Hi everyone,

In the latest version of TCAE (25.03v1), it is possible to set new parameters in the SIMULATION/Controls section: the solver max and min iterations (photo attached). What exactly do these iterations correspond to?

Thanks in advance.

Zacharie Prigent

Hello everybody,

I have a few questions regarding TCAE transient simulations.

1) Are the transient simulations robust?

2) Do you have any recommendations for applying transient simulations  to centrifugal compressors?

3) How do I control the recording of intermediate time steps? I haven't found a way to control it in the GUI, and the controlDict file in ../system/ is automatically restored to its previous version (with the adjustableOnEnd option in the writeControl section), even if we manually modified it before running the calculation!

Zacharie Prigent

I came across your report on the DJI 9450 and found it very interesting. I do have a few questions:

1. What is the source of the CAD file, and how did you determine the airfoil details?

• 2. Why did you choose to compare the results with a full quadcopter instead of isolated rotor data, which is also available?

• 3. It would also be interesting to see an OASPL comparison to evaluate how well your tool predicts rotor noise. the shape of the PSD is important but OASPL is the final objective.

  
  

  Thanks!

Hi everyone,

I’m running a steady-state simulation of a centrifugal compressor impeller and I keep running into an issue where the residuals settle but don’t properly converge, even after several thousand iterations. The solution looks stuck, and I’d like to understand if the problem is with my setup, mesh, or solver controls.

Case setup

• Geometry: Centrifugal compressor impeller with inlet passage and outlet

• Mesh: ~1.6 million cells, generated in TurboGrid and exported as cgns into TCAE

• Interfaces: Mixing plane, 7 mixing planes total across 2 interfaces

• Fluid: Air, perfect gas; μ = 1.78e-5, ρ = 1.2, p = 1 atm (defaults)

• Rotation: 110,000 RPM (tested both +111000 and −111000, same behavior)

• Flow regime: Transonic option enabled

Boundary conditions

• Inlet:

  • Total pressure = 1 atm

  • Total temperature = 288.15 K

  • Turbulence intensity = 5% (k = 82.14)

  • Turbulence length scale = 0.015 m (blade height) → ω = 604.207

• Outlet:

  • Mass flow = 0.35 kg/s

• Walls: No-slip, adiabatic, standard wall functions

Solver settings

• Turbulence model: k-ω SST (default values)

• Numerics: Second order, non-orthogonal mesh correction enabled

• Under-relaxation factors: Set to 0.15 (started higher but reduced due to stability issues)

• Physical limits:

  • p: 50,000 – 800,000 Pa

  • ρ: 0.1 – 100

  • v: 0 – 800 m/s

  • T: 250 – 700 K

• Initial conditions:

  • p = 1 atm

  • T = 288.15 K

    v = 0 , 0, 148 Got it from a 1D code as the absolute velocity at the inlet.

  • k = 0.01

  • ω = 100

Problem

Residuals drop initially but then flatten out and refuse to converge further. Monitors also don’t stabilize in a meaningful way, I think the monitors get stuck because the residuals do not drop further. I have tried with the fixed mean static pressure outlet condition as well but still the same thing. One thing I suspect is that I think there maybe be some unsteadiness in the flow which maybe causing this, is there a way to set a pseudo time scale or something. Any help would be appreciated!

Hello everybody, 

I am setting my first CFD transient simulation on a centrifugal compressor and I would like to know if you have any recommendations on the values of parameters like CFL number or PIMPLE algorithm settings. I assume that the default value of CFL number is relatively large (=20 hence >>1) because the PIMPLE algorithm is flexible and that's common to use higher values for turbomachinery applications?

Also, how is the monitoring and post-processing of the results different from the ones of steady state simulations? 

Any clarifications and recommendations would be very helpful. 

Thank you and have a nice day ! 

Alex

CAE simulations. The art of the possible.

What factors contribute to making CAE projects successful? In the company I work for, in 15 years, we have delivered hundreds of CAE projects to industrial companies (most of them in the turbomachinery field). Some projects were highly successful, while others were not. In this article, I would like to share a few thoughts and lessons learned about project-success patterns and engineering productivity in general.

The Game

In engineering, we don’t simulate reality. We merely simulate our understanding of reality with currently available resources. In other words, the game we play here is about turning our knowledge and effort (and talent) into the best possible results. CAE projects, like software, are never really finished. They only have their versions. At any point, you can make them better. When chasing accuracy, the effort grows exponentially, so it’s smart to recognize the point when the results are good enough. Having clear, measurable goals is critical to prevent infinite drift, resource waste, and disappointment. Well-defined goals help to navigate, focus, and prioritize. The game we play is all about goals and their feasibility with the available knowledge and effort.

Continue reading on CFD SUPPORT website >>> https://www.cfdsupport.com/cae-simulations-the-art-of-the-possible/

Component 5, (Nacelle_Top) and Component 7 (Nacelle_Bottom) are experiencing failure to mesh. Can you take a look? It might be obvious to you.

Here's a download link to the compressed project file for your review. Please see my comment for a better Component map image for reference.

Edit: I've even tried performing the meshing operation using Salome-Meca. Meshing just one stl fails with it too, but unlike TCAE, takes several hours to fail completely. The component 5 (fuchsia) is Nacelle_Top, the patch in question is named Solid_Top_Bell-Mouth_inlet_and_Duct_Surface_08_21_25a.

I suspect Nacelle_Bottom is going to be just as bad, or worse, than Nacelle_Top. It is slightly smaller in diameter, but it's a more complicated surface.

Thanks in advance,

David

The previous iteration of this TCAE project experimented with omitting a central component from the topology, the Duct_Separator, going from the Top_Fan rim (sometimes called a hub, in this case an open outlet interface), through which air not used by the Top_Fan flows from the Top_System_Suction outlet interface, and continues directly to the inlet interface of the Bottom_Fan open rim, skipping the Duct Separator. Confusing, I know, but the Bottom_Fan is upside-down compared to the Top_Fan, so it takes in air not from the shroud inlet interface, as in the case of the Top_Fan, but from the Bottom_Fan's open rim inlet interface.

This iteration is more like the actual setup, Suction, Top_Fan, Duct_Separator, Bottom_Fan, Nacelle, Outlet_Extension. Please see my comment for a more complete image of the Component Map.

Who knows? It might eliminate some setup errors seen previously.

Working through the Check for Errors exercise finally presented only this orange border in the Components Map. Other than TCAE Output messages, there's no textual description of what or where things have gone awry. I'm assuming it's displayed somewhere in the TCAE Output messages, but what should I be looking for? Is it because the component Duct Separator (Co6) is without a partner, present in the group, barely visible, but no interaction with any other?

Still working through the Check exercises. Narrowing the errors down (hopefully!).

Hello everyone,

We are a team of university students currently working on a project to replicate the CFD simulation of the DJI 9450 propeller. First of all, we would like to thank the content creators for the excellent "Acoustic Benchmark Propeller DJI 9450" study. It has been an invaluable resource for our work.

As we try to reproduce the simulation results, we've encountered some confusion regarding the benchmark target values and would be very grateful for any clarification from the community or the official team.

Issue 1: Discrepancy Between Two Reported Results

We have been referencing two main documents:

 [1] The formal PDF research report (Acoustic Benchmark of DJI 9450.pdf).

 [2] The web page report, available at: https://www.cfdsupport.com/download/report/DJI-9450-Propeller-Benchmark/tcfd/TCFDReport.html

We noticed a significant difference in the thrust and torque values at 6000 RPM between these two sources. Specifically:

 * The PDF Research Report [1] lists a target Thrust of 4.256 N and a target Torque of 0.066 N·m.

 * The Web Page Report [2]shows a computed Thrust of 3.438 N and a computed Torque of 0.058 N·m.

Furthermore, the simulation result graph in the PDF report (approx. 4.2 N) also differs from the web page report's result (3.44 N).[1] We suspect this might be due to differences in mesh density. Could anyone confirm if this understanding is correct, and which set of values should we consider the definitive target for our validation?

Issue 2: Question About the Source of the Benchmark Target Value

To delve deeper, we located the original experimental paper cited in the PDF report (Intaratep, N., et al., AIAA 2016-2873).[1, 1] However, upon reviewing this paper, we found that the measured experimental thrust for a single rotor at 6000 RPM is approximately 6.1 N (as read from Fig. 6).[1,1]

This experimental value is considerably different from the benchmark target of 4.256 N listed in the PDF report, which has caused us significant confusion.

Our specific questions are:

 * Could anyone clarify the source of the benchmark target values (Thrust = 4.256 N, Torque = 0.066 N·m) used in the PDF report? Why does this target differ from the ~6.1 N we found in the original experimental paper (AIAA 2016-2873)?

 * To help us perform a more accurate validation and learn from this work, would it be possible to get access to the mesh file (e.g., in OpenFOAM or MSH format) or the complete geometry file (STL/STEP) used for the high-fidelity simulation presented in the PDF report?

Any clarification would be immensely helpful for our academic research.

Thank you for your time and assistance.

Best regards

That I've gotten this far, in my estimation, is cause for celebration. 5-lime margarita time!

(they only yielded 4 oz. of juice from those small organic limes, but it'll do).

I'm amazed at the Check functionality. I've been eliminating one similar error after another until now.
From the directory for the component named "Top_Fan", I copied and pasted an interface patch (.stl) into the directory for the component named "Hull__Inlet__Outlet", same file name, same type: "outletInterface" with the intention to prevent this from happening. It seems to me that in that instance it should be an inletInterface (just saying, I tried it that way...didn't help), Static Reference frame, another, different component.
Setup Problem is displayed upon selecting Check, listing the source, the copied patch in Top_Fan as the problem.

When I go into the Top_Fan component to connect the patch to the patch of same name in the Hull__Inlet__Outlet component, I don't see it listed as a choice, nor do any of the available listed options seem to work.
Changing the name slightly of the file in Hull__Inlet__Outlet had no effect.

How can I fix this? I'm stuck. Your help is appreciated in advance.

David

Hi everyone,

I have a question concerning the mixing plane interface method : it seems to me that the method can generate numerical errors when reverse flow occurs on the interface.

To be more specific, I have a radial interface between the outlet of a centrifugal impeller and the inlet of its diffuser. On a specific zone of the interface, reverse flow occurs with a radial circumferential angle -180° < circAng < -90°, whereas on the rest of the interface, there is no reverse flow and 90° < circAng < 180°. In one of my former post on the forum, you confirmed to me that the weighted surface average of the circumferential angle might be distorted in this situation. It seems to me that the mixing plane method at the interface also encounter issues in this situation to estimate the value of circumferential angles for the inlet patch of the interface, in the strips where circAng oscillate between 90° < circAng < 180° and 180° < circAng < -90°. Indeed, I can see this kind of numerical errors when post-processing my simulations.

Do you have some recommendations to avoid this kind of problems ? For example, use specific configuration options, or different interface conditions ?

Thanks in advance !

Zacharie