Numerical Simulation And Noise Reduction Technology Research Of Cruise Ship Air Conditioning And Ventilation System

The air conditioning and ventilation pipe flow noise of large cruise ships is a major factor affecting the comfort of ship cabins.Air-conditioning noise is mainly divided into two major noise sources: air-conditioning unit noise and ventilation pipe flow noise.Due to the advancement of technology,the noise level of air-conditioning machinery and equipment,such as compressors,has been greatly optimized,and air-conditioning ventilation pipe flow noise has become the main noise source of the air-conditioning system.The flow noise of airconditioning piping system mainly arises from the pipe mutation structure.The research focus of this thesis is as follows:Firstly,the flow field and sound field of the elbow and the tee branch pipe are studied,and the mechanism of pipeline flow noise is proved: the pulsating pressure acting on the wall of the pipeline generated by the internal vortex movement of the pipeline.And the surface acoustic field of the elbow and tee branch pipe shows dipole distribution law,and the flow noise energy is mainly concentrated in the low frequency part below 200 Hz.The strongest part of the dipole sound source of the elbow and tee branch are located in the position where the velocity gradient changes dramatically,the elbow is located in the elbow,the tee is located in the corner of the main pipe and the branch,and the main pipe outlet flow noise is larger than the branch outlet by 8d B(A).The sound pressure level of the flow noise decreases with the increase of frequency and belongs to the broadband noise.Secondly study the effect of different parameters on the pipeline outlet flow noise,the study shows that the flow velocity is the most important factor affecting the pipeline flow noise,the entrance flow velocity increases,the sound pressure level increases at the monitoring point of the pipe mouth,and the flow velocity of 14m/s reaches the peak value.When the structural parameters of the pipe remain unchanged,with different inlet flow velocities,the spectral change trend of the sound pressure level at the outlet monitoring point of the ventilation pipe is similar,and the different flow velocities have no effect on the flow noise spectrum and peak characteristics,and the sound pressure level of the pipe flow noise decreases with the increase of the frequency.The outlet flow noise level of the tee branch pipe is affected by the main branch pipe flow rate ratio,with the gradual decrease of the branch pipe flow rate ratio,the outlet flow noise decreases first,and then remains basically unchanged,and the outlet flow noise is approximately the same for 35% and 25% flow rate ratios.The cabin air conditioning and ventilation system is established,and its noise distribution as well as the influencing factors are analyzed and studied,and the outlet flow noise is 53 d B(A)at most.Then study the noise reduction measures of pipeline flow noise,the elbow of the elbow built-in deflector sheet and the main pipe of the tee and the branch pipe of the corner of the transition structure.Optimize the flow field in the pipeline to reduce the level of outlet flow noise,in the absence of a deflector sheet,the side near the inner wall of the elbow of the elbow formed more eddy currents,generating flow noise.When the straight deflector sheet was added,the pressure difference at the outer wall of the elbow of the elbow was further increased,more vortices were formed,and the sound pressure level of the exit flow noise was instead increased by 3 d B(A).The addition of curved flow guide can effectively regulate the flow field inside the pipe,reduce the turbulence intensity and pressure pulsation level at the elbow of the elbow,reduce the number and size of vortices at the elbow of the elbow,and reduce the pipeline flow noise by 6d B(A),and with the increase of the curved flow guide,the lower the sound pressure level of the outlet flow noise.Different positions of the elbow pipe elbow pipe with the addition of arc-shaped guide vane can reduce the ventilation pipe flow noise,the guide vane installed throughout the elbow pipe elbow flow noise reduced by 4d B(A).Increase the transition structure can effectively reduce the flow noise at the outlet of the tee branch,through the arc-shaped transition structure,reduce the level of turbulence inside the pipe,weakening the pressure pulsation inside the pipe,three different angles of inclination type structure,30 ° inclination of the best results.The arc-shaped transition structure has the best optimization effect,and the outlet flow noise is reduced by 14 d B(A).The arc-shaped structure can effectively reduce the turbulence and pressure pulsation near the branch pipe.Finally,the test rig of the pipeline components is designed to investigate the flow noise law through the test method,which shows that the flow noise belongs to the broadband noise and the flow velocity is the main influencing factor,and the comparison with the simulation results proves the correctness of the simulation method.