Computational Fluid Dynamics Predicts 18% Reduction in Coal Ash Deposition with Hub End Wall Geometry Modification

Why It Matters

This research demonstrates the power of computational modelling in understanding complex physical phenomena like ash deposition in gas turbines. By simulating these processes, designers can iteratively test and optimize designs for improved performance and longevity without costly physical prototypes.

Key Finding

Computer simulations showed that changing the shape of the turbine's end wall reduced coal ash buildup by 18%, though it shifted some deposition to a different area.

Key Findings

• The Euler-Lagrangian two-phase approach with the standard k- turbulence model and a critical impact velocity sticking model can accurately predict coal ash deposition locations and quantities.
• A 30-degree reduction in the hub end wall inlet angle to the axial direction resulted in an overall 18% decrease in deposition mass.
• While the modified geometry improved deposition near the hub wall and pressure surface, it led to a slight increase in deposition in the mid-span region of the turbine vane.

Research Evidence

Aim: To simulate and quantify the deposition of coal ash on turbine nozzle guide vanes and evaluate the effectiveness of a specific hub end wall geometry modification in mitigating this deposition.

Method: Numerical simulation using Computational Fluid Dynamics (CFD) with an Euler-Lagrangian two-phase approach.

Procedure: A CFD model of a turbine passage was created using FLUENT software. The standard k- turbulence model was employed. Particle trajectories and deposition were predicted using a critical impact velocity sticking model, calibrated against experimental data. The model was validated against experimental results from a turbine rig. Finally, a modified hub end wall geometry was simulated to assess its impact on deposition.

Context: Gas turbine engineering, specifically focusing on the first stage of a GE-E 3 turbine operating with coal ash.

Design Principle

Utilize validated computational models to predict and optimize designs for complex fluid-particle interactions, such as deposition, before physical prototyping.

How to Apply

Use CFD software to model the flow and particle behaviour in your design. Experiment with different geometric parameters and validate your findings against available experimental data or established physical principles.

Limitations

The study focused on a specific turbine stage and coal ash composition. The accuracy of the sticking models is dependent on calibration to experimental data, and the critical viscosity sticking model required further calibration.

Student Guide (IB Design Technology)

Simple Explanation: Using computer simulations, researchers found that changing the shape of a part inside a turbine could reduce how much coal ash built up on it by 18%.

Why This Matters: This research shows how computer modelling can be used to solve real-world engineering problems, like preventing damage to turbines caused by ash buildup, which can save time and money in design projects.

Critical Thinking: How might the observed increase in deposition in the mid-span region of the turbine vane due to the hub end wall modification impact the overall efficiency and lifespan of the turbine?

IA-Ready Paragraph: Computational fluid dynamics (CFD) simulations, as demonstrated by Barker (2010) in the study of coal ash deposition on turbine vanes, offer a powerful method for predicting the impact of design modifications. Their research utilized an Euler-Lagrangian approach to simulate particle trajectories and deposition, successfully predicting an 18% reduction in ash mass through a specific hub end wall geometry change, highlighting the potential for CFD to inform design decisions aimed at mitigating performance degradation.

Project Tips

• When choosing simulation software, consider its capabilities for multi-phase flow and particle tracking.
• Ensure any empirical models used (like sticking models) are well-calibrated to relevant experimental data or are clearly stated as requiring further calibration.

How to Use in IA

• Reference this study when using CFD to predict the performance or behaviour of a design element, especially when dealing with fluid dynamics or particulate matter.

Examiner Tips

• Demonstrate an understanding of the assumptions and limitations of the CFD models and sticking models used in the simulation.

Independent Variable: Hub end wall inlet angle to the axial.

Dependent Variable: Deposition mass on turbine nozzle guide vanes.

Controlled Variables: Turbulence model (standard k-), sticking model (critical impact velocity), turbine stage geometry (base case).

Strengths

• Validation against experimental data provides confidence in the simulation's accuracy.
• Quantification of the geometric modification's impact (18% reduction) offers clear design insights.

Critical Questions

• What are the potential long-term consequences of the increased deposition in the mid-span region?
• How sensitive are the simulation results to variations in coal ash properties (e.g., particle size distribution, viscosity)?

Extended Essay Application

• A detailed CFD analysis could be used to investigate the impact of different material coatings on reducing ash adhesion in a simulated turbine environment.

Source

Simulation of Coal Ash Deposition on Modern Turbine Nozzle Guide Vanes · OhioLink ETD Center (Ohio Library and Information Network) · 2010