bluuebunny/crossref_metadata_2025 huggingface dataset:
Freezing of Molten Solder Droplets Impacting Onto Flat Substrates in Microgravity
Authors: Haferl Stephan E. , Butty Vincent , Poulikakos Dimos , Giannakouros Johannes , Boomsma Kevin , Megaridis Constantine M. , Nayagam Vedha
Published: November 2021

The axisymmetric impingement of solidifying molten solder droplets onto smooth metallic substrates in a microgravity environment is investigated numerically to provide basic information of the heat and fluid flow phenomena and to determine the governing parameters of the process. The numerical predictions are also tested against experimental data. Millimeter-sized droplet impact events in reduced gravity are employed for scale up modeling of the impingement of picoliter size droplets of molten eutectic 63%Sn-37%Pb solder used in electronic chip packaging. The present article reports on both numerical (the main focus of the paper) as well as experimental work. To this end, the employed numerical model considers the axisymmetric impact and subsequent solidification of an initially spherical, molten solder droplet on a flat, metallic substrate. The laminar Navier-Stokes equations, combined with the energy transport equations are solved simultaneously in the liquid region (melt) using a Lagrangian approach. In the solid (substrate and solidified droplet material) the heat conduction equation is solved. A time and space averaged model of the thermal contact resistance between the impacting droplet and the substrate, is also incorporated in the model. The numerical model is solved using a Galerkin finite element method, where a deforming, adaptive triangular-element mesh is employed to accurately simulate the large-domain deformations caused by the spreading and recoiling of the impinging droplet. The experimental work has been conducted in reduced gravity with technically relevant impact velocities of ∼0.2m/s, in order to provide validation of the numerical predictions. In reduced gravity of 2×10−4g to 5×10−4g, the impact conditions correspond to Re = O(100), We = O(1), and Fr = O(10000), Ca = O(0.001). Presentation of the numerical results in terms of the Froude and the Ohnesorge numbers aided their interpretation Among the results that stand out is the formation of a large number of frozen ripples on the droplet surface as a result of the simultaneous manifestation of rapid oscillations and solidification. Furthermore, a non-intuitive behavior of the solidification times is reported. To this end, the dependence of the final solidification time on the Froude number (representing the variation of the impact velocity) was not monotonic and featured a distinct minimum for all values of Ohnesorge numbers in this study. Despite the complexity of the phenomenon, the numerical model captures well the main features of the experimental results. In addition, it gives key insights on the influence of the Ohnesorge and Froude numbers on the solidification process.
Thermal Characteristics of a Compact, Passive Thermal Energy Storage Device
Authors: Bauer Candice A. , Wirtz R. A.
Published: November 2021

A Thermal Energy Storage (TES) system uses a Phase Change Material (PCM) to store heat during peak power operation of variable power dissipating devices via the latent heat effect. The TES composite developed is a plate-like structure that consists of a central core of foamed aluminum that is packed with a PCM. By considering the elements of the composite to be thermal resistors and constructing a flat-plate thermal conductivity apparatus, the plate-to-plate effective thermal conductivity is determined. The composite effective thermal conductivity is primarily composed of the thermal conductivity of the aluminum foam which is reduced by the effect of the aluminum foam-to-plate bond resistance. Heat flow through the PCM slightly augments the effective thermal conductivity. An increase in aluminum foam metal fraction results in an increase in the effective thermal conductivity of the composite because only about 2% of the heat flow is through the PCM, and the interfacial bond resistance decreases due to increased contact area. The trade-off is that as there is an increase in aluminum foam metal fraction, the volumetric latent heat decreases; thus, the storage time is reduced.
The Design of a Thermochromic Liquid Crystal Based Flow Visualization Surface
Authors: Lussier Brett A. , Lupino Gina , Anderson Ann M.
Published: November 2021

This paper describes the design, construction and testing of a thermochromic liquid crystal based, non-intrusive, surface flow visualization system. The system uses a pin-finned heat sink in contact with a thin sheet of liquid crystals and is easily mounted in a wind tunnel. When heated and placed in a fluid flow, the pin-finned heat sink produces teardrop-shaped thermal wakes that indicate the direction of the flow. We performed an optimization experiment and determined that the best flow visualization images are achieved for heat sink base temperatures that are 10–20 °C above the liquid crystal activation temperature. Under these conditions, the full range of the liquid crystals is utilized. We present liquid crystal flow visualization results for flow about streamlined and blunt objects and demonstrate the performance of the liquid crystal surface. We also compare liquid crystal images for flow about a blunt body to PIV data and show good qualitative agreement. The technique is repeatable, non-intrusive and instructive for learning about surface flow characteristics.
A Comparative Case Study in the Development of Thermal Manufacturing Curricula
Authors: Smith R. N. , Doumanidis H. C.
Published: November 2021

A collaboration between faculty at Tufts University and Rensselaer Polytechnic Institute has initiated a research-curriculum development program to promote high level technology transfer both with the classroom and through other educational venues in the area of Thermal Manufacturing and Materials Processing. One central aspect of this collaboration is the concurrent development of two new graduate courses at these respective institutions. The specific content of each of the two courses will be described in some detail in addition to some of the developmental background that constrained them. In particular, the technology transfer issue will be discussed, including a goal to communicate to a much wider audience some of the advances in this technical area without requiring a graduate level heat transfer background. Additional issues include our experiences with distance learning in thermal manufacturing and with the development of curriculum materials for use in other courses, at the graduate and undergraduate level, at both institutions.
Heat Transfer Coefficients for Simultaneously Developing Flow in Rectangular Tubes
Authors: Garimella Srinivas , Dowling William J. , Van derVeen Mark , Killion Jesse D.
Published: November 2021

A study of heat transfer in simultaneously developing flow through rectangular tubes is presented in this paper. Heat transfer coefficients were measured for three different tube sizes and shapes (Dh = 2.21 mm, α = 0.050; Dh = 3.02 mm, α = 0.108; and Dh = 1.74 mm, α = 0.029), which correspond to typical dimensions used in automotive heat exchangers. For each of these tubes, several different tube lengths were tested to measure the effect of developing flow on the Nusselt number. The study primarily focussed on the laminar and transition regimes, with some data in the turbulent regime, which is typical of the operating conditions for many automotive heat exchangers. The results demonstrate that developing flow enhances Nusselt numbers, especially for the short tubes used in heater cores, although for the geometry range studied, the effect of aspect ratio was not very significant. Heat transfer correlations were developed from the data, with excellent agreement between the data and the values predicted by these correlations. These correlations accounted for the effects of Reynolds number (118 < Re < 10671) Prandtl number (6.48 < Pr < 16.20), and bulk-to-wall property variations (0.243 < μb/μw < 0.630), and geometric features such as tube length, hydraulic diameter, and aspect ratio.
Fluid Mechanics and Biological Interaction in a Tubular Nitrifier Designed for Use in Space
Authors: Pickering Karen D. , Ungar Eugene K. , Vega Leticia M. , Campbell Melissa L.
Published: November 2021

Biological processes are currently being investigated for use in spacecraft wastewater treatment. In a biological wastewater processor, microorganisms are used to degrade organic and inorganic contaminants to carbon dioxide, water, and other metabolic products. One step in the process is nitrification, in which ammonium ions in the wastewater stream are converted to nitrate ions. Traditional reactor designs for nitrification, which include continuously stirred tank reactors and trickling filters, are unsuitable for use on spacecraft due to their reliance on gravity for aeration. A tubular reactor for aerobic nitrification in a microgravity environment has been developed to allow use of biological systems for wastewater treatment on spacecraft. The tubular reactor uses a 3.2 mm ID tube 305 m long with co-current air and wastewater flow. Aerobic microbes grow on the tube walls. Because of the small tube diameter and the high surface tension of the wastewater, the air/wastewater flow is gravity independent. Thus it is expected that the fluid flow and biological performance will be identical in Earth-normal gravity and in flight.
Uncertainty Estimation in the Determination of Thermal Conductivity of 304 Stainless Steel
Authors: Blackwell Bennie F. , Gill Walter , Dowding Kevin J. , Easterling Robert G.
Published: November 2021

The thermal conductivity of 304 stainless steel has been estimated from transient temperature measurements and knowing the volumetric heat capacity. Sensitivity coefficients were used to guide the design of this experiment as well as to estimate the confidence interval in the estimated thermal conductivity. The uncertainty on the temperature measurements was estimated by several means, and its impact on the estimated conductivity is discussed. The estimated thermal conductivity of 304 stainless steel is consistent with results from other sources.
Direct Refrigeration by Electron Field Emission From Diamond Microtips
Authors: Fisher T. S. , Walker D. G.
Published: November 2021

This paper describes a concept for creating high-capacity, direct electrical-to-thermal energy conversion for compact cooling based on electron field emission. Electron field emission involves the transport of electrons that tunnel through a potential barrier. The thermodynamics of field emission have remained relatively unexplored. However, emission from wide-band-gap semiconductors, such as diamond, is known to produce an energy filtering effects such that high-energy electrons possess higher probabilities of emission. Lower energy electrons replace the emitted electrons, and thus, this process can produce a refrigeration effect. The refrigeration capacity is proportional to the emission current density, which is very high for diamond emitters. This high electrical current density implies that high thermal current densities are possible. The present work provides a thermodynamic analysis and energy conversion predictions based on experimental current-voltage data from diamond tip emitters. Energy fluxes in excess of 100 W/cm2 are predicted by the theory for room-temperature operation.
Modeling Film-Coolant Flow Characteristics at the Exit of Shower-Head Holes
Authors: Garg Vijay K.
Published: November 2021

The coolant flow characteristics at the hole exits of a film-cooled blade are derived from an earlier analysis where the hole pipes and coolant plenum were also discretized. The blade chosen is the VKI rotor with three staggered rows of shower-head holes. The present analysis applies these flow characteristics at the shower-head hole exits. A multi-block three-dimensional Navier-Stokes code with Wilcox’s k-ω model is used to compute the heat transfer coefficient on the film-cooled turbine blade. A reasonably good comparison with the experimental data as well as with the more complete earlier analysis where the hole pipes and coolant plenum were also gridded is obtained. If the 1/7th power law is assumed for the coolant flow characteristics at the hole exits, considerable differences in the heat transfer coefficient on the blade surface, specially in the leading-edge region, are observed even though the span-averaged values of h match well with the experimental data. This calls for span-resolved experimental data near film-cooling holes on a blade for better validation of the code.
A Numerical Analysis of Gas Turbine Disks Incorporating Rotating Heat Pipes
Authors: Cao Y. , Ling J. , Rivir R. , MacArthur C.
Published: November 2021

Radially rotating heat pipes have been proposed for cooling gas turbine disks working at high temperatures. A disk incorporating the heat pipe would have an enhanced thermal dissipation capacity and a much lower temperature at the disk rim and dovetail surface. In this paper, extensive numerical simulations have been made for heat-pipe-cooled disks. Thermal performances are compared for the disks with and without incorporating the heat pipe at different heating and cooling conditions. The numerical results presented in this paper indicate that radially rotating heat pipes can significantly reduce the maximum and average temperatures at the disk rim and dovetail surface under a high heat flux working condition. In general, the maximum and average temperatures at the disk rim and dovetail surface could be reduced by above 250 and 150 degrees, respectively, compared to those of the disk without the heat pipe. As a result, a disk incorporating radially rotating heat pipes could alleviate temperature-related problems and allow a gas turbine to work at a much higher temperature.
Neural Network Based Control of Preform Permeation in Resin Transfer Molding Processes With Real-Time Permeability Estimation
Authors: Nielsen David , Pitchumani Ranga
Published: November 2021

Variabilities in the preform structure in situ in the mold are an acknowledged challenge to effective permeation control in the Resin Transfer Molding (RTM) process. An intelligent model-based controller is developed which utilizes real-time virtual sensing of the permeability to derive optimal decisions on controlling the injection pressures at the mold inlet ports so as to track a desired flowfront progression during resin permeation. This model-based optimal controller employs a neural network-based predictor that models the flowfront progression, and a simulated annealing-based optimizer that optimizes the injection pressures used during actual control. Preform permeability is virtually sensed in real-time, based on the flowfront velocities and local pressure gradient estimations along the flowfront. Results are presented which illustrate the ability of the controller in accurately steering the flowfront for various fill scenarios and preform geometries.
Parametric Study of the Ablation Characteristics of Absorbing Dielectrics by Short Pulse Laser
Authors: George Samuel , Mitra Kunal
Published: November 2021

This paper investigates the effect of ablation of absorbing dielectrics by two successive ultra short pulses from an excimer laser source. The numerical model is based on two photon absorption followed by thermal degradation and diffusion. Unlike most previous studies the present formulation considers the transient nature of laser propagation within the medium. Heating of the material is dependent on light absorption by chromophores while ablation occurs through sublimation of the material from the surface. The mathematical formulation takes into consideration the saturation effects within the framework of a three level system of the electronic structure of chromophores. This involves solving a set of coupled rate equations, heat diffusion equation, and the transient radiative transport equation, using Fromm’s scheme. Results for the temperature distribution and ablation depth are obtained for different laser parameters and material properties. Parametric study of the delay time between two successive pulses, laser pulse width, laser fluence, activation energy, and the relaxation time is only performed in this paper for the purpose of brevity. The results obtained by the consideration of the transient radiative transfer equation are compared with the steady state formulation and significant differences are observed in the temperature profiles and the ablation depth.
Effective Thermal Conductivity of Compressed Woods
Authors: Asako Y. , Nishimura H. , Kamikoga H. , Yamaguchi Y.
Published: November 2021

The total amount of lumbers consumed in Japan during a year, reaches to 1.1 billion cubic meter. However, 75 percent of them are imported. The resource of same 1.1 billion cubic meters is growing up every year in the domestic forest. This is due to the price difference between the domestic and imported lumbers. It is strongly required to improve the quality of the domestic lumber. One solution of the improvement of the domestic lumber is the compression of the wood. It results in a good strength characteristics. However, the thermal characteristics of the compressed wood has not been reported yet. In this study, the effective thermal conductivity of compressed Japanese cedar (cryptomeria japonica) were measured. And the characteristics of the effective thermal conductivity are discussed.
Optimization of Vacuum Assisted Resin Transfer Molding for Sandwich Panels
Authors: Dai Jean , Pellaton Dominique , Hahn H. Thomas
Published: November 2021

The vacuum assisted resin transfer molding (VARTM) of sandwich panels may be facilitated by using high permeability layers over the skins or adding grooves in the surfaces of the core. The present paper investigates the advantages and disadvantages of both methods in terms of manufacturing cost and time through simulations and experimental observations. Before comparison, each method is optimized through simulations. The panel geometry and the injection pressure are held constant. The design parameters are the number of high permeability layers, and the number and size of grooves. The optimized processes are finally compared with each other in terms of the aforementioned cost and time. Meanwhile, the sensitivities of several important parameters in the cost model to the optimal result are studied.
Study on the Behavior of a Wetted Area Right After Liquid-Wall Contact in Pool Film Boiling
Authors: Ohtake Hiroyasu , Satoh Hiroyuki , Koizumi Yasuo
Published: November 2021

The behaviors of the rewetting on pool film boiling, focusing on observations of a collapse of a vapor film, a wetted area and a contact angle on a superheated surface were investigated experimentally. Using a U-shaped platinum wire with 2 mm diameter and 140 mm long, pool film-boiling experiments were performed for saturated water at atmospheric pressure. After a stable film-boiling state at a prescribed initial wall temperature was established, saturated water from a nozzle, set above the test wire, was injected on the superheated surface in the stable film-boiling, then artificial rewetting was forced on the superheated surface. During forming the artificial rewetting, the temperature fluctuation right under the liquid injection and the behavior of the rewetting were obtained for the initial wall temperatures of 600, 420, 400 and 300 degree-C, respectively. The present experimental results showed that the propagative collapse of the vapor film occurred when the initial wall superheat was below 300 K. On the other hand, above the initial wall superheat of 320 K, the rewetting declined after liquid injection was finished then film boiling recovered. The temperature was related to the thermodynamic limit of superheat, according to the measured temperature fluctuation during supplying the liquid. The wetted area right after liquid-wall contact and the advancing velocity of the rewetting front increased as the initial wall superheat decreased. The measured angles between the liquid-vapor interfacial line and the heated wall corresponded to dynamic contact angles were close to the dynamic advancing contact-angles in room temperature.
Mixing of Two Streams, Steam and Water, in a Converging Nozzle
Authors: Aybar Hikmet S.
Published: November 2021

Mixing of two fluid streams can be seen in many applications in chemical processing and energy generation industries. The supersonic steam blows into the cold water in the mixing nozzle. When the steam condenses, steam transfers to water heat and mass (because of the temperature difference and condensation) and momentum (because of the velocity difference). The condensation should be fully completed before the end of mixing nozzle. Thus, the length of the mixing nozzle is important parameter. After the condensation is completed, the flow is single phase, that is, liquid water, and the subsonic water flows in the converging nozzle. In this study, the mixing of the supersonic steam and subsonic water in a converging nozzle is investigated. The problem is modeled using one-dimensional continuity, momentum and energy equations, and solved numerically. For the calculation of the rate of condensation, a correlation for the contact heat transfer coefficient is used.
Thermal Spreading Resistance of Eccentric Heat Sources on Rectangular Flux Channels
Authors: Muzychka Y. S. , Culham J. R. , Yovanovich M. M.
Published: November 2021

A general solution, based on separation of variables method for thermal spreading resistances of eccentric heat sources on a rectangular flux channel is presented. Solutions are obtained for both isotropic and compound flux channels. The general solution can also be used to model any number of discrete heat sources on a compound or isotropic flux channel using superposition. Several special cases involving a single and multiple heat sources are presented.
Transient Axial Free Jet Impinging Over a Flat Uniformly Heated Disk: Solid–Fluid Properties Effects
Authors: Bula Antonio J. , Rahman Muhammad M. , Leland John E.
Published: November 2021

Transient conjugate heat transfer process during axial free jet impingement on a solid disk of finite thickness was considered. As the fluid reached steady state, power was turned on and a uniform heat flux was imposed on the disk at its opposite surface. The numerical model considered both solid and fluid regions. Equations for conservation of mass, momentum, and energy were solved in the liquid region taking into account the transport processes at the inlet and exit boundaries, as well as at the solid-liquid and liquid-gas interfaces. Inside the solid, only the heat conduction equation was solved. The shape and location of the free surface (liquid-gas interface) was determined iteratively as a part of the solution process by satisfying the kinematic condition as well as the balance of normal and shear forces at this interface. A non-uniform grid distribution, captured from a systematic grid-independence study, was used to adequately accommodate large variations near the solid-fluid interface. Computed results include the simulation of six different substrate materials namely, aluminum, constantan, copper, diamond, silicon, and silver, and three different impinging liquids, FC - 77, Mil - 7808, and water. The solids and fluids selected covered a wide range of possibilities of conjugate heat transfer phenomena. The analysis performed showed that the thermal storage capacity, defined as density times specific heat, is an important factor defining which material will attain steady state faster during conjugate heat transfer process, like the thermal diffusivity does it for pure conduction heat transfer.
Comparison of Laser-Ceramic and Laser-Metal Material Processing
Authors: Deng G. , Gordon M. H. , Roe L. A. , Malshe A. P. , Schmidt W. F.
Published: November 2021

In an effort to better understand and thereby utilize laser processing, an existing code describing laser-metal (aluminum) interaction is modified to describe laser-ceramic (diamond) interaction. Comparisons between our modified code (diamond target) and the original code (aluminum target) highlight similarities and differences between laser-ceramic and laser-metal processing. Gas breakdown effects, which are expected for the simulated short (time duration), high energy laser pulses, are observed in both codes. Due to the lower sublimation heat of aluminum (1.1×104J/g) compared to diamond (5.3×104J/g), aluminum vaporizes more quickly and exhibits a faster expansion speed (1.4×107 cm/sec compared to 8×106 cm/sec for diamond) in the early stage of the laser pulse. Because aluminum requires significantly more energy to fully ionize than does carbon, our simulations show that the diamond plasma is fully ionized (6 of 6 electrons per atom) and the aluminum plasma is partially ionized (11 of 13 electrons per atom).
The Use of a Multizone Model for Prediction of Soot and NOx Emission in a D.I. Diesel Engine as a Function of Intake Air O2 Content
Authors: Gao Zhiming , Schreiber Will
Published: November 2021

A phenomenological model based on the use of multiple zones is described and compared with other experimental and analytical work. This multizone model is used to examine the effect on emissions of increasing the oxygen concentration in the intake air of a compression-ignition, direct-injection engine. It is concluded that O2-enriched air could only be useful if combined with other modifications such as auxiliary gas injection, split injection, and exhaust gas recirculation.
Heat Transfer in Suddenly Expanded Flow in a Channel With Porous Inserts
Authors: Rocamora Francisco D. , de Lemos Marcelo J. S.
Published: November 2021

This paper presents numerical results for laminar heat transfer and turbulent flow past a backward-facing step channel with and without a porous insert. The effects of thickness and permeability of the inserts on flow pattern and heat transfer features are assessed. It is found that for some combinations of thickness and permeability, the recirculating bubble right after the step is completely suppressed, improving the heat transfer characteristics for the lower wall.
On the Wall Boundary Condition for Computing Turbulent Heat Transfer With K–ω Models
Authors: Bredberg J. , Peng S.-H. , Davidson L.
Published: November 2021

A new wall boundary condition for the standard Wilcox’s k–ω model (1988) is proposed. The model combines a wall function and a low-Reynolds number approach, and a function that smoothly blends the two formulations, enabling the model to be used independently of the location of the first interior computational node. The model is calibrated using DNS-data for a channel flow and applied to a heat transfer prediction for a flow in a rib-roughened channel (Reb = 100 000). The results obtained with the new model are improved for various mesh sizes and are asymptotically identical with those of the standard k–ω turbulence model.
Inverse Heat Flux Problem in Quenching
Authors: Alam M. Khairul , Kuriger Rex J. , Zhong Rong
Published: November 2021

The quenching process is an important heat treatment method used to improve material properties. However, the heat transfer during quenching is particularly difficult to analyze and predict. To collect temperature data, quench probes have been used in controlled quenching experiments. The process of determination of the heat flux at the surface from the measured temperature data is the Inverse Heat Conduction Problem (IHCP), which is extremely sensitive to measurement errors. This paper reports on an experimental and theoretical study of quenching which is carried out to determine the surface heat flux history during a quenching process by an IHCP algorithm. The inverse heat conduction algorithm is applied to experimental data from a quenching experiment. The surface heat flux is then calculated, and the theoretical curve is compared with experimental results.
Role of Vibration-Induced Streaming in Float-Zone Crystal Growth
Authors: Anilkumar Amrutur V. , Grugel Richard N.
Published: November 2021

The streaming induced in a short vertical liquid column by the vibration of one of the supporting end walls has been utilized in this novel study. Vibration essentially drives a surface flow in the zone away from the vibrating wall, with the return flow in the bulk towards the wall. Preliminary measurements of the surface streaming velocity show that it increases with the frequency and amplitude of vibration and the zone length, and decreases with the viscosity of the zone liquid. This controlled surface streaming has been employed to balance a opposing, steady thermocapillary flow in model half-zones of silicone oil and Sodium Nitrate. In addition, in a float-zone solidification experiment with Sodium Nitrate - Barium Nitrate eutectic as the study material, we have demonstrated that streaming-based balancing of thermocapillary flow promotes a planar solid/liquid interface and a uniform microstructure.
Design of a Biomimetic Directional Microphone Diaphragm
Authors: Gibbons C. , Miles R. N.
Published: November 2021

A miniature silicon condenser microphone diaphragm has been designed that exhibits good predicted directionality, sensitivity, and reliability. The design was based on the structure of a fly’s ear (Ormia ochracea) that has highly directional hearing through mechanical coupling of the eardrums. The diaphragm that is 1mm × 2mm × 20 microns is intended to be fabricated out of polysilicon through microelectromechanical micromachining. It was designed through the finite-element method in ANSYS in order to build the necessary mode shapes and frequencies into the mechanical behavior of the design. Through postprocessing of the ANSYS data, the diaphragm’s response to an arbitrary sound source, sensitivity, robustness, and Articulation Index - Directivity Index (AI-DI) were predicted. The design should yield a sensitivity as high as 100 mV/Pa, an AI-DI of 4.764 with Directivity Index as high as 6 between 1.5 and 5 kHz. The diaphragm structure was predicted be able to withstand a sound pressure level of 151.74 dB. The sound level that would result in collapse of the capacitive sensor is 129.9 dB.. The equivalent sound level due to the self-noise of the microphone is predicted to be 30.8 dBA.
Prediction of Turbulence Ingestion Forces for Rotors With Arbitrary Rake and Skew
Authors: Gavin Joseph R. , Lauchle Gerald C. , Jonson Michael L.
Published: November 2021

It is well known that turbomachinery rotors produce low frequency forces when subjected to a turbulent inflow. Predictions to date have been based largely upon idealizations of radial blades operating in homogeneous isotropic turbulence. In the present work these models are slightly extended to include the effects of complex blade geometry. The credibility of the method is then tested through comparison to existing experimental data. These comparisons show that the method performs well regarding the shape of the frequency spectrum and the relative effects of complex blade geometries. However, the method tends to sometimes overestimate the absolute levels of the thrust spectra.
Realization of a Minimum-Order Power Flow Model and SEA Model Updating Using Time Domain Measurements
Authors: Gregory Joseph W. , Keltie Richard F. , Caulfield F. Donald
Published: November 2021

A time domain method for identifying middle to high frequency system parameters from sound and vibration measurements is presented. This work is part of a beginning investigation with an objective of enhancing experimental Statistical Energy Analysis (SEA). Thus far, it is seen that a state space realization method can be used to identify a first order power flow model from measured transient power and energy data. Specifically, the Eigensystem Realization Algorithm (ERA) is observed to accurately identify a minimum order model for a simple system. Additionally, it is found that the identified model can be used to improve an existing SEA model of the system.
Identification of Complex Noise Sources Using the HELS Method
Authors: Wu Sean F. , Rayess N. E. , Shiau Mae-Ming
Published: November 2021

In this paper, the Helmholtz Equation Least Squares (HELS) method (Wang and Wu, 1997; Wu and Wang, 1998; Wu and Yu, 1998; Wu, 2000) is used to reconstruct the radiated acoustic pressure fields from a replicated vehicle front end. To simulate sound radiation from a real vehicle, an engine noise simulator (ENS) is installed inside the front end at the location of the engine. The white noise emitted from the ENS is measured by a microphone. For convenience, measurements are taken over finite planar surfaces above, in front, and alongside of the structure. These measured data are taken as input to the HELS formulation to reconstruct the acoustic pressures on the top, front, and side surfaces of the vehicle. The reconstructed acoustic pressures are then compared with measured ones at the same locations. Also shown are comparisons of the reconstructed and measured acoustic pressure spectra at various locations on the surface. Results show that satisfactory reconstruction can be obtained based on relatively few measurements taken in the field. Experiments indicate that the accuracy of reconstruction can be further improved by taking more measurements over a conformal surface around the structure at closer range. However, planar measurements are easier to implement in practice, while conformal measurements often requires a programmed robot arm which may make the reconstruction process more costly. In any event, the HELS method has proven to be effective in reconstructing the radiated acoustic pressure field from a non-spherical source in the low-to-mid frequency and may become potentially a viable noise diagnostic tool for the practicing engineers.
A Source Reconstruction Process Based on an Indirect Variational Boundary Element Formulation
Authors: Zhang Zhidong , Vlahopoulos Nickolas , Allen T. , Zhang K. Y.
Published: November 2021

The objective of the work presented in this paper is the development of a computational capability for recreating the vibration of a source from acoustic field data. The formulation is based on the indirect variational boundary element method (IVBEM). The vibration of the source is computed from transfer functions defined between the field points and the surface of the source. The capability to account for the presence of obstacles in the field adjacent to the vibrating sources and the treatment of irregular frequencies are included in the IVBEM formulation. A singular value decomposition (SVD) solver is integrated with the IVBEM computations in order to evaluate the vibration of the source. An algorithm that identifies the optimum field points where the acoustic pressure of the original field must be prescribed in order to accomplish the most efficient source reconstruction is also developed. Several validation and application cases are presented.
Monitoring and Defect Detection of an All-Composite Road Bridge
Authors: Crane Roger M. , Gillespie John W. , Heider Dirk , Eckel Douglas A. , Ratcliffe Colin P.
Published: November 2021

This paper presents the results of an ongoing investigation into the use of broadband vibration data to monitor the structural integrity and health of an all-composite road bridge. Bridge 1-351 on Business Route 896 in Glasgow, Delaware, was replaced with one of the first state-owned all-composite bridges in the nation in the fall of 1998. The bridge consists of two E-Glass/vinyl ester sandwich core sections (13-ft × 32 ft) joined by a longitudinal joint in the traffic direction. Each sandwich core section consists of a 28-inch deep core and 0.4-0.7-inch thick facesheets.

Vibration data were obtained from the upper and lower surfaces of the bridge using a mesh of 1050 test points. From the modal information and the visualization of the data, several aspects of the structural behavior of the bridge were obtained. These characteristics include the interactions between the bridge and abutments; the effectiveness of the longitudinal joint to couple the deck sections; the effectiveness of the core to couple the face sheets; and the structural integrity and dynamic consistency of the entire structure. Mode shapes and natural frequencies were determined and are correlated with theoretical calculations and vibration analyses conducted for this bridge.

A novel algorithm using the vibration data is being developed that enables local perturbations sensitive to the state of the material (e.g. manufacturing defects, material degradation or service damage) to be detected and spatially located in the bridge. This technique has been successfully validated for locating damage in 1-D beam structures and is being extended to the 3-D sandwich configuration of the bridge. By coupling this damage detection algorithm with the more conventional modal technique, the quality assurance/quality control and health monitoring of large composite bridge can be obtained.
Analysis of the Reflection Coefficient of Rayleigh Waves From Surface-Breaking Cracks
Authors: Hassan Waled , Veronesi William
Published: November 2021

The interaction of surface acoustic waves with finite-size, surface-breaking, semi-circular cracks is studied theoretically, numerically, and experimentally. We focus on the behavior of the reflection coefficient of the Rayleigh wave from such cracks in both the far and near fields of the crack. It is shown that, in the near field, the reflection coefficient from such cracks is higher than the reflection coefficient measured in the far field. This is mainly due to the diverging nature of the Rayleigh wave reflected from the crack. In the high crack depth to wave length ratio, the finite element and experimental results approach the limiting value of the reflection coefficient from a 90-degree corner.
Adaptation of a Combustion Chamber for Gasified Biomass Combustion: Numerical Simulations
Authors: Duwig Christophe , Fredriksson Jan , Fransson Torsten
Published: November 2021

A gas turbine combustor was modified for addition of Low Heating Value (LHV) gas operation while retaining the original diesel option. New fuel inlets were designed and tested through numerical simulations.

CFD calculations have been made in order to investigate the new design combustion abilities. A commercial 3D finite-volume Navier-Stokes solver was used. The Eddy Dissipation model was used to simulate the combustion phenomena and the flow fields were given by using k-ε model, Algebraic Stress Models and Reynolds Stress Model.

The comparison between predictions using different turbulence models and grids showed some differences. The required grid for having grid independent results was found too CPU expensive. However, comparisons were done to investigate the influence of the turbulence description on the result. This influence was found significant. It was deduced that the mixing controlled the combustion process. The numerical description of quenching of the flame was found to have more influence on the emission predictions than the description of the reacting zone (swirl).

Simulations validated the modified design. Successful combustion operating conditions have been predicted in terms of CO emission. Ammonia conversion to NO was also investigated. The conversion rate was found to be between 65 and 73 %. NO emissions have been predicted, as the maximum temperatures in the combustor were over-predicted, ammonia conversion to NO was also over valued. However, the results show that the combustion process of LHV gas within a small combustor volume is achievable. The swirl was found to be an efficient way to promote the combustion process by improving the mixing. High NO emissions have been predicted. It came from the high conversion rate of fuel ammonia into NO.
Effect of Reduced Inlet Space on a Medium Flow Coefficient Centrifugal Compressor Stage
Authors: Hohlweg William , Amineni Naresh
Published: November 2021

Test versus CFD predictions are presented for a medium flow coefficient, centrifugal compressor stage with 10% shorter axial stage space. Short axial length is achieved by reducing the shroud radius of curvature of the upstream return channel inlet. Situations often occur in multistage compressor applications where either rotor dynamics on new equipment or existing casing length on revamped units necessitate shorter stage space. The effect of the reduced space on various stage performance parameters is discussed referenced to the original, full length, stage design. CFD analysis for both configurations is also presented to compare with the test results and help explain the aerodynamic source of the increased losses. The complete stage is modeled on the program CFX-TASCflow beginning with a radial inlet and continuing through the impeller, diffuser and return channel.
Thermomechanical Transformation Fatigue of SMA Actuators
Authors: Lagoudas Dimitris C. , Li Changcheng , Miller David A. , Rong Lijian
Published: November 2021

Thermally induced transformation fatigue experiments of Shape Memory Alloy (SMA) actuator wires are performed under different heat treatment conditions and different stress levels. The effect of various heat treatment conditions on the thermal transformation fatigue life of Ti-Ni-Cu (K-alloy) SMA wires is analyzed first and the optimal heat treatment condition is found. Results are then presented for the plastic strain accumulation as a function of the number of cycles to failure for different stress levels, and a relationship similar to the Manson-Coffin law is considered. Finally, fatigue results for partial phase transformation cycles are discussed.
Texture Evolution Induced by Electric Field in Piezoelectric Ceramics
Authors: Wan Shan , Bowman Keith J.
Published: November 2021

Piezoelectricity is strongly dependent on the preferred domain orientation. A fiber-like texture of a Navy VI Lead Zirconate Titanate (PZT) piezoelectric ceramic can be induced by electric poling. This texture can be further changed and strengthened by cross-poling, that is, applying a strong electrical field perpendicular to the original poling direction. In this paper we show preferred domain orientation changes and anisotropy transitions associated with poling and cross-poling in PZT piezoelectric ceramic. The poling and cross-poling induced textures can be explained by three-dimensional orientation dependent domain switching. Based on this discussion, we demonstrate that it is possible to tailor the preferred domain orientation distribution and improve anisotropic properties of piezoelectric ceramics by directional control of the 90° domain switching using cross-poling.
Damage Detection in Simulated Aging-Aircraft Panels Using the Electro-Mechanical Impedance Technique
Authors: Giurgiutiu Victor , Zagrai Andrei
Published: November 2021

The aging of aerospace structures is a major current concern of civilian and military aircraft operators. PZT active sensors offer special opportunities for developing sensor arrays for in-situ health monitoring of aging aircraft structures. In this paper, we examine the structural health monitoring of aging aircraft structures with the electro-mechanical (E/M) impedance method. Local impedance methodology as well as damage detection strategy were developed. The detection of damage due to corrosion, structural cracks, and active sensor self-diagnostics with electro-mechanical (E/M) impedance method are discussed. The paper emphasis is sensor fabrication and installation procedures. Consistency and repeatability of sensor fabrication and installation were perfected and confirmed by statistical tests on a number of nominally identical specimens. Experiments on simple metallic beams were then performed and the results were compared with readily available theoretical predictions. Experiments on square plates manufactured from aircraft grade thin-gage stock followed. Statistical analysis of plate data confirmed that consistent and repeatability results could be achieved with our methodology. Finally, experiments on realistic aircraft panels with simulated crack and corrosion damage were performed. An array of four sensors were installed along a line emanating at a right angle from the crack, and E/M impedance readings were collected from all sensors. Consistency of sensor readings was verified. Also, the tendency of frequency to shift in the vicinity of the crack was noticed. However, further data processing, and detailed FEM modeling are still needed before full understanding of the correlation between crack presence and sensors readings is achieved.
Disturbance Rejection Control of an Electromagnetic Bearing Spindle
Authors: Petteys Rebecca , Parker Gordon , Redmond James
Published: November 2021

The force exerted on the rotor by an active magnetic bearing is determined by the current flow in the magnet coils. This force can be controlled very precisely, making magnetic bearings a potential benefit for grinding, where cutting forces act as external disturbances on the shaft, resulting in degraded part finish. It is possible to achieve precise shaft positioning, reduce vibration of the shaft caused by external disturbances, and even damp out resonant modes. Adaptive control is an appealing approach for these systems because the controller can tune itself to account for an unknown periodic disturbance, such as cutting or grinding forces, injected in to the system. In this paper we show how one adaptive control algorithm can be applied to an AMB system with a periodic disturbance applied to the rotor. An adaptive algorithm was developed and implemented in both simulation and hardware, yielding significant reductions in rotor displacement in the presence of an external excitation. Ultimately, this type of algorithm could be applied to a magnetic bearing grinder to reduce unwanted motion of the spindle which leads to poor part finish and chatter.
Efficiency of Frequency-Rectified Piezohydraulic and Piezopneumatic Actuation
Authors: Nasser Khalil , Leo Donald J.
Published: November 2021

Piezohydraulic and piezopneumatic frequency rectification is analyzed with a steady-state model of work and energy transfer. In this paper, piezohydraulic actuation is defined as the use of incompressible fluid to rectify the oscillatory motion of a piezoelectric device into unidirectional motion; piezopneumatic actuation is the use of a compressible gas such as air. The steady-state analysis is based on the definition of two efficiency metrics. The mechanical efficiency is defined as the ratio of mechanical work transfered to the load to the total mechanical work performed by the actuator, and the electrical efficiency is defined as the ratio of electrical energy expended to the peak energy required. The analysis demonstrates that piezohydraulic rectification is inherently more efficient than piezopneumatic rectification due to the assumption of fluid incompressibility. The mechanical effieciency is 100% when using incompressible fluid (ideal) but drops to below 40% when using compressible gas. The maximum electrical efficiency of piezohydraulic rectification is also four times higher than that of piezopneumatic actuation (29% to 7%). The overall efficiency of the rectification process (defined as the product of the mechanical and electrical efficiencies) is an order of magnitude greater when using incompressible fluid than when using compressible gas (29% to 2.8%). Thus, frequency rectification using compressible gas will require peak energy inputs that are ten times greater than that of incompressible fluid for an equivalent amount of mechanical work output. The significant difference in peak energy requirements is attributed to the reduced coupling between the actuator and the load that occurs due to compressibility of the gas. These results represent an upper bound on the efficiency because they neglect other sources of system losses, such as material hysteresis and frictional losses within the piston and seals of the actuator.