# Is this flow turbulent or laminar?

• teoman
In summary, the onset of turbulence typically occurs for Re > 4000, but this is not always applicable to open systems like a wing. For external flow, the critical Reynolds number can vary and may require experimental testing. Generally, a wing at Re = 3.5*105 to 1.5*106 would likely have turbulent flow, especially near the upper end of this range. However, the presence of turbulence does not necessarily mean it is turbulent over the entire wing. The roughness of the wing surface can also affect the transition to turbulent flow.
teoman
Hello,

is it a case of turbulent flow over a wing if the relevant Reynoldsnumbers are 350.000 to 1.500.000?

Teoman

Isn't Re > 4.000 = turbulent only applicable to pipe flow?

Hello,

I thought Re > 4.000 = turbulent is only applicable to pipe flow?

Am I wrong?

Teoman

It's turbulent for any Re > 4000. The calculation of Re number depends on what type of flow it is. For open systems (such the wing is in this case) you have to use hydraulic radius instead of charasterictic length used in pipe flows.

There is a wikipedia article how to calculate certain flows hydraulic radius:

random54 said:
It's turbulent for any Re > 4000. The calculation of Re number depends on what type of flow it is. For open systems (such the wing is in this case) you have to use hydraulic radius instead of charasterictic length used in pipe flows.

There is a wikipedia article how to calculate certain flows hydraulic radius:
Not really. Hydraulic radius is for channel flow. For external (non-channel) flow, it's true that Re = 4000 is not necessarily the critical reynolds number. Unfortunately, it can be difficult to get the true critical reynolds number without experimentally testing it, but it can be anywhere from a couple thousand up to roughly 1 million. In general, for a wing at Re = 3.5*105 to 1.5*106, I would guess that the flow is turbulent, as it is near the upper end of this range. At the very upper end of this range (Re just under 106), you would probably only get laminar flow on a very smooth plate. Of course, just because turbulent flow exists doesn't mean that it's turbulent over the whole wing. If the wing surface is rough at all, you'd probably get a transition to turbulent flow pretty early on, but if the wing is smooth, a significant portion of the wing would have laminar flow. Again, I'm not sure how to determine exactly how much would be laminar aside from experimentally.

## 1. What is the difference between turbulent and laminar flow?

Turbulent flow is characterized by chaotic and irregular motion of fluid particles, while laminar flow is characterized by smooth and orderly motion of fluid particles.

## 2. How can I determine if the flow is turbulent or laminar?

The most common way to determine the type of flow is by calculating the Reynolds number, which is the ratio of inertial forces to viscous forces. A Reynolds number less than 2300 indicates laminar flow, while a number greater than 4000 indicates turbulent flow.

## 3. Is it possible for a flow to transition from laminar to turbulent?

Yes, it is possible for a flow to transition from laminar to turbulent, especially when the Reynolds number is in the transition range between 2300 and 4000. This transition can be influenced by factors such as velocity, viscosity, and surface roughness.

## 4. What are the applications of turbulent and laminar flows?

Turbulent flow is commonly seen in large-scale natural phenomena such as ocean currents and weather patterns, as well as in industrial processes like mixing and pumping. Laminar flow is often used in microfluidic devices, medical equipment, and precision manufacturing.

## 5. Can turbulence in flow be controlled or reduced?

Yes, turbulence can be controlled or reduced through techniques such as using flow control devices, altering the physical properties of the fluid, or changing the surface roughness of the flow boundary. However, complete elimination of turbulence is not always possible.

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