# What is the relationship between CD and the Reynolds number?

## What is the relationship between CD and the Reynolds number?

Note that the drag coefficient decreases with the Reynolds number, and it becomes almost a constant (CD = 0.4) for a Reynolds number between 103 and 2×105. As the Reynolds number increases (Re > 2×105), the boundary layer becomes thinner in the front of the sphere and begins its transition to turbulent.

## How is the Reynolds number related to drag for a sphere?

As the Reynolds number increases, the viscous forces decrease relative to the inertial forces (and therefore relative to the pressure gradient), so the point of separation moves upstream, towards the equator. As the Reynolds number is increased, the form drag increases relative to the skin fric- tion.

How do you find Reynolds number of a sphere?

The most widely studied case is the sphere. Figure 1 graphs the dependence of drag coefficient for a sphere and a cylinder in crossflow on the Reynolds Number Re = ρuD/η, where D is the sphere (cylinder) diameter, η the viscosity of liquid, and .

### What Reynolds number is turbulent sphere?

So, when the Reynolds number is below 2,300, we can expect the flow to be laminar, and when it is above approximately 4,000, the flow will be turbulent. In between these two limits, the flow is termed “transition flow.” Page 2 2 We can ascribe a certain physical significance to the Reynolds number.

### How do you find particle Reynolds number?

In the above, the particle Reynolds number is obtained as R=wtdn/ν, where dn is the nominal diameter of sediment particles of median size d. It is approximately taken as dn = d/0.9 .

What is the best shape to reduce drag?

the best shape to reduce drag is streamline.

#### How does Reynolds number effect drag coefficient?

Lift coefficient decreases rapidly and drag coefficient increases rapidly when Reynolds number is decreased below critical range. This occurs due to change in flow pattern near Gurney flap at low Reynolds numbers.