I am not sure about the specifics of the data from the literature that you are comparing with, i.e., whether the reference data applies to the same body shape as what you are analyzing or to a generic body shape such as a cylinder, etc. Regardless, the force coefficient data in the literature should have been accompanied by information regarding the reference area used to compute the force coefficient. Thus, in order to compare the numerical values of the force coefficients, you must use a reference area that is consistent with the literature. There are only a small number of options in general:

1. Frontal area of the body (equal to the diameter for a cylinder, and 0.205 meters for the body shape you are modeling) -- common option for bluff bodies such as that you are computing

2. V**(2/3), where V = volume of the body

3. If the body were to be streamlined, such as an airfoil, then it is common to use the nominal, planform area at zero angle of incidence as the reference area. However, this won't be very appropriate for the bluff shape you are considering.

4. Actual surface area of the body (used rarely, if ever)

Again, to make comparisons with literature, you must determine what choice they made, and use a consistent definition of reference area.

A body moving through a fluid experiences a drag force, which is usually divided into two components: frictional drag, and pressure drag. ... For a given frontal area and velocity, a streamlined body will always have a lower resistance than a bluff body.

is the flow speed of the object relative to the fluid, is the reference area. The reference area depends on what type of drag coefficient is being measured. For automobiles and many other objects, the reference area is the projected frontal area of the vehicle.

A body moving through a fluid experiences a drag force, which is usually divided into two components: frictional drag, and pressure drag. Frictional drag comes from friction between the fluid and the surfaces over which it is flowing. This friction is associated with the development of boundary layers, and it scales with Reynolds number as we have seen above. Pressure drag comes from the eddying motions that are set up in the fluid by the passage of the body. This drag is associated with the formation of a wake, which can be readily seen behind a passing boat, and it is usually less sensitive to Reynolds number than the frictional drag. Formally, both types of drag are due to viscosity (if the body was moving through an an in-viscid fluid there would be no drag at all), but the distinction is useful because the two types of drag are due to different flow phenomena. Frictional drag is important for attached flows (that is, there is no separation), and it is related to the surface area exposed to the flow. Pressure drag is important for separated flows, and it is related to the cross-sectional area of the body.

We can see the role played by friction drag (sometimes called viscous drag) and pressure drag (sometimes called form drag or profile drag) by considering an airfoil at different angles of attack. At small angles of attack, the boundary layers on the top and bottom surface experience only mild pressure gradients, and they remain attached along almost the entire chord length. The wake is very small, and the drag is dominated by the viscous friction inside the boundary layers. However, as the angle of attack increases, the pressure gradients on the airfoil increase in magnitude. In particular, the adverse pressure gradient on the top rear portion of the airfoil may become sufficiently strong to produce a separated flow. This separation will increase the size of the wake, and the pressure losses in the wake due to eddy formation Therefore the pressure drag increases. At a higher angle of attack, a large fraction of the flow over the top surface of the airfoil may be separated, and the airfoil is said to be stalled. At this stage, the pressure drag is much greater than the viscous drag .

When the drag is dominated by viscous drag, we say the body is streamlined, and when it is dominated by pressure drag, we say the body is bluff. Whether the flow is viscous-drag dominated or pressure-drag dominated depends entirely on the shape of the body. A streamlined body looks like a fish, or an airfoil at small angles of attack, whereas a bluff body looks like a brick, a cylinder, or an airfoil at large angles of attack. For streamlined bodies, frictional drag is the dominant source of air resistance. For a bluff body, the dominant source of drag is pressure drag. For a given frontal area and velocity, a streamlined body will always have a lower resistance than a bluff body. For example, the drag of a cylinder of diameter $D$ can be ten times larger than a streamlined shape with the same thickness .

Cylinders and spheres are considered bluff bodies because at large Reynolds numbers the drag is dominated by the pressure losses in the wake.

You see that as the Reynolds number increases the variation in the drag coefficient (based on cross-sectional area) decreases, and over a large range in Reynolds number it is nearly constant.

Meelan Choudhari Thank you, for your detailed answer.

Yes, I am analyzing the same body shape.

Case 4 (actual surface area) is working out in my case. (I have extracted the surface area by creating a three-dimensional model of the blunt-body using Creo Parametric).

However, I will check up the grid independence and finalise the results.

Thank you.