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Improving Deposition Modeling Through an Investigation of Absolute Pressure Effects and a Novel Conjugate Mesh Morphing Framework

Bowen, Christopher P
http://rave.ohiolink.edu/etdc/view?acc_num=osu1609778777404324

Abstract Details

2021, Doctor of Philosophy, Ohio State University, Aero/Astro Engineering.
The detrimental effects of deposition on gas turbine engine performance have become more pronounced as operation in climates with heavy concentrations of airborne particulate has increased over the past several decades. This has introduced relatively new and complex challenges for engine designers and maintenance teams who must account for and try to mitigate the host of negative consequences that can arise when particles accumulate on turbine hardware. The majority of deposition analysis is performed through experimental testing, whether it be in the full-scale engine environment or in a scaled-down facility. The cost involved with designing, manufacturing, and testing hardware can be exorbitant however, and thus computational models that can predict deposition behavior are an attractive and more affordable alternative. Over the past decade, a variety of models have been introduced to address this growing need. The aim of this work is two-fold and is addressed in two parts. The first goal is to improve the current state of deposition modeling by investigating the role that absolute pressure plays in the process. Experiments are first conducted in a High-Pressure Deposition Facility (HPDF) at the Aerospace Research Center (ARC) at the Ohio State University (OSU). Commercially available Arizona Road Dust (ARD) is delivered to an effusion cooling plate at a specified pressure ratio and flow temperature, and the absolute flow pressure is varied over a range of 14.77 atm to study the effect pressure has on the deposition levels and blockage of the effusion cooling holes. Two size distributions (0-3.5 and 0-10 µm) are investigated, and the results indicate that the deposition and blockage rates decrease monotonically as absolute pressure increases. This holds true for both sizes of dust, but the overall blockage rates are much higher for the 0-3.5 µm. The rate of decrease in hole blockage as pressure increases on the other hand is steeper for the 0-10 µm distribution. Three potential physical mechanisms were explored to determine what physics are primarily responsible for the trends seen in each distribution. It is demonstrated that the discharge coefficient causes the average flow velocities to increase in the effusion holes at elevated pressures. A targeted experiment is designed and conducted to determine if this is causing a significant reduction in deposition, and it is found that the effect is very minimal. The role of increasing shear removal forces is analyzed using an analytical order of magnitude analysis. The shear drag moments that create a rolling moment are determined to be orders of magnitude smaller than the adhesion forces that create a counter-moment and enable particles to stick to the surface. Some work is still required to determine whether removal of bulk structures is a variable of concern at elevated engine pressures, but the influence of shear forces on individual particles should be negligible even when the flow pressure exceeds 50 atmospheres. The role of increased particle drag is shown to be the primary mechanism that dictates the experimental behavior as a function of pressure. The role of the effective Stokes number is discussed as well as the importance of modeling the non-spherical drag effects on the particle. It is theorized that increasing drag with pressure causes small particles (0-3.5 µm) to impact surfaces less frequently and at shallower angles that promote particle rolling and separation from the surface. An experiment is run that proves that particles larger than 5 µm in a distribution can erode existing deposits and clear out blockages. Two simulations are run to model the 0-10 µm experiments at 1 and 15.77 atm using a technique called mesh morphing where the mesh boundaries are deformed to mimic the deposit growth. The physics of erosion are not modeled, however, the resulting deposit structures after 20 iterations of morphing show resemblance to the experimental deposits. The blockage trends in each simulation are used to support the thesis that small particles impact and stick less often, while larger particles impact and erode more aggressively at higher absolute pressures. The second improvement to deposition modeling is introduced in the form of a new conjugate mesh morphing framework. Experiments are run in an oversized impinging jet facility and impingement cones are built on a Hastelloy target. The evolution is visualized using Particle Shadow Velocimetry (PSV) and the ensuing reduction in target temperature is measured using infrared imaging. The mesh morphing is applied to a conjugate geometry and shows the ability to predict the reduction in the target backside temperature. This is achieved through application of an effective conductivity to the deposit cells in the solid region. It is shown that with further research into the thermal properties of the deposits, the framework will offer a more universal option that allows for insight into the effects of deposition on the cooling performance.
Jeffrey Bons (Advisor)
Randall Mathison (Committee Member)
Sandip Mazumder (Committee Member)
212 p.
Aerospace Engineering; Mechanical Engineering
particle deposition; mesh morphing; fouling; gas turbine cooling;

Recommended Citations

Citations

  • Bowen, C. P. (2021). Improving Deposition Modeling Through an Investigation of Absolute Pressure Effects and a Novel Conjugate Mesh Morphing Framework [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1609778777404324

    APA Style (7th edition)

  • Bowen, Christopher. Improving Deposition Modeling Through an Investigation of Absolute Pressure Effects and a Novel Conjugate Mesh Morphing Framework. 2021. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1609778777404324.

    MLA Style (8th edition)

  • Bowen, Christopher. "Improving Deposition Modeling Through an Investigation of Absolute Pressure Effects and a Novel Conjugate Mesh Morphing Framework." Doctoral dissertation, Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1609778777404324

    Chicago Manual of Style (17th edition)

osu1609778777404324
263
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This open access ETD is published by The Ohio State University and OhioLINK.