| Liquid ring pump ejector has important applications in the petrochemical,metallurgy,energy and electric power fields because of its advantages such as good suction ability,compact structure and no rotor parts.The operating range of the liquid ring pump is extended and the suction vacuum is increased when it matches the ejector.However,the complex shear vortex and the shock wave structure caused by the high speed jet in the liquid ring pump ejector lead to large hydraulic loss.Moreover,the flow law and coupling mechanism in the coupling system are unclear when the ejector is matched with the liquid ring pump.Based on this,the internal flow characteristics and coupling mechanism of the matching system between liquid ring pump and ejector were studied based on numerical simulation and experimental methods.Meanwhile,the flow law,energy conversion and flow loss mechanism of liquid ring pump ejector were studied,and a feature decomposition method was proposed to decouple the complex internal flow field of ejector.The main work and research results are as follows:1.Experimental studies on external characteristics,visualization of flow field and pressure pulsation of the coupling system between liquid ring pump and ejector were carried out.The results show that the glycerol atomizing tracer particles can be used to describe the flow structure distribution characteristics and dynamic evolution law of high speed jet in liquid ring pump ejector.The free interface of high speed jet has obvious fold characteristics because of enrolling low speed fluid.The effective working range of the modified ejector is 0.02MPa larger than that of the prototype ejector when matching with the liquid ring pump.The time domain variation of the pressure signal of each measuring point in the ejector has unstable fluctuation.With the increase of ejector vacuum,the absolute mean value of pressure pulsation signal at the same monitoring point in the ejector increases.Under different working conditions,the dominant frequency of pressure pulsation at each measuring point is mainly distributed at axial frequency fnand double axial frequency 6fnin the low frequency band.2.The unsteady flow characteristics in the coupling system of liquid ring pump ejector were revealed,and the influence of equal area ratio ejector on the hydraulic performance of the coupling system was analyzed.The results show that the numerical simulation of flow characteristics and hydraulic performance in the liquid ring pump ejector coupling system is in good agreement with the experimental results,and the root mean square error of hydraulic performance is 0.53%.The hydraulic performance of the liquid ring pump has been significantly improved within a certain working range due to coupling with the ejector.The prototype ejector does not match the liquid ring pump,and the vacuum of the pump inlet cannot be improved when the ejector does not match the liquid ring pump.On the basis of the prototype ejector,the vacuum and efficiency of the liquid ring pump ejector system can be improved by scaling up the geometry size of the ejector.Due to the influence of rotor-stator interaction of the liquid ring pump,the flow in the liquid ring pump ejector presents the characteristics of multi-frequency coupling,and its dominant characteristic frequencies are axis frequency fn,blade frequency f BPFand high harmonic frequency.3.Based on large eddy simulation method,the flow characteristics of liquid ring pump ejector were revealed,and the influence of area ratio and compression ratio of ejector on its internal flow field was studied.The results show that there are shock waves formed by high speed jet and shock trains structure formed by mutual interference between shock waves and jet shear layer.The jet flow field presents the characteristics of oscillation distribution due to the influence of shock trains.Under the action of strong velocity gradient,a cylindrical shear layer is formed between high and low speed fluids of jet.With the evolution of jet flow,wake shedding vortices are formed because the shear vortices fall off at the trailing edge of jet after stretching and breaking.The pressure pulsation signal in the core region of the jet presents obvious sinusoidal periodic fluctuation due to the impact of self-excited shock wave.The pressure pulsation signals near the trailing edge of the jet become disturbed due to the influence of wake vortex shedding,and high frequency broadband excitation signals appear.The position of the Mach disc gradually moves towards the nozzle throat and the size of the separation zone inside the nozzle gradually increases due to the increase of the area ratio of the ejector.The shedding position of shear vortex is advanced due to the increase of compression ratio.4.The energy transfer,flow loss and their relationship with the complex internal flow structure in the ejector were revealed.The dynamic evolution of the complex vortex structure in the ejector was studied based on the vortex identification criterion.The results show that there are multi-scale vortex core structures in the ejector,which are mainly vortex ring in the shear layer and vortex band structure around it.With the evolution of jet flow,the shape of vortex ring changes due to the interference of vortex band and then falls off at the trailing edge of jet flow.The energy transfer in the ejector mainly occurs in the cylindrical shear layer of the jet.Under the interaction of vortex ring and vortex band,the energy is gradually transferred from the high speed jet to the low speed fluid,accompanied by energy loss.The flow loss in the shear layer of the jet has a strong correlation with the shear vortex.The flow loss in the nozzle is closely related to the shock wave structure,and the flow loss near the inlet of the diffuser mainly depend on the flow separation near the wall.5.The POD,DMD and SPOD feature decomposition methods were used to extract the coherent structure of the turbulent jet,and the POD-RBF surrogate model was established to predict the flow field in the ejector.The results show that POD,DMD and SPOD methods can realize the spatiotemporal decoupling analysis of coherent structures in the ejector.Spatial distribution characteristics of shear vortex structures with different energies and scales in the ejector are obtained based on POD.The decoupling analysis of shock wave and jet shear flow structure at each characteristic frequency in the ejector is realized based on DMD and SPOD.The modes of jet vorticity and velocity field reflect the evolution law of banded large-scale shear vortex and the periodic shedding characteristics of wake vortex in the cylindrical shear layer,while the modes of density and pressure field represent the structural characteristics of shock waves.The POD-RBF surrogate model can realize the rapid reconstruction of jet field,and the root mean square error of velocity prediction is 0.48%. |
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