Multi-Source Generation Mechanisms for Low Frequency Noise Induced by Flood Discharge and Energy Dissipation from a High Dam with a Ski-Jump Type Spillway

Abstract

As excess water is discharged from a high dam, low frequency noise (air pulsation lower than 10 Hz, LFN) is generated and propagated in the surrounding areas, causing environmental hazards such as the vibration of windows and doors and the discomfort of local residents. To study the generation mechanisms and key influencing factors of LFN induced by flood discharge and energy dissipation from a high dam with a ski-jump type spillway, detailed prototype observations and analyses of LFN are carried out. The discharge flow field is simulated and analyzed using a gas-liquid turbulent flow model. The acoustic response characteristics of the air cavity, which is formed between the discharge nappe and dam body, are analyzed using an acoustic numerical model. The multi-sources generation mechanisms are first proposed basing on the prototype observation results, vortex sound model, turbulent flow model and acoustic numerical model. Two kinds of sources of LFN are studied. One comes from the energy dissipation of submerged jets in the plunge pool, the other comes from nappe-cavity coupled vibration. The results of the analyses reveal that the submerged jets in the plunge pool only contribute to an on-site LFN energy of 0–1.0 Hz, and the strong shear layers around the high-velocity submerged jets and wall jet development areas are the main acoustic source regions of LFN in the plunge pool. In addition, the nappe-cavity coupled vibration, which is induced when the discharge nappe vibrates with close frequency to the model frequency of the cavity, can induce on-site LFN energy with wider frequency spectrum energy within 0–4.0 Hz. By contrast, the contribution degrees to LFN energy from two acoustic sources are almost same, while the contribution degree from nappe-cavity coupled vibration is slightly higher.

Research on the Optimization Design of Abnormal Flip Buckets

“…e path and location of the high-speed water flow significantly influence the environment. Regarding the size of the flip bucket, it can be concluded that the water flow direction can be changed by changing the model size of the flip bucket or by splitting one flow into two so as to prevent landslides due to a scouring effect, thereby protecting the environment and the ecosystem from damage [19,[39][40][41][42].…”

“…e standard k − ε model is the simplest complete twoequation turbulence model, which has wide applicability, is economical, and achieves reasonable accuracy. It is extensively applied in the industrial flow field and in heat-exchange simulations [18,19].…”

“…e movement range of the ski-jump flow in the air was defined as a constraint, and a reasonable size range of the flip bucket was determined according to that in the experimental model, which was viewed as another constraint. e optimal solution could be found within this range [19,25].…”

A Brief Theoretical Analysis on the Ventilation Characteristics of the Multi-Intake-Well Air Supply System in a Spillway Tunnel

“…The rough results obtained in Step 1 are interpolated linearly for each section along the flow direction. Then, Equations (11)(12)(13)(14) are added to obtain the accurate air velocity and air pressure along the flow direction with further iteration.…”

“…If these wells are not designed sufficiently large and cannot meet the air demands, extreme negative air pressures will occur. Negative pressure can increase the possibility of cavitation and cause many secondary disasters, such as structure vibration [9,10] and low frequency noise [11,12]. It is clear that the prediction of the air demand of a spillway tunnel is fundamental work for the reliability of project design.…”