Krista M. Kecskemety

A Reduced Order Aerothermodynamic Modeling Framework for Hypersonic Aerothermoelasticity

The field of aerothermoelasticity will play an important role in the analysis and optimization of air-breathing hypersonic vehicles, impacting the design of the aerodynamic, structural, control, and propulsion systems at both the component and multi-disciplinary levels. One of the primary challenges for hypersonic aerothermoelastic analysis is accurate and efficient computation of the aerothermodynamics, where currently approaches are limited to either simple engineering level approximations or expensive Computational Fluid Dynamics (CFD). This study aims to fill the modeling gap between these two extremes using sophisticated reduced order modeling techniques to construct computationally efficient surrogates for CFD predictions of the hypersonic aerothermodynamics. Both Proper Orthogonal Decomposition (POD) and kriging approaches are considered and compared. In addition, two different sampling strategies are compared: a random one pass Latin Hypercube parameter space sampling and an adaptive sampling method based on an estimated mean squared error. The developed reduced order modeling framework is used to construct a CFD-based reduced order model for the three-dimensional aerothermodynamics over a hypersonic control surface. Input parameters include: freestream Mach number, altitude, angle-of-attack, side-slip angle, transient structural deformation, and spatio-temporally varying surface temperature. The developed reduced order models are compared to 500 full order CFD evaluation cases. Results illustrate that the developed ROMs require on the order of hundredths of a second to compute surface heat flux distributions and generally have less than 5% RMS error. However, a purely numerical “apparent” laminar to turbulent transition, which is highly nonlinear over the considered parameter space, regularly leads to 10 ‐ 20% L1 error in the surface heat flux.

The Influence of Wake Effects and Inflow Turbulence on Wind Turbine Loads

Wind turbines are emerging as an exciting and rapidly expanding form of renewable energy. However, there are numerous technological challenges that must be overcome before wind energy provides a significant amount of power in the United States. One of the primary challenges in wind turbine design and analysis is accurately accounting for the wake. This study represents an initial step towards including wake effects in wind turbine design and analysis codes. A free wake model is developed using a time marching vortex line method, and subsequently verified and validated against existing results. The model is then used to examine time step requirements in the presence of inflow turbulence. Finally, comparisons are made between the developed free wake model and typical aerodynamic modeling approaches such as Blade Element Momentum Theory and Dynamic Inflow. For the configurations considered, blade time step sizes of 10° in azimuthal angle are adequate for capturing the effect of inflow turbulence on the wake. Finally, the inability of Blade Element Moment Theory and Dynamic Inflow to predict blade loads with combined inflow turbulence and wake effects is demonstrated.

Wake Interaction Effects Using a Parallelized Free Vortex Wake Model

Turbine-wake interactions pose significant challenges in the development of optimal wind farm configurations. These interactions can lead to a marked reduction in wind farm power efficiency as well as an increase in structural loading, which reduces the functional lifetime. This work aims to develop a free vortex wake (FVW) model to capture turbine-wake interactions between multiple turbines. Analysis focuses on the impact of wake interaction on wake structure, rotor power, and blade root bending moments. Comparison to the DWM model demonstrates similar trends but also discrepancies in values. A parametric study yields expected power trends for all tested parameters. Additionally, a comparison of rotor power and bending moment standard deviations from the FVW and DWM models indicates that the FVW model produces higher standard deviations in wake-influenced turbines. This could have implications for prediction of turbine life and suggests that the transient as well as average response of turbines should be considered to fully capture the effects of wake interaction.

Aeronautical and Astronautical Engineering Major Selection in First-Year Engineering Students

Examining major selection and decision making can help us understand the recruitment and retention of engineering students. In majors that have identified overlap in terms of content and future careers, such as Mechanical Engineering and Aeronautical and Astronautical Engineering, it is important to understand the perspectives of students who decide to pursue these majors and if they change their major selection throughout the crucial first-year. This paper discusses results from a survey of engineering students throughout their first year of study. Pre-test, mid-test, and post-test survey results demonstrate that there are differences in certainty of major choice between those that intend to pursue Mechanical Engineering and those that intend to pursue Aeronautical and Astronautical Engineering, with the latter typically being a higher level of certainty. Open-ended responses highlight the differences in student perceptions of what engineers do in these two disciplines. It is hoped that the knowledge gained through this work may help inform recruitment activities, advising, and first-year engineering curriculum to allow students to make an informed decision about their major and future career.

Examining engineering students' major selection: Developing baseline quantitative results to investigate major selection and change

Improving recruitment and retention are goals of many engineering programs. One factor that is tied strongly to recruitment and retention is a students desire to study engineering in a specific engineering discipline. Some students switch between engineering majors during their undergraduate careers, which could increase their time to degree. Also, depending on the reasons students have for switching, the changes could also impact their motivation and personal commitment to engineering. Not all major changes are due to changes in student preference. Some changes may also result from external influences such as enrollment management. The research presented in this Work in Progress paper will be an initial step towards answering the question: Why and how do students change engineering majors throughout their college career? Through this research, we hope to gain added insights into how engineering students switch between majors so in the future we can seek a better understanding of why they switch.

Preliminary Study on Wake Interaction Effects Using a Free Vortex Wake Model

Wind energy is a renewable energy option that has made great advances in recent years. However, there are several issues that limit its growth. A significant challenge is wind farm configuration, where the energy density in the farm is limited due to interactions between turbines caused by the shed wakes. This paper discusses an on-going effort to develop an improved analysis tool for designing wind farm configurations. The tool is based on moderate fidelity free vortex wake models (FVW) to capture turbine-wake interactions between multiple turbines. As a first step, a loosely-coupled wake interaction model is developed between an upstream wake and a downstream turbine. Preliminary results are discussed for the impact of the interactions on wake structure, rotor power, rotor moments, and tip displacements for varying geographic and wind conditions.

Validation of an Enhanced Aeroelastic Analysis Code for Wind Turbines

Wind turbines are currently a rapidly expanding form of renewable energy. However, there are numerous technological challenges that must be overcome before wind energy provides a significant amount of power in the United States. One of the primary challenges in wind turbine design and analysis is accurately accounting for the aerodynamic environment. This study is focused on a comprehensive verification and validation of the NREL FAST code, which has been enhanced to include a free vortex wake model. The verification and validation is carried out through a comparison of wake geometry, blade lift distribution, wind turbine power and force and moment coefficients using a combination of CFD and experimental data. The results are also compared against Blade Element Momentum Theory, and results from a 2001 double-blind NREL study on the prediction capabilities of wind turbine modeling tools. Results indicate that the enhanced aeroelastic code generally provides improved predictions. However, in several notable cases the predictions are only marginally improved, or even worse, than those generated using Blade Element Momentum Theory aerodynamics. It is concluded that modeling of the aerodynamic environment remains incomplete, even after inclusion of wake effects. One important aspect identified is modeling of the unsteady aerodynamic lift characteristics of the rotor.

Investigation into the Impact of Wake Effects on the Aeroelastic Response and Performance of Wind Turbines

Wind turbines are currently a rapidly expanding form of renewable energy. However, there are numerous technological challenges that must be overcome before wind energy provides a significant amount of power in the United States. One of the primary challenges in wind turbine design and analysis is accurately accounting for the wake. This study represents a step towards including wake effects in wind turbine design and analysis codes. A free wake model is developed using a time-marching vortex line method, and subsequently coupled with FAST, an open source wind turbine aeroelastic code. The resulting model is verified and validated against existing results. Subsequently, comparisons are made in power predictions and aeroelastic responses between the developed free wake model and typical wind turbine aerodynamic modeling approaches such as Blade Element Momentum theory and dynamic inflow. Results indicate that the free wake model has an impact on the power, blade loads, and blade deflections.