FlowGrid - Air-inlet grille for axial and centrifugal fans

From "Accessory" to "Core"—A novel fan FlowGrid air-inlet grille that combines a bird-wing-edge biomimetic structure with a tapered flow channel technology, delivering measurable noise reduction and uncompromised efficiency for EC fans.

In Ventilation and Purification, the FlowGrid grille has long been regarded as a "necessary but secondary" mechanical accessory. However, as building energy codes become stricter and indoor environmental quality requirements rise, fan noise has emerged as a core pain point affecting user experience and equipment selection. Leveraging its R&D and testing center at Suzhou BLAUBERG Motor Technology Co., Ltd., BLAUBERG has systematically optimized both aerodynamics and acoustics and officially launched its noise-reducing FlowGrid grille. This product not only breaks away from the traditional "smooth grille + simple flow guidance" design paradigm but also establishes a clear technical path between bionics and real-world test data.

I. Acoustic Challenge of Traditional FlowGrid Grilles: Karman Vortex Street and Resonance Noise

Conventional fan FlowGrid grilles typically adopt a uniform cross-section with straight edges, made of metal or plastic. From an aerodynamic standpoint, while such a design provides basic protection and airflow redirection, it hides an inherent acoustic flaw—the Karman vortex street.

When uniform airflow passes across the edge of a grille plate, boundary layer separation generates alternating vortices of opposite rotation and similar size behind the plate. These periodically shedding vortices not only produce sharp noise with fixed frequency and concentrated energy, but more importantly, when the shedding frequency approaches the natural frequency of the FlowGrid grill structure, resonance occurs—further amplifying noise and accelerating fatigue of connecting components. Actual measurements from the BLAUBERG acoustic lab show that for a GL‑B355E‑EC‑05 fan running at a constant speed of 1900 rpm, with no FlowGrid grille installed, the A-weighted sound pressure level is close to 57 dB(A) at 1 VDC control voltage (about 1922 rpm); at 10 VDC (about 1973 rpm), it rapidly rises to 83.4 dB(A), with the 2k–4k Hz band being particularly prominent—exactly the most sensitive frequency range of human hearing.

II. Bionic Breakthrough: Inspiration from Bird Wing Edges and Fish Fins

In nature, many animals do not generate obvious vortex-induced noise when moving at high speed. For example, the comb-like structure on the leading edge of an owl's wing feathers and the nodular protrusions on the leading edge of a humpback whale's flippers have both been proven to suppress vortex shedding and reduce flow noise. The design team of the BLAUSTREAM FlowGrid grille translated these biomimetic principles into engineering language, introducing a "first continuous concave-convex structure" on the windward side (the upper edge) of the grille.

Specifically, this structure consists of a series of regularly arranged first grooves (which can be arc‑shaped, V‑shaped, or sinusoidal) on the upper edges of the circumferential and radial grille plates. The originally straight edges are transformed into a continuous undulating shape resembling "sawtooth" or "waves." When high-speed airflow enters the FlowGrid grille:

Active shearing at the convex parts: large-scale airflow is split into multiple small-scale jets;

Micro-vortex dissipation in the groove areas: the regular Karman vortex street is disrupted, replaced by irregular, energy-dispersed tiny vortices;

Periodic pressure pulses disappear: the lift acting on the FlowGrid grille surface no longer maintains a consistent direction, and the structural loading becomes uniform.

The patent document (CN121782202A) clearly states that the depth‑to‑width ratio (y/x) of the first groove on each radial grille plate gradually decreases from the inner side to the outer side and is strictly controlled between 25% and 53%. This gradual design matches the variation of airflow velocity at different radii—the inner side sees relatively lower velocity, requiring a larger y/x to ensure sufficient breakup; the outer side experiences higher velocity, where a smaller y/x breaks vortices without excessive flow obstruction, achieving an optimal balance between flow resistance and noise reduction.

III. Tapered Flow Channel: Noise Reduction ≠ Sacrificing Airflow

Conventional wisdom holds that any add-on structure will negatively affect fan aerodynamic performance. The BLAUSTREAM FlowGrid grille breaks this trade‑off through its "tapered flow channel design inside the grille grid."

Define the area of the first quadrilateral formed by connecting the upper ends of each grid's surrounding connecting parts (grille intersections) as A and the area of the second quadrilateral formed by the lower ends as B. Then (A‑B)/A is strictly controlled between 4% and 12%. This means that as airflow passes through each grid cell, its cross‑section uniformly narrows from top to bottom, creating an acceleration channel similar to a "nozzle." This design brings three benefits:

Flow rectification: reduces lateral turbulence, making the airflow entering the fan impeller more axially uniform;

Accelerated efficiency: increases exit air velocity without additional fan power consumption, indirectly compensating for the pressure loss caused by grille obstruction;

Backflow suppression: the tapered structure prevents the formation of stagnant vortex clusters inside the grid, further lowering self‑generated noise.

IV. Measured Data: BLAUSTREAM vs. No Grille vs. EBM FlowGrid Grille

All technical claims must be validated in a laboratory. On December 10, 2025, at the accredited laboratory of Suzhou BLAUBERG Motor Technology Co., Ltd., BLAUBERG conducted rigorous tests on the following three configurations:

Configuration 1: Fan only, no FlowGrid grille (GL‑B355E‑EC‑05, constant speed 1900 rpm);

Configuration 2: BLAUSTREAM 355 FlowGrid grille + same fan;

Configuration 3: EBM 355 FlowGrid grille + same fan.

The tests covered 10 control voltage points from 1 VDC to 10 VDC, simultaneously recording power, current, speed, airflow (m³/h & CFM), pressure (Pa & inH₂O), and efficiency. Noise was analyzed in 1/3 octave bands from 10 Hz to 20 kHz, a total of 35 frequency bands.

4.1 Noise comparison: FlowGrid grille is significantly better than no grille

Taking the low‑speed condition at 1 VDC as an example: without a FlowGrid grille, the A‑weighted total noise is 56.7 dB(A); after adding the BLAUSTREAM FlowGrid grille, it drops to 54.0 dB(A) – a reduction of 2.7 dB(A). At the high-speed condition of 10 VDC, the no-grille noise is 83.4 dB(A) and drops to 82.1 dB(A) with the grille—a reduction of 1.3 dB(A). Although the absolute reduction decreases slightly at higher speeds, note that at high speeds airflow exceeds 4000 m³/h, where any add‑on structure faces stronger aerodynamic excitation. The fact that the BLAUSTREAM FlowGrid grille still provides a net positive benefit is itself a design success.

More importantly, look at the frequency spectrum. Without the grille, there is a clear "hump" in the 1.6k–4k Hz range—a characteristic signature of the Karman vortex street. After adding the BLAUSTREAM FlowGrid grille, the energy in this band is effectively spread to adjacent bands, and the peak is lowered by 3–5 dB. The human ear perceives this broadening and peak reduction very clearly: the sharp "whistling" turns into a softer "wind noise."

4.2 Direct comparison with EBM FlowGrid grille

Under the same fan and speed conditions, the comparison between BLAUSTREAM and EBM FlowGrid grilles provides strong commercial reference. The test data show:

At 1 VDC: BLAUSTREAM 54.0 dB(A), EBM 54.1 dB(A) – essentially equivalent;

At 5 VDC (about 1900 rpm, a common operating point): BLAUSTREAM 69.4 dB(A), EBM 70.0 dB(A)—BLAUSTREAM leads by 0.6 dB(A);

At 7 VDC: BLAUSTREAM 74.9 dB(A), EBM 75.1 dB(A);

At 10 VDC: BLAUSTREAM 82.1 dB(A), EBM 82.0 dB(A) – the difference narrows to 0.1 dB(A), but at this point BLAUSTREAM's airflow (4288 m³/h) is slightly lower than EBM's (4285.5 m³/h). Further analysis of the efficiency curve shows that BLAUSTREAM maintains an advantage in air delivery per unit power in the ultra‑high airflow range.

4.3 Airflow and pressure: no significant loss, even outperforming in some conditions

In terms of aerodynamic performance, the fan's PQ curve after adding the BLAUSTREAM FlowGrid grille closely overlaps with the no‑grille state. Taking the constant speed of 1900 rpm as an example:

No‑grille maximum airflow (at 0 Pa) is about 5066 m³/h.

With BLAUSTREAM, the maximum airflow is about 5102 m³/h—slightly higher, thanks to the acceleration effect of the tapered flow channel compensating for the local resistance of the grille.

In the high‑pressure region (above 600 Pa), the airflow difference between the two is less than 2%.

Compared to the EBM FlowGrid grille, BLAUSTREAM shows better pressure performance in the low‑to‑medium airflow range (1000–2500 m³/h), meaning that under the same system resistance, BLAUSTREAM delivers a higher actual airflow.

V. More Than Just Noise Reduction: Synergistic Optimization from FlowGrid Grille to Full Air System

The BLAUSTREAM FlowGrid grille is not an isolated accessory. In BLAUBERG's BLAUAIR variable air volume air handling units (such as the BL1.2‑TVDH4E) and the BlauAir Modular AHU, the FlowGrid grille, EC fan, air guide ring, filter section, and heat recovery section together form a complete airflow management ecosystem.

5.1 Seamless integration with the air guide ring

A key element of the patented design: the upper part of the air guide ring features an "air ring" whose diameter gradually increases from bottom to top and whose cross‑section in the radial plane is an arc concave inward. The tangential line of the curved lower edge of the outermost circumferential grille of the BLAUSTREAM FlowGrid grille is designed to be parallel to the tangential line at the upper endpoint of the air guide ring's arc, with a gap controlled between 0 and 7 cm. This geometric fit ensures a smooth transition of airflow from the FlowGrid grille outlet to the air guide ring inlet, avoiding pressure loss and vortex regeneration caused by sudden expansion or contraction.

5.2 Dynamic performance in variable air volume systems

The BLAUAIR all‑air system uses EC fans and smart VFD control to adjust airflow in real time based on indoor CO₂, temperature, and humidity. The noise‑reducing characteristics of the BLAUSTREAM FlowGrid grille are especially valuable in such variable‑air‑volume scenarios—when the load decreases at night and fan speed drops, the overall system noise can be further reduced to below 30 dB(A), meeting the stringent "constant quiet" requirements of high‑end residences, sleep centers, hospital ICUs, and similar applications.

VI. Summary: An Underestimated Core Technology Upgrade

The BLAUSTREAM FlowGrid grille is not a simple "mold modification." It is a comprehensive solution that integrates:

Biomimetic edge design (suppressing Karman vortex streets);

Tapered flow channel aerodynamics (compensating for pressure loss);

Multi‑stage concave‑convex structure (breaking vortices throughout the flow path);

System‑level coordination (geometric and control synergy with the air guide ring and EC fan).

The dozens of lines of data in the test report PDF and the 19 claims in the patent document all point to one fact: the FlowGrid grill no longer has to be a sacrificial component—it can be a value‑adding part that actively contributes to noise reduction and efficiency improvement.

For OEM customers, system integrators, and end users, choosing the BLAUSTREAM FlowGrid grille means:

Lower acoustic risk – fewer on‑site complaints and less investment in additional silencers;

Higher energy efficiency – allowing the fan to run at a higher speed range under the same noise limit;

Longer equipment life—eliminating fatigue damage caused by periodic pressure pulses to the FlowGrid grille and fan connection structure.

The BLAUSTREAM series of FlowGrid grilles is now available for EC fans in 355 mm, 400 mm, and 500 mm sizes, with other dimensions available upon request. For detailed test reports, 3D models, or selection assistance, please contact your local BLAUBERG technical center or visit our official product page.