A wind rose diagram is a graphical depiction of wind direction, velocity, and duration at a particular location. A wind rose is used extensively in airport engineering, especially in the orientation of runways and the overall architectural layout of airports.
To make take-offs and landings less challenging, runways at airports should preferably face the wind’s direction. This is because lifting off into the wind increases the relative air speed of the aeroplane. More lift is thus created, which in turn facilitates easier take-off. This is where wind roses come into play because of their importance in providing information about winds in an airport.
What is a Wind Rose Diagram?
A wind rose is a chart used to represent the direction and frequency of winds at a given location over a specific period. Although they are often used to display wind direction and speed, they also have many other potential uses.
The diagram’s irregular shape resembles a rose, thus its name, a wind rose. Some wind roses contain information about the air temperature.
Wind rose diagrams help airport engineers identify potential engineering issues that may impact airport operations. Graphical vector analysis of a wind rose helps identify the best runway orientation for an airport.
Types of Wind Rose Diagrams
A typical wind rose consists of concentric circles, radial lines emanating from the circles’ centre and polar coordinates.
There are two main types of wind roses; Type-I and Type–II.
Type – I
This wind rose plots the wind’s direction and duration. The radial lines show the direction of the wind, while the circles indicate the duration of the wind in that direction.
Type – II
It shows the strength, duration and direction of wind. The size of the circles represents the speed of the wind. Each section’s value indicates the annual average percentage of time that winds of that strength blow from that direction. The angle of the radial lines indicates the direction of the wind.
Some Type-II wind rose diagrams have additional data encoded in the colours of their spokes. Every spoke is colour-coded to indicate a different range of speeds, and the length of the banding on the spoke denotes the frequency.
The size of the circle in the middle represents the percentage of times when wind conditions are calm (calm period). The larger it is, the more the times that calm wind conditions prevail. In a calm period, the wind speed from any direction is less than 6.4 kilometres per hour.
Wind data for a wind rose should be acquired for at least 5 years, and preferably for 10, to provide a credible average.
Application of a Wind Rose Diagram in Airport Engineering
Wind roses are an invaluable tool for airport engineering as they provide key insights that can be used to determine runway orientation and the best airport layout and approach/departure path design.
- Airport Runway Orientation
Wind roses are used to analyse wind patterns and plot out the best orientation for airport runways during the planning stage of airport layout. This is done by planning an approach route that allows for a safe landing of aeroplanes, considering factors like topography and local wind patterns.
A runway should be oriented along the longest line on a wind rose. This is to avoid crosswind components, which can dangerously affect aircraft movement. When the wind blows at an angle to the runway, creating a crosswind component, the plane is likelier to wander off the runway centreline.
If a plane experiences crosswind components that are too powerful for its design, its structure may be damaged on landing or, at worst, a crash during take-off or landing.
- Airport Layout Design
With the intensifying campaigns to develop green airports, one key focus is the use of energy-intensive HVAC systems to cool airport buildings.
Airport engineers and architects are increasingly using wind rose diagrams to better design airport buildings and terminals. When identifying where to put a new building or terminal in an airport, they are looking for ways to take advantage of the direction of the wind. This way, the building can get natural breezes that cool it down and cut down on the need for expensive, energy-hungry air conditioning and ventilation equipment.
The importance of wind data for airport engineering is paramount. Wind rose diagrams are an effective way for airport engineers to visualise this critical information. By plotting the speed and direction of common winds over a certain amount of time, these diagrams show how the winds move in a particular area and can be very helpful for airport engineering projects.