Air movement apparatus
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Solution Overview
Problem
Existing air movement apparatus in tunnels and car parks suffer from inefficiencies due to the Coanda effect, leading to increased frictional losses, turbulence, and noise, particularly when air jets attach to the tunnel walls, reducing ventilation efficiency and generating unacceptable noise.
Innovation Solution
The apparatus incorporates an outlet nozzle with a bellmouth and an insert providing an inclined surface to redirect the air jet away from the wall, reducing the Coanda effect and turbulence, and may include attenuating materials to dampen noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the outlet nozzle is directed at an angle from the fan axis to reduce the Coanda effect, then the air jet force is reduced and head space in the tunnel is reduced
Solution Approach 1:
The insert is positioned only at specific locations on the trailing edge (e.g., 30-40% of the periphery) rather than modifying the entire nozzle. This localized modification redirects air away from the wall only where needed to reduce the Coanda effect, while preserving the overall jet force and direction in other regions.
Solution Approach 2:
The trailing edge is divided into different functional zones: some portions have the insert to redirect air away from the wall, while other portions maintain the original geometry to preserve jet force. This segmentation allows simultaneous optimization of different aspects of air jet behavior.
2Object-affected harmful factors
If the outlet nozzle is directed at an angle from the fan axis to reduce the Coanda effect, then head space in the tunnel is reduced
Solution Approach 1:
The insert creates localized flow redirection only at specific angular positions, allowing the bulk of the air jet to maintain its original axial direction. This preserves the effective head space in the tunnel while still reducing wall attachment in critical regions.
3Object-affected harmful factors
If the nozzle trailing edge is inclined at an angle to the fan axis, then the Coanda effect is reduced but the trailing edge becomes non-circular increasing complexity and cost
Solution Approach 1:
Rather than inclining the entire trailing edge, only a segment of the trailing edge receives the insert. The overall circular symmetry of the nozzle is preserved, maintaining manufacturing simplicity while achieving the desired flow control in specific regions.
Solution Approach 2:
The insert can be designed as a standardized component that is copied and positioned at specific locations around the trailing edge, rather than creating a completely custom non-circular geometry. This reduces design complexity and facilitates manufacturing.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances ventilation efficiency by minimizing frictional losses and noise, improving airflow characteristics, and reducing turbulence, thereby increasing the effectiveness of the ventilation system.
Implementation Method 1
the jet of air leaving the apparatus is subject to the Coanda effect in which the outer part of the air jet attaches itself to the wall of the tunnel
Implementation Method 2
increased turbulence between the outer part of the air jet and the main body of the air jet
Data Source
Figure 1~8
Figure 3~7
AI summary
Air movement apparatus for installation adjacent a wall in an internal space to provide ventilation to the space, the apparatus comprising a fan for generating a ventilating flow, an inlet nozzle for drawing air through the fan and generating an outflow jet of air, and an outlet nozzle for directing the outflow jet of air.. the axes of the inlet nozzle, the fan and the outlet nozzle lie generally on a common longitudinal axis. The outlet nozzle has a trailing edge and has an insert providing an inclined surface reducing the outlet area of the trailing edge over a predetermined part of the periphery of the trailing edge, to direct the part of the air jet passing over the insert away from the wall.