How Close Is Too Close? Applying Fluid Dynamics Research Methods to PC Cooling

In April 2025, LinusTechTips visited NASA's Langley Research Center in Hampton, Virginia at the invitation of the Flow Physics and Control Branch, where they were hosted by Dr. Louis Edelman. Louis served as a researcher at NASA Langley from 2018 to 2026 but has left NASA since we filmed the LTT video. He is now an assistant professor in the University of Tokyo Department of Aeronautics and Astronautics.

The intent of this article is to accompany the LinusTechTips video (and Floatplane exclusive videos) on the testing conducted. Not all of the content could be included and it would be a shame for it not to be shared. Louis generously offered to write a paper delving into the test setups, methodologies, and conclusions. We hope you find it interesting and educational.

NASA Langley Research Center was founded in 1917 as the Langley Memorial Aeronautics Laboratory, predating NASA itself. It was the first government research laboratory for aeronautics in the United States and has been involved in nearly every advancement in the science of flight for the last 109 years. There are lifetimes worth of stories to tell about the rich history of Langley and the future its personnel are working to build today. For the LTT visit, the challenge before us was to distill some part of that immense legacy into a single video. We decided that the most impactful and honestly fun approach would be to perform an experiment that bridged the world of leading-edge flight research to the (hopefully leading-edge) PC sitting on your desk. An experiment that highlighted the tools, technology, and process behind the everyday in NASA’s “first A”, aeronautics.

The most obvious aerospace-adjacent component in a gaming PC is the humble case fan. So we set out to answer a deceptively simple question: does a restrictive front panel or placing your PC too close to the wall hurt the cooling potential of your fans? How close is too close? What if my intake fan is also my radiator cooling fan? In this article, we detail how we carried out the experiments in the LTT video, the history of the techniques and facilities we used, and some of the behind-the-scenes process.

Before we proceed any further, a disclaimer: The opinions expressed herein are those of the author and do not reflect the opinions of NASA or the Government of the United States of America. The detailed description and use of any hardware and software in this article is purely descriptive of their use and does not imply an endorsement of those products. With that out of the way, on to the science!

Experimental Methods

The core of the three experiments is a single Noctua NF-A12X25 120 mm diameter PC fan powered at 12V from a benchtop DC power supply and given a 100% PWM control signal through a Noctua NF-FC1 fan controller. A 3D printed bracket rigidly mounts the fan perpendicular to the table, lifting it up and away from any ground effects without disrupting the inlet or exhaust flow paths. A 3 mm thick acrylic sheet is laser cut to the outer dimension of the fan frame with a 105 mm square 4x6-32 clearance hole pattern for mounting. Four 75 mm long 6-32 screws are inserted into the fan frame and the acrylic plate is then slid onto them in front of, or upstream, of the fan face. This keeps the experimental space to a single parameter: the gap between the front plate and the fan face. 3D printed snap-on spacers are placed on the screws between the fan frame and the acrylic plate; these ensure the plate is nominally parallel to the fan face. The fan is set at 100% 12V PWM to reduce the complexity of the variable space. This is representative of typical PC case or PSU intake fan operating conditions during heavy load with the fan working at its maximum airflow and cooling potential.

With just one day of testing and several testing methodologies to demonstrate, keeping the parameter space one-dimensional was an absolute necessity. These considerations mirror the challenges of a production wind tunnel. There are always more questions to ask and parameters to test than you have tunnel time - or funding - to answer. Thus, you must minimize the number of variables while extracting the maximum amount of knowledge. This is called the design of experiments. It is its own field of study and one every lab environment must master.

Adjusting the fan to plate gap, we applied three testing techniques in this experiment: aerodynamic tufting, particle image velocimetry (PIV), and aeroacoustic measurements. We will discuss in detail some of the history of each technique as we discuss the methodologies and thought process behind implementing them.

Strings in the Wind: Aerodynamic Tufting

In fluid dynamic research, it is usually best to start simple. As with a large-scale wind tunnel or flight test, the first measurement technique we applied in our benchtop fan testing was “tufting”; the practice of affixing short strings on an aerodynamic surface to visualize flow separation. The first documented use of this technique was by Melvill Jones at the University of Cambridge in 1929 who glued “tufts” of wool to the wing of test aircraft to identify the onset of flow separation and stall. NASA evolved this technique to be non-intrusive and easier to image with fluorescent micro-tufting in the 1980’s. Because of its simplicity and detailed qualitative results, fluorescent micro-tufting remains a central methodology at NASA today, further enhanced by modern LED UV lamps and high-speed camera technology.

We used a custom 3D printed tufting jig that allowed us to weave fluorescent, glow-in-the-dark thread into equal length tufts and apply thin Kapton tape. For this application, three 50 mm tufts were mounted along the motor mount arm on the exhaust side of the fan. The objective of this stage is to narrow down the range of front plate gaps that create a noticeable impact on the flow with a minimum of effort.

We started with a 30 mm gap, where there was no observable impact on the tufts. We then halved the gap to 15 mm, where we observed some twitching on the innermost of the three tufts. Stepping in again at 5 mm, all three tufts began flopping around with the innermost tuft being pulled completely backwards into the fan indicating that the fan is sucking in air from the back. This initial exploratory mapping tells us that our area of interest is a fan face to front plate gap of approximately 5-15 mm.