Making CFD Accessible with Altair Inspire

An easy fluids simulation tool enables drivers and engineers to race classic cars.

Altair has submitted this post.  Written by Drew Buchanan, Engineering Manager, Trueinsight

Tinkering and building things has always been a passion of mine since my youth. I spent much of my childhood taking apart and reassembling things to make them more efficient or streamlined. Eventually, my childhood interests led me to enter college and begin my engineering career in Pittsburgh, Pennsylvania. While at university, I continued my tinkering and was active on my university’s SAE team. I recall one SAE meeting when a friend asked me if I was planning to attend the Pittsburgh Grand Prix the following week. At the time, I was totally confused and wondered, “What Grand Prix? We live in Pittsburgh, not Monte Carlo.”

However, much to my surprise, Pittsburgh is known for holding an annual summer racing event called the Pittsburgh Vintage Grand Prix. It is an automobile racing event where amateur racers drive vintage vehicles unrestricted through Pittsburgh’s city streets. Most of the racecourse is in Schenley Park and the Oakland neighborhood of Pittsburgh, which was directly adjacent to my college campus. So naturally, I went to check it out and had a blast. I continued to attend the Grand Prix every year I lived there.

Pittsburgh Vintage Grand Prix. (Image: Bigstock.)

Pittsburgh Vintage Grand Prix. (Image: Bigstock.)

At the Pittsburgh Grand Prix, all cars in the event must be classified as a “vintage vehicle” (at least 30 years old), and the drivers are typically recreational and not affiliated with a professional racing team. As a result, drivers typically service and replace parts on their own. As you can imagine, it can be very challenging to repair parts on cars that are at least 30 years old. In addition, if a part breaks, it is often hard to find a replacement. So, here’s how to do it.

Replacing Old Car Parts

There are some manufacturers who specialize in replacing parts for old vehicles, but for the most part, they tend to be in limited supply, if they are available at all. Additionally, the typical replacement parts are often designated for daily driving applications, and not built for performance or racing. As a result, many of the drivers that participate in the Vintage Grand Prix will hire small fabrication shops to make one-off custom parts by reverse engineering and either additive or subtractive manufacturing. One of the more critical parts is the intake manifold—a good intake manifold can increase horsepower—so let’s use it as an example.  

What is an Intake Manifold?

The intake manifold is the part of an engine that supplies air to the cylinders in the combustion chamber of an engine. It is imperative that the air delivered to the cylinders is consistent and uniform. Intake manifolds are designed so that when a driver pushes on the gas pedal it controls the amount of air that will enter the combustion chamber. Therefore, the effect of a highly efficient manifold can significantly increase engine performance while also increasing fuel efficiency. Consequently, having a good intake is essential for Pittsburgh Grand Prix drivers.

CAD model of an example intake manifold. (Image: Altair.)

CAD model of an example intake manifold. (Image: Altair.)

Current Intake Manifold Replacement Process for Vintage Vehicles

For most vintage vehicles, drivers can either see if they can get the original intake manifold from an afterparts manufacturer or rebuild a new one. More often than not, a new manifold will need to be designed and fabricated by a custom shop.

The fabrication and design process for a post market vehicle part looks something like this:

  1. Scan the original part and connectors.
  2. Translate the point clouds into CAD geometry.
  3. Perform simulations to optimize the geometry for part performance.
  4. Manufacture the part using additive and/or subtractive methods.

As step 3 suggests, a change in pipe dimensions will ultimately change the velocity and pressure of the air before it enters the combustion chamber. Thus, being able to determine the effect of geometric changes on velocity and pressure is vital to designing a brand-new intake manifold.

Using CFD to Reduce the Fabrication Prototypes

Since the geometry will ultimately influence the performance of an intake manifold, drivers need to optimize the part’s shape to improve their Pittsburgh Grand Prix experience. The current testing method for manifolds either requires someone to build a physical model, or to run a computational fluid dynamics (CFD) model to simulate the air effects in the manifold. The latter makes it faster and easier to update the geometry to optimize the air velocity or pressure. This is because iterations can happen faster digitally than with physical prototypes.

In other words, running CFD can be advantageous because everything can be done on a computer and users can test out a variety of intake manifolds without having to physically build it. By running a bunch of test cases, users can zero in on the appropriate model(s) to physically build. This can reduce the number of physical fabrications.

However, there has been one current challenge with running CFD: traditionally an engineering expert was required to utilize the tool. Since it requires a good bit of expertise, without a fluid dynamics background it could be hard to obtain reasonable results in a quick period of time. For this reason, utilizing CFD for the average hobbyist, racer or product designer has been prohibitive because of the lack of expertise in CFD modeling. Altair recognized this challenge and addressed it in a recent release.

Implementing Inspire Fluids to Test Manifolds Easily

The release of Altair Inspire 2022.3 introduces a very easy to use fluid dynamics tool that does not require fluid expertise to run. The flow tool is integrated into Altair Inspire, which is already well known for its easy-to-use structural analysis. In our case, I am going to take you through the process of testing out a sample manifold in Inspire Fluids. It should be noted that combustion is not being factored into this design, as combustion is not a feature in the tool.

Our first step is to import the CAD part or assembly into Inspire. I can then specify my model as the fluid domain (i.e., location of the gas or fluid). Next, I specify air as the fluid. Note that there are several fluids integrated directly into the Inspire Material database, but users can also key in custom fluids as well.

Specifying air as the fluid domain of the inlet. (Image: Altair.)

Specifying air as the fluid domain of the inlet. (Image: Altair.)

Next, we need to specify the inlet and outlet conditions of our system by clicking on the appropriate geometry faces. For our purposes, we can specify that the inlet velocity is 500 ft/s and 100F, which is what a typical manifold may expect to see. We can also express the outlet faces as ambient pressure. After setting these values, we can run our scenario. Much like the FEA tool in Inspire, meshing is done automatically to make the user experience easier.

Inlet and outlet boundary conditions of a manifold. (Image: Altair.)

Inlet and outlet boundary conditions of a manifold. (Image: Altair.)

Since Inspire Fluids leverages GPUs, I obtained results in minutes, a fraction of the time that traditional CFD requires. After running my scenario for my intake manifold, I can visualize the fluid velocity and fluid pressure values which are vital in determining an efficient intake manifold. The post processing in Inspire Fluids is very similar to the post processing in Inspire Structures. Users can create contour plots, iso-scales and adjust legends to visualize results easily and accurately. It can also create CFD specific plots like streamlines and animated fluid trajectories.

Intake manifold pressure results Inspire Fluids. (Image: Altair.)

Intake manifold pressure results Inspire Fluids. (Image: Altair.)
Intake manifold velocity results Inspire Fluids. (Image: Altair.)

Intake manifold velocity results Inspire Fluids. (Image: Altair.)

Through looking at both result plots, I can see that the outlet velocities are relatively uniform while also maintaining good pressure distribution. This is a great starting place for an intake. Based on this, I could potentially tweak the dimensions to see if it increased performance or not. Running these models virtually is an advantage because I can zero in on a model without having to build anything.

As an engineer, I am extremely excited to see the ease of use of this tool and how it will make the world of CFD even more accessible for designers. I look forward to seeing how various users utilize more accessible CFD tools like Altair Inspire in the coming years—much like designers have embraced Inspire and SimSolid for structural analysis. I am even more excited to see how vintage racers can implement this tool into their design and repair process for future Vintage Grand Prix events.

If you’re a vintage racer and want to test your intake manifold performance today, you can get a free Inspire Personal Edition License here. To learn more about Inspire and other simulation-driven design tools, check out Altair Inspire.