{"id":"06690724-6a59-4ea3-9825-92995bd132a9","arxiv_id":"2411.16661","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":1,"one_line_summary":"A CFD parameter study finds that moving walls, a hyperbolic-tangent inlet profile, a long enough inlet tube, and a mass-flow outlet reliably reproduce the left ventricular vortex ring in simulations.","lead":"This paper runs computer simulations of blood flow in a left ventricle model and tests which mesh, wall motion, and inlet/outlet settings best capture the swirl called the vortex ring. It serves as a practical recipe for cardiac flow modelers, with cross-checks between two commercial solvers.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The 2% mesh-convergence claim is based on whole-cavity total kinetic energy, but no quantitative vortex-ring metric is reported; the central claim that the recommended setup captures vortex-ring formation, tilt, instability, and dissipation is therefore under-supported.","rationale":"The reader's weakest assumption is the uniform-scaling wall motion of Eqs. (4)-(5). I agree that this is a real limitation, especially for patient-specific transfer, but the paper only advertises that wall model for the idealized semi-ellipsoid; the instruction to use plug profiles for patient-specific cases is separate. The concern I rank as most load-bearing is that the quantitative validation never measures the object the paper is about. TKE is a fine sanity check, but the central claim includes vortex-ring tilt, instability, and dissipation, which are spatial and local features; convergence of a global scalar does not imply convergence of those features. The reader's rationale already notes the absence of quantitative vortex metrics and the missing fixed-wall baseline, so there is partial agreement, but the named weakest assumption is different. I would retain the CONDITIONAL verdict; the paper should either add vortex-ring-specific convergence and error estimates or explicitly narrow its claim to TKE-converged global flow with qualitatively matching ring features. I also flag a separate reproducible inconsistency in Eqs. (4)-(5): with k=4 they give a=4b, incompatible with the stated a=2 cm, b=8 cm and Eq. (1); this should be corrected regardless of the verdict.","tokens_in":11489,"tokens_out":10139,"duration_ms":95802,"concrete_test":"On the existing medium and fine meshes from Tab. 3, compute one or more vortex-ring-specific metrics at t* = 0.16, 0.26, 0.40, and 0.56, e.g., circulation of the leading ring, volume of the Q-criterion isosurface inside the LV, vortex-core path, and tilt angle, or enstrophy restricted to the ring region. If the medium-to-fine relative error of such a metric is below 2%, the same threshold used for TKE, the concern is resolved; if it is materially larger than the TKE error, then TKE convergence alone is insufficient evidence for the paper's central claim.","verdict_should_be":"UNCHANGED","load_bearing_attack":"Fig. 6 and Tab. 3 quantify convergence only through TKE integrated over the ventricular cavity, excluding the tubes. TKE is a global L2-type quantity: it can be converged to 2% while the vortex-ring core position, circulation, tilt timing, or dissipation rate still shifts on finer meshes, because localized errors in different regions can cancel in the volume integral. The paper's selected observable, the vortex ring, is rendered only via Q-criterion isosurfaces (Fig. 7), with no quantitative metric of the ring (circulation, core path, isosurface volume, enstrophy, tilt angle). Thus the central claim overstates what the reported data demonstrate. This is an evidence gap rather than a claim that the simulations are wrong, but for a practical guide whose stated objective is to identify the vortex ring, convergence of a global energy integral is not a sufficient proxy. I also flag a separate reproducibility issue in Eqs. (4)-(5): with k=4 they imply a(t*)=4b(t*), contradicting the stated semiaxes a=2 cm, b=8 cm and Eq. (1); the wall-scaling recipe needs correction or clarification.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper presents a practical CFD configuration guide for simulating the left-ventricular vortex ring. Using an idealized semi-ellipsoidal LV geometry from Zheng et al. [15] and two patient-specific geometries that are introduced but not subsequently simulated in detail, the authors test moving versus fixed walls, inlet spatial profiles (plug, parabolic, hyperbolic tangent), inlet tube lengths, and outlet boundary conditions in Star-CCM+, and cross-validate the recommended setup in Ansys Fluent. The central recommendation is: laminar, incompressible Newtonian blood; moving walls driven by the integrated flow-rate curve with a fixed axis ratio; a velocity or mass-flow inlet with a hyperbolic tangent (or plug) profile; an inlet tube length of at least 2D; a mass-flow outlet; and a near-wall-refined mesh. This setup is claimed to capture vortex-ring formation, tilt, instability, and dissipation, with mesh-converged total kinetic energy (relative error below 2%).","tokens_in":11737,"tokens_out":8852,"duration_ms":82467,"significance":"The manuscript addresses a real gap in the cardiovascular CFD literature: most LV flow studies do not document mesh, inlet, outlet, and wall-motion choices in enough detail to be reproduced. The paper's main strengths are its explicit comparison of boundary-condition and mesh choices, its two-solver validation with Star-CCM+ and Ansys Fluent, the absence of fitted parameters, and its connection to the published benchmark of Zheng et al. [15]. If the wall-motion equations are corrected and quantitative vortex-ring metrics are added, the paper would be a useful recipe for researchers working on LV vortex dynamics. As it stands, however, the evidence presented does not fully support the strength of the central claim.","major_comments":[{"comment":"The wall-scaling equations are inconsistent with the stated geometry. The text says a 4-to-1 ratio is maintained between b(t*) and a(t*) with k=4, and the model has semiaxes a=2 cm and b=8 cm, so b/a=4. However, Eq. (5) reads a(t*)=k b(t*), which with k=4 gives a=4b; Eq. (4) is consistent with a=k b, not with b=k a. Please correct Eqs. (4)-(5) (e.g., b(t*)=k a(t*) with the corresponding volume formula) and verify that the morphing implementation used the intended ratio. As written, the recipe cannot be reproduced without guessing which relation was actually coded.","section":"Section 2.4.1, Eqs. (4)-(5)"},{"comment":"The mesh-convergence claim rests entirely on the total kinetic energy integrated over the ventricular cavity, excluding the tubes. TKE is a global volume-integrated quantity, so localized errors in vortex-ring circulation, core position, tilt angle, or dissipation timing can cancel in the integral. Since the paper's central claim concerns the vortex ring, the 2% TKE error does not by itself demonstrate that the ring features are mesh-converged. Please report quantitative vortex-ring metrics (e.g., circulation, ring centroid path, tilt angle, isosurface volume, or enstrophy) for the mesh study and for the Fluent/Star-CCM+ comparison, or explicitly qualify the convergence claim as applying only to the volume-integrated TKE.","section":"Section 3, Fig. 6, Tab. 3"},{"comment":"The moving-wall model imposes a spatially uniform scaling of the semi-ellipsoid with a fixed axis ratio. This is a uniform, twist-free deformation that does not represent real LV contraction and relaxation patterns. Moreover, although patient-specific geometries are introduced in Section 2.1 and mentioned in the abstract, no patient-specific wall-motion or vortex-ring results are presented, so the transferability of the recommended recipe to patient-specific cases is not demonstrated. Please state this limitation explicitly; if patient-specific guidance is part of the paper's scope, add at least one patient-specific demonstration or a sensitivity test to nonuniform wall motion.","section":"Section 2.4.1"},{"comment":"The recommended setup assumes laminar flow, but the text itself characterizes LV flow as transitional and reports Re≈5500 and α≈31. The laminar assumption is justified only by references [22,23], with no sensitivity test in the present moving-wall geometry. Since this is a practical guide whose recommendations others will adopt, please add a brief quantitative check (e.g., TKE or vortex-metric time histories from a scale-resolving or RANS computation on at least one configuration), or explicitly state that the laminar recommendation is inherited from the literature and may not hold for all patient-specific cases.","section":"Section 2.2"}],"minor_comments":[{"comment":"The text says that three mesh sizes were tested for each solver, but Table 3 lists four rows for each solver; the element counts are also given as bare numbers (0.3, 0.6, etc.) without units. Please harmonize the mesh descriptions and label the units (millions of cells).","section":"Table 3"},{"comment":"The normalization constant C in the hyperbolic tangent inlet profile is never specified or given a normalization condition. Since the flow rate must be matched exactly for reproducibility, please provide the value of C or the equation that determines it.","section":"Eq. (8)"},{"comment":"The comparison between fixed and moving walls is described only qualitatively (fixed walls 'were unable to accurately model the flow dynamics'). Because the moving-wall recommendation is central to the guide, a quantitative comparison (e.g., TKE or vortex metrics for both cases) would make the argument more persuasive.","section":"Section 2.4.1"},{"comment":"The paragraph beginning 'Given that the blood flow within the LV chambers is characterized by a regime of transition to turbulence' appears to contradict the subsequent conclusion that laminar modeling is sufficient; please rephrase to avoid confusing readers about the paper's actual turbulence-modeling recommendation.","section":"Section 2.2"},{"comment":"The claim that 'there are currently no articles in the literature' providing such a comprehensive guide is very strong and not supported by a systematic literature search; please soften the wording or provide a more targeted review of existing guidelines.","section":"Introduction"},{"comment":"Reference [13] is a project website rather than a peer-reviewed article, and the text says the practical guide 'can be found in Ref. [13]' even though the current article itself is framed as the guide. Please clarify the relationship between this article and the online tutorial.","section":"References [13] and Introduction"}],"recommendation":"major_revision","confidential_remarks":"The paper is within the journal's scope and has the potential to be a useful practical contribution. The main concern is that the title and abstract promise a guide for both idealized and patient-specific models, while the detailed results cover only the idealized geometry; the authors should either narrow the scope explicitly or provide the requested patient-specific evidence. I would also encourage the editor to treat the requested quantitative vortex-ring metrics as a necessary part of the revision, because the current TKE-only convergence analysis does not substantiate the central vortex-ring claim."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Quick take: this is a competent practical guide for setting up idealized left-ventricle CFD to visualize the diastolic vortex ring, not a new physical result. The main value is the systematic comparison of inlet profiles, tube length, outlet BC, and moving versus fixed walls, plus the two-solver validation on mesh convergence. That is real work and useful for practitioners.\n\nWhat deserves credit: the authors tested a sensible design space, give clear recommendations (tanh inlet for idealized, plug for patient-specific, tube length at least 2D, mass-flow outlet), and back them with two independent commercial CFD codes, Star-CCM+ and Fluent. The mesh-convergence numbers on total kinetic energy are below 2% for the medium meshes, and the Q-criterion images match Ref. [15] qualitatively. That is legitimate benchmark reproduction, not circularity. The tutorial link is a plus.\n\nThe soft spots: the central claim that this setup captures vortex ring formation, tilt, instability, and dissipation is supported mostly by isosurface pictures and a global TKE integral. TKE convergence to 2% says little about ring circulation, core trajectory, tilt angle, or dissipation rate; localized errors could cancel in the volume integral. A quantitative vortex metric would close that gap. The fixed-wall comparison is only qualitative, with no figure or numbers. The laminar assumption is delegated to references; at Re about 5500 and Womersley 31, that deserves at least a sensitivity note. The wall motion is uniform scaling of a semi-ellipsoid with fixed axis ratio, which is not physiological and limits transfer to patient-specific geometries; the plug-profile recommendation for patient-specific cases is asserted without showing patient-specific results in this paper. There is also a typo in Eqs. (4)-(5): b/a=4 means a(t*)=b(t*)/4, not a(t*)=4b(t*); as written, the geometry scaling is inconsistent with the stated a=2 cm, b=8 cm and Eq. (1). Minor to fix, but confusing for someone trying to reproduce.\n\nNone of these are fatal. The recommendations are reasonable and consistent with common practice, and the paper is honest about being a guide rather than a discovery. It deserves a serious referee; the revision should add a quantitative vortex metric and fix the wall-scaling equations before the setup is treated as authoritative. Useful for CFD people setting up idealized LV models.","headline":"Useful practical guide for LV vortex-ring CFD, but the evidence for 'capturing the vortex ring' is mostly qualitative and the wall-scaling equations have a fixable typo.","tokens_in":12223,"tokens_out":2971,"would_cite":false,"duration_ms":28475,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"This paper claims that moving ventricular walls, a hyperbolic-tangent inlet, and a mass-flow outlet reproduce the left ventricle's vortex ring to under 2 percent kinetic-energy error.","keywords":["left ventricle","vortex ring","computational fluid dynamics","cardiac hemodynamics","moving wall boundary condition","inlet velocity profile","mesh convergence","total kinetic energy"],"falsifier":"Run the same boundary-condition recipe in a geometry whose wall motion is taken from measured patient imaging (4D echocardiography or tagged MRI) instead of the uniform $k=4$ scaling; if the vortex ring's formation, tilt direction, or dissipation timing changes measurably, the uniform-scaling premise is the failing part.","tokens_in":11330,"feed_emoji":"🫀","tokens_out":9875,"duration_ms":83328,"temperature":0.7,"pith_summary":"This paper is a practical guide to configuring numerical simulations of blood flow in a model left ventricle so that the vortex ring—the doughnut-shaped swirl formed as blood enters through the mitral valve—is captured correctly. The authors claim that a small set of choices does the job: drive the ventricle wall by integrating a physiological flow-rate curve, feed the chamber through an inlet tube at least two diameters long with a hyperbolic tangent velocity profile, and let blood leave through a mass-flow outlet rather than a pressure outlet. With these choices and a wall-refined mesh, they report that total kinetic energy converges with relative error below 2 percent and that the ring's formation, tilt, and break-up match an independent solver's results. If the recipe transfers, it gives researchers a low-cost, reproducible starting point for vortex-focused cardiac flow studies.","feed_headline":"This flow-simulation setup reproduces the heart's vortex ring","feed_subtitle":"Moving walls, a hyperbolic-tangent inflow, and a mass-flow outlet converge to under 2 percent error in total kinetic energy.","key_machinery":"The machinery that carries the claim is the moving-wall boundary condition: the ventricular wall is a semi-ellipsoid whose axes are recomputed from the volume curve using Eqs. (4)–(5) with $k=4$, then morphed incrementally between end-systolic and end-diastolic volumes so the chamber volume tracks the integrated flow-rate data. Around that, the hyperbolic tangent inlet profile, Eq. (8), is the second load-bearing piece: it sets velocity to zero at the wall and approaches the plug value in the core, avoiding the wall discontinuity of a plug profile and the excess jet penetration of a parabolic profile. The vortex ring, visualized by Q-criterion isosurfaces, is the diagnostic object that the recipe is designed to preserve.","core_discovery":"On its own terms, the paper's contribution is a boundary-condition recipe for left-ventricle simulations focused on the vortex ring rather than on turbulence-resolving fidelity. The authors report that static walls fail to produce the ring or apical recirculation, so the wall must move; they generate that motion by integrating a physiological flow-rate curve and uniformly rescaling a semi-ellipsoidal chamber while holding the $k=4$ axis ratio fixed. For inflow, they find that a velocity or mass-flow inlet with a hyperbolic tangent spatial profile (plug for patient-specific geometries) and an inlet tube at least two diameters long is the most efficient way to get a clean jet; a parabolic profile perturbs the jet and slows the ring's tilt and decay. For outflow, a mass-flow outlet that is set to zero in diastole avoids the noise of switching a pressure outlet to a wall. With these choices and five prism layers near the wall, both Star-CCM+ and Ansys Fluent produce nearly identical total kinetic energy traces, converging to relative errors under 2 percent on medium meshes, and both reproduce the documented sequence of ring formation, clockwise tilt, instability growth, and dissipation.","pith_inferences":["An editor's inference: the same wall-driven, profile-adjusted recipe could be adapted to other valve-driven cavities where a single dominant inflow jet forms a ring, with the two-diameter tube rule and tanh profile as natural first guesses.","The uniform $k=4$ wall scaling is a testable simplification; if patient-specific wall kinematics are imposed instead, the ring's tilt and instability may change, which would mark the boundary of the recipe's validity.","Global convergence of total kinetic energy does not guarantee convergence of local vortex topology; a local metric such as the position and radius of the Q-criterion isosurface would strengthen the recipe.","The paper frames the vortex ring as the validation target; linking its tilt and dissipation timing to clinical indexes of diastolic function would be a direct next step."],"forward_implications":["A laminar solver is enough for early-diastole vortex ring studies, so researchers can skip turbulence models and save computational cost.","Inlet development length matters: tubes shorter than two diameters will distort the profile before it reaches the chamber, so the two-diameter rule is a practical lower bound.","Hyperbolic tangent inlet profiles converge on coarser meshes than plug profiles, lowering mesh requirements while preserving vortex dynamics.","The validated agreement between two independent solver implementations means the setup is not tied to a single code and the boundary-condition logic transfers.","A mass-flow outlet is preferred over switching between a pressure outlet and a wall because it avoids transition noise at valve closure."],"supporting_citations":[{"why":"Supplies the idealized LV geometry and the physiological flow-rate curve from which the moving-wall volume and inlet profile are derived.","marker":"[15]"},{"why":"Provides the prior modeling and validation benchmark for intraventricular flow and total kinetic energy that this study compares against.","marker":"[16]"},{"why":"Supports the claim that laminar flow modeling is sufficient to capture the vortex ring in early diastole.","marker":"[22]"},{"why":"Reports idealized left-ventricle vortex dynamics captured without turbulence models, backing the laminar assumption.","marker":"[23]"},{"why":"Companion conference paper documenting the two-solver validation of this setup in Ansys Fluent and Star-CCM+.","marker":"[27]"},{"why":"Companion practical guide with the detailed mesh and boundary-condition configuration that the paper's recipe references.","marker":"[13]"},{"why":"Documents the Star-CCM+ solver whose meshing and morphing tools implement the moving-wall recipe.","marker":"[6]"},{"why":"The Ansys Fluent implementation used as the independent validation solver.","marker":"[14]"}],"fun_headline_variants":["Moving walls and tanh inflow unlock heart vortex ring","Simulation recipe for accurate heart vortex ring","Key conditions for realistic heart vortex modeling","How to get the heart vortex ring right in simulations","Tweak these settings to reproduce the heart's vortex ring"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that a real ventricle can be represented as a semi-ellipsoid whose wall expands and contracts uniformly with its $4{:}1$ axis ratio fixed at every instant; if real wall kinematics—twist, regional contraction, valve motion—matter for the vortex ring, this recipe may not transfer to patient-specific models.","fun_headline_variants_meta":{"raw":{"variants":["Moving walls and tanh inflow unlock heart vortex ring","Simulation recipe for accurate heart vortex ring","Key conditions for realistic heart vortex modeling","How to get the heart vortex ring right in simulations","Tweak these settings to reproduce the heart's vortex ring"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000647,"raw_usage":{"total_tokens":2962,"prompt_tokens":926,"completion_tokens":2036,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":542,"completion_tokens_details":{"reasoning_tokens":1964}},"tokens_in":542,"tokens_out":2036,"duration_ms":14498,"temperature":1.0,"reasoning_tokens":1964,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-12T12:50:33.371729+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Run the same boundary-condition recipe in a geometry whose wall motion is taken from measured patient imaging (4D echocardiography or tagged MRI) instead of the uniform $k=4$ scaling; if the vortex ring's formation, tilt direction, or dissipation timing changes measurably, the uniform-scaling premise is the failing part.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the prior modeling and validation benchmark for intraventricular flow and total kinetic energy that this study compares against."},{"cited_title":"On the numerical simulation of left ventricle blood flow","cited_arxiv_id":null,"evidence_quote":"Companion conference paper documenting the two-solver validation of this setup in Ansys Fluent and Star-CCM+."},{"cited_title":"ModelFLOWs- cardiac: https://modelflows.github.io/modelflowsapp/ cardiacpathologydetection/","cited_arxiv_id":null,"evidence_quote":"Companion practical guide with the detailed mesh and boundary-condition configuration that the paper's recipe references."},{"cited_title":"CT-Based Analysis of Left Ventricular Hemody- namics Using Statistical Shape Modeling and Computational Fluid Dy- namics","cited_arxiv_id":null,"evidence_quote":"Documents the Star-CCM+ solver whose meshing and morphing tools implement the moving-wall recipe."}],"review_version":1}