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Reduce pres­sure losses, increase effi­ciency

Everyone is looking for the perfect fan for their refrig­er­a­tion and air condi­tioning appli­ca­tions. Simu­la­tion provides help with this: the behavior of a fan in the specific appli­ca­tion can be precisely calcu­lated and visu­al­ized with CFD (Compu­ta­tional Fluid Dynamics, i.e. numer­ical fluid mechanics).

Numer­ical aero­dy­namics and simu­la­tion are part of day-to-day devel­op­ment work for motor and fan manu­fac­turer ebm-papst. For many years, its engi­neers have been working on devel­oping their fans using powerful CFD tools, not only for opti­mizing complex impeller geome­tries (Fig. 1), but also for motor or elec­tronics cooling concepts or in the context of acoustic testing for noise char­ac­ter­is­tics. Customers benefit from this exten­sive exper­tise and from the aero­dy­namic design of their own end devices that are going to contain ebm-papst fans.

Fig. 1: CFD simu­la­tion is used to contin­u­ally improve the impeller geom­etry of the fans – for greater effi­ciency and better air flow. (Image | ebm-papst)

Poten­tial simu­la­tion in the product devel­op­ment process

The simu­la­tion of fluid mechanics makes flow and flow vari­ables such as pres­sure or velocity visible in the entire calcu­lated area. In terms of measure­ment, it is often not possible to measure at certain points or, under certain circum­stances, the measuring instru­ments influ­ence the flow, or a variety of measuring sensors and methods are required to obtain compa­rable infor­ma­tion. The measuring set-up that results is then complex and expen­sive. In addi­tion, a sample device that can be measured must have been set up before­hand. If an unfa­vor­able flow situ­a­tion is then found in the device during such tests, this can often only be imple­mented with a successor product as part of a redesign for time and cost reasons.

That is why it is better to simu­late the instal­la­tion situ­a­tion for aero­dy­namics in the early devel­op­ment phases of a customer device. This facil­i­tates a flex­ible response to aero­dy­namic weak­nesses in the design because the customer’s digital proto­type can be opti­mized before a first sample is actu­ally set up. The calcu­la­tion result of the actual state forms the basis for assessing the quality of adapted design vari­ants.

This ensures at an early stage that the installed fan really works with the desired prop­er­ties without high costs accu­mu­lating. It is there­fore worth taking advan­tage of the possi­bil­i­ties of CFD at an early stage of devel­op­ment. (Fig. 2).

Fig. 2: Ideally, the simu­la­tion is used at the begin­ning of a project as far as possible so that solu­tions can be assessed at an early stage. (Image | ebm-papst)

Simu­la­tion as a service

CFD can be used to calcu­late, visu­alize and improve the flow condi­tions in the customer device, or to compare different concepts with one another. The fan’s energy consump­tion and sound depends on how the housing encour­ages air flow, whether it is drawn in axially from the front, centrifu­gally from all sides or on one side. In poor cases, this can double the power consump­tion or halve the effi­ciency, and can signif­i­cantly increase the noise level. CFD helps in under­standing the aero­dy­namic condi­tions in the device (Fig. 3).

Fig. 3: Visu­al­iza­tion of air flow through a venti­lation unit. (Image | ebm-papst)

Before the simu­la­tion begins, the objec­tive should first be defined and a few ques­tions answered. Does air have to flow through a heat exchanger as evenly as possible? Is the simu­la­tion supposed to detect pres­sure losses? Does the customer want to perform a general check on the choice of fan? Is the device in which the fan oper­ates supposed to be as quiet as possible? Once these types of ques­tions have been clar­i­fied, the 3D CAD data and the expected oper­ating point (pres­sure, air flow, speed) of the fan provide the basis for simu­la­tion. In addi­tion, there are also char­ac­ter­istic curves from the filters, heat exchangers or guard grills installed in the device, for example. The data are cleared up and unnec­es­sary details are removed (cleaning). Then the simu­la­tion is prepared in a prepro­cessing phase, meaning that certain boundary condi­tions are spec­i­fied and the geome­tries are networked. The grid struc­ture divides the space that the air passes through into many indi­vidual cells, which form the basis of the math­e­mat­ical calcu­la­tion. The simu­la­tions then run on high-perfor­mance computers that are in a server room at the ebm-papst site in Hollen­bach.

Prac­tical exam­ples: Exploiting poten­tial for opti­miza­tion

Using the simu­la­tion results, the engi­neers then esti­mate the poten­tial for opti­miza­tion and develop concrete sugges­tions for improve­ment. For example, a customer devel­oped an air purifi­ca­tion device in which the fan was to be used for pushing air out. However, the simu­la­tion showed signif­i­cant turbu­lence (Fig. 4), which increased the power consump­tion at the oper­ating point. Using the fan to draw air in, i.e. changing its instal­la­tion posi­tion, proved to be helpful here. The air flow is now very uniform, the power consump­tion is decreased and there is also a posi­tive effect on oper­ating noise.

Fig. 4a: In an air purifi­ca­tion unit, the air flow could be signif­i­cantly improved by changing the fan instal­la­tion posi­tion ...

Fig. 4b: ... The power consump­tion dropped and the device oper­ates more quietly. (Photo | ebm-papst)

Another example: Using simu­la­tion results, the effi­ciency of a heat pump could be signif­i­cantly improved. Thanks to geometric changes, the pres­sure losses in the device fell by a total of 17 percent. The indi­vidual sub-areas in the device were assessed sepa­rately and the product design was adapted accord­ingly. Here too, the user bene­fited from the oppor­tu­ni­ties provided by CFD calcu­la­tion.

These exam­ples show that it is worth­while for end device manu­fac­turers to rely on numer­ical flow simu­la­tion and to apply these at an early stage of devel­op­ment to avoid subse­quent devel­op­ment costs. ebm-papst supports this with its long-standing CFD expe­ri­ence and offers such eval­u­a­tions and calcu­la­tions to ensure that the fans operate as effi­ciently as possible in the appli­ca­tion. Even small opti­miza­tions to the instal­la­tion situ­a­tion can reduce pres­sure losses, increase effi­ciency, or mini­mize running noise.

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