Study Of The Numerical Simulation Method For Thermal Plume In Airplane Cabin Based On Equivalent Compensation Of Viscosity

In closed spaces such as airplane cabin,the air environment directly affects the safety and comfort of passengers,which is one of the important projects adopted for China’s independent research and development of large airliner.The thermal plume generated by the temperature difference is one of the key factors affecting the circulation of air flow,and is an essential research content of the cabin air environment.Due to the high Reynolds number flow from the air supply system coexisting with the low Reynolds number flow of the human plume in the cabin space,the air flow in cabin presents the characteristics of multi-scale,strong fluctuation and unsteadiness.The numerical simulation of the flow field of whole cabin is required to be able to capture simultaneously the quantitative characteristics and the interactions between the overall large-scale vortex structure and the local plume flow.It imposes higher requirements on conventional turbulence models and unsteady numerical simulation techniques.In addition,in view of the large geometrical dimensions of the cabin and complex airflow conditions,a huge number of grids are required to achieve the accuracy of numerical simulations.However,it is expected to obtain rapid assessment of design results with less grids and calculation amount for practical engineering cases.Therefore,the numerical simulation of unsteady flow field in airplane cabin faces great difficulties.In order to solve the unsteady quantitative characteristics of thermal plumes in multi-scale flow environment and to develop numerical simulation strategies and models meeting the actual engineering design requirements,the following research works are conducted:1)By means of Direct Numerical Simulation(DNS)method and comparing with the experimental data,the unsteady flow of typical natural convection and human thermal plumes are numerically calculated.The average flow field and unsteady fluctuation components of the thermal plumes are quantitatively analyzed and confirmed.The unsteady development process and quantitative data of thermal plumes are successfully obtained by numerical simulation.The characteristics of the vortex shedding around heat source and the quasi-periodic fluctuation are determined.The frequency spectrum analysis shows that the thermal plume is mainly dominated by low-frequency fluctuation of quasi-periodic frequency less than 1 Hz.2)The numerical dissipation of the low-resolution grids and the turbulent viscosity of the standard k-ε turbulence model are discussed and validated in unsteady flow calculation.An improved simulation model based on numerical dissipation and turbulent viscous equivalent compensation(ECV k-ε model)is proposed to focus on the modification of low Reynolds number flow region without solving additional equations.It can improve the accuracy of natural / forced mixed convection calculation.The effectiveness of the proposed method in the calculation of unsteady flow field of thermal plumes under the condition of low-resolution grids and k-εmodel is verified.3)The ECV k-ε model is applied to the numerical calculation of single-row cabin and compared with the experiment results.Furthermore,the whole cabin flow field of a new type of large passenger plane with 20 rows of passengers is simulated.The distribution and evolution of airflow in space and time domain are analyzed.The unsteady flow characteristics of the whole cabin are successfully captured under the condition of less mesh number.The results meet the requirement of fast and correct numerical simulation of cabin flow field in engineering practice.This research provides a fast and effective numerical calculation strategy for the unsteady characteristics of the cabin complicated airflow environment including human thermal plume,and provides a basis for the optimization design of unsteady flow field of the cabin.