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Flow simulation at the world market leader for mobile cranes

CFD simulations in crane development at Liebherr

The third part of the series on numerical simulation at Liebherr-Werk Ehingen is about flow calculation - CFD for short. Hydraulics, pneumatics or air conditioning are application areas of a simulation discipline that many might not immediately associate with crane development. In parts 1 and 2, the simulation itself and the topic of mechanics were highlighted.

CFD analyses in crane development

FEM and structural engineering calculations in connection with a crane design immediately come to mind. For Liebherr-Werk Ehingen, however, flow simulation is also a decisive factor when it comes to optimizing processes and improving quality.

Every mobile crane has an engine and a hydraulic drive with a wealth of flow tasks and numerous temperature-sensitive controls and sensors. Worldwide use in sometimes extreme climates must nevertheless be guaranteed. This also applies to questions of comfort in the driver’s cab, to which CFD analyses have an answer.

  • The market trend for mobile cranes is towards ever more powerful, compact models with greater load lifting capacity.
  • At the same time, there is a demand for more fuel-efficient and environmentally friendly equipment that, of course, complies with current emission control regulations.
  • Every unit, for example, the one used for air conditioning, should be optimized in terms of space and weight.

At the same time, the time span from the initial idea to the delivery of a new crane model is getting increasingly shorter (time-to-market). The development of new crane types often has a direct impact on the accompanying CFD topics. Test and simulation results of a previous model are of limited help. In most cases, recalculations are necessary, since new performance horizons are reached.

CFD flow simulation enables LWE to answer questions about the flow, heating and cooling behavior of the unit in advance and to quickly determine the optimum from several possible variants in a well-founded manner.

Quick answers required

Helmut Späth is responsible for CFD simulation at Liebherr-Wert Ehingen. He describes the challenges:

“For the new crane types currently being developed, there have been and still are a whole series of inquiries from the design departments on the topics of engine air intake, engine cooling, exhaust gas flow, cooler arrangement, hydraulic intake and hydraulic tank flow. Ideally, the 3D CAD models for this are prepared for CFD simulation in the design department.”  

“Our goal in CFD simulation is to give designers an answer to their questions as quickly as possible. These concern, for example, the behavior at certain temperatures, pressures and air velocities as well as the selection of the appropriate optimal design variant from the multitude of possibilities. In general, the question is how an assembly can be further optimized. The speed factor in answering the questions is the key to the successful application of simulation, since the development time should not be increase by the simulation.”

“Only a speedy simulation process, with a very fast execution of CAD model preparation, meshing and simulation, allows the virtual testing of several variants to optimize the system. If this process is too slow, the simulation only has the function of a confirmation calculation on released assemblies. The effort to change an assembly once it has been released is much higher than to reject an unsuitable variant in advance, because we are then much further along in the overall development process. Therefore, we try to avoid this with CFD simulation.”

 Helmut Späth CFD Simulation Engineer, Liebherr-Werk Ehingen GmbH
Helmut Späth
CFD Simulation Engineer, Liebherr-Werk Ehingen GmbH

We know for a fact that if we ever get stuck, CADFEM’s proven support will be there.

Decision is bolstered

Using Ansys as the simulation software was a company-wide decision made by the Liebherr Group. The software Ansys SpaceClaim, Ansys Fluent and other Ansys tools used at LWE for flow simulation were selected as development tools within the framework of the group agreement made with CADFEM as Ansys partner. A very pleased Helmut Späth comments,

“Ansys Fluent is used in several plants of the Liebherr Group, where I receive positive feedback. So, that we feel encouraged in our decision. In addition, a number of our service providers and suppliers use Ansys Fluent. I see the reasons for the strong popularity in the impressive range of functions and the successful support from CADFEM. We know for a fact that if we ever get stuck, CADFEM’s proven support will be there.”

Typical CFD analysis fields

  • In the case of vehicle engines,questions surrounding the flow behavior of air intake, exhaust gas purification and exhaust gas discharge are of interest.
  • In the case of hydraulics, the focus is on optimizing pressure losses, intake behavior and air separation in the tank.
  • It is also important to reliably cool the engine unit and the hydraulics, as well as cooling water, charge air, transmission oil and temperature-sensitive control units and sensors must be reliably cooled or protected from overheating, especially in hot climates with air flow. The resistance to extreme climates increases the regional operating range and accelerates readiness for use even at extremely low temperatures, as functions such as preheating can be optimized.
  • There are also comfort issues that must be addressed both for the driver’s cab of the crane when driving on the road and in the crane cab in the uppercarriage when lifting loads. Depending on the ambient temperature, both need a pleasantly heated or well cooled workplace in order to be able to safely perform heavy lifting tasks with high concentration.
  • In addition, there is the avoidance of noise and the fogging or icing of windows. As more in-depth examples of CFD use, we have picked out two use cases below that provide an insight into the analyses.
CFD application case: oil cooler

In one of the cranes under development, an optimum position for the oil cooler was sought and found. First, the oil cooler plus enclosure was modeled in Ansys SpaceClaim and divided into the three volume elements: housing, cooler area and fan. Then the cooler was modeled as a porous zone with heating capacity according to the manufacturer’s specifications. Then came the modeling of the fan as a “3D fan zone” according to the supplier's fan characteristic curve.

The installation variant with the greatest cooling capacity was sought because it enables a crane to work at full capacity for the longest time in a hot environment. Using simulation, a whole series of various installation locations and variants were tested.

The optimal position was found quickly and reliably with Ansys. In some cases, the flow Q was smaller because the environment gave more resistance. In other cases, the flow was high, but the temperature difference was smaller because some of the cooler air moved from behind the cooler back in front of it. Determining the optimal arrangement without the aid of simulation would be impossible, simply because the air pressure conditions on the vehicle vary widely at different positions and driving speeds. The sheer number of variants requires software support.

CFD application case: diesel oxidation catalyst

A further task was to provide verification that the uniform distribution of the flow velocity over the flow cross-section during the flow through the DOC (diesel oxidation catalytic converter) is above the required uniformity index of UI = 94 %. Ansys CFD also solved this task with ease, as the figure shows.

Valuable functions

Helmut Späth sees the advantages in the versatility of Ansys Fluent:

 “Velocity, pressure and temperature, directional vectors of flow velocity, flow lines, wall representations with surface mesh and, of course, any combination of these can be easily determined. With the Ansys simulation tools, we can quickly and clearly show our colleagues from the design department how the flow conditions will affect the respective model in reality.”

Helmut Späth
CFD Simulation Engineer, Liebherr-Werk Ehingen GmbH

Without CFD simulation, many questions in the design phase could not be answered.

High value CFD simulation

For Helmut Späth, the advantages of the Ansys Fluent simulation software for LWE are obvious:

“Without CFD simulation, many questions in the design phase could not be answered. Before we were able to carry out in-house flow simulations, complex CFD questions were outsourced. Simpler questions were deferred until prototype commissioning and only then became apparent. This costs time and money. We simply don't want any more unpleasant surprises during prototype testing. If the modified designs first start at that point, it means additional work and project delays.

Ansys saves us from this. Even when looking at the use of Ansys CFD analysis software in the medium term, there is an increase in the benefits of the products and a reduction in costs. By setting up our own CFD analysis area, we are in a position to develop in-house know-how. The design departments now request CFD simulations more frequently, and we can handle them more easily, quickly and with less bureaucracy than would be possible with external service providers. This improves quality and makes us more flexible and independent. In-house, quickly determined CFD simulation results represent a high value for Liebherr-Werk Ehingen.”

The first part of the series gives an overall view of the simulation at Liebherr-Werk Ehingen.

Read in the second part how LWE manages to overcome apparent contradictions with structural-mechanical calculations. In the third and last part of our LWE series, learn how CFD simulation significantly shortens the time to market.

Liebherr Werk Ehingen GmbH

Author: Thomas Löffler
Images: © Liebherr
Published: June 2022

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