PIV Experimental Study On The Interactions Between Ice Ridges And Stratified Fluids

Global warming has the most direct contact with the accelerated melting of glaciers in polar regions.As an important part of the global climate system,the changes of sea ice not only affect the sea and air's energy or momentum transfer,but also cause salinity layer instability,causing snow flooded,floods and other natural disasters of glaciers,which will threaten the safety of human living environment eventually.So the scientific community increasingly attach great importance to the research of sea ice dynamics.Sea ice drag coefficient is an important parameter in sea ice dynamics,the parameterization study is also gradually developed and perfected.However,the stratification in the ocean beneath ice is not considered in the current parameterization of ice-ocean drag coefficient.In fact,the freshwater produced by the rapid melting of sea ice has made the depth of halocline under ice become lower than before.So that,the influence of halocline on the drift of sea ice cannot be ignored under the background of rapid ice melting.Laboratory experimental study was carried out in this study to investigate the interactions between ice ridge and stratified fluid using the method of Particle image velocimetry(PIV).First of all,based on the changes of drag force of ice ridge in uniform fluid and stratified fluid,using the method of PIV on ice flow test to obtain the PIV imagery of velocity vectors.Due to poor environmental conditions in the Polar Regions,it is very difficult to carry out in-situ observations on the flow field under ice.Physical modeling tests in laboratory experiments can meet this deficit,and compensate the limitations in weather conditions and measurement technology during the observations on ice-ocean interface.The physical processes in sea ice dynamics can also be thoroughly investigated owing to the man-made test conditions.Combining the two research methods,select appropriate tracer particles,use the tank to set up a two-layered fluid simulation of Arctic halocline,make different ice ridge models,calibrate the moving speed and design the experimental scheme.Secondly,the draft of ridge keel model D is set to be 2,4,6,8 and 10 cm,and the velocity of ridge model U is set to be 3,6,7,8,9,10,12,15,18,24 and 30 cm/s,and the incline angle of ridge model ? is set to be 10 °,20 °,30 °,45 °,60 ° and 90 °,adding up to 330 cases.It is clear that a vortex shows a positive correlation with the draft,the velocity and the incline angle of ridge keel.For a constant draft,multiple vortex centers occur in the wake field as the drift velocity increases to a certain level.In addition,movement of ice ridge on water surface will introduce internal waves on the interface between two layers with different density in the stratified fluid.The wave height and the draft,the velocity,the incline angle of ridge keel was positively related.To counted the vertical distance between wave crest and trough,found that the vertical distance increases with the increase of incline angle and the draft of ice ridge,but the change between wave height and the velocity of ice ridge was not monotonic.The wave peak gradually approaches the lee-side of ridge keel with the increasing D or ?,but it is far away from the lee-side of the ridge keel.Finally,make some discussion on the relationship between the internal waves,the PIV imagery of velocity vectors,the drag force and the drag coefficient.Analysis shows that,in uniform fluid,the drag force of ice ridge increased with the increasing of the draft,velocity and incline angle of ice ridge.The incline angle of ice ridge is the main factor affecting the drag coefficient of ice ridge.In stratified fluid,the change between drag force and the incline angle or the draft of ice ridge in similar with the uniform fluid,but the change between drag force and the velocity was not monotonic.In addition to the influence of the inclination angle of the ice ridge,the influence of the Froude number on the drag coefficient is also obvious.The internal wave will pose external resistance on the ridge keel,and make the variations of drag force on ridge keel in the stratified fluid to be non-monotonic for different Froude numbers,further proving the impact of stratified fluid on the drag coefficient of ice ridge.