Complex Turbomachinery Flow
The ME Department at JHU houses the Axial Turbomachine Facility, a unique laboratory funded by the Air Force and the Navy that is used to study the flow in turbomachines. The term “turbomachine” refers to a device that uses rotating elements to transfer energy either to or from a continuously moving fluid. Machines such as compressors and pumps add energy to the fluid, increasing the fluid pressure. Gas, steam, or hydraulic turbines absorb energy from the fluid, generating power in the process.
Designing highly efficient, durable, and quiet turbomachines is one of the “holy grails” of mechanical engineering. Better turbomachine technology would affect all of us, from improvements in power generation to quieter commercial airplane engines. But design tools for turbomachines are far from optimized, due to the complex fluid motion around the rotating elements and the sheer numbers of elements in a typical turbomachine. A compressor for a commercial jet engine has 37 blade rows, each containing 30–100 blades, resulting in a very complex machine with an impressive 50,000 pounds of thrust. In the turbulent flows around the blades, secondary flow phenomena such as wakes and trailing vortices, and leakage adversely affect efficiency and performance. Noise is also a big problem, from suburban homeowners under commercial flight paths to highly sensitive applications such as pumps in the reactors that power submarines. A better understanding of the fluid dynamics within these turbomachines is therefore critical to improving design parameters, and Professors Joseph Katz and Charles Meneveau, with funding from the Air Force and the Navy (in separate projects), employ novel flow visualization techniques to gain insight into the nature of the flow.
In a technique known as Particle Image Velocimetry (PIV), a laser beam is expanded into a thin sheet of light, illuminating a section of the fluid, and a camera records a multiple exposure image of the cloud of particles. The displacement of particles between exposures reveals the 2D instantaneous velocity distribution. The problem with using this technique to study flow in turbomachines is that the multiple blades limit access, both to the laser and to the camera. Prof. Katz recently solved this problem by using acrylic blades and a fluid that has the same index of refraction as the blades, rendering them invisible. This flow visualization allowed them to obtain, for the first time ever, data on the flow at any point of the turbomachine.