Turbo - Recent Threads

Analysis of Flow Physic within Tip Clearance Gap of an Unshrouded high pressure Turbine Blade

FA20260604939 — Fri, 05 Jun 2026 02:10:10 GMT

Hello everyone,

I'm currently using Fidelity Turbo to generate a mesh for an unshrouded high-pressure turbine blade. This particular blade features a sharp pressure-side gap corner and a tip thickness that is five times the gap height (t > 4h). Before I run the simulation, I would appreciate it if someone could provide an explanation of the following question:

What is the most accurate description of the expected flow physics within the tip clearance gap, and what is the primary driving mechanism behind the resulting efficiency losses?

The options are as follows:

A) The flow will separate at the sharp corner and remain entirely detached across the gap, with the main loss being driven by centrifugal forces mixing at the hub.

B) A separation bubble will form at the sharp corner, but the flow will reattach before exiting, with the primary loss being driven by the pressure differential moving flow from the pressure side to the suction side.

C) The flow will remain perfectly attached due to the high thickness-to-gap ratio (t/h = 5), and the primary loss will be strictly due to over-tip thermal heat transfer penalties.

D) A vena contracta will form, causing immediate supersonic choking, with the primary loss being driven by shockwave-boundary layer interaction near the stationary casing.

RE: Analysis of Flow Physic within Tip Clearance Gap of an Unshrouded high pressure Turbine Blade

Gaurav — Tue, 09 Jun 2026 11:44:46 GMT

When flow enters a tip gap with a sharp pressure-side corner, it undergoes a sharp contraction, resulting in a flow restriction known as a vena contracta. This phenomenon causes a separation bubble to form immediately after the corner. Whether the flow reattaches to the blade surface depends largely on the ratio of the blade tip thickness (t) to the gap height (h).

There are two distinct scenarios based on this ratio:

For thin blades, where the thickness is less than four times the gap height (t < 4h), the separation bubble dominates the flow, often extending across the entire blade thickness and preventing the flow from reattaching.

In contrast, for thicker blades, where the thickness exceeds four times the gap height (t > 4h), the physical surface area is sufficient for the flow to mix, recover, and reattach to the blade tip before exiting into the suction side. Specifically, given the blade's thickness being five times the gap height, reattachment of the flow is assured.

In the context of unshrouded turbomachinery blades, the primary driving force behind leakage is the aerodynamic load on the blade, specifically the pressure difference between the high-pressure (pressure side) and low-pressure (suction side) surfaces. This pressure gradient effectively forces fluid through the clearance gap.

The resulting over-tip leakage flow has two significant consequences:

1. Aerodynamic losses: These losses account for approximately one-third of the total losses in a turbine stage. Even a relatively small gap height, equivalent to just 1% of the total blade span, can result in a stage efficiency penalty of 1 to 3 percent or more.

2. Thermal losses: The high-velocity over-tip flow significantly enhances convective heat transfer coefficients, subjecting the blade tip region to extreme thermal loads.

Turbulence Model Comparison for Compressors SST vs k-ω vs RSM

Gaurav — Mon, 16 Mar 2026 04:46:17 GMT

Turbulence modeling plays a vital role in compressor simulations by enabling accurate prediction of complex flow phenomena. These phenomena, including strong pressure gradients, boundary-layer separation, and rotational effects, pose significant challenges for numerical simulations. To address these complexities, various turbulence models have been developed, each offering unique advantages and limitations. The choice of turbulence model, such as the Shear Stress Transport (SST) K-omega, Standard K-omega, and Reynolds Stress Model (RSM), significantly affects the accuracy, numerical stability, and computational cost of the simulation. Selecting the most suitable model is crucial to achieving reliable results while minimizing computational resources.

The SST K-Omega turbulence model, also known as the Shear Stress Transport model, is widely regarded as an industry standard for turbomachinery and compressors. This model effectively combines the near-wall accuracy of the K-Omega model with the free-stream independence of the K-Epsilon model. The resulting hybrid approach enables excellent predictions of flow separation under adverse pressure gradients. As a result, the SST K-Omega model is well-suited for addressing complex compressor flows. Its reliability in predicting compressor performance and capturing separation in diffusers has made it a preferred choice in industry applications. However, its accuracy can be limited in highly curved flows unless curvature corrections are applied.

The Standard K-Omega turbulence model is widely used in computational fluid dynamics for its ability to accurately capture near-wall boundary layer flow. This model is notable for its improved performance in the viscous sublayer, yielding more accurate results than the K-Epsilon model without the need for complex damping functions. The Standard K-Omega model is particularly well-suited for capturing fluid flow behavior in regions with significant near-wall interactions. However, its application is often limited by extreme sensitivity to inlet boundary conditions, which can lead to instability and inaccuracy in complex or rapidly changing flows. In compressor simulations, the Standard K-Omega model has largely been superseded by the SST K-Omega model due to stability concerns. Despite its limitations, the Standard K-Omega model remains a widely utilized tool in turbulence modeling.

The Reynolds Stress Model (RSM) is a turbulence modeling approach that delivers high-fidelity simulations of complex, highly swirling, or rotating flows, making it an attractive choice for applications that require detailed flow-field analysis. By directly solving the Reynolds stress transport equations, RSM relaxes the isotropic eddy-viscosity assumption commonly used in K-Omega models, allowing for a more accurate capture of turbulence anisotropy in rotating impellers. This, in turn, enables the model to effectively simulate the intricate flow dynamics present in such applications. However, the increased accuracy of RSM comes at a high computational cost, requiring up to 7 equations to be solved, which can lead to convergence issues and reduced numerical stability.

Understanding GPU Acceleration in Fidelity Fine Turbo Solver

Gaurav — Tue, 03 Mar 2026 03:17:56 GMT

This article explains key considerations for using GPU acceleration in Fidelity Fine Turbo Solver, including the maximum number of queues, former RAM limitations, and how to submit a GPU job. By understanding these concepts, users can optimize their solver configurations and take full advantage of GPU acceleration.

Troubleshooting GPU simulation setup in Fidelity Fine Turbo 2025.2

Common Mistakes in Rotor–Stator Interface Setup

Gaurav — Mon, 09 Feb 2026 05:15:42 GMT

Correctly defining the rotor–stator interface is one of the most critical—and most frequently mishandled—steps in turbomachinery CFD. Even with good mesh and solver settings, small mistakes at the interface can lead to non‑physical losses, convergence problems, or completely misleading performance predictions.

What are Rotor-stator connections?

If two neighboring domains have different rotational speeds, a rotor-stator connection is required between them.

When a rotor-stator connection is present, the user has to:

Create a connection
Define the rotor-stator boundaries (automatic)
Select a rotor-stator treatment approach to simulate the interaction between the two domains

Using the Wrong Interface Type

Mistake
Applying an inappropriate interface model, such as:

Using Frozen Rotor when strong unsteady effects are present
Using the Stage / Mixing Plane when blade-to-blade interaction is important

Why It’s a Problem

Frozen Rotor preserves circumferential non-uniformity but assumes a steady relative position
Mixing Plane circumferentially averages the flow, eliminating wakes and potential fields
An incorrect choice can suppress or exaggerate losses, pressure rise, and unsteadiness

How to Avoid

Use a Full Non-Matching Frozen Rotor for:

Steady-state approximation

Initial convergence or design screening

Use a Full Non-Matching Mixing Plane for:

Overall performance maps

Steady

A pitchwise averaging of the flow solution is performed at the rotor-stator interface, and the exchange of information at the interface depends on the local direction of the flow.

Unsteady (Harmonic)

A pitchwise averaging of the flow solution is performed at the rotor-stator interface for the turbulence equations. For other equations, a reconstruction based on the spatial Fourier decomposition is used to ensure continuity at the rotor-stator interface, and a 1D non-reflecting treatment is applied. The exchange of information at the interface depends on the local direction of the flow.

Use Transient Sliding Mesh when:
- Wake passing, blade vibration, or noise is important
- Accurate unsteady forces are required

Are there any other useful tips or points that others could share for the benefit of fellow CFD users?

RE: Common Mistakes in Rotor–Stator Interface Setup

Gaurav — Mon, 16 Feb 2026 01:45:57 GMT

Some other points that can affect the Rotor-Stator Interface setup are as follows:

2. Inconsistent Rotational Speed or Axis Definition: A mistake in this regard can lead to errors in the setup.

Specific mistakes to watch out for include:

The rotor speed is being defined incorrectly in terms of its sign, magnitude, or units.
The rotor axis is not aligned with the geometry.

Why is this a problem?

It causes incorrect calculations of Coriolis and centrifugal forces.
This, in turn, results in incorrect predictions of swirl, pressure rise, and efficiency.
Often, these errors lead to subtle but severe performance issues.

How to avoid these mistakes:

Double-check the following:

o The magnitude and direction of the angular velocity.

o The origin and orientation of the rotation axis.

Visually confirm the rotation direction by:

o Examining velocity vectors.

o Analyzing relative frame plots.

3. Poor mesh quality at the interface includes:

A significant cell size discrepancy across the interface.

Highly skewed or non-orthogonal faces at the interface.

Non-matching meshes with inadequate interpolation quality.

Why is this a problem?

Maintaining poor mesh quality at the interface can lead to:

Increased numerical diffusion.

Smearing of wakes and secondary flows.

Unstable convergence or excessive residual values.

To avoid these issues:

Ensure consistent cell sizes on both sides of the interface.

Verify the following:

Low skewness.
Smooth growth rate when approaching the interface.

Refine the mesh in the following areas:

Wake regions, Tip clearance zones near the interface.

Turbomachinery Mesh Topologies: When to Use H, C, or O-Grids?

Gaurav — Sun, 25 Jan 2026 13:09:35 GMT

The choice of mesh topology directly impacts accuracy, convergence, and computational cost in turbomachinery simulations.

H-Grid

Structure: Grid lines form an “H” pattern across the domain.

Best Use Cases:

- Far-field regions where flow is relatively uniform.
- Simple geometries with minimal curvature.
- Capturing inlet/outlet boundary conditions in turbomachinery passages.

Advantages:

- Easy to generate and extend to infinity (good for external flows).
- Efficient for coarse far-field resolution.

Limitations:

- Poor resolution near trailing edges and wakes.
- Not ideal for curved blade surfaces.

C-Grid

Structure: Grid wraps around the trailing edge, forming a “C” shape.

Best Use Cases:

- Turbomachinery blades with sharp trailing edges.
- Capturing wake development and downstream flow separation.
- High-speed flows.

Advantages:

- Excellent wake resolution behind blades.
- Smooth clustering near trailing edges.

Limitations:

- More complex to generate than H-grids.
- May require hybridization with O-grids near leading edges.

O-Grid

Structure: Grid lines wrap around the blade surface in concentric “O” rings.

Best Use Cases:

- Resolving boundary layers around curved surfaces (airfoils, turbine blades).
- Capturing secondary flows in blade passages.
- Handling strong curvature and tip leakage flows.

Advantages:

- High-quality boundary layer resolution.
- Smooth orthogonality near walls → better y+ control.

Limitations:

- Difficult to extend to far-field without combining with H-grids.
- More computationally expensive due to clustering near walls.

Key Considerations:

Hybrid Topologies: O-grids near blades, C-grids at trailing edges, and H-grids in the far field are often combined for optimal accuracy and efficiency.

Physics-driven choice: Select topology based on whether the priority is boundary layer resolution (O-grid), wake capture (C-grid), or far-field uniformity (H-grid).

Computational trade-off: O-grids give the best accuracy near walls but increase cell count; H-grids are cheapest but least accurate near complex blade regions.

If anyone would like to share additional information based on their experience, it would benefit CFD users.

How to Improve Convergence in Multi-stage Axial Compressor Simulations ?

Gaurav — Sun, 18 Jan 2026 07:14:07 GMT

Achieving stable and accurate convergence in multi-stage axial compressor simulations can be challenging due to the complex unsteady flow physics and high computational demands. Here are the essential best practices that will significantly improve convergence:

Use high-quality structured meshes with adequate resolution near blade surfaces, tip gaps, and hub regions.
Ensure smooth grid transitions between stages to minimize numerical oscillations.
Apply mesh refinement in critical flow regions such as boundary layers, wakes, and tip leakage paths.
Start with steady RANS solutions before moving to unsteady simulations.
Apply physically realistic inlet/outlet boundary conditions with proper turbulence intensity and flow angles.
Select robust implicit time stepping schemes for unsteady runs.
Use relaxation factors and under-relaxation for pressure and velocity coupling to dampen oscillations.
Track mass flow balance across stages to ensure physical consistency.
Monitor blade loading and pressure-ratio trends rather than relying solely on residuals.
Consider multi-grid acceleration to improve solver efficiency.
Apply periodic boundary conditions carefully to reduce the domain size while maintaining accuracy.

If anyone would like to share additional information based on their experience, it would benefit CFD users.

What are the key considerations for simulating turbomachinery with tip gaps?

Gaurav — Mon, 08 Dec 2025 05:13:23 GMT

Turbomachines often feature clearance gaps between rotating blade tips and the stationary casing. Tip leakage flow occurs through these gaps, producing substantial losses. The magnitude of these losses is approximately linearly proportional to the gap height, with the proportionality constant (leakage loss slope) depending on the blade design.

Turbine tip leakage flows account for approximately one-third of the total loss in a turbine stage. Tip leakage loss increases roughly linearly with the height of the tip gap and incurs a penalty of 1-3 percent or more in stage efficiency when the gap height equals 1 percent of the blade span. Additionally, the over-tip flow can enhance heat transfer in the tip region.

The flow through the gap can be modeled using a vena contracta with a coefficient of discharge. A separation bubble forms if the pressure side gap corner is sharp. However, the flow reattaches before exiting the gap if the blade tip thickness is greater than approximately four times the gap height.

Two primary blade designs exist: shrouded and unshrouded. Unshrouded blades have a gap between the tip and the casing, where pressure drives flow from the pressure side to the suction side. This leakage flow creates losses within the gap and also upon mixing with the mainstream flow. Shrouded blades, on the other hand, have a seal-forming endwall at the blade tips, minimizing leakage flow. The leakage flow in unshrouded blades can significantly impact the efficiency of turbomachines. Understanding the dynamics of tip leakage flow is crucial for optimizing the performance of turbomachines.

In the case of a thick blade, the flow mixes and reattaches in such a way that the separation bubble does not extend across the entire blade thickness, unlike in the case of a thin blade. For both thick and thin blades, the vortex and its direction of rotation are on the suction side of the blade passage.

When simulating tip-leakage flow, several important points should be taken into consideration.

Key factors to keep in mind include:

Ensuring the tip height is accurate and matches the design specifications.
Verifying that the tip gap is fully meshed, free from holes, and negative volumes.
Maintaining a proper boundary layer thickness on the blade tip.
Achieving sufficient resolution to effectively capture the leakage vortex core.
Ensuring a smooth mesh transition between the main passage and the tip gap.

Are there any additional important points that others can contribute based on their experience and research?

RE: What are the key considerations for simulating turbomachinery with tip gaps?

Gaurav — Mon, 05 Jan 2026 11:35:25 GMT

This information will guide you on how to add and define a tip gap in the Fidelity Turbomachinery application. A tip-gap is a critical feature in turbomachinery design, and accurately modeling it is essential for precise simulations.

To add a gap, follow these steps:

In the Geometry context, select the blade entity in the left tree.

Open the Hub gap/fillet or Tip gap/fillet tab in the properties panel.
Activate Gap definition. Note that when a gap is added, the Fillet definition is blocked, except for partial fillets.

There are two ways to define the gap geometry:

Method 1: Importing a Defined Curve

Click on the Import gap geometry curve from DAT file icon or Link gap geometry curve from CAD icon.

Select a curve data ".dat" file or link curve(s) in the geometry view.
If the import or link is successful, a message will appear indicating "Curve imported successfully" or "Curve linked successfully".
The Defined curve option is automatically selected.
The Width at leading/trailing edge values are updated accordingly.
Use the Toggle curve visibility icon to preview the gap curve in the meridional view.

Important Note: The imported or linked curve must not intersect any control lines defined outside the blade.

Method 2: Channel Offset

Select the Channel offset option.

Specify the Width at leading edge and the Width at the railing edge to determine the size of the gap at the leading and trailing edge of the blade.
The gap curve is constructed as a linear offset of the hub (or the shroud) based on the specified values.
Use the Toggle curve visibility icon to preview the gap curve in the meridional view.

By following these steps, you can accurately add and define a gap geometry in the Turbomachinery application, enabling you to perform precise simulations and optimize your turbomachinery design.

RE: Automate Fine/turbo workflow

Delfim Sa — Mon, 25 Aug 2025 11:22:44 GMT

Thank you very much for your reply. Sorry for my late follow-up. I got married in the meantime.

I am following your advice, and I can create the .py script for the run file, but not for the mesh. I do the mesh, and when I go to File>Scripts>Save All the .py for the meshing appears empty?

What am I doing wrong?

Automate Fine/turbo workflow

Delfim Sa — Thu, 10 Jul 2025 13:36:12 GMT

Hello,

I am doing a otimization without using the available with the Fine/turbo software. I have a python script that generates geometries and I want to use a genetic algorithm to obtain the optimized geometry.

For this I need to fully automate the mesh generation, the simulation setup and simulations start. Using pythong or macro.

My question is: is there any tutorial or manual where I can find this information? Is this possible with the fineturbo software?

Regargs,

Delfim Sá

Fidelity Fine Turbo Simulation on Linux: How to Set Up and Run in Sequential and Parallel Modes

Gaurav — Tue, 15 Jul 2025 07:30:22 GMT

support.cadence.com/.../ArticleAttachmentPortal

This document is divided into three main sections, each addressing a distinct aspect of
using Fine Turbo on a Linux machine.
• The first section briefly overviews creating a simulation directory using the
Fine/Turbo GUI.
• The second section delves into the process of creating a simulation directory and
running the file in interactive mode.
• The third section offers detailed instructions on setting up and running a parallel
simulation in interactive mode, catering to users who require more advanced
simulation capabilities

RE: Automate Fine/turbo workflow

Gaurav — Mon, 14 Jul 2025 10:27:16 GMT

I understand you're looking to automate the mesh generation, simulation setup, and simulation start process using Fine/turbo software. While we don't have a dedicated tutorial for fully scripting this workflow, I can guide you through an alternative approach.

Step 1: Perform the workflow manually in the GUI: Set up your mesh generation, simulation setup, and simulation start once through the Fine/turbo graphical user interface (GUI). This will create a baseline configuration for your automation process.

Step 2:Record the macro: While performing the workflow manually, record a macro using Fine/Turbo's macro recording feature. This will capture the sequence of actions taken during the setup and simulation process.

RE: Optimization on Fine/turbo

Delfim Sa — Tue, 20 May 2025 13:03:55 GMT

Thank you for you reply. But i have a geometry generation code and want to couple it to Turbo using a genetic algorithm to do this optimization. Has it been done before? Any tips?

Optimization on Fine/turbo

Delfim Sa — Tue, 13 May 2025 09:37:05 GMT

Hello,

I am going to do a optimization of a turbine rotor using Fine/turbo and wanted to know if any member of this community was ever done a optimization.

I am looking for tips or tricks that you used. Or even a full tutorial.

Thank you.

Regards,

Delfim Sá

RE: Optimization on Fine/turbo

Gaurav — Wed, 14 May 2025 08:42:41 GMT

You can go through the Fine/Design3D tutorial, specifically Tutorial 1: "AXIAL COMPRESSOR ROTOR37." This tutorial provides more information on how to perform optimization.

RE: Making a air duck in FineTurbo

Delfim Sa — Tue, 13 May 2025 09:31:26 GMT

Thank you for your help. I was able to do it

Making a air duck in FineTurbo

Delfim Sa — Wed, 16 Apr 2025 15:07:24 GMT

Hello,

I need to study an air duct with no blades. I will only change the duck's geometry. Is it possible to mesh and simulate a bladeless duck in FineTurbo?

How would I do it?

RE: Making a air duck in FineTurbo

KBBKBB — Tue, 29 Apr 2025 05:22:47 GMT

Why? Can't you find the entry in the manual? It should look like this:

And I think what you are looking for is an example autogrid project.
But unfortunatly I can't help with that.

RE: Making a air duck in FineTurbo

Delfim Sa — Thu, 17 Apr 2025 15:40:51 GMT

Is there any geoturbo file available as an example?

RE: Making a air duck in FineTurbo

Delfim Sa — Thu, 17 Apr 2025 11:31:44 GMT

Thank you for your reply. Yes, I meant air duct. I will look into bladeless mesh.

RE: Making a air duck in FineTurbo

KBBKBB — Thu, 17 Apr 2025 06:05:54 GMT

Hi Delfim,

By any chance, did you mean air duct?

In any case, I recommend checking the Fine/Turbo documentation and searching for “bladeless.”

Bladeless Mesh

The option allows to mesh a row without a blade. To correctly setup the inlet/rotor-stator/outlet, a blade entity is defined but only by its leading/trailing edge: only the leading and trailing edges intersecting the channel curves should be linked to the blade and no surfaces should be imported for the blade.

Then the mesh will be a 5 H-blocks topology controlled by the flow paths & the blade-to-blade parameters. The H-blocks position and grid points are controlled only by the blade-to-blade parameters and not by the leading and trailing edge positions. The row is without blade thus no control on the blade geometry (gap/fillet) and on the blade-to-blade topology (staggered, blunt,...) is allowed.

Cheers

RE: FineTurbo: Solver gets stuck

KBBKBB — Thu, 17 Apr 2025 05:40:29 GMT

Hi Delfin,

Some of my colleagues, who primarily use the legacy Fine/Turbo tools (but the newer versions), occasionally experience similar issues. They often have to restart the simulation to get it running properly.

Are you working on a Windows system? Running the simulations on Linux might help avoid such problems. Personally, I mainly work with Fidelity and haven’t encountered these issues.

I agree—getting this kind of error during an optimization run is really inconvenient.

Here’s what I would suggest:

Periodically check the log file where the output is written (is that the .std file, perhaps?). If the last entry doesn’t change for a certain amount of time, abort the simulation and restart it.
Alternatively, you could monitor the size of the .std file. If it doesn’t increase over time (as it should while more entries are being added), take that as a sign to abort and restart the simulation.

FineTurbo: Solver gets stuck

Delfim Sa — Fri, 20 Dec 2024 21:08:00 GMT

I am using FineTurbo 18, and when I put in a simulation, most of the time, it gets stuck on this:

BLOCK 47 : Transfer initial solution for turbomachinery
BLOCK 4 : Transfer initial solution for turbomachinery
BLOCK 31 : Transfer initial solution for turbomachinery
BLOCK 43 : Transfer initial solution for turbomachinery
BLOCK 37 : Transfer initial solution for turbomachinery
BLOCK 42 : Transfer initial solution for turbomachinery
BLOCK 11 : Transfer initial solution for turbomachinery
BLOCK 28 : Transfer initial solution for turbomachinery
BLOCK 14 : Transfer initial solution for turbomachinery

Then, I need to stop it and rerun it until it passes this phase.

What do I do to avoid this?

I am planning on doing an optimization, and I don't want this type of problem.

What do I do?

Regards and Merry Christmas and a Happy New Year,

Delfim Sá