Calculator Inputs
Large screens use three columns, medium screens use two, and mobile uses one.
Plotly Graph
The graph tracks how Reynolds number, pressure drop, and drag change across a velocity sweep based on your current setup.
Example Data Table
| Case | Density (kg/m³) | Viscosity (Pa·s) | Velocity (m/s) | Length (m) | Reynolds Number | Flow Regime |
|---|---|---|---|---|---|---|
| Air Duct | 1.225 | 0.0000181 | 8.0 | 0.12 | 64,917 | Turbulent |
| Water Pipe | 998 | 0.0010 | 1.5 | 0.05 | 74,850 | Turbulent |
| Oil Channel | 870 | 0.0800 | 0.8 | 0.03 | 261 | Laminar |
Formula Used
Re = (ρ × V × L) / μ
ν = μ / ρ
Q = A × V
ṁ = ρ × Q
q = 0.5 × ρ × V²
Ptotal = P + q
a = √(γ × R × T)
M = V / a
ΔP = f × (L / D) × (0.5 × ρ × V²)
FD = CD × (0.5 × ρ × V²) × Aref
ΔtCFL = CFL × Δx / V
Δtdiff = CFL × Δx² / (2 × ν)
Use consistent SI units for reliable output interpretation. These formulas help with pre-processing, validation, and quick engineering checks before deeper simulation work.
How to Use This Calculator
- Enter fluid properties like density, viscosity, temperature, and pressure.
- Add geometric values such as characteristic length, diameter, and flow area.
- Provide solver-oriented values like grid spacing and target CFL number.
- Set friction and drag coefficients for internal and external force estimates.
- Click Calculate CFD Metrics to show the results above the form.
- Review Reynolds number, Mach number, time-step limits, and force or loss outputs.
- Use the graph to inspect trends with changing velocity.
- Download CSV or PDF copies for reports, reviews, and design notes.
Frequently Asked Questions
1) What does this CFD calculator estimate?
It estimates common pre-simulation quantities such as Reynolds number, Mach number, flow rates, pressure drop, drag force, total pressure, and practical time-step limits. It is useful for setup checks before detailed numerical modeling.
2) Is this a full numerical solver?
No. It does not solve Navier–Stokes equations on a mesh. It gives fast engineering estimates that support boundary-condition checks, grid planning, and early validation before running a dedicated CFD package.
3) Why is Reynolds number important?
Reynolds number compares inertial and viscous effects. It helps identify whether a flow is likely laminar, transitional, or turbulent. That affects turbulence-model choice, expected mixing, wall behavior, and numerical treatment.
4) When should I care about Mach number?
Mach number matters when compressibility becomes significant. For low-speed flows it may be negligible, but as the value rises, density variation, wave effects, and compressible formulations become more important.
5) What is the CFL time-step estimate used for?
It gives a practical upper limit for explicit time stepping based on velocity and grid spacing. Smaller cells or faster flow usually require smaller steps to maintain stable calculations.
6) Why are flow area and diameter both included?
Flow area is used directly for volumetric and mass flow calculations. Diameter is commonly used in internal-flow loss relations and equivalent circular interpretations. Keeping both inputs makes the tool more flexible for mixed engineering cases.
7) Can I use liquids and gases here?
Yes. The calculator works for either, provided you use consistent SI units. For incompressible liquids, Mach number is less meaningful, but the remaining transport and pressure estimates stay useful.
8) How accurate are the results?
Accuracy depends on the quality of your inputs and assumptions. These equations are standard engineering estimates, but final design decisions should still be checked with validated experiments or detailed numerical simulations.