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This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 955923
MARIE SKŁODOWSKA-CURIE ACTIONS Innovative Training Networks (ITN) Call: H2020-MSCA-ITN-2020
The main objective of this WP is the identification of a set of industrial problems with enough relevance to guide the research and improve synergies and collaboration between the ESRs.
In this line, 5 different test case were identified and studied. Details of the test cases and results can be found in Deliverables D1.1 to D1.6. Here a short description of work performed in each test cases is included.
The focus of TC1 is on detailed aerodynamic simulations, identifying flow structures responsible for detachment, and developing control strategies.
The proposed test case TC1 is a full Formula 1 configuration provided by McLaren Racing Ltd, serving as the final demonstration case to showcase algorithmic and process improvements developed throughout the project. The primary challenges of TC1 are its geometrical complexity and high computational cost.
To address these, a structured hierarchy of progressively complex test cases was derived, ensuring representative yet computationally manageable setups.
Efforts in this Task include (ESR1, ESR4, ESR5, ESR7, ESR8,ESR11, ESR12, ESR13, ESR16)
High-Fidelity Meshing for Complex Geometries.
A novel meshing workflow was developed, integrating high-order accuracy with finite volume flexibility. The process included generating a straight-sided mesh, reconstructing CAD-mesh connectivity, and optimizing the mesh curvature. This methodology improved geometric accuracy and CAD robustness, enabling simulations of the extruded Imperial Front Wing (IFW), the full IFW, and an entire F1 car. The approach was refined to reduce manual effort, enhance pyramid-prism-tet splitting, and improve y+ resolution control in high-order adaptations.
Aerodynamic Performance and Higher-Order Schemes.
Investigations into the front wing flow physics validated and enhanced higher-order numerical schemes, improving computational efficiency for large-scale industrial applications. This research informed future full TC1 geometry simulations and opened new avenues for temporal discretization strategies.
Flow Stability Analysis.
A stability analysis of detached flow over airfoils at high angles of attack provided insights into instability onset and transition paths, relevant for understanding F1 front wing aerodynamics.
Large Eddy Simulation (LES) Guidelines.
Studies focused on optimizing LES methodologies for F1 geometries, including a mesh convergence study to assess sensitivity to mesh parameters. These efforts significantly improved the understanding of F1 front wing flow physics and provided LES meshing guidelines for future research.
The advancements in TC1 contribute significantly to the development of high-fidelity aerodynamic modeling, meshing strategies, and LES methodologies. The structured test cases and improved numerical frameworks enhance predictive accuracy while managing computational demands, making them highly valuable for Formula 1 aerodynamics research and industrial applications.
Test Case 2 (TC2), a low-pressure turbine blade, is established as a reference case based on experimental research conducted by the PETAL group at Purdue University. The study replicates the suction side of low-pressure turbine blades using a bump geometry. The primary bump shape is derived from experiments conducted by Prof. Paniagua’s PETAL group, with additional reference geometries, including the NASA hump, which is widely used for studying flow separation. Figure 4 illustrates the Purdue bump test article under both laminar and turbulent boundary layer separation conditions.
Three main studies have been conducted by ESR2 and ESR11, all performed numerically using either Direct Numerical Simulations (DNS) or Large Eddy Simulations (LES). Two solvers have been utilized: the in-house UPM high-order solver HORSES3D and the Cadence Fidelity CharLES code. These studies include:
Significant advancements have been made in this TC, focusing on low-pressure turbine flow physics. Several novel findings have been reported and analyzed. The first study examined separation scenarios under harmonic inflow fluctuations. The second study mapped sensitivity to active actuation, aiming to reduce separation length. The third study highlighted relaminarization effects in the experimental setup and emphasized the need to extend the height of the refined grid region beyond the boundary layer thickness. Additionally, it demonstrated how turbulence levels influence separation characteristics.
These new insights contribute to a deeper understanding of low-pressure turbine blade aerodynamics, paving the way for improved design methodologies and analysis techniques.
Figure 4 Illustration of the test article in the experimental setup
Test Case 3 (TC3) aims to enhance the performance of drop-on-demand (DOD) inkjet printheads. A key objective for printhead manufacturers is to increase jetting frequency while maintaining uniform droplet size and shape. This requires damping mechanical reverberations before the next droplet ejection. To achieve this, waveform engineers optimize the motion of the piezoelectric actuator (the waveform) to cancel reverberations as quickly as possible. However, these experiments are costly and must be repeated for each ink type and printhead geometry.
To address this challenge, ESR6 presents two complementary frameworks. The first identifies the optimal actuator motion to cancel acoustic reverberations while ensuring the desired droplet volume within a given actuation time. This is formulated as an optimization problem, numerically accelerated using adjoint methods. The second framework refines our physical model using experimental data, improving quantitative accuracy. This model serves as a digital twin, enabling predictive simulations of real inkjet printhead configurations. Together, these frameworks provide waveform engineers with insights into wave reflection and transmission within the printhead, offering strong starting points for experimental campaigns and reducing time and resource costs.
This deliverable specifically addresses TC3 for improving DOD inkjet printing, with a focus on the bulk-type configuration used by Xaar. Our framework computes optimal waveforms that efficiently dissipate mechanical reverberations while maintaining a target droplet volume within a specified actuation time.
Experimental data from Xaar reveals significant cross-talk between microchannels, particularly in bulk-type printheads. Shared actuators transmit reverberations to adjacent microchannels, impacting performance. To account for this, we integrate cross-talk effects into our model and refine it using experimental data to infer energy reflection and transmission through the actuators. A simplified 14-parameter model demonstrates sufficient accuracy for reliable predictions.
Obtaining optimal waveforms is traditionally time-consuming and costly due to extensive trial-and-error experiments. However, by combining the two frameworks presented in this report, waveform engineers can significantly reduce experimental effort. This approach provides an effective starting point for optimization, leading to more efficient inkjet printhead design while conserving valuable time and resources.
TC4 synthesizes insights from three advanced investigations into boundary layer instability phenomena, focusing on the effects of surface irregularities, discrete roughness elements, and surface waviness on boundary layer receptivity and stability.
The ESR9 studied the impact of forward-facing steps on transition to turbulence. The geometry under study is a swept-wing model that mimics the experimental setup of Rius-Alberto Vidales in the Low Turbulence Tunnel (LTT) at the Delft University of Technology. The impact of two forward-facing steps was analyzed by means of linear stability analysis. LST-2D/PSE-3D methodologies were able to retrieve the most unstable mode featured by the larger step height, which is likely to be the one triggering the laminar-turbulent transition process in the immediate downstream of the step.
The first investigation applies two-dimensional linear stability theory (LST-2D) and three-dimensional parabolized stability equations (PSE-3D) to examine the effects of forward-facing steps (FFS) on the secondary instabilities of stationary crossflow vortices. Using direct numerical simulation (DNS) data as the base flow, the study reveals that FFS configurations significantly alter instability characteristics.
The second investigation explores the receptivity of two-dimensional boundary layers on a flat plate with a super-elliptical leading edge in the presence of a discrete roughness element (DRE). DNS is used to examine the parameter space defined by the element height relative to the boundary layer displacement thickness and the Reynolds number. Results indicate that localized volumetric forcing and synthetic free-stream turbulence (FST) strongly influence disturbance amplification. Notably, interactions between Tollmien-Schlichting (T-S) waves and the DRE led to significant amplification at specific frequencies (ω = 0.21 and ω = 0.29) and turbulence intensities (Tu = 0.03% and Tu = 0.3%). These findings highlight the critical role of DRE height and external forcing in modulating boundary-layer disturbance growth.
The third study employs linear global stability analysis to examine a laminar separation bubble induced by surface waviness. The eigenspectrum reveals a globally unstable mode responsible for three-dimensionalizing the bubble, along with a family of low-frequency stable modes. Adjoint sensitivity analysis identifies a high-sensitivity region upstream of the bubble’s reattachment point. Further insights from DNS and linear impulse response analysis show that transition via self-excited mechanisms generates low-frequency upstream-propagating waves within the bubble. These waves, absent in linear impulse analysis, are linked to low-frequency stable modes activated through nonlinear effects during transition.
Together, these studies improve the understanding of stability mechanisms in boundary-layer flows, with implications for flow control and aerodynamic design.
Moreover, ESRs 9, 10, and 15 collaborated on a numerical investigation of the effect of surface irregularities on the transition to turbulence using a DNS code. ESR 10 coordinated the effort to produce deliverable D1.5. ESR 10’s individual contribution included a receptivity analysis of an incompressible, two-dimensional boundary layer exposed to free-stream turbulence in the presence of a discrete roughness element (DRE). DNS was performed for various flow configurations over a flat plate with a semi-elliptic leading edge, comparing the evolution of perturbations in each case.
A meshed flat-plate surface, including the elliptic leading edge and the DRE, was generated. The size and location of the DRE were modified for visualization purposes.
ESR 15 investigated the effect of surface waviness on the transition to turbulence. Stability and adjoint sensitivity analyses were conducted, along with direct numerical simulations (DNS) and linear impulse response analyses. DNS results show that, when transition occurs due to self-excited mechanisms, low-frequency upstream-propagating waves form inside the bubble—whereas linear impulse analysis does not capture this effect. It is conjectured that these waves correspond to low-frequency stable modes in the spectrum, which become active through nonlinear effects during transition. These findings deepen the understanding of laminar-turbulent transition in laminar separation bubbles induced by surface waviness.
This test case highlights the complex interplay between fluid dynamics, structural vibrations, and acoustics in subsonic confined flows. ESR8 developed and validated a numerical and experimental framework, providing critical insights into aero-vibro-acoustic interactions, particularly in configurations representative of vehicle underbodies. Key advancements include efficient partitioned simulation strategies, spatial mapping techniques, and experimental validation methodologies.
The experimental campaigns, centered on the TC5 setup, investigate how obstacle configurations influence pressure fluctuations and noise radiation. Additionally, the integration of locally resonant metamaterials (LRMs) demonstrates their potential for mitigating noise and vibration. The combination of Operational Modal Analysis (OMA) and model updating techniques enhances boundary condition modeling, improving numerical prediction accuracy.
For precise numerical prediction of vibro-acoustic interactions in flow ducts—particularly in the low-frequency region—an advanced structural boundary condition model is essential. This study proposes an indirect methodology that employs two-port acoustic data for iterative optimization. Since the two-port approach is independent of duct inlet and outlet conditions, it is especially useful in early design stages when the full system configuration is not yet defined. A finite element model incorporating frequency-independent stiffness and damping parameters improves prediction accuracy compared to standard boundary conditions.
OMA further validates the optimized numerical model by capturing the fundamental vibro-acoustic physics. A parameter study confirms the robustness of this methodology, demonstrating that structural boundary estimations remain independent of material properties. Moreover, non-contact acoustic monitoring using microphones provides a cost-effective alternative to Laser Doppler Velocimetry (LDV) for structural vibration assessment, reducing the need for expensive experimental setups.
These findings refine predictive tools and experimental strategies, enabling early-stage noise mitigation in lightweight engineering designs.
SSeCoID | Stability and Sensitivity Methods for Flow Control and Industrial Design
MARIE SKŁODOWSKA-CURIE ACTIONS | Innovative Training Networks (ITN)
Call: H2020-MSCA-ITN-2022
