Research Of Flowing In Generalized Transitional Regime Based On Experiment And DNS Methods

Laminar, turbulent and transitional regimes are three important part of fluid flow states. Today, as flowing natural is unclear, the research of fluid characteristics in generalized transitional regime is very helpful to further reveal the flow and transition mechanism, and has theoretical significance for enhancing people’s knowledge about the fluid mechanics. Talking from the actual production and life, mastering the fluid characteristics well in transitional regime is the precondition of thermal meters’precision work. Therefore, research of fluid characteristics in transitional regime has very important engineering significance, too. Be known from the working principle of ultrasonic flowmeter, ultrasonic flowmeter’s accuracy is based on the profile-linear average speed relationships (coefficient k) in the pipe. Considering the two different reflection structure of ultrasonic flowmeter, I adopts the methods of experiment and direct numerial simulation (DNS) to study the fluid characteristics, and gives the relevant laws in this paper. That’s including:Establish the DNS method used for calculation in pipe and calculate the program when the Reynolds number is5300. The calculation results of DNS are compared with the existing LES results and classical experimental data, and it is found:in this Reynolds number, the DNS results is superior to the LES results. When the Reynolds number is below5300, LES does not apply to the calculation, so the DNS has a greater superiority.DNS method is adopted to calculate when the Reynolds number is3600,4000,7000,12000, and so on. And use of statistical average to calculate the defined coefficient k. As to some incident angle, I compare the results with the coefficient k coming from PIV experiment, and give the difference. It is found the DNS calculation results are similar with the PIV experimental result.Using PIV system to do the experimental study in DN40smooth transparent pipe in generalized transitional regime, I find my PIV experimental results are similar to the classical experimental results when the Reynolds number is about5300, and my experimental results are agree with theory resolutions when the Reynolds number is between2000and2400. With the development of Reynolds number, the velocity profilev distribution is changed from the parabola shape of laminar flow into the logarithmic curve of fully developed turbulent flow gradually. These imply the experimental data is credible, and the range of the experiment includes the whole transition regime.Taking defined coefficient k according to profile-linear average velocity relation as characteristic parameter, and combining ultrasonic flowmeter’s U type and V type paths, I study the velocity distribution profile relationships on difference horizontal paths and45°oblique path specifically, and give coefficient k fitting formula on horizontal axes path in the pipe.