Noise Emission And Thermal Behavior Of Parallel Multiple Jets In The Scarfing Engineering

With the increasing attention paid to high value-added steel,the scarfing engineering has gradually become an indispensable metallurgical process in continuous casting slab.Different from the multi-jet cases such as sparying,drying and aerospace engineering,the scarfing engineering has such characteristics as follows:large jet number,parallel distribustion,large jet-to-plate spacing and oblique impingement.The present work focuses on the parallel multiple interacting jets,aiming to reveal the formation mechanism and controllable factors of surface grooves,and to elaborate the acoustic characteristics and noise reduction methods.The complicated regimes of flow,heat transfer,noise emission and combustion are investigated by combining emperiments and numerical simulations.The multi-physics processes in the scarfing engineering have been studied step by step from single jet and dual jet to parallel multi-jet,from single row of multiple jets to double row of multiple jets,from free jet to impinging jet,from cold jet to combustion jet.The obtained results have great significances to solve the existing issues of surface groove and noise pollution.Single jet and dual jet are the foundations of parallel multiple jets.The large eddey simulation(LES)and Ffowcs Williams-Hawkings(FW-H)integral equation are employed to predict the flow field and acoustic field of the most representative high Mach number,low Reynolds number compressible jet.The function mechanism of jet entrainment features on flow development and noise propagation has been revealed.The dual jet interaction is described by introducing the comcept of Coanda effect.The results indicate that the merging point(MP)and the combined point(CP)increase exponentially with the increase of the jet-to-jet spacing.The flow and acoustic characteristics of the dual jet are compared to the single jet by equivalent area principle,suggesting that the dual jet noise is lower and the propagation directivity is deflected radially.The parallel multiple impinging jets are the basic feature of scarfing technique.The mutual interaction behavior and corresponding impinging performance have been investigated by experimental and numerical approaches.The oil flow testing is performed to reproduce the surface grooves,using the practical scarfing configuration and identical operating parameter.The Realizable k-ε turbulence model(RKE)and analytical wall function(AWF)are conducted to predict the flow and heat transfer details.The multi-jet combining and recombining features have been revealed.The results indicate that the flow evolution morphology of parallel multiple interacting jets and corresponding impinging performance play a decisive role in the surface groove generation.The effects of jet-to-jet spacing,jet-to-plate spacing and jet Reynolds number on the flow and heat transfer characteristics have been examined to summarize the effective methods for surface quality improvement.The surface grooves can’t be completely eliminated,but can be improved through structural optimizations.In comparison to the single jet and the dual jet,the noise emissions of the parallel multiple jets are enhanced by the mutual interaction.Moreover,noise spectrum shifts to low frequency and the wave propagation deflects to the radial direction.The impinging process mainly increases the dipole sources.In consequence,the noise directivity has two peaks above the plate and the frequency is lower than the free jet.The influences of impinging height,impinging angle and jet Reynolds number are investigated by parameter studies.And the new characteristics of the impinging multi-jet noise compared to the single jet are highlighted.With the increase of the impinging height,the noise intensity increases first and then decreases.The noise propagation is deflected to the axial direction and the spectrum shifts to low frequency.As the impinging angle decreases,the noise intensity gradually increases.The noise directivity is deflected to the flat plate and the spectrum shifts to high frequency.The non-premixed combustion plays an important role in the preheating stage of scarfing process.The multi-physics process of flow,combustion and noise emission has been investigated through experimental and numerical approaches.Due to the direct flame measurement is difficult to capture the small temperature differences between the parallel multiple jets,the thermocouple-plate indirect temperature measurement is proposed to represent the impact of multi-jet interaction on flame morphology.The numerical simulation contributes to overcoming the testing limit and revealing the physical details of flow field,temperature field,concentration field and sound field.The flow and combustion results at different characteristic locations indicate that the multi-jet interactions are beneficial to the gas mixing and the combustion reaction.Moreover,the mutual entrainment can increase the noise intensity and shift the spectrum to low frequency.The acoustic results of cold jets and hot jets,non-combustion jets and combustion jets are compared,indicating that the thermal effect and the combustion chemical reaction help increase the noise intensity and reduce the noise frequency,but have little effect on the propagation directivity.