Hi everyone,

It seems to me that the field bounding limits are only applied in stationary simulations, and not in transient simulations. Indeed, in one of my transient tests, many cells of my domain reach values (the velocity in my case) well above the max velocity indicated in SIMULATION/Controls.

Are you aware of this comportment ?

Thanks in advance !

Zacharie

Hello everyone,

I have some questions regarding case initialization:

1) In steady-state simulations, I assume that the conditions defined in the "Initial Conditions" section are only used to initialize the first point of each speedline, and that subsequent points are then initialized from the previously calculated point in the speedline. Is that correct?

2) In transient cases, a new option appears in the "Initial Conditions" section: "Initialize points from the previous point." What happens if this option is not selected? Is each point then initialized with the conditions defined in this section, regardless of its position in the current speedline?

3) Do you recommend simulating the speedline from the highest flow rate to the lowest flow rate, or the other way around (in the case of a centrifugal compressor for example) ?

Thanks in advance!

Zacharie

Hi everybody, 

I ran a steady state + transient CFD simulation on a centrifugal compressor (with a k-omega SST model) and when post-processing the results and comparing the stationary part to the unsteady part of the calculation I have significantly different results. Indeed, the unsteady part shows a higher mass flow rate. This seems to be due to a higher flow speed and a different flow angle, noticeable directly at the inlet of the rotor. On the picture attached you see these differences (on the left: unsteady part; on the right: steady state part). Is it possible that this difference in flow rate could be explained by the fact that the dynamic mesh in the unsteady part could aspire the flow in the rotor and thus change the angle and speed of this one? And maybe this effect could have been lower if I would have set a lower CFL (kept for now to 20 in my case)? 

If you have any ideas about this phenomenon that would be very helpful. 

Thanks and have a great day,

Alex 

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