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Optimization design of inner-structure of the slot-jet in aircraft cabin based on investigation of multi-scale characteristics of slot turbulent jet flow
Pages: 32-37
Year: Issue:  5
Journal: Experiments and Measurements in Fluid Mechanics

Keyword:  aircraft cabininner-structureslot-jethot-wire anemometrywavelet transform;
Abstract: In order to solve the distribution heterogeneity problem of the mean span-wise velocity field of the slot outlet in MD-82 airliner cabin,we designed the slit-shaped inner core structure in order to make the final mixture of the slot flow more uniform,the development of the turbulence is more sufficient and the distribution of the mean stream-wise velocity field is more homogeneous.Hot-wire anemometry is used in the simplified cabin model experiments,based on which the research is carried out on the optimization design of inner structures of the slot-jet in aircraft cabin and the multiscale characteristic analysis of the turbulence.The slot-jet flow fields in model cabin environment with different inner-structure are finely measured by constant-temperature anemometry system.The resolution of the constant-temperature anemometry system is higher than the smallest time-scale of turbulence(inner structure and dissipation time-scale).The actual velocity field is analyzed in the stream-wise direction and normal direction respectively.Furthermore,based on the comfort theory,the wavelet-transformations are applied for the characteristic analysis of the multi-scales eddy and the analysis of the distribution of energy.The variation of the mean velocity beyond the slot outlets reveals the decaying regularity of the velocity in the stream-wise direction and the flow irregularity in the normal direction.Results from the wavelet transformation analysis indicate that the change of energy proportion of different scale eddies is connected with the evolution of the slot-jet flow field.It can be seen from the results that small scale vortices generate entrainment and merge into large scale vortices on account of the increase of the viscosity and the decrease of the inertness in the far field of the turbulence jet flow field,which is called inverse energy cascade.It has a significant impact on the thermal transmissionand the diffusion of contaminant.It’s the main reason of the draft sensation discomfort.By the contrast experiments,the slit-shaped core inner structure is designed so that the final mixture of the slot flow is more uniform and the development of the turbulence is more sufficient.From the perspective of comfort analysis on the flow fluctuation frequency,the flow characteristic frequency of the flow field beyond the outlet with the designed core structure has remained to be about21.83 Hz,while the air fluctuation frequency which results in highest discomfort is 0.2~0.6Hz.Therefore the design is worked.
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