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Low-speed wind tunnels often show flow issues that are not obvious during initial setup. Velocity can be controlled without much difficulty, but flow behavior over time is harder to manage. Small disturbances tend to stay in the system.
Most of these disturbances come from upstream.
Fans introduce swirl. Bends and transitions add lateral components. At low speed, there is not enough inertia for these effects to decay naturally.
This is usually where a honeycomb straightener is added.
The purpose is not to make the flow “ideal”. It is mainly to reduce lateral movement. Each cell limits sideways motion and forces the flow to remain directional over a short distance.
What actually improves is consistency.
The flow entering the next section behaves more the same from run to run. Absolute uniformity may change only slightly, but repeatability improves.
Cell geometry matters, but only within limits. Smaller cells suppress crossflow better, but pressure loss increases quickly. Longer cells help, but the benefit does not scale linearly. In low-speed systems, these trade-offs are felt immediately.
Pressure margin is usually limited.
A honeycomb that works well on paper may restrict airflow too much in practice. This often shows up after installation, not during design.
Placement inside the tunnel is usually adjusted based on testing. Too close to the fan, and strong swirl remains. Too far downstream, and the effect weakens before the test section.
Manufacturing quality also becomes visible at low speed. Small variations in cell alignment or bonding can cause local differences in the flow. These are rarely obvious during inspection, but they tend to appear during calibration or long test runs.
Because of this, a Honeycomb Straightene is normally treated as one element in a larger flow-conditioning sequence. Its role is limited but important. It reduces sensitivity to upstream disturbances and makes the system easier to control.
In low-speed wind tunnels, this kind of control often matters more than theoretical flow perfection.
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How Planar Wave Shielded Ventilation Panels Work
A Planar Wave Shielded Ventilation Panel is mainly used when equipment needs airflow but cannot tolerate EMI leakage through vent openings.
Its basic idea is simple. Instead of using open holes or mesh, the panel forms a set of flat, narrow channels. Each channel behaves like a waveguide with a defined cutoff frequency. Signals below that cutoff cannot pass through the channel and are gradually attenuated along the length.
From a structural point of view, shielding performance is controlled by channel width, depth, and length. Narrower channels raise the cutoff frequency. Increasing the channel length improves attenuation. These parameters are usually determined early in the design phase based on the target frequency range.
Airflow moves straight through the planar channels. Compared with complex honeycomb or woven structures, pressure loss is easier to predict, and flow distribution is more uniform. This makes the panel suitable for cabinets that rely on forced-air cooling.
In real installations, the panel itself is only part of the shielding system. Contact between the panel frame and the enclosure, surface flatness, and grounding continuity all affect the final EMI result. Even with a well-designed panel, poor mechanical integration can reduce shielding effectiveness.
Because the shielding function relies on geometry rather than coatings, Planar Wave Shielded Ventilation Panels tend to remain stable over time. There is no conductive layer to wear off, and performance is less sensitive to airflow velocity or long-term thermal cycling.