Penn State

Mechanical & Nuclear Engineering

Turbine Heat Transfer and Aerodynamics Group

Rim Seal Perfomance Studies

Illustration showing leakage paths in a turbine.

One of the biggest challenges in the gas turbine engine industry is the high fuel costs that contribute substantially to end user operating budgets. It is imperative that gas turbine propulsion systems and land-based power generation systems become more fuel efficient. Nearly one quarter of the total air flow through a gas turbine engine bypasses the combustor and is used for cooling turbine airfoils, disks, and other turbine components. Since this cooling flow results in a penalty to engine efficiency, it is vital to reduce the needed cooling flow.

In a gas turbine, one area of particular interest for reducing the cooling flow requirements is the internal cavities that are below the airfoils in the main gas path. These cavities must be protected from the hot external flows, which is achieved by using the coolant flow to act as a sealing mechanism to prevent any ingress of the hot gas into the cavity region.

Method using CO2 tracing gas for determining sealing performance.

The rim seal geometry in the START test turbine is constructed from actual engine hardware such that it represents a modern-gas turbine architecture. There are a myriad of flow complexities that affect the rim seal performance including: local pressure distributions in the main gas path as well as in the cavity; rotational effects resulting from the stationary vane and rotating blade; sealant flowrates and introduction of the flow into the cavity; and relevant leak paths. This project is investigating a range of parameters on the performance of rim seals through the use of static pressure measurements and CO2 gas tracing.

Sealing effectiveness values for the vane only tests in the START test turbine.

Additive Manufactured Coupon Characterization Studies

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Recent technological advances in the field of additive manufacturing (AM), particularly with direct metal laser sintering (DMLS), have increased the potential for building gas turbine components with AM. Using DMLS for turbine components broadens the design space and allows for increasingly small and complex geometries to be fabricated with little increase in time or cost. Challenges arise when attempting to evaluate the advantages of DMLS for specific applications, particularly because of how little is known regarding the effects of surface roughness.

Optical profilometer measurements (left) and CT scan results (right)
showing microchannel roughness and resulting build features.

This research involves measuring pressure drop and heat transfer for flow through small, as produced microchannels that have been manufactured using DMLS in an effort to better understand build direction effects as well as surface roughness. Results showed significant augmentation of these parameters compared to smooth channels, particularly with the friction factor for mini-channels with small hydraulic diameters. However, augmentation of Nusselt number did not increase proportionally with the augmentation of the friction factor.

Resulting pressure loss and heat transfer measurements for a range of microchannel coupons.