Engineering Simulation for Performance and Noise Reduction in Lawn Mowers: A Case Study of VIKING GmbH

• Sensors - Flow Meters
• Sensors - Level Sensors

• Equipment & Machinery

• Product Research & Development

• Manufacturing Process Simulation
• Virtual Reality

VIKING GmbH, a subsidiary of ANDREAS STIHL AG & Co. KG, is a manufacturer of gardening equipment including lawn mowers. The company is committed to continually improving the performance of its lawn mowers, specifically in terms of mowing performance and noise emission levels. However, the company faced a challenge in understanding the aerodynamics within the deck of the lawnmower. The curved, double-edged blade of the lawnmower induced a highly unsteady airflow, which resulted in vortices that periodically struck the wall of the chute, impacting both the noise emission levels and the catching performance. The fast blade rotation, unsteady pressure, and high fluctuations of the air velocity within the deck created a complex airflow that made traditional development and measurement methods almost impossible. The company needed to find a way to improve the catching performance and simultaneously meet outdoor noise emissions regulations.

VIKING GmbH is a 100 percent subsidiary of ANDREAS STIHL AG & Co. KG, based in Austria. The company is an innovative, service-oriented manufacturer of gardening equipment, including lawn mowers, lawn scarifiers, lawn tractors, garden shredders, and tillers. In its lawn mower division, the company is focused on offering the most comfortable and efficient tools possible by continually improving mowing performance and meeting the outdoor noise emissions regulations of their products. VIKING GmbH is committed to innovation and service, continually seeking ways to improve its products and meet the needs of its customers.

To overcome the challenge, VIKING engineers decided to use ANSYS CFX fluid flow simulation software to simulate the airflow in the lawn mower deck. The goal was to see if numerical simulation could be implemented in the design process. This required confirming the accuracy of results with experimental measurements and verifying the benefits that can be gained from the insight provided with computational fluid dynamics (CFD). The engineers set up the wall, counter rotating wall, and opening boundary conditions in ANSYS CFX-Pre. They then performed URANS simulation with a transient rotor stator model using ANSYS CFX software and performed post-processing in ANSYS CFD-Post. This approach allowed them to compare the computed characteristic parameters of the airflow with measurements in the chute of the lawnmower.

• The use of ANSYS CFX software provided VIKING engineers with a deeper understanding of the aerodynamics within the deck of the lawnmower. They were able to localize and optimize the main vortices, which are a source of sound emissions, by identifying areas of high turbulent fluctuations. They also discovered boundary separation in the lawn mower chute and were able to prevent this separation by filling the separation area. The software also gave them the ability to consider flow within the entire three-dimensional lawnmower and select and evaluate the most important variables that are characteristic for the fluid flow but cannot be measured experimentally due to the rotating blades. This has resulted in improved catching performance and reduced noise emissions, enhancing the overall performance of the lawnmowers.

• Good agreement achieved with velocity measurements in the chute of the mower
• Prevented boundary separation in the lawn mower chute in a second step by filling the separation area
• Optimized the main vortices, a source of sound emissions, by identifying areas of high turbulent fluctuations