The Multiplier Fan Review

7/24/2019 The Multiplier Fan Review

http://slidepdf.com/reader/full/the-multiplier-fan-review 1/3

The Multiplier Fan: A Short Review

The multiplier fan blows air from a ring with blades are hidden in its base. It is also called as

“bladeless fan” because it has not any external blades. Dyson has developed its designs from first

idea created by Toshiba. By accelerating air over a profile like airfoil, it eliminates the buffeting

and turbulence associated with these traditional household fans. Initially, Dyson engineers relied

on physical prototyping for design development. Then they used CFD software from ANSYS to

complement experimental testing and reduce development time.

A thin, high-speed sheet of air that induces surrounding air through a fan is produced. This unique

provided a much smoother movement of air without external blades. Basically, the impeller is put

inside the base to draw air from outside and lead it to the ring. The air is accelerated through an

annular chink and passed over an airfoil – shaped ramp. The overall process takes a total of two

weeks including building ring design, measuring, hand finishing, assembling and testing the ring.

Therefore, it also takes a lot of time and cost when the ring is redesigned.

Without the need for a physical prototype, the company’s engineers overcame this problem by

using ANSYS FLUENT software to simulate fluid flow. They have found rapid improvements by

their intuition throughout analysing numerical solution of the fluid flow. The computing domain

is divided into subdomains. The subdomains in and around the ring contained a very fine mesh to

maximize accuracy in this critical area. When the design is modified after each improvement, the

team had to re-mesh only the subdomain that contained the change , and thus the time for re-

meshing was reduced appreciably (from over an hour to about 10 minutes ). In this case, the

analysis time in solver can takes a little long time because of the contact problem.

The contours of velocity magnitude.

Firstly, the initial prototype is simplified in 2 – D problem, steady – state, incompressible, turbulent

air flow using the k – epsilon turbulence model. Although this model has advantages in meshing

and analysis time, the flow field is not approximate with practical one. However, they use the result



to predict performance trends reasonably. A series of design iterations are evaluated with the

main goal of increasing the amplification ratio. That means the fan must to move the possible

maximum amount of air for a given dimension and power consumption. They proposed some

factor having major effect on performance: the crack in the ring, the profile of the ring and external

ramp.

The team investigated 200 different design iterations using simulation to gain an amplification

ratio of 15 to one. Physical testing was used to validate this ratio to ensure it correlated well with

the numerical one.

In another investigation, Mansson and Larsen studied this problem in 3 – D geometries to know the

flow characteristics of the Air Multiplier using both of k – epsilon and k – omega turbulent models.

They also used high – resolution mesh at small dimensions and larger – sizing mesh in far – field of

the fan.

3D geometries in the upper part and 2D geometries in the lower part.

They assess that both turbulence models successfully predicts but the results in the k−ε model has

the highest correlation. The k−ω model just takes the highest correlation in the manitude of

velocity.

Velocity contour plot in xy-plane of 3D geometry simulation. Left: k − ε model. Right: k − ω



model.

They have some conclusion in their study: the real turbulent circumstances inside the airfoil are

unknown, but the simulations show turbulence around the crack of the ring. However, the flow is

relatively laminar in the far – field of the fan as what Dyson claims.

The Multiplier Fan Review

Documents

Transcript of The Multiplier Fan Review