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.

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?

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?

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

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

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

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?

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

Mesh Non-Orthogonality Issue in AutoGrid5

sima101f — Tue, 26 Nov 2024 08:35:41 GMT

Dear Numeca Team,

I am using AutoGrid5 for my turbomachinery simulations in OpenFOAM, but I’m struggling to achieve a sufficiently good mesh due to high non-orthogonality.

I’ve enabled the expert controls and set the skewness control and gap skewness control to "medium." While the mesh metrics meet Numeca standards, the exported mesh consistently shows very high non-orthogonality near the leading edge across the span during the mesh check (see attached picture).

Could you advise on what might be causing this issue? Despite trying various adjustments, some cells remain problematic, leading to simulation crashes.

Thank you for your help.

Best regards,

Sid

FINE/Turbo cannot open file?

Delfim Sa — Tue, 08 Oct 2024 11:42:32 GMT

I have this simulation file that i what to open with FINE/turbo but when i try to open it says that it cannot open the file i click OK and then this appears:

I am almost certain that all the files are present. This file is more than one year old. Could this be the problem? What do I do?

Regards,

Delfim Sá

CPU Booster residuals oscillating

cfd enthusiast — Thu, 22 Aug 2024 14:42:16 GMT

Hello Everyone,

I am simulating using the Open solver. When i start a simulation using the results of another simulation that is close to the solution I get really high residulas that also oscillate like this:

when I use the cpu booster on my grid the residulas oscillate violently like this: (I am using 3 grid levels with CGI)

when i turn the CPU Booster off:

I don't understand why the residuals behave the way they do here.

My simulations are successful but the convergence isn't reached. The Physical solutions are not too off from reality, however I am worried that my simulation isn't trustworthy because of the reasons above.

What could be the causes that effect?

Thank you!

Python API: Simulation context

cfd enthusiast — Mon, 12 Aug 2024 07:03:40 GMT

Hello Everyone,

I'm trying to automate my simulation settings and I've stumbled upon a hurdle. I want to set the initial solution in my domain to "From solution" and then set my last finished simulation as the simulation to initialize with. I have figured out the first

line of code, which would be: (HexstreamDomainNumericalParameters)....set_initialization_type("From solution"). However, I can't seem to figure out which line of code I should use to load the initial solution from a certain simulation.

Thank you!

Secondary Flow/Vortex Analysis in Streamcut Plane

CFDVoyager — Tue, 06 Aug 2024 21:33:36 GMT

Hello All, I am analyzing secondary flows in a streamcut plane and came across a paper that looked into this however it does not adequately describe a plot(fig attached). The color contour in the paper is relative Mach number, but there are

also contour line-like structures with directions. What do these represent and how do I plot those? Are these q-criterion/lambda-criterion?

Simulation: monitored physical quantaties

cfd enthusiast — Mon, 05 Aug 2024 07:48:58 GMT

Hello Everyone,

I wanted to know how fidelity calculates the physical quantaties (namely the efficiency) in the monitor window during the simulation. I think the efficiency being calculated during the simulation is for the polytropic one, but I'd still like to get a better idea of the formula being used.

Are the equations listed in the documentation? if so where?

Thank you!

transient table in openlabs?

sriluta — Fri, 26 Jul 2024 08:34:50 GMT

Hello together,

iam doing an unsteady Simulation with Omnis. At the inlet iam simulating among others the total temperature as you can see in the picture. The total temperature changes with the azimuth angle theta and the time. So far I reconstructed the points with the fourier series and inplemented in openLabs. Is it also possible to insert a transient table in openlabs as I see an example in the documentary?

Tt(theta, time) = 1650 + (-112)*cos(1.9*tCoord - PI*Time/timePeriod) + 4*sin(1.9*tCoord - PI*Time/timePeriod) and with the other terms. TimePeriod is the time, the shockwave needs to travel around the annulus of my axial turbine.

greetings Hussein

CFView: Unsteady state visualiation

Delfim Sa — Thu, 25 Jul 2024 18:59:09 GMT

I am doing an unsteady state simulation of a stator and rotor, and now I can't visualize the rotor in different positions relative to the stator.

Do I need to have multiple output files?

I am using the steady state initiation.

Regards,

Delfim Sá

Residuals

cfd enthusiast — Mon, 15 Jul 2024 16:02:49 GMT

Hello Everyone,

I've been having some trouble getting my Simulation (using Open Solver) to converge to the Residual I want (-4). I'm using coarse grid initialization and 3 grids for the Simulation. on the first two grids it looks fine, but as soon as the finest grid is reached the residuals don't drop anymore and seem stuck on one value (above -4).

I'm trying to understand what could be causing that. What might help me further is understanding what type of Residuals I'm dealing with; hence my main question would be: How are the representative residuals calculated in fidelity (what metric is being used? L1,L2...). Maybe a convergence criterion of -4 is too high depending on the metric that's being used to get the representative residulas.

Thank you!

Pitch in Unsteady FINE/Turbo

Delfim Sa — Sun, 14 Jul 2024 21:52:47 GMT

When I try to simulate an unsteady case of my turbine, I get this error:

!PITCH ANGLE OF THE MESH SHOULD BE THE SAME AT R/S

After reading the manual, I found that I need to change the number of my guide vanes to match the number of my rotor blades. Is this correct?

What is the best method?

Multigrid in the simulation context

cfd enthusiast — Wed, 10 Jul 2024 12:31:58 GMT

Hello everyone,

I created a Mesh with 3 grids in the Mesh context. In the simualtion context I choose to simulate on one grid instead of all 3. Does fidelity simulate on the fine or the corase mesh if I do that?

Thank you!

Unsteady Tutorial for FINE:Turbo

Delfim Sa — Mon, 08 Jul 2024 13:02:15 GMT

Good morning,

I am looking for a tutorial or a run down of how to a unsteady simulation from the mesh to the post-processing for FINE:Turbo.

Where should I start?

Regards,

Delfim Sá

Python API in the Simulation context

cfd enthusiast — Mon, 01 Jul 2024 12:21:26 GMT

Hello Everyone,

I am currently writing a script to automate the simulation context.

In the simulation context I want to access the static pressure of the inlet and outlet in the Turbo initial solution tab.

I belive I have to fill them out correctly if i choose "for turbomachinery" in the initial solution tab under one of the domains.

I can't find the code to set those static pressures in the API user manual.