| The combustion in engines involves complex interactions between fluid dynamics,thermodynamics and chemical processes.For further investigation,it’s essential to verify those influence factors separately.In this paper,a systematic experimental study was conducted to clarify characteristics of turbulence field generated by two opposite fans in a cubic constant volume combustion chamber(CVCC).The effect of the fan speed(1000–2900 r/min)and ambient pressure(0.1–3.0 MPa)on root-mean-square fluctuations,probability density functions,integral length scales and energy spectra was investigated.To overcome the limitation of the 2D-PIV,three sheet velocity fields were measured to reconstruct the three-dimensional boundary of the homogeneous region.Experimental results showed that a nearly homogeneous turbulence field in a flat region around the center of the CVCC was generated while a slight departure from isotropy was unavoidable in the current configuration.The turbulence intensity was independent of the ambient pressure,but positively proportional to the fan speed.Thus,it can be accurately estimated by linear interpolation method according to the fan rotational speed,regardless of the gas pressure.Absence of both fan speed and ambient pressure’s effect was observed for the integral length scales,the longitudinal integral length scales was found to be stable at around 5.65 mm.In addition,the slopes of the energy spectrum in the logarithmic scale consistent with the Kolmogorov’s-5/3 law,analysis of the turbulent energy spectra implied that the increase of fan speed and ambient pressure resulted in a smaller critical eddy scale where the viscosity dissipation effect started emerging.Besides,PDFs of velocities fluctuations are proved to be symmetric and nearly obey the normal distribution.This article addressed characteristics of turbulence field,including turbulence intensity,through measurement and statistical analysis.It provided data for experiments of premixed combustion and diffusive combustion.In addition,experimental data can be also used to verify the numerical simulation in the future. |
