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Daniel Guggenheim School of Aerospace Engineering

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https://hdl.handle.net/1853/70742

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College of Engineering

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Aerospace Design Group

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Aerospace Systems Design Laboratory (ASDL)

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Air Transportation Laboratory

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Cognitive Engineering Center

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Space Systems Design Laboratory (SSDL)

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Publication Search Results

Now showing 1 - 10 of 54

Numerical Simulations of the HVAB Rotor in Hover

(Georgia Institute of Technology, 2022-11-29) Mali, Hajar

Numerical simulations of compressible viscous flow over the Hover Validation and Acoustic Baseline (HVAB) rotor in hover are presented. The commercial flow solver, ANSYS Fluent, has been employed. The effects of transition are modeled using the Langtry-Menter k-ω SST-γ-Reθ model at three different pitch settings. Comparisons with HVAB test data and other publications are discussed. These include integrated thrust and power coefficients, figure of merit, velocity inflow, surface pressure distribution, lift distribution, transition locations, and vortex structures.
Development of a Sonic Sensor for Aircraft Applications

(Georgia Institute of Technology, 2021-12-14) Carroll, Jonathan D.

The field of aeroacoustics has been an area of constant research over the past six decades. Acoustic waves have some special characteristics that allow for heating, cooling, and even active flow control over airfoil shapes using synthetic jets and other methods. They can also be used to measure properties of the flow over an aircraft, including the free-stream pressure ratio, density ratio, and total temperature. The current measurement techniques to obtain these parameters applied to aircraft require a specific probe. It is desired to apply knowledge of acoustics to develop an aircraft sensor that can measure multiple flow properties with minimal impact to the flow field. Adding a sensor that can read total temperature, static temperature, airspeed, and angle of attack will have the added benefit of reducing the number of sensors sticking into the flow and may result in a reduction in failure mode analysis due to the minimization of the number of sensors on the aircraft. This work explores the applicability of sonic anemometry to aircraft for high subsonic and sonic speeds. A computational simulation is developed as a validation of the concept and low speed experiments are shown to validate the theory. This effort identifies the underlying issues associated with applying sonic anemometry to high-speed flows and provides methods to overcome them. This work investigates the use of phased array technology to increase the accuracy and applicability at the higher speeds and smaller footprints (lighter and fewer systems). Phased arrays use the constructive and destructive interference to boost and direct the desired signal, in this case, acoustic waves. These acoustic waves have been shown to provide haptic feedback and levitate small particles utilizing a relatively inexpensive ultrasonic phased array system. It is shown that the ultrasonic phased array overcomes the hydrodynamic noise to produce a strong signal for use in the calculation of the flow parameters up to the maximum speed tested. It is also shown that the signal is strong enough to produce consistent time delay estimations, via cross-correlation, with a 0.05 second sample time to integrate into modern air data systems.
Application of Extended Messinger Model for Ice Accretion on Complex Geometries

(Georgia Institute of Technology, 2021-10-11) Gupta, Avani

Ice accretion can significantly degrade the performance, stability, availability, and affordability of an airborne vehicle. It is imperative that this phenomenon be modeled accurately. While ice accretion studies have been performed on airplane wings, propellers, and helicopter blades, there are very few attempts to model the process on more complex geometries such as fuselages. In this study, an existing in-house Extended Messinger methodology is generalized for complex geometries by modeling the flow field and water droplet transport on unstructured grids, and carrying out the ice accretion calculations along surface streamlines. A general framework has been developed, allowing the use of two-dimensional and three-dimensional, structured, and unstructured, public domain and commercial CFD analyses. The methodology is primarily spilt into three steps: the continuum flow field analysis, the dispersed water phase computations, and the ice accretion module. In the present study, in-house methodologies as well as commercial solvers such as STAR-CCM+ and ANSYS Fluent have been used for the flow field and droplet dispersed phase computations. The in-house methodologies for the dispersed water droplet transport are done using an Eulerian approach, with a one-way interaction between the air flow and the dispersed phase via the drag force exerted on the droplets by the air flow. The ice accretion is carried out along surface streamlines, or optionally along two-dimensional section cuts, using an in-house icing methodology based on the Extended-Messinger model. The predictions from the present approach are compared to available experimental data, and predictions using other solvers such as LEWICE and STAR-CCM+. Several configurations with varying levels of complexity are modeled. These include 2-D airfoils, swept wings, and helicopter fuselage configurations. Time and space sensitivity studies have been done.
A PHYSICS-BASED MODEL FOR INFLOW CHARACTERISTICS OF MULTI-ROTOR CONFIGURATIONS

(Georgia Institute of Technology, 2021-08-13) Chen, Po-Wei

A physics-based model for modeling helicopter and autonomous rotor configurations, previously developed for isolated rotors and coaxial rotors in hover and forward flight, has been extended to more general multi-rotor configurations. Simulations for coaxial and tandem rotor configurations have been performed for a number of low and high Reynolds number configurations, and comparisons with test data have been made. The physics behind the rotor interactions has been explored through visualization and analysis of vortex wake structure and inflow velocity distributions. As part of this effort, a fast off-body velocity field analysis that employs GPU processors has been implemented. In addition to computation of inflow velocity field above or below the rotor disks, this approach is capable of rapidly computing and visualizing velocity field on any user specified plane. In many helicopter design studies, the adverse interactions caused by the main rotor wake should be considered in the placement of horizontal and vertical stabilizers, as well as the tail rotors and pusher-propulsors. This capability for rapid calculation and visualization of the off-body flow field would greatly aid the designers in the placement of these components. A previously developed algebraic transition model that regulates the magnitude of the production term in the Spalart-Allmaras one-equation turbulence model has been independently implemented in the present solver. In the present work, this model has been also validated for large scale rotors in hover.
A Unified Approach for Modeling Fluid-Structure Interactions of Large-Scale Offshore Wind Turbines

(Georgia Institute of Technology, 2021-07-26) Pichitkul, Auraluck

Wind turbine technology has grown over the past several decades and has been globally accepted as an economically viable form of renewable energy. Further development in size and power production of wind turbine demands continuous advances in the underlying technologies - aerodynamics, structures, engineering materials, aeroelasticity, electrical systems, mechanical and hydraulic control, and manufacturing. In this study, focus is placed on two aspects of these technologies – aerodynamics and structures – with the primary goal of economically and accurately predicting the power production of very large-scale flexible wind turbines. To fulfill the first objective, a loose-coupling technique relying on an in-house hybrid CFD solver, and an in-house Euler-Bernoulli CSD solver is developed and used in investigating aeroelastic behavior of a large-scale offshore wind turbine. A 5 MW wind turbine system developed by National Renewable Energy Laboratory (NREL) is analyzed. The aerodynamic loads predicted by GT-Hybrid and the elastic deformations computed by the CFD solver are exchanged using file I/O. The study shows that the NREL 5 MW rotor undergoes significant bending deformations, especially at rated wind speeds. The loss of performance, in terms of power production, should be accounted while performing analyses. To satisfy the second objective of exploring alternative design for large-scale offshore wind turbines, a biplane rotor concept proposed by Wirz, et. al. at the University of California Los Angeles is explored. The study shows that that biplane rotors, with a reduced chord, are effective in producing power comparable to conventional wind turbines at rated condition with considerable mass and cost savings.
Computational fluid dynamics simulation of three-dimensional parallel jets

(Georgia Institute of Technology, 2018-12-11) Liu, Zhihang

High-speed air jets are often used in industry for manufacturing thin fibers through a process known as melt-blowing (MB). In melt blowing, high-velocity gas streams impinge upon molten strands of polymer to produce fine filaments. For a very high quantity of fibers to be produced, many small-scale jets placed side by side are needed, these jets draw the air from the same compressed air storage tank, so the fiber formation is critically dependent on the aerodynamics of the impingement jet flow field. However, the real-word MB devices always have complicate internal structures such as mixing chambers and air channels between air tank and die tip, which may cause instability and cross flow in the jet flow filed and had a significant impact on the formation of fibers and non-woven webs with small scale jets. The purpose of this study was inspired by the necessity to understand the effect of the internal geometry on the jet flow filed and tried to prevent the flow instability with fluctuation reduction devices. The MB process in this study was modeled as a pair of two jets placed at an angle of approximately 60 degrees to each other, and when there are many such jet pairs, a stream so that multiple streams of fibers may be simultaneously produced. All internal structures of the MB device were modeled based on US Patent 6,972,104 B2 by Haynes et al. The flow field resulting from the two similar converging-plane jet nozzles was investigated using a computational fluid dynamics approach. The case in which there are flow fluctuation reduction devices installed and the case without the devices installed were studied. The k-ω turbulence model was used, and the model parameters were calculated according to the inlet conditions of the air flow. This study consists of three parts: (a) a baseline case without any flow fluctuation reduction devices was studied to understand the mechanism of the instability and to investigate the details of the internal flow filed; (b) a wired mesh screen was placed between the air plates and the die tip, to study the effect on both the velocity and pressure distribution across the screen; (c) a honeycomb installed near the exit of last mixing chamber trying to reduce the velocity across the flow direction and turbulent intensity. Finally, the effect of the two different flow fluctuation reduction devices was compared in detail using time series measurements and time average flow contours.
A hybrid Navier Stokes/vortex particle wake methodology for modeling helicopter rotors in forward flight and maneuvers

(Georgia Institute of Technology, 2018-04-11) Battey, Luke Sterling

Maneuvering flight and high-speed flight are critical design points in any rotorcraft’s operating envelope. These conditions give complex flow phenomena, creating high stresses and vibrations. To accurately predict the flow properties over the relatively flexible rotor blades, coupling between computational fluid dynamics (CFD) and computational structural dynamics (CSD) is required. In this work, GT-Hybrid, a hybrid wake rotorcraft CFD code that is coupled to DYMORE, is used. A vortex particle method has been implemented, in place of the existing lattice wake methodology, that has been anticipated to better emulate a convecting wake of a rotor while providing some computational benefits. Several UH-60A flight conditions, including high-speed steady level flight as well as diving-turn and pull-up maneuvers, are simulated using the vortex particle method. Results are compared with those using the traditional wake method and available experimental data both qualitatively and quantifiably. The quantifiable comparison, which consists of a linear regression analysis, shows the vortex particle method improves prediction accuracy for maneuvers and has only minor effects on steady forward flight when compared to the lattice method results. Additionally, computational efficiency is improved by using the vortex particle method and time savings exist in every simulation.
Aerodynamics and aeroacoustic sources of a coaxial rotor

(Georgia Institute of Technology, 2018-04-10) Schatzman, Natasha Lydia

Vehicles with coaxial, contra-rotating rotor systems (CACR) are being considered for a range of applications, including those requiring high speed and operations in urban environments. Community and environmental noise impact is likely to be a concern in these applications. Design parameters are identified that effect the fundamental aerodynamics and fluid dynamic features of a CACR in hover, vertical, and edgewise flight. Particular attention is paid to those features affecting thickness, loading, blade vortex interaction (BVI), and high speed impulsive (HSI) noise. Understanding the fluid dynamic features is a precursor to studying the aeroacoustics of a coaxial rotor. Rotor performance was computed initially using Navier-Stokes solver with prescribed blade section aerodynamic properties, the results validated against generic experimental test cases. The fluid dynamics of blade interactions was simplified and broken into a 2-D blade crossing problem, with crossing locations and velocity fields from the rotor results. Two trains of 8 airfoils passing were simulated to understand the effects due to shed vorticity. The airfoils are displaced vertically by a distance equivalent to the typical spacing between the upper and lower rotors of a coaxial system. A 2D potential flow code and 2D OVERFLOW compressible-flow Navier-Stokes solver were used to investigate the complex coaxial rotor system flow field. One challenge of analyzing the CACR is the difficulty in envisioning all the possible interactions and their possible locations as flight conditions and rotor designs change. A calculation tool has been developed to identify time and location of blade overlap. The tool was then integrated with a wake aerodynamics model to identify locations and instances of upper rotor tip vortex interaction with a lower rotor blade. This tool enables rapid identification of different types of BVI based on relative rotor orientation. Specific aerodynamic phenomena that occur for each noise source relevant to CACR are presented, along with computational tools to predict these occurrences.
Assessment of the icing characteristics of single and coaxial rotors

(Georgia Institute of Technology, 2016-12-06) Obayashi, Nana

Icing on blade surfaces adversely affects the aerodynamic performance and safety of helicopters through loss of lift, loss of power, increase in drag, decrease in stall angle and dangerous ice shedding events. Equipping rotor blades against the effects of icing increases the helicopter cost and puts higher demand on the power plant. In the field of CFD, efforts have focused on modeling the effects of icing, including the resulting rotor performance degradation. Single rotor helicopters have been the primary focus of existing models for ice accretion, leaving an opportunity to expand modeling efforts to other types of helicopters, such as coaxial rotors. Although the coaxial rotor has a number of advantages attributed to its symmetric aerodynamic environment in any flight direction, additional work is needed using physics-based models, in order to analyze the complex flow interactions between the upper and lower blades. An in-house ice accretion model was improved upon prior work by implementing a 3-D Eulerian approach integrated into the CFD flow solver, GT-Hybrid, in order to solve for water droplet collection efficiency on the surface of the rotor blade. This model implements an extended Messinger model with the Stefan condition at the ice/water interface in order to predict ice accretion based on droplet collection and establishment of a thermodynamic balance for phase shift. These improvements have allowed this model to reduce the limitations and empiricism inherent in existing models. The model has been validated based on a limited number of cases with promising predictive power compared to the industry standard ice accretion model by NASA, called LEWICE. The present work contributes to the efforts behind the in-house ice accretion model in two ways. First, ice shape prediction using the in-house model is validated against existing experimental ice accretion data for a single rotor configuration in three different flight conditions. An analysis of the simulated and experimental results presented shows promising evidence of the model’s predictive power, especially at the inboard blade locations where the ice is predominantly rime. Second, the in-house model is adapted for application to a coaxial rotor configuration. In order to validate the flow solution, performance analysis is completed for a coaxial rotor in hover using GT-Hybrid and Star-CCM+ in the absence of ice accretion. Then, ice accretion is simulated for the same rotor for three collective pitch angles and the ice shapes are presented. Finally, the performance degradation of the coaxial rotor due to ice is estimated.
A new rotorcraft design framework based on reliability and cost

(Georgia Institute of Technology, 2016-07-26) Scott, Robert C.

Helicopters provide essential services in civil and military applications due to their multirole capability and operational flexibility, but the combination of the disparate performance conditions of vertical and cruising flight presents a major compromise of aerodynamic and structural efficiency. In reviewing the historical trends of helicopter design and performance, it is apparent that the same compromise of design conditions which results in rotorcraft performance challenges also affects reliability and cost through vibration and fatigue among many possible factors. Although many technological approaches and design features have been proposed and researched as means of mitigating the rotorcraft affordability deficit, the assessment of their effects on the design, performance, and life-cycle cost of the aircraft has previously been limited to a manual adjustment of legacy trends in models based on regression of historical design trends. A new approach to the conceptual design of rotorcraft is presented which incorporates cost and reliability assessment methods to address the price premium historically associated with vertical flight. The methodology provides a new analytical capability that is general enough to operate as a tool for the conceptual design stage, but also specific enough to estimate the life-cycle effect of any RAM-related design technology which can be quantified in terms of weight, power, and reliability improvement. The framework combines aspects of multiple design, cost, and reliability models – some newly developed and some surveyed from literature. The key feature distinguishing the framework from legacy design and assessment methods is its ability to use reliability as a design input in addition to the flight conditions and missions used as sizing points for the aircraft. The methodology is first tested against a reference example of reliability-focused technology insertion into a legacy rotorcraft platform. Once the approach is validated, the framework is applied to an example problem consisting of a technology portfolio and a set of advanced rotorcraft configurations and performance conditions representative of capabilities desired in near-future joint service, multirole rotorcraft. The framework sizes the different rotorcraft configurations for both a baseline set of assumptions and a tradespace survey of reliability investment to search for an optimum design point corresponding to the level of technology insertion which results in the lowest life-cycle cost or highest value depending on the assumptions used. The study concludes with a discussion of the results of the reliability trade study and their possible implications for the development and acquisition of future rotorcraft.