Numerical Simulation And Preliminary Experimental Study On Mean-flow Acoustic Engine With Cross Junction Configuration

Mean flow is generally a one-way flow with remarkable kinetic energy, including natural wind, gas flow in piping system, etc. Acoustic oscillation can be induced in a closed branch tube by a mean gas flow in a trunk tube passing the opening of the branch tube. This effect is named mean flow-induced acoustic oscillation effect, which can convert the kinetic energy of mean flow into acoustic energy. Based on this principle, a new type of engine named Mean-flow acoustic engine (MFAE) with no mechanical moving part which can use wind power as driving source can be manufactured. MFAE can be used in fields of thermoacoustic refrigeration, power generation, noise and vibration reduction, etc. However, the theoretical and experimental study on MFAE is in the early stage, and the working mechanism of MFAE is still unclear. In order to explore the working mechanism of MFAE, we carried out the numerical and experimental study on MFAE with cross junction configuration.In this thesis, large eddy simulation (LES) of turbulence was first employed to numerically calculate the internal flow field inside MFAE. As a result, the stable standing acoustic field was obtained in the resonator and the features of the flow field, the acoustic field, the coupling relationship of vortex in the mouth of resonator and acoustic field were analyzed. The results show that:at different mean flow velocities acoustic fields are in different stable and unstable statuses and the stable acoustic fields at different mean flow velocities bear different acoustic modes; in the case of stable acoustic field, periodical vortex occurs in the mouth of resonator and the number of vortices simultaneously appearing there indicates different hydrodynamic modes. Besides, the computational results of four MFAEs with non-cross junction configuration indicate that two areas with no or little influence of mean flow are required to build a stable standing wave in the resonator.A test rig of MFAE was designed and built and preliminary experiments were done in a MFAE with cross junction configuration. In experiments, the features of acoustic fields with different acoustic modes at different mean flow velocities were shown and the reliability of numeric model was verified. Also, the effects of temperature, mean flow velocity and mean pressure on acoustic field were analyzed. The analysis of the dimensionless number in both experimental and computational results shows stable acoustic oscillation occurs in certain Strouhal number ranges which can denote the hydrodynamic mode. This conclusion provides a basis for optimizing the operating conditions of MFAE. The maximum value of pressure amplitude at the closed end of resonator is 2.10 kPa, with the corresponding mean flow velocity of 44.55 m/s, oscillation frequency of 547 Hz, pressure ratio of 1.04, and acoustic energy of 6.358×10-3 J stored in resonator, which provides good reference for wind energy utilization by MFAE.