SAE Notchback Model

CFD Validation - 1st Automotive CFD prediction workshop

SUMMARY

In recent years, computational fluid dynamics (CFD) has become an essential tool for the design and optimization of various engineering systems, including automotive vehicles. However, the accurate and reliable prediction of fluid flow around complex geometries remains a challenging task. To address this issue, the Automotive CFD Prediction Workshop was established to evaluate the predictive capability of CFD codes for road-car geometries. This workshop provides a set of mandatory geometries, boundary conditions, and computational grids to enable a fair comparison between different CFD codes and to establish best practices for modeling and simulation.

In this context, we have conducted a CFD validation case for the SAE notchback model from the Automotive CFD Prediction Workshop, using Symula CFD software. The main objective of our study was to assess the accuracy and predictive capability of Symula CFD for road-car geometries, particularly with regard to turbulence modeling, meshing, and numerical schemes. To this end, we have obtained results for the three levels of precision available in Symula and compared them to the benchmark experimental data provided by the workshop.

Through this validation case, we aim to demonstrate the performance and reliability of Symula CFD software for automotive applications and provide practical modeling guidelines to the automotive community. The results of our study could potentially contribute to the development of more accurate and efficient CFD tools for the design and optimization of road-car geometries, with implications for improved vehicle performance, fuel efficiency, and safety.

3D MODEL

The geometry of this simulation case corresponds to a simplified vehicle shape under wind tunnel conditions and is intended to capture the important flow field structures without the need to model complex geometric details. This model features a 20 degree tail angle and is based on the 1/5 scale notchback reference model (Cogotti 1988) with an experimental campaign conducted at Loughborough University (Wood, Passmore and Perry 2014).

RESULTS

DRAG FORCE VALUES

The values ​​obtained for the calculation of the force of resistance are shown in the following graph. Results for the 3 levels of precisions offered in the Symula platform are compared with respect to experimental data obtained in wind tunnel facilities, as well as with respect to the rest of the participants, CFD software and turbulence models.

  • “Conceptual” Precision: The error obtained for this precision is around 30%. Although it is a high error value if we compare it with the exact experimental value, at this level of precision, an order of magnitude is offered by Symula.
  • “Accurate” Precision: In this case the error is considerably reduced and stands at 10% with respect to experimental values. In addition, for this precision Symula is already within the range of values ​​obtained by the rest of the participants.
  • “Realistic” Precision: For the maximum precision offered by the Symula platform, the error is reduced to 2% with respect to experimental values. Greatly improving the results obtained by most participants and CFD softwares.
CD values for the SAE Notchback Model

LIFT FORCE VALUES

Additionally, the values ​​obtained for the calculation of the lift force are shown in the following graph. Results of the 3 precisions offered in the Symula platform are compared with respect to experimental data obtained in a wind tunnel, as well as with respect to the rest of the participants, CFD software and turbulence models. In this case, following the guidelines of the “workshop”, no relative errors have been calculated, although the comparison is shown with respect to the rest of the results and participants.

CL values for the SAE Notchback Model

AERODYNAMIC RESULTS

Some images of results obtained for the fluid-dynamic behavior of air are also shown. Results of velocity contours, wind pressure over the vehicle, stream lines, and drag contours are displayed.

These results are the ones we offer automatically on the Symula web platform, in addition to allowing the download of results to work with programs like Paraview to be able to perform any type of post-processing operation locally.

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