Advertorial feature | Liburdi Turbine Services
Identifying Damaged Mechanism of Industrial Aeroderivative HPT Blades Leads to Proposed Design Upgrade
Operators discovered an industrial aeroderivative gas generator was experiencing costly excessive scrap rates of high-pressure turbine (HPT) blades. The generator drives pipeline compressors. Upon
investigation, Liburdi concluded that oxidation on the aftmost row of film cooling holes at mid-airfoil on the pressure side caused the high scrap rate. The oxidation attack generated a significant loss of thickness and base material, shown in Figure 1, limiting part life and impacting the engine overhaul interval.
Figure 1: Aeroderivative HPT Blade Film Cooling Hole Oxidation
A detailed comparison between the industrial aeroderivative HPT blade and its aeroengine version identified differences. The aeroderivative blade has two tip cavity holes and more film cooling holes on the pressure side of the airfoil. The inclusion of a metering plate on the aeroderivative cooling air inlet (Figure 2) shows the differences.
Using the aeroengine configuration as a baseline, Liburdi developed a compressible flow network analysis (CFNA) model to understand the blade’s internal air flow rate, flow distribution, and pressure drop along the flow path.
Figure 2:Comparison of HPT Blade Cooling Design
The CFNA model predicted a significant pressure drop across the metering plate of the aeroderivative design compared to the aeroengine design shown in Figure 3. The low internal pressure difference across the row 3 film cooling holes on the pressure side of the airfoil could become zero. This could cause no flow (cooling hole starving), or even negative air flow, resulting in flow reversal (hot gas ingestion) during transient or off-design conditions.
Figure 3: Comparison of Pressure Drops Along the Flow Path
In the laboratory, dimensional and airflow rig testing confirmed suspicions - the inlet metering plate combined with a large total exit flow area of the aeroderivative HPT blade design reduced cooling flow, altered internal flow pattern, and reduced internal pressure.
Liburdi concluded that hot gas ingestion during off-design or transient conditions could cause oxidation of the HPT blade row 3 film cooling holes. As mitigation, Liburdi recommended upgrading the design to introduce more cooling flow to the trailing edge circuit and reduce the risk of hot gas ingestion. Liburdi’s complete analysis included a review of the impact of additional cooling air extraction on the other components in the engine.
To see how Liburdi can save you money by maximizing your equipment’s operation and extending the life of your parts, contact Bob Tollett at
rtollett@liburdi.com.
www.modernpowersystems.com | July 2019 | 29
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