Penn State

Mechanical & Nuclear Engineering

Turbine Heat Transfer and Aerodynamics Group

ExCCL Facilities

Big-Blue Wind Tunnel
High Density Ratio
Film-Cooling Rig
Internal Cooling Channels


Big-Blue Wind Tunnel

[Back to Top]

Schematic of Big-Blue facility (top) and photo of the
combustor-turbine interface within Big-Blue (bottom).

The cornerstone of PSU ExCCL, our "Big-Blue" wind tunnel facility has been in operation since 1995 and has moved from Wisconsin-Madison, to Virginia Tech, and finally Penn State. This recirculating wind tunnel features a 50 hp axial fan that can move 44.4 CFM of air that passes through a linear cascade of turbine blades. The cross section of the wind tunnel is 44 by 22 inches, which allows us to perform experiments on scaled-up turbine models, providing high resolution measurements.

The most common experiment performed in Big-Blue is endwall heat transfer measurements. We use infrared (IR) cameras to obtain a highly detailed map of the surface temperatures on the endwalls. By measuring surface heat transfer coefficients and adiabatic cooling effectiveness, we can evaluate film-cooling designs such as the comparison between flat and contoured endwalls. To compare the turbulent flow with the surface heat transfer, we often measure the turbulent flow using laser Doppler velocimetry (LDV). In the image at right, Amy and Jeffrey are using LDV to measure the turbulence in the turbine cascade while using an infrared camera to measure the effectiveness of a film-cooling pattern.

Amy Mensch and Jeffrey Gibson making measurements of
turbulent flow using LDV and turbulent heat transfer
using an IR camera.

Recent support from Pratt & Whitney has provided PSU ExCCL with a time-resolved, digital particle image velocimetry (TRDPIV) system which is used to capture the turbulent flowfield developing in time. The image at right shows the TRDPIV system in action, capturing the turbulent flow in the stagnation plane upstream of a turbine blade.

The laser and high-speed camera from the TRDPIV system may also be used to track the motion of foreign particles in our Big-Blue facility. Molten wax particles to simulate engine fly-ash and the position of these foreign particles were tracked as seen in the images at right. In actual engine hardware, the fly-ash particles could be expected to follow a similar trajectory. In addition to tracking foreign particle motion, we are also able to simulate the buildup of molten engine particulates. In the second image at right, we have found that geometric modifications, such as endwall contouring, can prevent the build-up of molten foreign particles.

Left: TRDPIV system being used to measure turbulence upstream of a turbine vane.
Top right: Molten wax particles being tracked using components from the TRDPIV
system. Bottom right: Buildup of molten engine particulates showing better
resistance to buildup when contoured endwalls are employed.

High-Density-Ratio (HDR) Film-Cooling Rig

[Back to Top]

Molly Eberly and Robert Schroeder measuring film cooling
effectiveness in the HDR test facility.

Comparison of film cooling effectiveness at low density ratio
(left) and at high density ratio (right).

Recent funding support from Pratt & Whitney has allowed the installation of a second recirculating wind tunnel, similar to Big-Blue. The HDR rig is used to investigate innovative film-cooling geometries at actual-engine density ratios, as shown in the image at right. The cross section of the HDR rig is 12 inches by 12 inches which allows us to perform experiments on scaled-up film-cooling models, providing high resolution measurements.

In the HDR test facility, surface heat transfer experiments are performed to evaluate film-cooling designs. As with experiments in Big-Blue, IR cameras are used to capture a high-resolution map of the surface temperatures. Liquid nitrogen is used to reduce the temperature (increase the density) of the coolant air while electric heaters are used to raise the temperature (lower the density) of the mainstream air. As a result, a high density ratio between coolant and mainstream flow is achieved, similar to actual engine operating conditions. In the image at right, adiabatic cooling effectiveness measurements have been performed at various density ratios. Increasing density ratio has been shown to increase cooling effectiveness for a typical row of cylindrical film cooling holes.

Future experiments in the HDR rig will include shaped film-cooling holes. In addition to heat transfer measurements, TRDPIV measurements will be performed in the HDR rig to determine how density ratio affects the turbulent flowfield for film-cooling holes.

 

Internal Cooling Channels

[Back to Top]

Katie Kirsch making pin-fin heat transfer measurements
using an IR camera (left) and Jason Ostanek making
preparations for turbulence measurements in a
pin-fin channel (right).

While much of the research taking place at PSU ExCCL focuses on the flow and heat transfer on the outside of turbine blades, internal flow and heat transfer are equally important for keeping hot-section components from premature failure. The first stages of turbine blades and vanes exiting the combustor are subjected to extreme temperatures and are cast hollow with internal cooling channels to remove excess heat. At PSU ExCCL, we have two parallel test rigs used to study internal cooling, as shown in the image at right. These recirculating channels feature radial blowers capable of moving 1400 CFM across a 54 inH2O pressure drop.

The internal cooling channels are interchangeable such that we can swap geometric configurations to study ribbed or pin-fin channels. As with our external heat transfer facilities, the internal cooling facilities are scaled-up such that we can obtain high resolution measurements. Typically, one of the internal facilities is used to measure internal heat transfer while the second facility is used to measure turbulent flowfield and aerodynamic losses.

Heat transfer experiments are performed for internal cooling channels using an IR camera. A high resolution map of surface temperatures is used to determine the heat transfer coefficients across the entire channel. The image at right shows an example of heat transfer coefficients measured in a pin-fin channel.

Turbulent flowfield measurements are also performed using TRDPIV and LDV. The first image at right shows the LDV in action in the flowfield facility. LDV measurements are used to obtain turbulence statistics at a single point in the flow. The second image at right shows the TRDPIV in action in the flowfield facility. TRDPIV measurements allow for an entire plane of turbulence statistics to be calculated.

Left: TRDPIV system being used to make turbulence measurements in the wake of a multiple row pin-fin channel. Top right: Heat transfer contours in a typical pin-fin channel. Bottom right: LDV system being used to measure turbulence in the wake of a single row of pin-fins.

Foreign Particle Deposition Rig

Turbine blade from a land-based gas turbine
with rust particles built up near the blade root.

At PSU ExCCL, we not only test turbine heat transfer but we also perform experiments on foreign particle deposition. After all, turbine performance relies on clean parts as well as efficient cooling schemes. Using compressed air, we inject sand, dirt, rust, and dust into actual engine components and representative parts to determine how much the flow through small passages is blocked. Experiments are performed at engine-realistic pressure ratios.

To test the effect of actual engine temperatures on particle deposition, the test apparatus may be placed inside a kiln for the deposition experiment. By heating the engine hardware and the foreign particles to high temperatures, we can determine how phase changes, conglomeration, and melting of foreign particles changes their deposition characteristics. The maximum temperature of the kiln is 2300°F (1260°C).

Left: Kiln used for heating sample of foreign particles. Right: Test rig for particle injection in non-rotating engine hardware.

Centrifuge used to accelerate engine parts to 12,000g.

 

 

In some instances, the effects of centrifugal forces may play an important role in particle deposition and flow blockage. We have modified a commercial centrifuge to spin while passing foreign particles through the engine parts. The centrifuge is capable of spinning parts at engine-representative centrifugal accelerations up to 12,000g.