DRAG
Overview
The DRAG function calculates the drag coefficient (C_D), a dimensionless quantity that characterizes the drag resistance of an object moving through a fluid. This coefficient is fundamental in aerodynamics, hydrodynamics, and many engineering applications where understanding fluid resistance is critical.
The drag coefficient relates the drag force experienced by an object to the fluid’s dynamic pressure and the object’s projected area. This implementation uses the fluids library, a comprehensive Python package for fluid dynamics calculations. For detailed documentation, see the fluids.core module reference.
The drag coefficient is calculated using the standard formula:
C_D = \frac{F_d}{A \cdot \frac{1}{2} \rho V^2}where F_d is the drag force in Newtons, A is the projected area in square meters, \rho is the fluid density in kg/m³, and V is the characteristic velocity in m/s. The denominator represents the dynamic pressure (or velocity head) multiplied by the reference area.
The drag coefficient depends on the object’s shape, surface roughness, and the Reynolds number of the flow. For common shapes, C_D values range from approximately 0.04 for streamlined airfoils to 1.0-1.2 for flat plates perpendicular to flow. This function is particularly useful when the drag force has been measured experimentally and the dimensionless coefficient is needed for scaling or comparison purposes.
This example function is provided as-is without any representation of accuracy.
Excel Usage
=DRAG(F, A, V, rho)F(float, required): Drag force in Newtons (N)A(float, required): Projected area in square meters (m²)V(float, required): Velocity in meters per second (m/s)rho(float, required): Fluid density in kilograms per cubic meter (kg/m³)
Returns (float): Drag coefficient (float), or error message string.
Examples
Example 1: Demo case 1
Inputs:
| F | A | V | rho |
|---|---|---|---|
| 1000 | 0.0001 | 5 | 2000 |
Excel formula:
=DRAG(1000, 0.0001, 5, 2000)Expected output:
400
Example 2: Demo case 2
Inputs:
| F | A | V | rho |
|---|---|---|---|
| 500 | 0.05 | 10 | 1000 |
Excel formula:
=DRAG(500, 0.05, 10, 1000)Expected output:
0.2
Example 3: Demo case 3
Inputs:
| F | A | V | rho |
|---|---|---|---|
| 250 | 0.02 | 8 | 900 |
Excel formula:
=DRAG(250, 0.02, 8, 900)Expected output:
0.434
Example 4: Demo case 4
Inputs:
| F | A | V | rho |
|---|---|---|---|
| 120 | 0.01 | 15 | 1.2 |
Excel formula:
=DRAG(120, 0.01, 15, 1.2)Expected output:
88.89
Python Code
import micropip
await micropip.install(["fluids"])
from fluids.core import Drag as fluids_drag
def drag(F, A, V, rho):
"""
Calculate the drag coefficient (dimensionless) for an object in a fluid.
See: https://fluids.readthedocs.io/fluids.core.html
This example function is provided as-is without any representation of accuracy.
Args:
F (float): Drag force in Newtons (N)
A (float): Projected area in square meters (m²)
V (float): Velocity in meters per second (m/s)
rho (float): Fluid density in kilograms per cubic meter (kg/m³)
Returns:
float: Drag coefficient (float), or error message string.
"""
try:
F_val = float(F)
A_val = float(A)
V_val = float(V)
rho_val = float(rho)
except Exception:
return "Invalid input: could not convert arguments to float."
if A_val == 0:
return "Invalid input: area cannot be zero."
if V_val == 0:
return "Invalid input: velocity cannot be zero."
if rho_val == 0:
return "Invalid input: density cannot be zero."
if A_val < 0:
return "Invalid input: area must be positive."
if rho_val < 0:
return "Invalid input: density must be positive."
try:
result = fluids_drag(F_val, A_val, V_val, rho_val)
except Exception as e:
return f"Error: {str(e)}"
return result