Eddy grooves in hydrodynamic bearings for turbomachinery: How targeted turbulence reduces temperature

One of the biggest limitations in the development of turbomachinery is heat build-up in the bearing area: if temperatures exceed critical thresholds, this jeopardizes the service life of the bearings and ultimately the operational safety of the entire machine.

With the introduction of Eddy Groove technology, Miba offers an innovative solution. In this article, we show

• why targeted turbulence is a decisive lever for increasing the efficiency of modern turbomachinery and
• what specific advantages this offers for design and operation.

In conventional hydrodynamic bearings of turbomachinery, laminar flow of the lubricating oil usually prevails under typical operating conditions. This is characterized by layer-by-layer movement without significant mixing.

The problem with this is that heat conduction in the oil is relatively low. This results in pronounced temperature gradients, especially between the bearing shell and the rotor.

However, if a flow transition occurs, in which the laminar flow changes to turbulent flow (e.g., due to Taylor vortices), radial flow components are created. These ensure more efficient mixing of the lubricating film and thus a more homogeneous temperature distribution.

The result: significantly lower maximum temperatures in the hydrodynamic bearings of turbomachinery.

However, this effect on temperature naturally occurs almost only with very large bearing diameters or extremely high speeds. Typical diameter ranges of small and medium-sized hydrodynamic bearings in turbomachinery usually remain in the laminar range. This is where Eddy Grooves technology comes into play.

Optimization of temperatures in hydrodynamic bearings for turbomachinery

In order to lower the maximum bearing temperature and thus reduce the specific bearing loads, the following solution is often the only option:

• Geometric adjustments: Increasing the bearing width or bore diameter can reduce specific bearing loads.

However, such adjustments often have undesirable side effects:

• Higher oil consumption and increasing power losses.
• More space required for the bearing design.

Geometric changes are often difficult to implement, especially in existing housing designs or hydrodynamic bearings that are already in operation, which underscores the need for alternative solutions.

Overview of the mechanisms at work:

• Disruption of laminar flow: The geometrically defined grooves initiate local turbulence.
• Reduction of temperature on the running surface: Dangerous hot spots on the bearing surface are reduced.
• Maintenance of load-bearing capacity: The arrangement and depth of the grooves are selected so that hydrodynamic pressure generation is maintained.

Eddy Grooves thus enable a targeted improvement in temperature conditions, especially in highly stressed areas of turbomachinery hydrodynamic bearings – an optimization that is virtually impossible to achieve with conventional bearing designs.

In order to objectively evaluate the efficiency and temperature reduction potential of Eddy Groove technology, Miba conducted extensive tests on a specially equipped test bench. The focus was on realistic operating conditions as they occur in modern turbomachinery hydrodynamic bearings.

What test conditions were simulated?

A high-performance plain bearing test bench with the following key data was used for the test series:

• Bearing diameter: 120 mm
• Axial bearing length: 75 mm
• Maximum circumferential speed: up to 125 m/s
• Maximum specific bearing load: up to 7 MPa
• Oil type: VG 32 (mineral oil)
• Oil inlet temperatures: 45 °C and 55 °C
• Oil flow control: variable to sim

What results were measured – and how significant was the effect?

The measurement results impressively demonstrated the positive influence of Eddy Grooves:

• Reduction in surface temperature: maximum temperatures up to 17 K lower than with the standard design.
• Reduction in temperature in the 75% measurement range: also significant, albeit less pronounced than on the surface.
• No measurable increase in friction losses: the efficiency of the bearings remained unchanged.
• No negative effects on wear or structure: Even after intensive test cycles, no material damage to the whirl grooves was apparent.

Particularly noteworthy: The effect of the Eddy Grooves was particularly pronounced with increasing bearing loads and higher sliding speeds. This is precisely where conventional hydrodynamic bearings in turbomachinery reach their thermal limits.

How do designers and operators benefit from Eddy Grooves in turbomachinery hydrodynamic bearings?

The integration of Eddy Grooves in turbomachinery hydrodynamic bearings offers concrete advantages throughout the entire life cycle:

• Higher operational reliability: The significant reduction in bearing temperatures reduces the risk of material fatigue and bearing damage.
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• Increased power density: Bearings can withstand higher specific loads at the same temperature – ideal for more compact designs and higher machine performance.

• Longer intervals between oil changes: The slower aging of the lubricant reduces maintenance costs and operating costs.

• More flexible design: Hydrodynamic bearings can be smaller or designed for lower oil supply without compromising safety.

In summary: Why eddy grooves are a milestone for hydrodynamic bearings in turbomachinery

With eddy groove technology, Miba offers an effective solution for specifically shifting the thermal limits of modern turbomachinery hydrodynamic bearings. Targeted turbulence

• significantly reduces maximum bearing temperatures,
• increases operational reliability, and
• creating new opportunities for more compact, more powerful machine designs.

Miba is thus providing important impetus for the further development of plain bearing technology in high-performance applications.

We are happy to answer your questions!