The Experimental Study On Influence Of Aeration Concentration On Water Noise

In hydraulic engineering,the overflow and underflow are commonly used energy dissipation methods.In bucket energy dissipation,water flows from bucket into downstream stilling basin,which collides with downstream water body.Air will be mixed near the incident point to produce huge rolling,and water noise will be generated.In underflow energy dissipation,water discharged from overflow weir to stilling basin will mix with air and produce water noise.Water noise is not only related to the turbulence of water flow,but also to the amount of gas mixed into the water flow.In order to solve the mechanism of water noise,the influence of aeration concentration on water noise was also explored.Starting from the aeration caused by droplets and beams falling to the water surface,the test conditions of droplets,overflow and underflow are set up to analyze the distribution of aeration concentration in each working condition.At the same time,the spectrum of water noise is analyzed,and the influence of aeration concentration on water noise under different working conditions is obtained.The main factors affecting water noise are obtained.The dimensionless number of influencing factors and water noise are introduced for regression analysis,and water noise is obtained.Regression equation of noise with respect to Froude number and aeration concentration.The experiment uses high-speed camera to observe images of water droplets enter the water.By changing the droplet size,droplet dropping height and droplet number,the experiment is carried out under different working conditions.The distribution of aeration concentration is obtained by using photoshop image processing software and CAD mapping software to post-process the images under different working conditions.Using CQ6-2005 resistance aeration concentration meter,the distribution of aeration concentration in stilling pool under bottom flow from overflow to plunge pool was measured,and the distribution law of aeration concentration in plunge pool and stilling pool under different working conditions was obtained.The velocity of water cushion pool and power pool was measured by using a propeller flow meter,and the flow field distribution under different working conditions was obtained.The main rules are as follows: the contact area between droplets and liquid surface increases with the increase of droplet size,the turbulent energy transformed from lagging kinetic energy to liquid surface increases,and the aeration concentration decreases.The velocity gradient in the plunge pool increases with the increase of flow rate in the flip flow test.The flow rate,the falling height and the plunge pool in the plunge pool increase with the increase of flow rate.In the test of underflow,the discharge and the height of stilling pool tail sill have great influence on the distribution of flow field and aeration concentration in stilling pool.The discharge affects the velocity gradient in stilling pool,and the height of stilling pool tail sill affects the position of aeration after the weir.Using Zonic Book professional vibration and noise analysis system and AWA6228 +multifunctional sound level meter,water droplets fall,water flow is projected into plunge pooland bottom stilling pool to collect water noise.According to 1/3 octave frequency range,water noise is divided into low frequency,medium frequency and high frequency.The fluctuating radiation noise produced by turbulence of water flow is low frequency,and the frequency range is 20-500 Hz.During droplet falling,gas is mixed into bubbles to form bubbles,and the frequency of water noise produced by bubble bursting is medium-high frequency.The frequency of the first bubbles is high frequency,ranging from 2000-8000 Hz,while the water noise produced by the second bubbles is medium-high frequency.Intermediate frequency,frequency range is 500-2000 Hz.According to the analysis of the frequency spectrum,the following main rules are obtained: the sound pressure level of water noise produced by droplet falling is related to the concentration of aeration and turbulence of liquid level,and the frequency of water noise is mostly in high frequency range;the flow noise in parallel direction of water cushion pool tends to decrease in the flow diversion test,and the flow noise radiated by air bubbles breaking noise and water pulsation noise within a certain distance from the falling point In the bottom flow test,the flow noise in stilling basin is composed of two parts: bubble burst noise and turbulent noise.The frequency range is high,medium and low frequency,but mainly high frequency.The water noise in the stilling basin without aeration is mainly pulsating radiation noise,the main frequency range is concentrated in low frequency,and the tone of the noise is low.Through the spectrum analysis of the collected water noise data,the main factors of water noise under various working conditions are determined,and the main factors of water noise are the turbulence of water flow and aeration concentration.The Froude number represents the turbulence of water flow,and the aeration concentration represents the incorporation of gas in the process of water flow falling.The dimensionless Froude number Fr and the aeration concentration C are introduced to analyze the dimensionless and water noise.The regression equation of water noise with respect to dimensionless number Froude and aeration concentration C is obtained:L_P=63.28+0.80Fr+0.54C...