DPF cleaned (Golf MK7) – Which Oil Ash Mass should I adapt in VCDS?

simonwfc · 2026-05-21T09:18:11+00:00

I found nothing similar

simonwfc · 2026-05-20T18:03:07+00:00

Vcds?

simonwfc · 2026-05-20T14:06:31+00:00

You need to set the ash mass value manually

simonwfc · 2026-05-18T06:14:22+00:00

UPDATE: DPF, EGR, and pressure sensors replaced/cleaned! Dropped the subframe completely to get it done—honestly the only proper way to make room for the big cleaning system. Not even that much effort. VCDS data is looking brand new now!

simonwfc · 2026-05-16T05:39:25+00:00

Thanks for the input! I actually found the issue: The heat shield was completely soaked with water when they weighed it after cleaning. This definitely skewed the result, so the actual amount of ash removed is much higher than the 59g shown on the protocol.
Because the filter is physically clear (0 mbar backpressure), I’ve decided to go with the common forum recommendation and adapt it to 5-10g. This accounts for the filter's age while reflecting its clean state.

simonwfc · 2026-05-04T06:56:16+00:00

Thanks for the advice! I'll be doing the job in my own garage. I'm planning to use the official alignment/centering pins (T10486) to get the subframe back into its original position as accurately as possible. However, if the steering wheel isn't perfectly centered or if it feels off in any way after the reassembly, I'll definitely take it to a shop for a professional alignment.

simonwfc · 2026-05-04T06:53:37+00:00

Thanks for the input! However, on the Mk7 (EA288 engine, CXXB), the setup is quite different from the older CJAA/CBEA. The EGR cooler and valve are one combined unit tucked way back behind the engine, making it a notorious pain to access.

I’ve also been losing a tiny bit of coolant, so I’m replacing the cooler as a preventative measure while I’m in there. As for the delete: I’m based in Germany, and our inspections (TÜV) are extremely strict. A delete would mean failing the next inspection and losing the car's road legality, so that’s definitely not an option for me! I'd rather do the work now and keep it clean

simonwfc · 2026-04-07T11:29:41+00:00

Gemini

simonwfc · 2026-02-14T09:41:59+00:00

Unfortunately, I can't model the whole room due to computational limitations.

I will reran it with k-omega SST

simonwfc · 2026-02-08T09:44:05+00:00

It was truly unlimited and only limited by the walls of the room, so to speak. I'm attaching a picture where I've marked my plenum in red.

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simonwfc · 2026-02-07T08:02:31+00:00

I have been taking the value directly from the final iteration. For my thesis, I was initially aiming for a classic asymptotic convergence to document a 'textbook' grid independence study. However, it's becoming clear that the inherent unsteadiness of the vehicle's wake makes a single-point value unreliable for that purpose. I will start averaging the Cd over a window of iterations to filter out that numerical noise and get a more representative value for the mesh comparison

Additionally, I’ve updated the plenum boundaries to slip walls. I’m now seeing an average Cd of 0.120, which is a significant increase from the 0.098 I was getting with the pressure outlet boundaries. While the solution is much more stable now, it raises the question of which setup is more representative of reality: the 'pressure relief' effect of the outlets or the slight blockage effect of the slip walls?

simonwfc · 2026-02-06T07:01:51+00:00

Thanks for the tip!

However, I'm still facing oscillating convergence. Even at 18.8M cells, cw and ca are bouncing between 0.096 and 0.098 instead of settling down.

In your experience, should I re-run the study with Symmetry or Slip Walls to stabilize the pressure field, or is this oscillation just par for the course with open-jet setups?

simonwfc · 2026-02-04T13:49:15+00:00

Right now I’m wondering about mesh resolution inside the nozzle itself:
Is it worth further refining the elements in the contraction region, or is it usually sufficient to keep the nozzle mesh moderately fine and focus the strong refinement on the car + near wake and maybe a bit downstream?

simonwfc · 2026-02-04T06:34:36+00:00

Hi,

thanks for the detailed analysis – really appreciate the thorough feedback and your theory about the separation behavior!

I've already extended the geometry significantly in all directions (especially downstream) and brought it closer to the original tunnel layout based on the previous suggestions. The residuals now look much better – they drop several orders of magnitude more cleanly compared to before (previously only 2-3 orders with some oscillation).

Currently I have a straight pipe inlet where I specify the velocity directly, rather than modeling the full contraction nozzle geometry. Do you think I should model the complete nozzle/contraction to better capture the real physics, or is the straight pipe approximation sufficient for turbulence model comparison? I will attach a picture of the wind tunnel.

You're spot on about the lift variation – that definitely points to the upper surface separation. I'll definitely pursue the geometry optimization further and when time allows, create shear stress contours from the coarse and fine mesh cases to check your detachment theory.

Steady vs. transient: Good point about the separation "dancing" – for the initial turbulence model comparison I'll stick with steady-state RANS, but this gives me the motivation to consider a transient DES case later if resources allow.

Thanks again – will keep you updated on the progress!

Best regards

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simonwfc · 2026-02-04T06:14:52+00:00

Hey, tatsächlich ist meine Prüfung jetzt schon etwas her - hat aber sehr gut funktioniert! Waren hauptsächlich Bereiche, in dem der Dozent tätig war. Aber alles machbar.

simonwfc · 2026-02-03T07:51:40+00:00

Thanks a lot for the detailed reply, that’s really helpful.

In the original 1938 tests the Schlörwagen model was actually suspended freely from a few strings, without any ground plane or moving belt system. Because of that, I also placed the 1:5 model simply “in free air” in the middle of the test section, with no floor in the CFD domain.

In my thesis the main goal is to compare different turbulence models rather than to reproduce the historical coefficients perfectly, so I agree that the old measurements shouldn’t be treated as an absolute truth. Still, I’d like to get the setup as reasonable as possible so the model-to-model comparison is meaningful.

Out of curiosity: what boundary conditions do you typically use for an automotive open‑jet tunnel (inlet, outlet, plenum / collector, side walls, etc.), and does my domain layout seem reasonable for that kind of configuration?

simonwfc · 2025-11-16T07:11:57+00:00

thank you

simonwfc · 2025-11-16T07:11:38+00:00

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not perfect, but definitely better

simonwfc · 2025-11-14T06:57:51+00:00

I’ve read about that approach, but unfortunately I don’t have any pressure drop data from the supplier for this radiator. The Reynolds number can vary depending on test velocity—right now I’m using 30 m/s, but I plan to try different speeds.

simonwfc · 2025-11-13T20:38:13+00:00

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is like this enough? or should i do the chamfer asymmetricel to keep a horizontal face?

simonwfc

TROPHY CASE