CASE STUDY: Mixed Flow Fan (156mm) Avionics Cooling

Overview

High-density avionics racks push cooling fans into an uncomfortable corner: they need real static pressure to force air through tightly packed equipment, but only at modest airflow rates, and usually within a fan envelope that can't grow. This case study covers a 156mm mixed flow fan engineered specifically to sit in that corner for a helicopter avionics cooling application. 

Customer Challenge

The customer needed a substantial increase in static pressure at very low airflow rates to ensure reliable and efficient cooling within a high-density rack system. This requirement was critical to maintaining thermal performance in a confined space. 

That combination high pressure, low flow, tight envelope is exactly the condition that causes a conventional axial fan to stall. As onboard electronics density increases and packaging gets tighter, the airflow resistance a cooling fan has to overcome rises even as the available space to generate that pressure shrinks. 

Our Solution

Using Ansys flow development tools, we engineered a mixed-flow impeller design incorporating additional half blades to deliver a more centrifugal performance characteristic. This blade geometry allowed us to achieve and even exceed the required static pressure rise at the lower flow rates the application demanded, without resorting to a larger-diameter or higher-speed fan that would have cost weight, noise, or power budget. 

Precise trimming of the impeller's trailing edge was then applied to fine-tune the design, ensuring the finished fan stayed within the customer's power limitations while still hitting the pressure target. 

This is the same mixed flow principle behind our wider fan range: combining the high airflow of an axial design with the high-pressure tolerance of a centrifugal design in one compact unit, so a single fan family can be tuned through blade count, blade shape, and trailing-edge trim to sit anywhere along that axial-to-centrifugal performance spectrum depending on what the installation actually needs.

Technical Highlights 

• 156mm mixed-flow impeller
• Additional half-blades for centrifugal lift
• Ansys-driven flow development
• Trailing-edge trim for fine-tuning
• Met power limitations at target pressure