Turbine Simulation Yields Better, Safer Engines

Wednesday, December 21, 2011 @ 10:12 AM gHale

Turbomachinery has quite a few uses, but in the industrial setting it sees use in everyday areas such as pumps, fans, compressors, turbines and other machines that transfer energy between a rotor and a fluid.

To achieve the most efficient propulsion and power systems – and ultimately safety, engineers need to understand the physics of very complex air-flow fields produced within multiple stages of constantly rotating rotors and stators.

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That is where Jen-Ping Chen, Ph.D., associate professor of mechanical and aerospace engineering at The Ohio State University, comes in. He is working to improve the computational fluid dynamics (CFD) software engineers use to simulate and evaluate the operation of turbomachinery. Chen was the chief architect of that type of computer code, appropriately named TURBO, which he developed earlier for NASA.

Chen is leveraging the computational power of the Ohio Supercomputer Center (OSC) to refine the software as it validates the flow field of engine components, specifically as it applies to high-pressure compressors and low-pressure turbines.

“The world is demanding increasingly cleaner, more efficient and reliable power systems,” said Ashok Krishnamurthy, interim co-executive director of OSC.

Each turbomachinery component has unique physical characteristics that present difficulties in design and operation, such as stall in a compressor and cooling in a high-pressure turbine. With a validated and optimized simulation tool able to run efficiently on a large computer cluster, engine designers will have more physical insight to the complex flow field, which will lead to reduced testing, reduced risk, faster time-to-market and lower costs.

While traditional wind-tunnel testing is often the most straightforward approach, it also comes with high costs and severe constraints on placing the measurement probes, Chen said. Numerical simulation, using CFD, has provided an alternative for studying such flows at a lower cost and with unconstrained probe placement. Yet, the accuracy of a simulation depends on the accuracy of the mathematical model behind the simulation.

“Our goal is to develop a reliable prediction technology to help improve turbomachinery component design,” said Chen. “The successful combination of CFD simulation and experimentation can greatly supplement the understanding of fundamental fluid behavior of gas turbine systems, thus enhancing the ability of engineers to develop more advanced engine components.”

The obvious correlation is the more efficient the components, the smoother running and safer the system becomes.

Chen’s team is investigating three specific areas of current industrial interest: Coupled fluid-structure interaction, active flow control and turbine film cooling. Improved numerical simulation will allow engineers to analyze complex flow fields and aeroelastic phenomena, such as flutter, limit-cycle oscillations, forced response, nonsynchronous vibrations and separated-flow vibrations, which arise from fluid-structure interaction.

Application of a newly developed flow control simulation model for vortex-generating jets in low-pressure turbines will help improve engineers’ understanding of how flow control can help increase the performance and operability of gas turbine engines. And, finally, simulations can help engineers accurately predict the effectiveness of film cooling on heat transfer in a three-dimensional, unsteady, rotating environment with actual engine geometry.

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