REVIEW 3 major objections 5 minor 23 references
Four deep-learning operator models are benchmarked for predicting surface pressure in aerodynamics, and the ranking points to Transolver and BSMS-GNN as the most promising surrogates.
Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →
T0 review · deepseek-v4-flash
2026-08-02 03:27 UTC pith:XG5O6PWY
load-bearing objection The 2D airfoil benchmark is careful and useful, but the 3D ranking reversal is a single-run artifact with unequal training budgets — don't take BSMS-GNN's lead over Transolver++ seriously yet. the 3 major comments →
Evaluation of State-of-the-Art Deep Learning Architectures for Aerodynamical Predictions
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
On the paper's own terms, the central discovery is a performance ranking: on the 2D airfoil dataset, the highest accuracy is achieved by Transolver, followed tightly by BSMS-GNN, then GAOT, and somewhat behind, UPT; on the NASA CRM dataset, BSMS-GNN achieves the lowest errors across all metrics, followed by Transolver++, then GAOT, and UPT performs markedly worse. The authors further find that the best results in both settings are produced by the most lightweight models in terms of parameters and training time, and they highlight BSMS-GNN and Transolver(++) as promising surrogate models for aerodynamical applications.
What carries the argument
The comparison is carried by the architectural mechanisms underlying each model: BSMS-GNN's bi-stride multi-scale graph construction with a U-Net structure permits efficient long-range information exchange on user-provided graphs; Transolver's Physics attention groups mesh points into a small number of learned slices, making self-attention linear in the number of points; UPT uses a GNO encoder to pool input points into latent tokens processed by a transformer, with predictions via cross-attention; GAOT uses a multiscale attentional GNO (MAGNO) encoder to map input clouds to a regular latent grid. The benchmark protocol itself—hyperparameter optimization and ten repeated instantiations on 2D,
Load-bearing premise
The 3D ranking assumes that a single training run per model, with hyperparameters chosen by transferring results from 2D or scaling them ad hoc, is enough to fairly establish the NASA CRM hierarchy, so an unlucky or favorable configuration for any architecture could change the reported order.
What would settle it
Retrain each model on the NASA CRM dataset with multiple seeds and a per-architecture hyperparameter optimization (e.g., systematically varying learning rate, batch size, and pooling radii). If, across repetitions, Transolver++ or another model achieves lower MAE and RMSE than BSMS-GNN with non-overlapping confidence intervals, the paper's 3D ranking is falsified.
If this is right
- Practitioners building surrogate models for similar aerospace pressure-prediction tasks can prioritize BSMS-GNN and Transolver(++) over UPT and GAOT, based on the reported error metrics.
- The reversal of the top-two ranking between the 2D and 3D datasets indicates that architecture choice should depend on geometry complexity and dataset size, not just on general-purpose claims.
- Since the most accurate models were also the most computationally efficient, large parameter counts are not necessary for good performance on these aerodynamic datasets.
- All models degrade in the presence of strong shocks, especially near design-space boundaries, so shock prediction remains a shared weakness that future work would need to address.
- The NASA CRM dataset's data-scarcity setting suggests that BSMS-GNN and Transolver++ can generalize from roughly 100 training samples to industrial-scale meshes, which is relevant to real engineering workflows.
Where Pith is reading between the lines
- The 3D ranking rests on a single training run per model with hyperparameters largely transferred from the 2D study or scaled manually; a fairer multi-seed comparison with per-model tuning on the CRM dataset could plausibly change the BSMS-GNN/Transolver++ gap.
- The fact that the simpler, physics-attention-based Transolver matches or beats heavier hybrid architectures on 2D suggests that explicit multiscale graph construction is not always necessary for learning surface pressure on modest geometries.
- The consistent misplacement of shocks across models points to a concrete research direction: incorporating shock-capturing or discontinuity-aware loss terms into operator learning could improve aerospace surrogate accuracy more than further architecture search.
- If the reported 3D ordering holds under repeated runs, it implies that for high-resolution surface meshes with scarce training data, a deliberately coarsened graph with multi-scale message passing may generalize better than transformer-heavy latent-token designs.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper benchmarks four operator-learning architectures (BSMS-GNN, Transolver/Transolver++, UPT, GAOT) for surface-pressure prediction on two aerodynamic datasets: a 2D airfoil dataset (598 CST-perturbed RAE2822 geometries) and the industrial-scale 3D NASA CRM dataset (149 samples, 454k surface points each). The 2D experiment performs per-model hyperparameter optimization on a validation split, trains ten instantiations per model, and reports 95% confidence intervals; the ranking is Transolver > BSMS-GNN > GAOT > UPT. The 3D experiment trains a single instantiation per model with 2D-derived or ad hoc hyperparameters and reports BSMS-GNN > Transolver++ > GAOT > UPT, with the two best models separated by 32–34% in several error metrics. The paper concludes that BSMS-GNN and Transolver(++) are the most promising surrogate models.
Significance. If the results hold, the paper provides a valuable practitioner-oriented comparison for a class of problems (aerodynamic surface pressure prediction) where public benchmarks are scarce. The 2D experiment is a model of good empirical practice: hyperparameter search on a held-out validation split, ten retrained instantiations, 95% confidence intervals, a local error analysis as a function of flow parameters, and explicit discussion of failure cases, including shock-capture behavior. The derivation of supernode pooling radii in Appendix A.3 is a useful methodological detail. However, the 3D experiment, which drives the reversal of the ranking and the final recommendation, is based on one run per model without a statistically valid comparison. The paper itself disclaims any statistical statement for the 3D results (Section 5.1). The load-bearing 3D claim therefore needs either additional repetitions or a substantially softened interpretation.
major comments (3)
- [Section 5.1, Table 9] The central claim that BSMS-GNN surpasses Transolver++ on the NASA CRM dataset rests on a single training run per model. Section 5 states that the authors "abstained from doing repetition runs" and Section 5.1 states that the results "do not allow us to make any statistical statement." The paper attempts to substitute the lack of confidence intervals by appealing to gaps "multiple times larger" than the 2D confidence intervals, but this does not control for run-to-run variance in the 3D setting, where training is more unstable and hyperparameters were not optimized. The ranking reversal and the conclusion "BSMS-GNN and Transolver(++) as promising surrogate models" (Section 7) depend on this single-run comparison. At minimum, the 3D ranking should be reported as preliminary, and the conclusion should be correspondingly qualified.
- [Section 5.1, Table 10] The comparison between BSMS-GNN and Transolver++ is confounded by unequal numbers of gradient updates. BSMS-GNN, UPT, and GAOT were trained with batch size 1, while Transolver++ used batch size 4 to "keep its training time feasible." Over 10,000 epochs with 105 training samples, this yields roughly 1.05M parameter updates for BSMS-GNN versus roughly 262.5k for Transolver++ — a factor of 4. The reported 32–34% error gap (Section 5.1) may therefore reflect training effort rather than architectural superiority. A fair comparison should equalize the number of gradient updates (or use repetitions over several update budgets) and should report the update count for each model.
- [Section A.1 and Section 6] The 3D setup choices are not demonstrably fair to all architectures. Section 6 notes that prior experience with BSMS-GNN "exceeds the experience present with all other three architectures," and Appendix A.1 shows that BSMS-GNN uses the dataset-specific adjacency matrix, while the other models' 3D hyperparameters (e.g., UPT's 20,480 supernodes, GAOT's 131,072 supernodes, Transolver++'s four layers and hidden size 256) are chosen by "previous experiences" or "to the best of our knowledge." Because the paper recommends BSMS-GNN, the absence of a documented process for equal tuning effort (e.g., a small validation-based search or ablations for all models) is a load-bearing concern. The 3D ranking should be labeled as conditional on the selected hyperparameters, or the authors should provide evidence that the ranking is robust to reasonable alternative settings.
minor comments (5)
- [Appendix A.2] The RMSE and Rel. L2 metrics are defined as the mean over samples of the per-sample values. This is an unconventional choice; readers may expect a pooled RMSE over all points. Please state explicitly that these are per-sample averages and justify why this is preferable for this benchmark.
- [Section 4.1] UPT received a second round of hyperparameter optimization and a custom exponential-decay scheduler, while the other models did not receive comparable additional tuning. This is a reasonable response to the initially poor performance, but the asymmetry should be discussed as a possible source of bias, and the final ranking should be interpreted with this in mind.
- [Section 5] The caveat that the 3D experiment has no hyperparameter optimization and no repetition runs appears only in Section 5. Given that the abstract and conclusion emphasize the 3D results, this limitation should be stated in the abstract and revisited in the conclusion so that readers are not misled.
- [Throughout] Several typos and minor language issues: "quadradic" (Section 2), "archtitecture" (Section 1), "tupel" (Section 2), "noticable" (Section 5.1), "opimization" (Section 4.1). A careful proofread is needed.
- [Tables 11–18] The appendix tables are detailed and helpful. However, the connection between the entries and the corresponding paragraphs in Section A.1 could be made clearer by referring to table numbers in the text (e.g., "see Table 11 for BSMS-GNN").
Circularity Check
No circularity: an empirical benchmark with fresh held-out evaluations; self-citations are to the models/datasets under test, not load-bearing support.
full rationale
This paper is an empirical benchmark, not a derivation, so the equation-level circularity patterns do not apply. The central ranking claims are produced by training the compared architectures on the stated datasets and evaluating on held-out test samples (2D: ten instantiations with confidence intervals; 3D: single runs explicitly disclosed as statistically non-decisive). No fitted parameter is renamed as a prediction, and no result is defined in terms of itself. The self-citations (Hines and Bekemeyer 2026 for BSMS-GNN; Bekemeyer et al. 2025 for the datasets) reference the architectures and data objects under evaluation rather than supplying evidence for the ranking; the comparisons are run fresh against public baselines. The paper even flags its own limitations (“we abstained from doing repetition runs”, “the results presented in Table 9 do not allow us to make any statistical statement”, and the greater prior experience with BSMS-GNN). These are legitimate robustness/fairness concerns, not circularity. The 3D single-run and unequal-batch-size issues are threats to the strength of the ranking, but they do not make the benchmark’s output equivalent to its inputs by construction. Accordingly, no circular step is present and the score is 0.
Axiom & Free-Parameter Ledger
free parameters (6)
- 2D training epochs per model =
Transolver 2,500; BSMS-GNN 10,000; UPT 15,000; GAOT 5,000
- 3D batch size =
BSMS-GNN/UPT/GAOT = 1; Transolver++ = 4
- 3D UPT supernodes/latent tokens =
20,480 supernodes, 5,120 latent tokens
- 3D GAOT supernodes grid and pooling radius =
Grid [64,64,32], radius 0.066
- 2D UPT/GAOT pooling radii =
UPT 0.062; GAOT 0.066/0.072
- BSMS-GNN 3D graph construction =
Dataset adjacency (~4 neighbors), 11 scales, min-distance-to-center seeding
axioms (4)
- domain assumption The DLR TAU RANS + Spalart-Allmaras CFD solutions in the two datasets are treated as ground truth for pressure and lift.
- ad hoc to paper The ~24-neighbors-per-supernode guidance from Alkin et al. (2024) is a valid design choice for UPT and GAOT.
- ad hoc to paper 2D hyperparameter findings transfer to the 3D NASA CRM dataset, with ad hoc scaling where needed.
- ad hoc to paper A single training run per model on NASA CRM, with gaps much larger than the 2D confidence intervals, is sufficient to infer the 3D ranking.
read the original abstract
Surrogate models are used to substitute classical numerical solvers in engineering applications where the computational cost of the latter becomes infeasible. For instance, in aerodynamics such models offer cost-effective alternatives to computational fluid dynamics in problems such as shape optimization and load analysis, which oftentimes require high-fidelity simulations for a multitude of different parameter combinations. A specific class of deep learning-based surrogate models termed operator learning models directly approximates the solution operators to the partial differential equations underlying the physical phenomenon, thereby learning to replicate solutions to entire families of problems. However, while nowadays numerous architectures of this type get published, corresponding benchmark studies remain scarce. In this article, we advance the study of AI-based surrogate methods by thoroughly benchmarking four state-of-the-art operator learning models on their aptitude for applications in aerospace engineering. In two experiments, we assess the models' capabilities of predicting the surface pressure distribution on two-dimensional airfoil shapes of varying complexity and on an industrial-scale three-dimensional aircraft configuration. Thereby, we evaluate the models' abilities to fulfill frequent requirements in aerodynamics such as capturing discontinuities (shocks) in the solutions, scalability towards excessive amounts of mesh points and handling of data scarcity. Accompanied by a careful analysis, our findings drive forward the field of AI-based surrogate modeling by providing detailed insights into the strengths and weaknesses of the individual architectures, thus allowing to identify priorities for future developments. In particular the Bi-Stride Multi-Scale Graph Neural Network and Transolver(++) are highlighted as promising surrogate models for aerodynamical applications.
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