Press Room - Caterpillar moves the earth with STAR-CD

Caterpillar moves the earth with STAR-CD

Caterpillar is well known for world leadership in the production of equipment for the construction and mining industries, including huge earth-moving vehicles. The bigger and more complex the machine, the more sophistication in design is required to ensure reliability. Here we describe how CFD analysis was used during vehicle development to avoid damage caused by cavitation within the hydraulic system.

One of the components of the hydraulic system is a partially filled tank, which receives the return flow of the fluid from the implement pump. The flow shoots into the top of the tank with high velocity, creating strong flow circulation. Perforated rectangular baffles aim to calm the flow, but aeration can occur. Aerated fluid is then carried via suction lines to the implement and fan pumps, increasing the chance of cavitation in the pumps. Caterpillar's design challenge was to use STAR-CD to catch the problem at its source, by finding ways to calm the strong fluid circulation inside the tank and reduce aeration.

STAR-CD was used to predict qualitatively and quantitatively the fluid circulation in the tank, and specifically to find the fluid pressure and velocity distribution for standard flow rates. The model represented the flow conditions in the tank, including details of the perforated baffles(modeled as porous media), suction lines, flow rates and fluid properties. In addition to modeling the baseline configuration, three new designs were simulated:

* With baffles encircled by a porous circular tube to more uniformly distribute the high flow jets from baffle holes

* The whole left and right sides of the baffle plates perforated to increase the area open to the fluid

* Extra holes added on each left and right baffles to provide more open flow area

STAR-CD was able to predict significant differences of flow circulation as well as other flow parameters in each case.

The magnitude of the flow circulation dictates the severity of aeration in the tank, and a comparison of the vector plots from STAR-CD showed that the first design variation has lowest circulation and is therefore the best solution of the aeration problem. Furthermore, the porosity of the circular tube was found to play a major role in determining the pressure drop in the tank; as porosity increases the pressure drop decreases. This aspect of the design could also be optimized. In this preferred design, high flow jets are dispersed and flow proceeds uniformly inside the tank.

In summary, Caterpillar found that the CFD approach using STAR-CD provides detailed understanding of the flows and allows optimization of the design before building and testing prototypes. Overall time and cost of design modifications and the number of actual hardware tests could be reduced.