| The quenching process is a core working step in the metal heat treatment process,and the air-cooling quenching has obvious advantages compared with the conventional water-cooling quenching,oil-cooling quenching and mist-cooling quenching: Cooling is uniform and stable;The work-piece is not easy to occur after quenching Deformation;Unclear on the surface of the work-piece;Nozzles will not block;Economical and environmentally friendly.In air-cooled quenching systems,the nozzle(or jet head)is the most critical component in the cooling unit.With the advent of the Laval nozzle,the use of compressed air through the Laval nozzle,the supersonic airflow can be obtained,and the effect of enhanced heat transfer cooling is achieved.Therefore,domestic scholars have done a lot of research on supersonic nozzles.For the slender and flat work-pieces in air-cooled quenching,when multiple small-diameter circular supersonic nozzles are used for spraying,it is impossible to avoid mutual coupling between the nozzles and the external surface of the nozzle,and it is difficult to achieve uniform cooling of the work-piece surface.The sonic nozzle can reduce the jet interference between the nozzles and improve the flow field uniformity of the jet surface.Our research group has designed a double-line rectangular supersonic nozzle,and through research and analysis,it is found that the nozzle has the advantages of uniform internal flow field and no shock wave.When air quenching,the gas flow field is the main influencing factor of the work-piece temperature field.Therefore,the nozzle is used to study the impact jet characteristics of the external flow field.The specific research contents and results are as follows:Study on jet characteristics of single-nozzle,double-nozzle and three-nozzle flow fields.A rectangular supersonic nozzle impinging jet model was established,and the FLUENT software was used to simulate nozzle impinging jets at different jet angles,jet heights and jet spacing.The jet characteristics of the external flow field,namely the impact pressure,the turbulent kinetic energy,the wall shear force and the horizontal velocity are the indicators.The research shows that the impact pressure on the jet impact surface is the same as the turbulent kinetic energy,and the wall shear force is the same.The trend is the same as the horizontal speed change;in the double nozzle,on the impact surface of the inclined jet,the flow characteristics of the right nozzle flow field are reduced,and the jet interference between the nozzles occurs near the geometric impact point of the right nozzle jet,and a hysteresis occurs at the position.Stop zone;when three nozzles,the jet angle has the greatest influence on the uniformity of jet impact surface cooling,followed by the jet spacing,and the minimum is the jet height.When the jet angle is 45°,the jet height is 60 mm,and the jet spacing is 40 mm,the flow field of the jet impact surface is evenly distributed.Using this process parameter can improve the cooling uniformity of the jet impact surface.Three nozzle impinging jet PIV experiment.In order to verify the theoretical analysis,the particle flow velocity measurement technology is used to measure and process the external flow fields of the vertical jet and oblique jet of three rectangular supersonic nozzles,and the instantaneous flow field structure and average flow field distribution are obtained.Experimental results and simulation The results are consistent,indicating that the theoretical analysis is correct.This study has important reference value for the application of rectangular supersonic jet. |
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