Is your new building or bridge likely to produce annoying whistling tones?
Use the Whistle-Quick-Scan to find out in 3 minutes!
Perform the check per façade element (Need help? Contact me).
- Is the façade element located on the ground floor and between the built environment?
- Does the façade element consist of a repetition of gaps or bars of the same diameter (think of bars or gratings)?
- Can wind reach the object in a straight line? Note; if there is a net or wall behind it this is not the case.
- Does the repeating object have sharp edges? The rounder an edge, the higher the air velocity needs to be to create a whistle.
- Are the gaps wider than 15 cm? The wider the gap, the higher the air velocity needs to be to create a whistle.
Some pointers on how to read the Whistle-Quick-Scan:
- green: no worries! Build your design... the chances of whistles around your building in normal windy weather is negleglible.
- yellow: there is a low risk of whistles.
- orange: This solution has a significant whistle risk. Make an adjustment to one of the 4 parameters that are conditional for the whistle, see Analysis Origin of whistle. Or contact me to discuss the prevention of whistles.
- red: whistles can be expected with this solution. Make an adjustment to one of the 4 parameters that are conditional for the whistle, see Analysis: Origin, and Prevention of Whistles. And feel free to contact me.
Note: This diagramm is based on Dutch weather conditions! Hurricanes are not taken into account.
Question 1: Are the facade elements of the building outside the built environment?
- Yes → Within Built Environment
- No → Outside Built Environment
There are so many obstacles in the built environment, there is virtually no laminar flow here. Whistling tones can only occur when building on the edge of the building, at 'windstreets' and at extreme wind speeds. In these situations choose 'within the built environment'. Outside the built-up area are the buildings that can be flooded freely by wind and that experience little or no nuisance from other buildings. This includes buildings along the coast or in an open field. This also includes buildings on the outskirts of the city and the upper parts of high-rise buildings in the built environment. In case of doubt, choose the option 'outside the built environment'.
Question 2: Do these façade elements consist of a repetition of at least 9 slits of the same width?
- Yes → No Regularity (< 9)
- No → Regularity (≥ 9)
With gaps in façade elements, pressure differences occur behind these gaps. When the gap extends along the length, these pressure differences can reinforce each other. The same phenomenon occurs with a row of bars or gratings. By repetition is meant "an alternation between open and closed parts in a facade element". This is the case with gratings, bars or mesh. The repetition must take place at least 9 times with the same diameter, shearing in a possible wind direction. A possible wind ricthing is always parallel to the ground plane. With bridges in the Netherlands it is generally the case that the direction of the wind is only horizontal.
Question 3: Can the façade element directly be approached by wind?
- Yes → Disturbed Current
- No → Laminar Flow
Only when the wind can flow straight to the object without disturbance can a laminar flow occur. When the flow is disturbed, one of the whistling requirements, the laminar flow, is absent. Whistle tones can no longer arise. To disrupt a laminar inflow, the disruption must occur directly around the object.
With a rough surface of an object, the flow around the object becomes turbulent. Many small pressure fluctuations arise around and behind the object instead of a few large pressure differences. The roughening of the surface leads to more and smaller vertebrae. The sound that can still occur has a lower intensity (less pressure difference) and consists (almost) entirely of noise (turbulent flow). When two objects of the same size are in each other's flow, they will influence each other's flow. The periodic whistle-producing vertebrae cannot arise.
Nets, or jamming strips for roughening the surface are obvious methods of disturbing the flow.
Question 4: Are the sharp edges on corners on the elements rounded?
- Yes → Rounded Corners
- No → Sharp Corners
The streamlining of objects influences the vortex production and therefore the production of whistling tones. Angular objects create greater pressure differences than streamlined objects (greater amplitude and loudness). As wind is not a constant factor, it is virtually impossible to completely streamline elements. However, a rounding of corners to a radius of just a few millimeters significantly influences the sound production, and can even stop whistling sounds completely. Without extra processing, plate material has sharp edges and corners. The impact is as follows; the rounder the egdes, the higher the air velocity needs to be to create a whistle
Question 5: Are the gaps wider than 15 cm?
- Yes → Slits > 15cm
- No → Slits ≤ 15cm
The smaller the gaps, the louder the whistle and the higher the whistle produced. Also, the larger the gap, the higher the air velocity must be to produce whistle. A larger diameter is therefore always better when it comes to avoiding whistle. From a diameter of 15 cm, the tones disappear completely for most gaps and gratings.
This concerns the gap distance in a possible wind direction. For this step it is important whether the smallest regularity of gaps smaller than 15 cm in a possible wind direction.