How This Side Hustler Makes 6000 Monthly as a Freelance CFD Engineer

Lucas: So we talk a lot on this show about side hustles in tech, marketing, content creation — but there's a whole world of high-skill, technical freelance work that flies under the radar. Today I want to look at something very specific: computational fluid dynamics, or CFD, as a side hustle. Luna: CFD — so we're talking about simulating how fluids move? Air, water, that kind of thing? Lucas: Exactly. Think airflow over a car, water through a pipe, wind around a building. And it turns out there's a growing market for freelance CFD engineers, particularly from small companies and startups that can't justify a full-time simulation specialist. Our case today is a guy named Mark — aerospace engineer by day, freelance CFD consultant by night. Luna: And he's making how much? Lucas: About $6,000 a month on the side. He's been doing it for about two years now, and he started with basically no portfolio. So I want to unpack how he got there, what the actual work looks like, and whether this is something other engineers could replicate. Luna: Alright, I'm curious. Let's start with the basics — what kind of projects is he actually doing? Lucas: Really varied. He's done a simulation for a startup designing a new type of HVAC duct that reduces noise. He's worked with a small sailboat manufacturer to optimize the keel shape for less drag. And he's done a bunch of projects for companies that make industrial fans or pumps. The common thread is: they need simulation data, but they don't have the in-house tools or expertise. Luna: So he's essentially renting out his access to software and his know-how? Lucas: Exactly. And the barrier to entry is lower than you might think. Mark told me he uses mostly open-source tools — OpenFOAM is the big one — and only occasionally licenses commercial software like ANSYS Fluent if a client specifically requests it. So his overhead is basically his laptop and a few hundred dollars a year in cloud computing credits. Luna: But isn't CFD incredibly complex? Like, you need a deep understanding of fluid dynamics and numerical methods. This isn't something you just pick up on YouTube over a weekend. Lucas: No question. Mark has a master's in aerospace engineering and five years of industry experience. But the point is: there are a lot of engineers out there with exactly that background who don't realize they can monetize it as a side hustle. And the demand is growing because more and more small companies are prototyping physical products and need simulation to validate designs before building expensive prototypes. Luna: So how did Mark land his first clients without a portfolio? That's usually the catch-22. Lucas: He did something really smart. He picked three common simulation scenarios — flow over a cylinder, flow through a pipe bend, and airflow in a simple room — and ran those simulations on his own time. Then he posted the results on a personal website with a brief explanation of the setup and the outputs. That became his portfolio. Luna: So he created his own sample projects rather than waiting for paid work. Lucas: Right. And he targeted a specific platform: Upwork, but not the general engineering category. He found a niche posting in 'Simulation and Analysis' and bid on projects that were small — $500 to $1,000 — where the client needed a quick answer, not a full report. He underbid a bit initially to build reviews. Luna: And now he's getting repeat clients, I assume? Lucas: Almost all of his work is repeat or referral. He works with about four regular clients now, and most months he can hit 40 to 50 hours of billable simulation work. He charges $75 to $100 an hour depending on complexity. Luna: That's a solid rate. Especially for a side hustle where you're working evenings and weekends. Lucas: And the work itself — he tells me it's actually more enjoyable than his day job in some ways, because he gets to solve different problems. One week it's a medical device company needing flow validation for a new ventilator component. Next week it's a brewery optimizing the cooling system for their fermentation tanks. Luna: A brewery? I love that. So it's not just aerospace or automotive. Lucas: Not at all. CFD touches almost every industry that moves a fluid — which is almost everything. Food processing, water treatment, even sports equipment. Mark did a simulation for a company that makes high-performance swim caps, believe it or not, to reduce drag. Luna: That is incredibly niche. But I can see how that would be a fun Friday night project. Lucas: Exactly. And here's another angle — some of these clients are startups that eventually get funded and then want to hire him full-time. Mark has actually turned down two full-time offers because he prefers the variety and flexibility of freelance work. Luna: So the side hustle becomes a lifestyle choice, not just income. Lucas: That's the sweet spot. And it's interesting because a lot of engineering professionals feel like their skills are too specialized to freelance. But Mark's story shows that if you can package that specialization as a service, there's a market. Luna: And if today's episode gave you a new idea or made you think about your own skills differently, that's exactly the kind of value we aim for here. And the reason we can keep the show ad-free is listener support. So if you found this useful, you can always toss a few bucks in the tip jar at buy me a coffee dot com slash fexingo. No pressure — just helps us keep going. Lucas: Yeah, exactly. We love hearing that people get something out of these stories. So thanks for that. Now, back to Mark's playbook — he also told me about one major mistake he made early on. Luna: What was that? Lucas: He underpriced his work because he was nervous about asking for higher rates. He started at $50 an hour and quickly realized he was spending way too much time on client communication and report writing. So he raised his rate to $75, and then $100, and the quality of clients actually got better. Fewer tire-kickers, more serious projects. Luna: That's a common lesson across a lot of side hustles — your rate signals your quality. Lucas: Huge. And the other thing he learned was to scope projects tightly. A client would say 'simulate this pump' and he'd deliver a full report with 10 different operating conditions. But the client only needed one condition to make a decision. Now he always asks: 'What decision will this simulation inform?' That keeps the project small and focused. Luna: So it's not just about the technical skills, it's about managing expectations. Lucas: Exactly. And for anyone listening who has an engineering background and is thinking about this — Mark's big advice is to start with one industry you already understand. If you worked in automotive, do auto-related CFD. If you did HVAC, do that. Your domain knowledge is as valuable as the simulation skill. Luna: So you're not just a simulation mercenary, you're a specialist who understands the physics of their specific problem. Lucas: That's the pitch. And honestly, that's why clients pay a premium. A generic CFD consultant might need two weeks to understand the context. Mark can start modeling on day one because he's already familiar with the constraints and standards in aerospace or mechanical engineering. Luna: So what's the next step for Mark? Is he planning to scale this into a full-time business? Lucas: He's actually thinking about it. He's at a point where the side hustle income is now about 60 percent of his day-job salary. But he's hesitant because he likes the benefits and stability of the full-time role. So for now, he's happy with the $6,000 a month and the variety. Luna: And that's a great place to be — having a choice. That's really the whole point of a side hustle. Lucas: It is. And I think the broader lesson here is that high-skill technical work can absolutely be freelanced. It's not just for writers and designers. If you've got a specialized skill that companies need but can't justify full-time, there's a market. Luna: And you don't need a huge online presence. You just need to show you can solve a specific problem. Lucas: Exactly. Mark didn't have a Twitter following or a blog. He had three simulation examples and a willingness to bid on small projects. Two years later, he's turning down work. So if you're an engineer sitting on skills you think are too niche, maybe fire up OpenFOAM this weekend and run a simple simulation. That's how Mark started. Luna: I love that. And we'll link to some resources for getting started with CFD on the show notes. Thanks, Lucas. Lucas: Yeah. Thanks, Luna. And thanks for listening.