Particle Transport Analysis of Sand
Inclusive Dates: 07/01/04 - 10/01/04
Background - The aim of the proposed project is to develop a software tool that will allow SwRI to provide detailed analysis of the kinematic behavior of sand and other particulates inside a jet engine gas turbine. Based on this tool's output information, improved (intelligent) inlet air filtering techniques, engine maintenance, and components designs can be realized. These improvements will be based on real data rather than the current simple approach of crude inlet filtering, component over-design and/or reactive internal parts fixes to existing equipment.
In parallel with the analytical work of this project, particle injection into a simple rotating impeller will be tested on SwRI's high-speed rotating machinery test rig to verify the method and optimize the model's implementation to reflect rotating machinery particle impact behavior more accurately. Thus, once the particle transport model has been fine-tuned, a generally applicable method will be available to accurately predict the motion and impacting of sand, and other impurities on the internal structures of an aircraft's gas turbine jet engine.
Approach - The project includes the analytical and numerical implementation of the particle transport model in a gas turbine jet engine (Task 1). Task 2 will be the experimental verification and calibration of this model using sand ingestion data from SwRI's high-speed turbomachinery test stand. Tasks 1 and 2 will be performed in parallel to assure proper feedback for the model calibration tasks.
Accomplishments - The following project activities have been initiated or scheduled: (1) testing sand kinematic behavior over an airfoil using flow visualization and paint abrasion in small wind tunnel, (2) modeling the same airfoil using computational fluid dynamics (CFD), (3) correlating CFD and test results, (4) testing sand kinematics in a high-speed turbomachine with paint abrasion, and (5) modeling the turbomachine using CFD, verifying and adapting the sand transport model.
Testing Sand Kinematic Behavior: Sand kinematic behavior was studied around NACA 0009 airfoils for various flow incidence angles. This study was performed to evaluate the relative influence of streamline curvature and particle size on the motion of particles in the airflow, as well as to test some basic particle kinematic theories. For this task, a small wind tunnel was constructed and a 500-mW Argon-Ion laser was employed to visualize particles carried by the flow using a basic particle image velocimetry (PIV) technique. The illustration below shows a typical example of flow visualization results.
In parallel to the experimental work, a simple two-dimensional computational fluid dynamics (CFD) model was employed to determine the streamlines (velocity and local curvature) of the flow around the airfoil. Combining both CFD and experimental results showed that, within the uncertainty of the test results (~10% on velocity), the motion of a particle can be determined based on a simple model that balances inertial, centrifugal, and drag forces on the particle. Namely, a physical model with some (yet to be refined) coefficients seems to adequately predict the motion of sand particles around a stationary airfoil.
When expanding the above simple model to the rotating frame, particular care has to be given to the inertial terms because the particles in the fluid will also be affected by global centrifugal and Coriolis forces. To develop this model for the rotating frame, experimental sand injection work will be performed in a high-speed compressor at SwRI. CFD results will be correlated to the experimental results with the aim of developing a generalized model for sand transport in a high-speed turbomachine.