非圧縮性流体の中心差分法によるCFDプログラムの開発とその検証

(非定常レイノルズ応力効果)

抄録

It was known that the circular pipe flow with a large initial turbulence was stable up to Reynolds number 1500, and became unstable over that, but did not transition to turbulence up to Reynolds number 2300. CFD by the central finite difference method was applied to the circular pipe flow with a large initial turbulence in the Reynolds number range over 1500. The calculation result of the unstable flow showed that the pressure value at the center was smaller than that at the wall surface. As a result of the experiment, it was found that the static pressure at the center was larger than that at the wall surface, contrary to the calculation result. It was considered that the transient Reynolds stress acted like pressure, and it was confirmed that the calculated value of the sum of the transient Reynolds stress and the pressure was larger at the center than at the wall surface. Furthermore, when the transient Reynolds stress was added to the right side of the Navier-Stokes equation of motion, it was confirmed that transient Reynolds stress had the effect of delaying the divergence of solution. The effect was remarkable when the Reynolds number was 1500 to 2000. In an actual circular pipe flow with a large initial turbulence, the fact that the flow could maintain a laminar flow up to Reynolds number 2300 was considered to be due to the transient Reynolds stress.