Decay of turbulence in a tube following a combustion-generated step in temperature

This paper reports that an essentially abrupt change in temperature owing to thermally stabilized combustion produces a correspondingly abrupt decrease in Reynolds number from the 3000-6000 range down to 650-1550 for an ethane-air flame in a 9.5-mm channel. Since the Reynolds number downstream from the flame front is below the transitional value for a tube (approximately 2100), the turbulence decays with distance from the flame front. The decay of turbulence and the consequent development of a parabolic velocity profile were investigated theoretically using a modified k-ε model of Jones and Launder. The predictions of the velocity at the centerline and axial gradient of pressure are in qualitative agreement with experimental results throughout the system, although the predicted approach to the asymptotic value for laminar flow was faster than that which was observed. This discrepancy identifies a nonphysical characteristic of the modified k-ε model which was utilized in the current study