Research On The Cavitation Characteristics And Performance Test Of Deep-Water Cage Netting Cleaning Equipment

Affected by factors such as the squeeze of nearshore aquaculture space,overexploitation of natural resources,backward equipment and technology,unreasonable development layout and so on,it is the inevitable trend of fishery development to expand the new mode of deep-sea aquaculture space development.Compared with the traditional aquaculture cage,deep-water aquaculture cage is more advanced in productivity,which provides equipment and technical support for fishery to expand culture space,and also achieves good ecological and economic benefits.In deep-water aquaculture cage,marine fouling organisms multiply on the surface of the netting due to the long-term immersion of the netting in sea,which not only leads to the great increase in the weight of the netting,which makes it difficult to replace the netting,but also leads to the poor exchange of water inside and outside the cage,which leads to the lack of oxygen in the cage and affects the normal growth of fish.Cage netting cleaning is one of the key technical problems to be solved urgently in the management of deep-water cage aquaculture.The cavitation jet netting cleaning equipment can realize the direct cleaning of underwater netting,which is more efficient,economical and practical than traditional manual cleaning methods.This research is mainly based on the cavitation jet netting cleaning equipment independently designed and developed by the research group.The hydrodynamic characteristics of unsubmerged jet and submerged jet are studied by numerical simulation.The erosion mechanism of cavitation jet cavitation bubbles collapse is revealed through the impact test of cavitation jet on aluminum alloy template.Based on the principle of fluid mechanics,the numerical simulation study on the mechanical characteristics of the internal flow field of the nozzle with the right-angle L-shaped and circular-arc L-shaped channels structures of the diversion turntable of the netting cleaning equipment was carried out.According to the numerical calculation results,the flow field velocity,pressure,turbulence kinetic energy and vapor volume fraction of the nozzle channel were compared and analyzed.At the same time,the orthogonal test method was used to carry out the cleaning test of the netting hanging board,The factors influencing the removal rate of fouling organisms in netting were studied.At present,the research level of domestic netting cleaning equipment is far from that of developed countries,and there are few related researches on the cleaning performance of cavitating jet netting cleaning equipment.In order to solve the problem of removing fouling organisms from netting in deep-water cage culture industry,this study analyzed the cavitation characteristics of submerged nozzle and the removal rate of fouling organisms from netting under different working conditions by using numerical simulation method combined with prototype test,which provided theoretical basis and technical support for the performance optimization of cavitation jet netting cleaning equipment in deep-water aquaculture cage and the research on the removal mechanism of fouling organisms from netting.The main conclusions of this paper are as follows:1.A kind of underwater cavitating jet netting cleaning equipment suitable for deep-water cage aquaculture management was developed.It mainly consists of high-pressure pumping station,rotary joint,diversion turntable,cavitation nozzle,high-pressure sealing mechanism,propeller and controller,etc.The maximum output pressure of the high-pressure pump is 18 Mpa,the rated power is 18 kw and the nominal flow rate is 50 L·min^-1.The length of the central bearing is 112.5 mm,and the outlet thread of the rotating shaft is 1/2-4 inch.The rotating speed of the diversion turntable is 30.8～112.2 r·min^-1,and the nozzle aperture is 0.8～1.2 mm.Propeller controller includes motive force power switch,potentiometer,power switch,adapter and step-down module.Provide equipment and technical support for improving the technical level of cage aquaculture management and expanding the space of marine culture in China.2.Under the same working conditions,the submerged jet has shorter effective range,faster diffusion speed and more energy dissipation than the unsubmerged jet,and the axial velocity of the submerged jet attenuate much faster.Underwater netting cleaning equipment mainly uses cavitation jet generated by nozzle of special device to clean fouling organisms on the surface of netting.Cavitation jet from submerged nozzle causes erosion damage to the surface of aluminum alloy template.The impact of high-speed jet center section on the center area of test template results in a pit with a certain depth in the center of the template.The collapse of a large number of cavitation bubbles caused by shear cavitation near the jet boundary layer results in a circular cavitation area around the template.When the inlet pressure is 12 Mpa,the change of nozzle outlet angle causes cavitation in different degrees;With the increase of nozzle length-diameter ratio,the inner diameter of annular cavitation decreases,the area of annular cavitation area increases,and the distribution of cavitation pits on the inner surface of annular area gradually deepens;The smaller the nozzle diameter is,the more obvious the erosion effect on aluminum plate samples is.3.The phenomenon of flow separation and wall attachment occurs in the right-angle L-shaped channel,and vortices are formed on both inner and outer sides;Only the outer side of circular-arc L-shaped channel has vortex flow.Compared with the right-angle L-shaped channel,the circular-arc L-shaped channel has a smaller velocity change rate and a higher jet velocity at the nozzle outlet;The maximum velocity at the outlet of right-angle L-shaped channel nozzle is 156 m/s;The maximum velocity at the outlet of the circular-arc L-shaped channel nozzle is 178 m/s.The flow field pressure drop of right-angle L-shaped channel is 16.95 MPa;The flow field pressure drop of circular-arc L-shaped channel is 19.65 MPa.The maximum vapor volume fraction in right-angle L-shaped channel is 0.29;The maximum vapor volume fraction in circular-arc L-shaped channel is 0.53.The maximum vapor volume fraction of the right-angle L-shaped channel accounts for about 45.3%of the maximum vapor volume fraction of the circular-arc L-shaped channel.Severe cavitation occurred in the nozzles of both channels,and the cavitation area and the maximum vapor volume fraction of the circular-arc L-shaped channel nozzle are much larger than that of the right-angle L-shaped channel nozzle.Compared with the right-angle L-shaped channel,the circular-arc L-shaped channel has higher nozzle jet velocity,less energy loss and higher cavitation degree,which is beneficial to improve the cleaning performance of the netting cleaning equipment.The circular-arc L-shaped channel is more suitable for the optimized structure of the diversion turntable for netting cleaning equipment.4.The fouling organisms of netting in deep-water aquaculture cage are mainly filamentous algae,shellfish and barnacles,including Ectopleura crocea,Perna viridis,Amphibalanus reticulatus,Chlamys nobilis et al.The removal rate of fouling organisms in netting is influenced by many factors,such as target distance,nozzle aperture,angle between nozzle and diversion turntable,etc.Removal rate of fouling organisms from netting hanging board is between 30.26%and 72.55%.The orthogonal test analysis shows that when the nozzle aperture of the netting cleaning equipment is 1.0 mm,the angle between nozzle and diversion turntable is 60°,and the target distance is 0 cm,the removal rate of fouling organisms on the netting hanging board reaches the maximum value of 72.55%.The results show that under certain conditions,and the target distance has the most significant influence on the removal rate of fouling organisms on the netting,followed by the angle between nozzle and diversion turntable,and the nozzle aperture has the least influence.