Research And Experiments On The Mechanism Of High Pressure Hot Air Deep Loosening To Reduce Resistance In Sandy Clay Loam Soil Environment

Sandy clay loam has the characteristics of both sand and clay.Because of these characteristics,both frictional resistance and adhesive resistance occur between the soil and tillage tool during operation.The combined effect of the two frictional forces increases the external friction angle between the soil and tillage tool,thus increasing the working resistance.In order to solve the problem of excessive subsoiling resistance in sandy clay loam,a drag reduction method of high-pressure hot gas coupling was proposed based on the research on drag reduction in subsoiling at home and abroad.Mechanistic analysis and experimental research were conducted to verify that the high-pressure hot airflow between the deep pine shovel and the soil can indeed achieve the purpose of reducing the operating resistance.The main work accomplished in the thesis is as follows:(1)The experimental device was designed and soil parameters were measured.In order to investigate the effect law of high-pressure hot gas coupling on the external friction angle of sandy clay loam soil,a self-made external friction angle determination device and a high-pressure hot gas supply device were designed,and the diameter of the pore was determined to be 1 mm.Parameters such as texture,moisture content,firmness and bulk weight of the test soil were determined.(2)Soil tests were conducted and the regularities were summarized.Relying on the external friction angle measurement device,high-pressure airflow test and high-pressure hot gas test were conducted respectively.The results of the high-pressure airflow test showed that the external friction angle decreased as the airflow pressure increased,and it was found that the external friction angle of the soil increased and then decreased with the increase of soil moisture content,and reached the maximum at 30% soil moisture content,regardless of whether it was filled with high-pressure airflow.Heating on the basis of a high-pressure air stream was found to reduce the water content of the subsoil in contact with the touchdown component by a hot air curtain.With 30% moisture content as the boundary,when the high-pressure hot air reduces the moisture content of the subsoil to below 30% can reduce the external friction angle,and vice versa will increase the external friction angle.(3)A high-pressure hot gas drag reduction mechanism study was conducted.Theoretical calculations proved that increasing the area of the air curtain layer could effectively reduce the friction between the metal and the soil.The mechanism of the influence of high pressure airflow on the external friction angle was analyzed,and the air curtain layer images were processed using Matlab software to extract the data of air curtain layer area,air curtain layer width,and soil surface flatness,and the analysis showed that the air curtain layer area had the greatest influence on the external friction angle with a correlation of 0.9726.The mechanism of the effect of high-pressure hot gas on the external friction angle was analyzed.By analyzing the thermal imaging images to determine the study of the subsoil temperature,temperature gradient,and water content of the subsoil,it was concluded that the subsoil temperature had the greatest effect on the external friction angle with a correlation of 0.884,which in turn led to the conclusion that the key factor determining whether the external friction angle increased or decreased after heating was the soil water content.(4)Simulation test and soil trough test of high-pressure hot gas type deep pine shovel.The high-pressure hot gas type deep pine shovel was designed,and in the simulation test,the shovel tip fluid simulation model and shovel tip-soil discrete element simulation model were established.The coupling test between Rocky Dem and Fluent proves that the high-pressure hot gas method can effectively reduce the resistance,and the reduction rate is 16.6%.A three-factor,three-level orthogonal test was conducted in a soil tank test rig.The most important factor affecting the drag reduction rate was the soil water content by Design-Expert 11 software.The optimal parameter combinations were obtained as follows:airflow pressure of 0.4 MPa,airflow temperature of 100°C,and soil moisture content of24%.The optimum combination of parameters can achieve 15.9% drag reduction rate,which indicates that the maximum drag reduction rate of high-pressure hot gas coupling can be achieved when the soil moisture content is less than 30%.In turn,it also proves that the high-pressure hot gas coupling has good resistance reduction effect in the actual deep pine operation.