An attempt to realize experimental isotropic turbulence at low Reynolds number

This paper presents an attempt to realize experimental isotropic turbulence at low Reynolds number. For this aim an experimental apparatus, a turbulence chamber "Box", was designed and built to generate a turbulent flow field in the center of the chamber. The turbulent airflow field was generated by eight electrical fans placed symmetrically at the eight internal corners of the externally cubic chamber. The turbulence intensity was controlled by the fans speed. Laser Doppler velocimeter (LDV) in single and two-point velocity measurements was used to fully characterize the turbulent field inside the chamber. The main results indicate that the turbulence is homogeneous and isotropic with a quasi-zero mean velocity within a spherical region of 20 mm radius from the center of the chamber. The measured turbulent integral length scale was found to be constant and independent of the turbulence intensity (or fans speed). Furthermore, a noticeable spectral inertial subrange as prescribed by the Kolmogorov theory has not been observed at the range of Reynolds number explored here, where Re*l < 100. But rather a scaling region characterized by an exponent that is lower than the Kolmogorov value, -5/3, has been identified. Moreover, the value of this exponent showed no defined trend, while the width of the inertial scaling region expands as the microscale Reynolds number increases.