Ask a question about stagnation turbulence
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Which of the following statements about fluid laminar flow and turbulent flow is correct? A. Whether the fluid medium and operating conditions are the same or not, the flow velocity in turbulent flow is always greater than that in laminar flow. B. Whether it is a liquid medium and the operating conditions are the same or not, the Re number for laminar flow is always lower than that for turbulent flow. C. Turbulent flow generally occurs when the cross-sectional area of the flow channel is large, while laminar flow generally occurs when the cross-sectional area is small. D. Laminar flow has no radial fluctuations, whereas turbulent flow does have radial fluctuations. Multiple-choice question: B or D?
Oh, so you’re considering non-Newtonian fluids, right?~~~
These kinds of problems are really frustrating; they’re word games. By definition alone, Re below 2000 is laminar flow, between 2000 and 4000 it is the transitional region, and above 4000 it is turbulent flow. The transition zone can be either turbulent or stagnant, so B is inaccurate. As for D, from a macro-molecular perspective, there is indeed no pulsation. Choose D
What if it’s a non-Newtonian fluid? So still choose D
What makes non-Newtonian fluids different? ? ?
Only D can be chosen; the others are not necessarily correct. What’s most confusing is option B: regardless of whether the liquid medium and operating conditions are the same or not, the Re number for laminar flow is always lower than that for turbulent flow. As an example, the Re number for laminar flow in a circular pipe can be 1000, while the Re number for the fluid flowing outside a heat exchanger tube is 100, which indicates turbulent flow
D. Whether it is turbulent or laminar flow is determined by the Reynolds number, which depends not only on the flow velocity but also on density and viscosity; therefore, a high flow velocity does not necessarily mean turbulent flow
Whether it is turbulent or laminar flow is defined by the Reynolds number; if the Reynolds number is 100, can it be considered turbulent flow? “\"Are the media the same?\" I think this is incorrect; if it’s a non-Newtonian fluid, then the conditions are not met.