# Time-Averaged Slice Output

Time-Averaged Slice Output in Flow360 allows you to calculate and visualize time-averaged flow variables on 2D cutting planes through the computational domain. This provides statistical data essential for analyzing unsteady flows while keeping file sizes much smaller than full volume outputs.

Note: Time-averaged outputs are only available when using unsteady time stepping methods.

# 📋 Available Options

Option	Description	Unit
`Name`	A descriptive name for the output
`Output Format`	Format for saving slice data
`Slices`	Definition of slice planes
`Output Fields`	Flow variables to include in the output
`Frequency`	How often to save outputs	time steps
`Frequency Offset`	Time step at which to start the output animation	time steps
`Start Step`	When to begin time-averaging	time steps

# 🔍 Detailed Descriptions

# `Name`

A descriptive identifier for this time-averaged slice output.

Default: Time average slice output
Example: Time Averaged Wing Section
Notes: Choose a name that helps identify the purpose of this output.

# `Output Format`

The file format used to save the slice output data.

Default: paraview
Example: both
Notes: Options include "paraview", "tecplot", or "both".

# `Slices`

Defines the 2D cutting planes through the computational domain.

Example: {"name": "MidSpan", "origin": [0, 0.5, 0], "normal": [0, 1, 0]}
Notes: Each slice requires a name, origin point, and normal direction vector.

# `Output Fields`

Select the flow variables to include in the slice output.

Default: None selected
Example: Mach, pressure, velocity
Notes: See detailed field descriptions in the Slice Output page. Only select fields you need to analyze to keep file sizes manageable.

# `Frequency`

How often to save outputs, in number of physical time steps.

Default: -1 (only at end of simulation)
Example: 10
Notes: Higher frequencies provide better temporal resolution but increase storage requirements.

# `Frequency Offset`

The time step at which to start the output animation.

Default: 0 (beginning of simulation)
Example: 100
Notes: Useful when you want to skip initial transient flow development.

# `Start Step`

Specifies the physical time step to start calculating time averaging.

Default: -1 (automatic detection)
Example: 50
Notes: Set this to begin averaging after initial transients have died out. When set to -1, the solver will automatically determine when to start averaging based on flow convergence.

💡 Tips

Time-averaged slice output is particularly useful in the following scenarios:

Analyzing unsteady flows: For flows with inherent unsteadiness (like vortex shedding, turbulent wakes, or separated flows), time-averaging on strategic slice planes provides mean flow statistics.
Reducing storage requirements: Instead of saving many instantaneous snapshots, you can capture the statistical behavior with a single time-averaged result.
Flow stability assessment: Time-averaged slices help determine if a flow has reached a statistically steady state in key regions, even if instantaneous values are fluctuating.
Strategic slice placement: Position time-averaged slices at these key locations for maximum insight:
- Wake regions to capture mean wake structures
- Boundary layer regions to observe mean separation behavior
- Shear layers to analyze mean mixing characteristics
- Rotor disk planes for time-averaged BET analysis

# Visual Analysis Tips

When analyzing time-averaged slice data:

Compare with instantaneous slices at the same location to identify regions of high unsteadiness
Look for smoothed features in the time-averaged data that might be obscured by fluctuations in instantaneous snapshots
Create streamlines on time-averaged slices to visualize mean flow patterns
Use multiple slices at different positions to construct a 3D understanding of the mean flow field

❓ Frequently Asked Questions

When should I use time-averaged slices instead of instantaneous slices?
Time-averaged slices are ideal when:
- You're analyzing statistically steady turbulent flows
- You need to filter out transient features or numerical noise
- You want to reduce storage requirements while still capturing overall flow behavior
- You're interested in mean flow characteristics rather than instantaneous snapshots
- You need to identify average positions of features that move over time (e.g., shock waves, separation points)
How does the Start Step parameter affect my results?
The Start Step parameter controls when the solver begins accumulating statistics for time-averaging:
- Setting it too early may include unwanted transient effects in your averages
- Setting it too late may not give enough time for statistical convergence
- The automatic setting (-1) detects when force coefficients begin to oscillate around a mean value
- For better control, monitor your force history and set it manually once transients have subsided
Can I get fluctuation intensity or RMS values from time-averaged slices?
Currently, Flow360 time-averaged outputs include mean values only, not RMS or fluctuation intensities. To obtain these:
- Export both instantaneous and time-averaged slice data
- Post-process using ParaView/Tecplot to calculate RMS values
- For turbulence quantities, consider using the k and omega fields which represent turbulent kinetic energy and specific dissipation rate
How many slices can I define for time-averaging?
There is no hard limit on the number of slices you can define for time-averaging, but consider:
- Each slice adds memory overhead during the simulation
- Too many slices may impact performance
- Start with strategically placed slices and add more if needed
Can I use both time-averaged and instantaneous slice outputs in the same simulation?
Yes, you can define separate outputs for:
- Time-averaged slices for statistical analysis
- Instantaneous slices for capturing transient phenomena This approach provides comprehensive coverage of both mean flow characteristics and unsteady features.

🐍 Python Example Usage

# Example of configuring time-averaged slice output
from flow360 import u
import flow360 as fl

# Define time-averaged slice output settings
time_avg_slice = fl.TimeAverageSliceOutput(
    name="Time Averaged Wing Sections",
    output_format="paraview",
    slices=[
        fl.Slice(
            name="Root", 
            origin=(0, 0, 0) * u.m, 
            normal=(0, 1, 0)
        ),
        fl.Slice(
            name="Midspan", 
            origin=(0, 0.5, 0) * u.m, 
            normal=(0, 1, 0)
        ),
        fl.Slice(
            name="Tip", 
            origin=(0, 1.0, 0) * u.m, 
            normal=(0, 1, 0)
        )
    ],
    output_fields=["Mach", "pressure", "velocity", "Cp", "Cpt"],
    frequency=10,           # Save results every 10 time steps
    frequency_offset=100,   # Start saving at time step 100
    start_step=50           # Begin averaging at time step 50
)

# Add to simulation parameters
simulation_params = fl.SimulationParams(
    # ... other simulation parameters ...
    outputs=[time_avg_slice]
)

← Slice Output Probe Outputs →

# Time-Averaged Slice Output

# 📋 Available Options

# 🔍 Detailed Descriptions

# Name

# Output Format

# Slices

# Output Fields

# Frequency

# Frequency Offset

# Start Step