Example: Internal Pipe Flow

Example: Internal Pipe Flow#

This example demonstrates simulating turbulent flow through a pipe system with bends. You’ll calculate pressure drop, visualize velocity profiles, and examine secondary flow patterns at bends.

Objective#

  • Generate a mesh inside a pipe geometry with boundary layers

  • Run a RANS simulation for turbulent pipe flow

  • Calculate total pressure drop across the system

  • Visualize velocity profiles and secondary flows at bends

Step 1: Create a Meshing Project#

  1. Dashboard → New Project → Meshing

  2. Name: “Pipe Flow Analysis”

  3. Upload your pipe geometry (STEP preferred for clean face identification)

Step 2: Geometry Check#

Internal flow geometries need special attention:

  • The geometry defines the fluid volume (the inside of the pipe)

  • Inlet and outlet faces must be identifiable (flat faces at pipe ends)

  • The pipe wall must be a closed, connected surface

If your CAD file is a solid pipe (not the fluid volume), you’ll need to extract the internal volume in your CAD software before uploading.

Step 3: Domain Configuration#

In the Setup tab:

  1. Select Internal Flow domain type

  2. Studio detects the fluid volume inside the geometry

  3. Inlet and outlet faces are identified automatically (or select them manually)

Tip

For straight pipes, add a development length of 10× pipe diameter upstream of any features of interest. This allows the flow to become fully developed before reaching the bend or restriction.

Step 4: Surface Naming#

Surface

Name

Type

Pipe entrance

inlet

Velocity inlet

Pipe exit

outlet

Pressure outlet

Pipe wall

pipe_wall

No-slip wall

Step 5: Mesh Settings#

For a pipe with diameter D:

Parameter

Value

Target cell size

D / 20

Min cell size

D / 100

Refinement levels

8

Boundary layers

Enabled

Number of layers

10

First layer height

Based on y+ target

Growth rate

1.2

Sizing Example (50 mm diameter pipe)#

Parameter

Value

Target cell size

2.5 mm

Min cell size

0.5 mm

BL first layer

0.05 mm (y+ ≈ 30 at 5 m/s)

BL layers

10

Bend Refinement#

Add a refinement zone around each pipe bend:

  • Shape: Cylinder (aligned with bend axis)

  • Radius: 1.5× pipe radius

  • Extends: 2× diameter before and after the bend centerline

  • Cell size: 2× finer than base mesh

Step 6: Generate Mesh and Create CFD Project#

  1. Generate the mesh (expect 1–5 million cells for a medium pipe system)

  2. Create a new CFD project using this mesh

Step 7: Simulation Setup#

Setting

Value

Turbulence model

k-ω SST or k-ε

Inlet velocity

Bulk velocity (e.g., 5 m/s)

Outlet pressure

0 Pa

Pipe wall

No-slip wall

Turbulence intensity

5% (typical for pipe flow)

Turbulent viscosity ratio

10

Max iterations

800

Reynolds Number Check#

Calculate the Reynolds number to confirm turbulent flow:

Re = (ρ × V × D) / μ

For water at 20°C (ρ = 998 kg/m³, μ = 0.001 Pa·s) in a 50 mm pipe at 5 m/s:

Re = (998 × 5 × 0.05) / 0.001 = 249,500 (fully turbulent)

Turbulent pipe flow requires Re > ~4,000.

Step 8: Results Analysis#

Pressure Drop#

  1. Use the Probe tool to measure pressure at the inlet and outlet

  2. Pressure drop = P_inlet - P_outlet

  3. Compare with the Darcy-Weisbach equation for validation:

ΔP = f × (L/D) × (ρV²/2)

Where f is the friction factor from the Moody chart.

Velocity Profiles#

  1. Add slice planes perpendicular to the pipe axis at locations of interest:

    • Upstream of bend (fully developed profile)

    • At the bend (distorted profile)

    • Downstream of bend (recovery)

  2. Color by velocity magnitude

What to look for:

  • Fully developed flow shows a symmetric profile (parabolic-like for turbulent flow)

  • At bends, the maximum velocity shifts toward the outer wall

  • Recovery length downstream is typically 10–20 diameters

Secondary Flow at Bends#

  1. Add a slice plane at the bend cross-section, colored by through-plane velocity

  2. Add streamlines to visualize Dean vortices (counter-rotating vortex pairs)

  3. These secondary flows are driven by centrifugal effects at the bend

Wall Shear Stress#

  1. Color the pipe_wall surface by velocity gradient

  2. High shear regions appear at the outer wall of bends

  3. Low shear regions (potential for separation) appear at the inner wall

Validation Reference#

For a smooth straight pipe at Re = 100,000:

Quantity

Expected Value

Friction factor (f)

~0.018 (Moody chart)

Centerline velocity

~1.23 × bulk velocity

Skin friction Cf

~0.0045

Pipe Flow Tip

If your results show an asymmetric profile in a straight section, the mesh may be too coarse or the inlet development length too short. Increase the upstream straight section to at least 10D.

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