directly targeting noise reduction at its source. The large eddy simulation approach is used for flow calculations, and the Ffowcs Williams and Hawkings aeroacoustic analogy is adopted for far-field acoustic predictions. Orthogonal designs and the backpropagation algorithm optimized by the genetic algorithm (BP-GA) is used to explore the effects of jetting factors on noise and identify the optimal parameters. Orthogonal design analysis shows that the most influential among the factors is jet orifice diameter, followed by jet velocity and jet angle. The use of the BP-GA algorithm for optimization reveals that the optimal jet parameters are jet velocity of 118.28 m/s, jet angle of 3.17°, and jet orifice diameter of 76.74 mm. The algorithm predicts a minimum noise level of 91.04 dB, which is close to the simulated noise level of 90.74 dB. The jetting process achieves a maximum noise reduction of 4 dB. Results demonstrate that the proposed method for cavity leading edge jetting effectively reduces turbulent kinetic energy and horseshoe-shaped vortices in the cavity, leading to noise reduction. This method also minimizes the effects of aerodynamic noise on distant areas, such as waiting areas and residential buildings. This work provides a theoretical basis for increasing high-speed train speeds.

Control effect on deep cavity noise by slanted walls at low Mach numbers

Experimental and numerical studies on noise radiated by flow past a rectangular two-dimensional deep cavity with passive control are conducted to research the mechanism of cavity noise reduction at low Mach numbers. The clean cavity has a depth-to-length ratio of 1.5 and a width-to-length ratio of 3. The passive control method is used by slanting the front and rear walls. Using acoustic microphones, both the surface noise and far-field noise are tested in an aeroacoustic wind tunnel. It is observed that the slanted rear wall can suppress the noise effectively, but for the slanted front wall, the tones will be enhanced at some velocities. Numerical simulation is conducted to reveal the mechanism. The results reveal that the slanted rear wall can reflect the unsteadiness back to the shear layer and break up the vortices in it. These vortexes will diffuse after impacting the rear wall and prevent the perturbation from moving deeper, which brings a stable flow field into the cavity. As for the slanted front wall, the vortices will be enlarged and become accelerated in the shear layer, which makes the impingement of it to the rear wall more intense, thus leading to an increase in the noise level.

Aeroacoustic Characteristics of Cavity and Effect Study of Mesh on Noise Suppression

To explore the noise suppression effect of mesh on cavity, the wind tunnel experiment is carried out based on the analysis of clean cavity flow characteristics. The meshes are arranged both in the cavity and at the leading edge of the cavity. Through the analysis of pressure distribution on the cavity bottom and the noise spectrum monitored at front and rear walls respectively, noise suppression effects of mesh programs relative to the clean cavity and changes in the flow field are studied, the results show that the mesh inside the cavity has a better noise reduction effect. The work in this paper provides an effective way for cavity noise reduction.

Concurrent mechatronic design approach for active control of cavity noise

Active control is a potential solution to many noise and vibration problems for improving the low-frequency performance. Cavity noise reduction as encountered for instance in aircraft cabins and vehicle interiors is a typical example. However, the conventional design of these active solutions may lead to suboptimal products, since the interaction between the vibro-acoustic plant dynamics and control dynamics is usually not considered. A proper way to design such active systems would be considering control and plant parameters concurrently. To cope with this approach, a methodology to derive a fully coupled mechatronic model that deals with both the vibro-acoustic plant dynamics as well as the control parameters is proposed. The inclusion of sensor and actuator models is investigated, since it contributes to the model accuracy as it can confer frequency, phase or amplitude limitations to the control performance. The proposed methodology provides a reduced state-space model derived from a fully coupled vibro-acoustic finite element model. Experimental data on a vibro-acoustic vehicle cabin mock-up are used to validate the model reduction procedure. Regarding noise reduction, optimization results are presented considering both vibro-acoustic plant features, such as thicknesses, and control parameters, such as sensor and actuator placement and control gains. A collocated sensor/actuator pair is considered in a velocity feedback control strategy. The benefits of a concurrent mechatronic design when dealing with active structural–acoustic control solutions are addressed, illustrated and experimentally validated.