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Automated Optimization of Automotive HVAC Design
Posted Mon December 15, 2003 @10:03AM
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Application When Visteon Climate Control Systems sought assistance in optimizing its automotive heating/air conditioning systems, they chose Optimal Solutions. Optimal Solutions’ Sculptor™ software gave the design engineer the ability to interactively modify (deform) and automatically optimize the CFD mesh models without remeshing so that they were able to modify an existing defroster design quickly and efficiently, resulting in significantly improved performance of the system, as well as demonstrating Sculptor™s ability to decrease time-to-market.

Using the one-of-a-kind Arbitrary Shape Deformation (ASD) technology developed by Optimal Solutions’ engineers, an ASD volume was designed to deform the defroster CFD grid to improve performance without having to remesh.


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After initially testing the defroster deformation, three more parametric planes of control points were added as indicated by the arrows in Figure 1 in order to control the deformation of each outlet independently. One of the constraints of the design was that the shape of the outlets must not be changed. Therefore, another plane of control points was added along the top of the volume along the boundary of the outlets.

original volume
Figure 1. Original ASD volume. Arrows show where new parametric planes were added.

Figure 2 shows what the ASD volume looked like after inserting these four planes.

ASD volume
Figure 2. The ASD volume with four new parametric planes added.

Some minor ‘smoothing’ and repositioning of control points was completed to have a plane of control points as close to the left and right edges of each outlet duct as possible. This provided ‘fine local control’ of the deformations that was necessary to reshape the ducts into a better shape.

The new control point configuration is shown in Figure 3. The control points along the top have been moved a small amount so that all nodes are inside of the ASD volume. It was then necessary to define the groups that were to be used for design variables. In this problem, it seemed intuitive to want to change the straight nozzle duct section into curved shapes to redirect the flow to the center of the windshield corresponding to what the driver sees in a straight-forward-looking direction. Therefore, the designer defined an objective function to maximize the flow velocity at a point directly in front of the driver.

new ASD volume
Figure 3. The new ASD volume with the control points in the desired locations.

The results of an automatic shape optimization session in Sculptor™ resulted in the shape shown in Figure 4. Note that the designer only allowed five variables to change for this optimization example. The objective for the results in Figure 4 was to maximize the velocity magnitude at a point directly in front of the driver’s eyes. The original value of the velocity at this point was 1.3 m/s. The design shown here achieved a velocity value of 3.7 m/s—a significant improvement.

improved design
Figure 4. An improved design with only five variables in the Y-direction.

Figure 5 shows the comparison of the original velocity contour profile on the windshield versus the velocity profile on the windshield for the design in Figure 4.

velocity profile comparison
Figure 5. A comparison between the original velocity profile and the improved velocity profile on the windshield.

Looking at this solution, there was considerable improvement in front of the driver; however, it was at the expense of the center of the windshield. At this point, the designer set up an objective function with several points along the driver’s line of sight across the windshield. Three points were defined as “Surface Points” in Fluent to be used as post-processing Report Surface entities to get the velocity magnitudes into the transcript file for a new optimization session. These three points were 1) directly in front of the driver, 2) at the center at the same altitude, and 3) directly in front of the passenger.

Figure 6 shows the final design, which demonstrates an optimal compromise between the driver’s side and the center point’s velocity magnitudes. A comparison of the original and Figure 6’s Velocity Magnitude Contour Plots are shown in Figure 7.

optimal design
Figure 6. An optimal defroster design.

 

velocity comparison
Figure 7. A comparison of the velocity magnitude contour profiles between the original design and the optimal design on the windshield.

Because of the capabilities of Optimal Solution’s Arbitrary Shape Deformation technology to perform the design optimization on the Visteon Corporation’s windshield design in real-time, the design engineers were able to reduce the need for costly physical testing and prototyping. Numerous mesh generation iterations were not required—which can, depending on the optimization problem, take hundreds or even thousands of man-hours of work and rework time.

Using the Sculptor™ software, not only was the result a more accurate design, but the design optimization took hours—rather than the normal days—to complete. Visteon Corporation was able to save time and money on this project.

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