bluuebunny/crossref_metadata_2025 huggingface dataset:
Particle Size and Concentration Effects on Solid Particle Erosion With PIV Measurements of Particle Velocities
Authors: Rajkumar Yeshwanth R. , Shirazi Siamack A. , Karimi Soroor
Published: October 2020

Solid particle erosion is one of the most commonly encountered problems faced by the oil and gas industries during production and transportation processes. The severity of solid particle erosion is affected by multitude of factors such as particle properties, fluid flow properties and flow geometry, flow regime, and target material properties. The present work investigates the effect of particle size on solid particle erosion in gas flows. Sharp quartz particles with nominal sizes of 75, 150, 300 and 600 μm are used in this work. Particle Image Velocimeter (PIV) is used to measure the particles velocities distributions for various particle flow rates. An average particle velocity of 24 m/s is used to conduct erosion experiments for various particle sizes and two particle rates on Stainless Steel 316 at two different impact angles of 15 and 90 degrees. Comparison of measurements for two particle flow rates of approximately 0.02% and 0.002% by volumes demonstrates that increased particle flow rate can affect the carrier fluid’s flow field and change particle velocities within the carrying fluid. In the erosion experiments, the magnitude of erosion ratio increases as there is an increase in particle size. A preliminary erosion model is developed that can be used in CFD simulations of solid particle erosion for various particle sizes.
Theory of Uncertainty Analysis With Application to Naval Hydrodynamics (Keynote Paper)
Authors: Park Joel T.
Published: October 2020

The modern methodology for quantifying the quality of experimental data is uncertainty analysis. This paper is a review of current methods with some examples primarily from naval hydrodynamics. The methods described are applicable to fluids engineering. The paper discusses the history of uncertainty analysis, US and international standards on uncertainty analysis, verification and validation standards for computational fluid dynamics, and instrument calibration. One important result is that random loading in force calibration can produce a lower uncertainty estimate than sequential loading.
Physical and Rheological Properties of Active Fluids Under Shear Stress: Suspensions of Synechocystis
Authors: Mehdizadeh Allaf Malihe , Habibi Zahra , Samadi Zahra , DeGroot Christopher T. , Rehmann Lars , de Bruyn John R. , Peerhossaini Hassan
Published: October 2020

Design of photobioreactors (PBRs) for microalgae and cyanobacteria cultivation involves the interplay between fluid flow, microbe biokinetics, and radiative transport phenomena, in which the physical and rheological properties of the active fluid play a crucial role. In this study, we focus on the variation of physical and rheological properties of dilute suspensions of Synechocystis sp. CPCC534 with the shear stress applied to the fluid.

Experiments were carried out at three different stirring rates in well-controlled conditions and the results were compared with stationary conditions where only molecular diffusion and cell motility govern the transport phenomena, and cell growth. Our results show that the growth and biomass production of Synechocystis sp. under various shear conditions were improved significantly, and the yield was nearly doubled by adding agitation to the system.

The viscosity of Synechocystis suspensions, subjected to different shear stress levels, was measured with two different methods. The viscosity data showed shear stress independent Newtonian behavior. However, the viscosity of Synechocystis suspensions increased moderately with cell volume fraction up to 10%, beyond which it increased more rapidly. The shear stress history of the cell suspensions did not show any effect on the fluid viscosity.
CFD Simulation of Wall-Bounded Laminar Flow Through Screens: Part II — Mixing Characterization
Authors: Abou Hweij W. , Azizi F.
Published: October 2020

This paper characterizes the mixing behavior of laminar flows within a circular pipe equipped with plain woven meshes or screens, acting as static mixers. In this quest, their performance was numerically investigated using the Lagrangian particle method in a commercial CFD solver, whereby the effect of changing the screen geometry, number of screens, inter-screen spacing, and operating conditions were considered.

Mixing was addressed from a distributive and dispersive perspectives using both qualitative and quantitative descriptions. The distributive mixing indicated that a central injection of a single fluid should be coupled with a short inter-screen spacing to better spread the particles and enhance mixing as opposed to a larger inter-screen spacing. On the contrary, the mixing of two immiscible fluids of similar properties reveal that a large inter-screen spacing is recommended. From a dispersive mixing perspective, extensional efficiency contours revealed that the fluid would undergo all three modes of flow behavior, each of which dominating a certain region depending on the location with respect to the screen. Finally, it was interesting to find that a coarser screen geometry consistently outperformed finer screens in spreading and mixing the particles.
Stochastic Analysis of LES Atmospheric Turbulence Solutions With Generative Machine Learning Models
Authors: Rodriguez Arturo , Cuellar Carlos R. , Rodriguez Luis F. , Garcia Armando , Gudimetla V. S. Rao , Kotteda V. M. Krushnarao , Munoz Jorge A. , Kumar Vinod
Published: October 2020

The Large Eddy Simulations (LES) modeling of turbulence effects is computationally expensive even when not all scales are resolved, especially in the presence of deep turbulence effects in the atmosphere. Machine learning techniques provide a novel way to propagate the effects from inner- to outer-scale in atmospheric turbulence spectrum and to accelerate its characterization on long-distance laser propagation. We simulated the turbulent flow of atmospheric air in an idealized box with a temperature difference between the lower and upper surfaces of about 27 degrees Celsius with the LES method. The volume was voxelized, and several quantities, such as the velocity, temperature, and the pressure were obtained at regularly spaced grid points. These values were binned and converted into symbols that were concatenated along the length of the box to create a ‘text’ that was used to train a long short-term memory (LSTM) neural network and propose a way to use a naive Bayes model. LSTMs are used in speech recognition, and handwriting recognition tasks and naïve Bayes is used extensively in text categorization. The trained LSTM and the naïve Bayes models were used to generate instances of turbulent-like flows. Errors are quantified, and portrait as a difference that enables our studies to track error quantities passed through stochastic generative machine learning models — considering that our LES studies have a high state of the art high-fidelity approximation solutions of the Navier-Stokes. In the present work, LES solutions are imitated and compare against generative machine learning models.
Experimental Study of Evaporation Frictional Pressure Drop in Horizontal Enhanced Tube
Authors: Gu Zong-bao , Guo Yu , Ma Xiang , He Yan , Li Wei
Published: October 2020

An experimental investigation for evaporation frictional pressure drop in horizontal enhanced tubes with an outer diameter of 12.7 mm was studied using R410A as the working fluid. The experiment was conducted: the mass flux in the range of 100 kg/(m2s) to 200 kg/(m2s), over a vapor quality range of 0.2 to 0.8, an average saturation temperature at 279 K. The inner tubes were the tested tubes, which included a smooth tube, a three-dimensional enhanced tube (a tube enhanced by protrusions and petal arrays background patterns), respectively. The results show that the frictional pressure drop increases with the mass flux increasing. Moreover, the frictional pressure drop of the enhanced tube is 1.6∼2.4 times than that of the smooth tube. This is mainly due to the increase of the flow resistance inside the enhanced tube, which is caused by the increased interfacial turbulence, flow separation and secondary flow. It is also observed that the pressure drop increases with vapor quality increasing. In addition, some existing correlations are used to compare with our experimental data and verify their accuracy. A new modified correlation is proposed to predict the frictional pressure drop of EHT-1 tube.
Experimental and Numerical Investigation of Various Tube Geometries for Improved Heat Transfer in Solar Central Receivers
Authors: Ismail Salman M. , Rashwan Mohammed M. , Ghani Saud
Published: October 2020

Central receiver of Concentrated Solar Power technology constitutes 15% of the total initial cost and plays an important role in achieving high operating temperatures. Central receiver systems are composed of tubes with heat transfer fluid flowing inside that transports heat from radiation on the outer wall of tubes. This work investigates radiation heat transfer to fluid in tubes of various geometries. Experimental and numerical analysis were conducted to observe the boundary layer temperatures, bulk fluid temperatures, and fluid mixing near the tube walls. Four different samples of corrugated tubes adopted from literature were compared to a circular tube and a generic tube designed to provide larger surface area exposed to radiation without corrugation. The circular tube had high temperature in the boundary layer but low bulk fluid temperature due to lack of fluid mixing at wall. A spirally corrugated tube was found to have the highest bulk fluid temperature due to turbulent mixing and low temperature at boundary layer. The generic tube had higher bulk temperature compared to circular tube and two other corrugated tubes.
Fluid Dynamics Investigation on the Body Structure Inside a Sleeve Regulating Valve
Authors: Wu Jia-yi , Yue Yang , Yang Jia-ming , Jin Zhi-jiang , Qian Jin-yuan
Published: October 2020

The sleeve regulating valve is a typical flow regulating component, which is indispensable in various industrial applications. This work investigates the effects of the body structure on the overall performance and the flow characteristic of a sleeve regulating valve. The anterior cavity h, the diameter of the center cavity Dc, and the eccentricity of the center cavity e are studied in a parametric way. When the relative increment of h, Dc, and e all take the value of 0.15, the rated flow coefficient Kve of the optimized valve is promoted by 33.99% relative to the Kve of the original model. The optimized model presents less wear between the valve core and the sleeve relative to the original model. It results from the fact that the non-centrosymmetric pressure distribution is reduced on the valve core. Besides, the optimized model has smaller lateral fluid force imposed on the valve core FL than the original model when the relative travel L/Lmax > 0.625, and they have close FL in the other range. Also, the optimized model has larger axial fluid force imposed on the valve core FA than the original model when L/Lmax > 0.875, and they have close FA in the other range.
Investigation of Applying Physics Informed Neural Networks (PINN) and Variants on 2D Aerodynamics Problems
Authors: Tay Wee-Beng , Damodaran Murali , Teh Zhi-Da , Halder Rahul
Published: October 2020

Investigation of applying physics informed neural networks on the test case involving flow past Converging-Diverging (CD) Nozzle has been investigated. Both Artificial Neural Network (ANN) and Physics Informed Neural Network (PINN) are used to do the training and prediction. Results show that Artificial Neural Network (ANN) by itself is already able to give relatively good prediction. With the addition of PINN, the error reduces even more, although by only a relatively small amount. This is perhaps due to the already good prediction. The effects of batch size, training iteration and number of epochs on the prediction accuracy have already been tested. It is found that increasing batch size improves the prediction. On the other hand, increasing the training iteration may give poorer prediction due to overfitting. Lastly, in general, increasing epochs reduces the error. More investigations should be done in the future to further reduce the error while at the same time using less training data. More complicated cases with time varying results should also be included. Extrapolation of the results using PINN can also be tested.
Solids Distribution in Sediment-Laden Open-Channel Flow: Experiment and Prediction
Authors: Matoušek Václav , Krupička Jan , Picek Tomáš , Zrostlik Štěpán
Published: October 2020

Solid-liquid flow is studied in an open channel with a mobile bed at the condition of intense transport of solids. It is flow of high-concentrated mixture of coarse sediment and water over a plane surface of the bed eroded due to high bed shear. In the flow, solid particles are non-uniformly distributed across the flow depth. The flow develops a transport layer, adjacent to the the top of the bed, in which transported particles interact with each other.

Results are presented of experimental investigations of the sediment-laden open-channel flow in a recirculating titling flume. The experiments included measurements (using ultrasonic techniques) of the distribution of solids velocity across the transport layer. The related distribution of solids concentration was deduced from the measured distribution of velocity and from other measured flow quantities. Since recently, a direct measurement of the solids distribution across the transport layer has been added to the experiments using a measuring technique svideo camera and a laser sheet.

This work discusses results of combined measurements of the distributions of solids concentration and velocity in steady uniform turbulent flow for two lightweight solids fractions and various flow conditions (a broad range of the bed Shields parameter, discharge of solids, discharge of mixture, and the longitudinal slope of the bed). Furthermore, the camera-based measuring method and the deducing method for a determination of solids distribution are discussed and their results compared to show a good agreement in a majority of the test runs.

The experimental results are compared with predictions of a recently developed bed-load transport model. Among other outputs, the model predicts the position of the top of the transport layer and the local velocity of sediment particles at this position. The presented model predictions agree well with experimental results based on the measured distibutions.
Ball Passage and Impeller Types Do Not Characterize the Functional Performance of a Sewage Pump
Authors: Tilcher David Konstantin , Pöhler Michael , Thamsen Paul Uwe
Published: October 2020

During the development of sewage pumps their functionality and efficiency have been continuously improved. Different impeller types have been developed; types to reduce clogging, types for associated maintenance during the various stages of the wastewater transport system, and types to increase the efficiency of the pumps.

In the current market, energy requirements and efficiency play an increasingly important role. The design of pump impellers with the aim of improving efficiency may increase the susceptibility of clogging. So far there is no test describing both the energy efficiency and the wastewater pumping functionality. Operators can only describe in tenders, a desired efficiency and the indication of plausible experience with respect to the impeller geometry: the impeller shape and the ball passage.

It is generally assumed that the susceptibility of clogging can be derived from the impeller shape and the ball passage (or freely passable space). Under this assumption, the vortex impeller should have the lowest susceptibility to clogging. With single and dual-channel impellers, accordingly, the largest possible ball passage points to a low susceptibility of clogging. Both, the hydraulically disadvantageous form of the vortex impeller and an enlargement of the ball passages beyond the hydraulic requirements leads to a significant reduction of efficiency. Generally, it is inferred from these circumstances that clog-free pumps are associated with low efficiency. This assumption, which is also found in the literature, requires a uniform test procedure for the objective assessment of the clogging behavior of sewage pumps. Such a test did not exist.

At the Chair of fluid system dynamics, TU Berlin a test stand was developed to examine such assumptions to investigate the functionality and the clogging behavior of sewage pumps.

More than 30 different wastewater pumps were tested in this procedure. The results may suggest a correlation between the susceptibility to clogging and the shape of the impeller or ball passage of various sewage pumps. Based on investigations already carried out at the Chair of fluid system dynamics, TU Berlin, the following conclusions are drawn from the measurements:

• the superordinate impeller form (Vortex, Channel, etc.) gives no evidence about the susceptibility to blockages,

• the ball passage does not indicate the susceptibility to blockages.

From these observations it can be deduced:

• a sewage pump with an appropriate efficiency may have a low susceptibility to clogging.

It can therefore be concluded that the ball passage and the type of impeller are not appropriate parameters to characterize the functional performance of a sewage pump.
Dynamics and Breakup Regime of a Vapor Bubble Traveling Through a Heated T-Shaped Branching Microchannel
Authors: Yan Zhe , Li Shanshan , Li Lichun , Deng Bili , Pan Zhenhai
Published: October 2020

Dynamics and breakup characteristics of a vapor bubble when traveling through the T-junction of a heated branching microchannel are numerically investigated with the Volume of Fluid-Continuum-Surface-Force (VOF-CSF) method. The moving reference frame method, which has been demonstrated to help suppressing the unphysical spurious velocity around the liquid-vapor interface (Numer. Heat Trans. 67, 1–12), is employed and coupled to the VOF-CSF model. In order to evaluate the influence of the wall heating on the growth and breakup of vapor bubble, the saturated-interface-volume phase change model is further coupled to account for the phase change on the bubble interface. The numerical model is first validated against experimental results in literature. Then the effect of wall superheat on bubble dynamics and heat transfer coefficient is investigated. Bubble motion, growth, breakup and heat transfer characteristics at different wall superheats are analyzed in detail. Four bubble breakup regimes are observed, namely non-breakup (NB), breakup with tunnel (TB), combined breakup (CB) and breakup with permanent obstruction (OB). The present study reveals the transport details around an evaporating vapor bubble and helps understanding the underlying physics of bubble behaviors when traveling through a T-shaped branching microchannel.
Length Reduction of a Compressor Multi-Spool Transition Annular S-Duct
Authors: Agrawal M. , Sinha D. , Das S. P. , Vidhyashankar N. , Abbas R.
Published: October 2020

Increasing interest in improving the efficiency of the turbo-fan engine results in a large low pressure compressor and small high pressure core. The consequence of the increment in radial offset is that the importance of the transition duct is growing. Shortening this transition duct length can effectively reduce the weight of the engine. However, it conflicts with the need to avoid flow separation within the duct. Further, radial struts are also present in duct passage for support. In present work, numerical investigations were performed on an annular S-duct with bypass suitable for connecting the compressor spools of a small turbofan engine. The length of S-duct was reduced by 6%, 12%, and 18% from the original S-duct length. The wall contour was selected based on the optimum value of the total pressure loss coefficient for the particular length. It was found that the loss coefficient is a weak function of duct length as long as the flow is attached. Further, the effect of the radial strut on the selected contour for two different lengths was studied. The increase in loss for 100% and 88% length in the presence of all struts was 17% and 27%.
Attached Jet Velocity Profiles in Mixing Tanks
Authors: Pease Leonard F. , Bamberger Judith Ann
Published: October 2020

Free jets have been studied in detail over much of the last century, but the theory for offset and attached jets remains incomplete. Attached jets differ from free jets in that they lose momentum to nearby surfaces, attenuating their velocities. The velocity profiles of free circular jets are nearly Gaussian, with quantitative mathematical descriptions derived from first principles by Goertler and Tollmien (Rajaratnam, 1976). In contrast, mathematical descriptions of three-dimensional attached jets from circular nozzles remain much less mature. Agelin-Chaab and Tachie (2011) used particle imaging velocimetry of a three-dimensional attached jet to show that the scaled velocity decays with scaled distance from the nozzle with a power law exponent between −1.15 and −1.20, which is larger in magnitude than that of a free jet. However, quantitative analytical expressions for the velocity profiles of attached jets similar to those of free jets remain elusive. This paper addresses this critical gap.

Here we evaluate the velocity profiles of three-dimensional offset jets emerging from circular nozzles that become attached jets. These jets lose momentum due to interactions with nearby surfaces and are important to evaluating flows in mixing vessels and to suspending solids and trapped gases in radioactive waste tanks. Despite the importance of attached jets, prior insight has been purely experimental, limited to overly simplistic analytical models, or restricted to computationally expensive computational fluid dynamics case studies. We compare the expression of Verhoff (1963) to experimental results to find reasonable quantitative agreement.

As stated by Agelin-Chaab and Tachie (2011), “detailed velocity measurements of 3D offset jets are rare.” Such remains the case. This study adds to the literature by providing information at two additional Reynolds numbers (1.43 · 106 and 1.87 · 106) and evaluating simple but accurate expressions for velocity profiles. These Reynolds numbers and corresponding velocities are higher, typically orders of magnitude higher, than other reports. The semi-empirical stream wise velocity profile perpendicular to the surface proposed by Verhoff (1963) is in approximate agreement with these velocity profiles, which is surprising because these attached jets are three-dimensional instead of two-dimensional as evaluated by Verhoff. However, additional work is necessary to fully describe these profiles quantitatively.
Experimental Comparison of Newtonian and Non-Newtonian Multiphase Flow in Horizontal Pipes
Authors: Ben Rajeb Faraj , Odan Mohamed , Aborig Amer , Imtiaz Syed , Zhang Yan , Awad Mohamed M. , Rahman Mohammad Azizur
Published: October 2020

Two-phase flow of gas/Newtonian and gas/non-Newtonian fluid through pipes occurs frequently in the chemical industry as well as in petroleum refining. Extensive experimental and theoretical research has been carried out on these systems in order to better understand their behaviour under different conditions regarding pressure, temperature and mixture concentrations. In this study, experimental apparatuses are used to investigate two-phase flow of gas/liquid systems through pipes. Air is used as the gas in the experiments, while water is used as the Newtonian fluid and Xanthan gum as the non-Newtonian fluid. The objectives of the study are to compare pressure drops when the same gas flows simultaneously with Newtonian and non-Newtonian fluids through tubes. The comparison here is between experimental pressure drops and estimated pressure drops, based on available empirical correlations for gas/Newtonian and gas/non-Newtonian flow. The trend exhibited by the pressure drops in both systems helps us to better understand the relationship between mixture flow pressure drops in Newtonian and non-Newtonian fluids and thereby develop a new experimental model. The tube diameter for the flow loop is 3/4 inch and the flow type ranges from transient to turbulent.
Disruption Behavior of Aggregates in a Rotating/Oscillating Cylindrical Tank and Implications for Particle Transport in the Ocean
Authors: Song Yixuan , Rau Matthew J.
Published: October 2020

Particle size and settling speed determine the rate of particulate mass transfer from the ocean surface to the sea bed. Turbulent shear in the ocean can act on large, faster-settling flocculated particles to break them into slower-settling primary particles or sub-aggregates. However, it is difficult to understand the disruption behavior of aggregates and their response to varying shear forces due to the complex ocean environment. A study was conducted to simulate the disruption behavior of marine aggregates in the mixed layer of the ocean. The breakup process was investigated by aggregating and disrupting flocs of bentonite clay particles in a rotating and oscillating cylindrical tank 10 cm in diameter filled with salt water. This laboratory tank, which operated based on an extension of Stokes’ second problem inside a cylinder, created laminar oscillating flow superimposed on a constant rotation. This motion allowed the bentonite particles to aggregate near the center of the tank but also exposed large aggregates to high shear forces near the wall. A high-speed camera system was used, along with particle tracking measurements and image processing techniques, to capture the breakup of the large particle aggregates and locate their radial position. The breakup response of large aggregates and the sizes of their daughter particles after breakup were quantified using the facility. The disruption strength of the aggregated particles is presented and discussed relative to their exposure to varying amounts of laminar shear.
Evaporative Emissions From Automotive Gasoline Fuel Tank Refueling: Experimental Activity and Numerical Simulation
Authors: Romagnuolo Luca , Frosina Emma , Andreozzi Assunta , Senatore Adolfo , Fortunato Francesco , Mirante Vincenzo
Published: October 2020

Vehicle evaporative emission is one of the most important sources of pollution from a gasoline-fueled vehicle. Since international regulations on Volatile Organic Compounds (VOC) emission are becoming increasingly stringent every year, the study of the VOC generation has become of fundamental importance.

It is known that VOC generation is particularly high during the refueling phase: fresh fuel coming from the refueling nozzle impacts on the filling pipe wall and it is a source for sloshing in the fuel tank. Fuel vapor generated can be collected by a vapor recovery nozzle and stored in the gas station tank (Stage II vapor recovery system, European normative) or trapped by the vehicle carbon canister (On-board Refueling Vapor Recovery system, U.S. normative).

In this activity, an automotive gasoline fuel tank for U.S. applications has been used for both experimental and numerical analyses, provided by FCA. Experiments were performed in FCA laboratories, in a sealed and thermal controlled environment (mini-SHED): vapor flow exiting the fuel tank during refueling has been measured, and fuel vapor mass has been evaluated by dynamically measuring the weight variation of a carbon canister filter connected to the fuel tank vent system. A CFD model was built based on CAD geometries provided by FCA, and numerical analysis of the refueling process has then been executed by using a commercial 3D CFD software. Results were then compared with experimental data.

This activity is a part of a collaboration between University of Naples Federico II and FCA Italy about fuel vapor emissions control and prediction.
Large Eddy Simulation of Active Flow Control Over SD7003 at Reynolds Number of 60,000
Authors: Kamari Djavad , Tadjfar Mehran , Tarokh Ali
Published: October 2020

Large Eddy Simulation for active flow control (AFC) by employing synthetic and continuous blowing is done to investigate their effects on resizing separation. The flow around an SD7003 airfoil at Reynolds number of 60,000 and angles of attack of 13° is considered where a widespread separation occurs at post stall. In this work, the Dynamic Smagorinsky model is used as to calculate the turbulent viscosity.
Impact of Print Parameters on Pressure Drop in Turbulent Flow Through 3-D Printed Pipes
Authors: Shepard Thomas G. , Wentz John , Bender Tucker , Olmschenk Derek , Gutenberg Alex
Published: October 2020

Flow conduits made via additive manufacturing, commonly referred to as 3-D printing, are of increasing interest for a variety of industrial applications due to the ability to create unique and conformal flow paths that would not be possible with other fabrication techniques. Fused filament fabrication (FFF) is an additive manufacturing technique that is seeing new interest in the creation of internal flow channels with its ability to print high-temperature polymers and soluble supports. Printing parameter choices in the FFF printing process result in surfaces that can have significant profile differences that may significantly impact the flow characteristics within the conduits. In this study, two print parameters were experimentally studied for turbulent water flow through circular pipes created by fused filament fabrication out of acrylonitrile butadiene styrene (ABS). The print layer orientation relative to the flow was investigated for printing layers parallel, perpendicular, and at 45 degrees from the flow axis. Layer thickness were varied from 0.254 mm to 0.330 mm and all channels were created using soluble support structures. Pressure drops were measured for fully developed flow through pipes with an inside diameter of 5 mm and Reynolds numbers up to 62,000. Results are presented in terms of relative pressure drops as well as the wall surface roughness that would lead to such impacts. These flow-determined grain surface roughnesses are then compared against measurements of print surface roughness.
Parameter Sensitivity and Statistical Correlation Found in Atmospheric Turbulence Studies
Authors: Rodriguez Luis F. , Kumar Vinod , Rodriguez Arturo , Kotteda V. M. Krushnarao , Gudimetla V. S. Rao , Munoz Jorge A.
Published: October 2020

We have simulated atmospheric turbulence at several instances of possible laser propagation paths and turbulent flow regime regions within the area of interest. At a control volume that is in between two Hawaii mountains. We have applied statistical correlations between Large-Eddy Simulations results using CFD modeling and parametrizing optical variables of interest, such as refractive index structure function. By comparing our Large-Eddy Simulations with specified parameters against other Large-Eddy Simulations with almost all same parameters except for one allows us to perform a sensitivity study. To study the changes on how a parameter can affect other scenarios of Large-Eddy Simulations parametric studies. With the end goal of validating the capacity of a sensitivity analysis study using Large-Eddy Simulations versus other Large-Eddy Simulations by a way of simulating and parametrizing turbulent flow studies found in the field of CFD modeling. Allowing us to achieve our stochastic analysis by applying sensitivity studies to see how our distributions change as a function of different parameters, but one at a time. After a comparison between CFD modelling simulations we have found that after a complete parametric study, a correlation was formed between turbulent flow parameters and optical parameters of interest.
Evaluation of Erosion Equations in Submerged Impinging Jets
Authors: Wang Qiuchen , Huang Qiyu , Sun Xu , Zhang Jun , Karimi Soroor , Shirazi Siamack A.
Published: October 2020

During petroleum production, small sand particles can be entrained with the transported carrier fluid despite of any sand exclusion process and these sand particles can erode inner walls of pipelines. Therefore, the ability to accurately predict erosion rate caused by particles in oil and water is important to pipeline safety. There are erosion equations available in the literature to predict this phenomenon. However, most of the widely used erosion equations are derived by analyzing gas-solid erosion process, which were later validated and shown to be less accurate in predicting slurry erosion. Modified slurry erosion equations are then proposed to improve the prediction accuracy, while overpredictions occur when particle sizes vary. In this study, the available mechanistic and empirical equations are evaluated by experimental and numerical study. Computational Fluid Dynamics (CFD) is used to simulate the fluid flow and track particles to obtain impact information. Erosion equations then connect the particles’ impact information with erosion rate. The slurry erosion experiments are conducted using quartz silica particles with similar shapes and different sizes ranging from 25 micrometers to 600 micrometers in oil and water as carrier fluids. Finally, the erosion models are evaluated by comparing predicted erosion profile with experimental data.
The Effects of Upstream Wall Roughness on Separated and Reattached Flows Over a Forward-Facing Step
Authors: Kumahor Sedem , Fang Xingjun , Ediger William , Tachie Mark F.
Published: October 2020

Separating and reattaching turbulent flows induced by a forward-facing step submerged in thick oncoming turbulent boundary layers developed over smooth and rough walls were investigated using time-resolved particle image velocimetry. Both smooth and fully rough upstream bottom wall conditions were examined and the resultant oncoming boundary layer thickness were 4.3 and 6.7 times the step height, respectively. The Reynolds number based on the step height and free-stream velocity was 7800. The mean velocities, Reynolds stresses analyzed in both Cartesian and curvilinear coordinate systems, eddy viscosity, correlation coefficient and third order moments are discussed. The results indicate that, due to the enhanced turbulence intensity and shear rate in the fully rough case, distinct elevated regions of vertical and shear Reynolds stresses are consistent upstream of the leading edge of the step while the magnitude of the Reynolds stresses are consistently higher than observed in the smooth case. The correlation coefficient, eddy viscosity and third order moments also show distinct elevated regions upstream of the leading edge of the step in the fully rough case. Above the step, distinct elevated regions of the Reynolds stresses, eddy viscosity and correlation coefficient are observed in both cases with the peak values at a vertical location corresponding to the maximum elevation of the mean separating streamline.
The Effects of Upstream Wall Roughness on the Spatio-Temporal Characteristics of Flow Separations Induced by a Forward-Facing Step
Authors: Kumahor Sedem , Fang Xingjun , Nematollahi Ali , Tachie Mark F.
Published: October 2020

The unsteady characteristics of flow separations induced by a forward-facing step immersed in thick oncoming turbulent boundary layers developed over smooth and fully rough upstream walls were experimentally studied using time-resolved particle image velocimetry. The upstream boundary layer thicknesses were 4.3 and 6.7 times the step height in the smooth and fully rough wall cases, respectively. The Reynolds number based on the step height and free-stream velocity was 7800. The effects of upstream wall roughness on the instantaneous separated shear layer, frequency spectra and two-point correlations are critically examined. Proper orthogonal decomposition (POD) is employed to investigate the mechanism underlying the unsteadiness of turbulent separation bubbles over the step. The first two POD modes exhibit the same topology in both cases. The energy fraction of the first mode is significantly larger in the rough wall case, signifying the enhanced large-scale motion residing in the incoming turbulent boundary layer. The correlation between the reverse flow area over the step and the first POD mode coefficient is much stronger in the rough wall case than in the smooth wall case. High levels of vertical fluctuating velocity immediately upstream of the leading edge of the step is mostly associated with the first POD mode in the rough wall case, but is further influenced by the higher POD modes in the smooth wall case. Irrespective of the upstream wall roughness, the vertical fluctuating velocity over the step are mostly induced by vortex shedding motion from the leading edge of the step.
On How the Generation of Lift Can Be Explained in a Closed Form Based on the Fundamental Conservation Equations
Authors: Epple Philipp , Babinsky Holger , Steppert Michael , Fritsche Manuel
Published: October 2020

The generation of lift is a fundamental problem in aerodynamics and in general in fluid mechanics. The explanations on how lift is generated are often very incomplete or even not correct. Perhaps the most popular explanation of lift is the one with the Bernoulli equation and with the longer path over an airfoil as compared to the path below the airfoil, assuming the flow arrives at the same time at the trailing edge on both paths. This is an intuitive assumption, but no equation is derived from this assumption. In some explanations the Bernoulli equation is also complemented with Newton’s laws of motion. In other explanations Newton’s law is said to be the only explanation. Other explanations mention the Venturi suction effect to explain the generation of lift. In books of aerodynamics and on the homepage of well-known research institutes the explanations are, although better and partially correct, still very often incomplete. In this contribution the generation of lift is explained in a scientific way based on the conservation principles of mass, momentum and energy and how they have to be applied to close the system of equations in order to explain the generation of lift. The most common incomplete or incorrect explanations of lift are also analysed and it is explained why they are incomplete or wrong. In this work the generation of lift is explained based on the conservation equations. It is shown how and when they apply to the problem of lift generation and how the system of equations has to be closed.
Cavitation in Hydraulic Machines: Measurement, Numerical Simulation and Damage Patterns
Authors: Benigni Helmut
Published: October 2020

Cavitation is a phenomenon that occurs in liquid media when the pressure drops below the vapor pressure. Cavitation is accompanied by damage when the imploding vapor bubbles implode in the vicinity of components. Cavitation is known in all hydraulic machines, be it a pump or a turbine, and it can occur within all components that are flowed through and have a low-pressure side or area.

In the last 100 years, a lot has been done to understand the damage caused by cavitation, and cavitation has been classified within the entire range of component-damaging mechanisms. Nevertheless, users are now interested in the behavior of different machine types and different specific speeds and need information for a particular installation situation, while hydraulic developers are interested in a methodology for the rapid assessment of CFD results.

This paper presents examples of damage to all kinds of hydraulic machines as well as numerical simulations of cavitation. Cross-comparisons between single-phase numerical calculations are realized with the histogram method, and multi-phase calculations are carried out and then compared with test rig investigations.

Often, it is not possible or economically feasible to completely avoid cavitation. With the help of dimensionless values and the assumption of complete cavitation, a generally valid physical limit curve can be specified for turbines.
Impact of Bubble Size on Flow Response to Transient Pressure Drop Through Converging Nozzle
Authors: Garbaly Aleksey , Shepard Thomas
Published: October 2020

For homogenous two-phase bubbly flows, the theoretical speed of sound is dramatically reduced at moderate void fractions to speeds much lower than the speed of sound for either single phase. This theoretical speed of sound would suggest a propensity for bubbly flows to reach choked conditions when traveling through a convergent nozzle. However, for a bubbly flow to be considered homogenous requires assumptions that may not be realized in practical applications. In this experimental study, a bubbly flow was sent through a convergent nozzle before entering a large chamber. By setting steady flow conditions upstream and then reducing the chamber pressure via a vacuum pump, the transient response in terms of gas and liquid flow rates and upstream channel pressure was determined. The bubble size was carefully varied from ∼0.3–1 mm while holding gas and liquid flow rates constant in order to study how bubble size affects the transient flow characteristics. High-speed imaging was used for measuring the bubbles. Experiments were also conducted at two gas-liquid mass flow ratios. Results are presented to demonstrate the impact of bubble size and gas-liquid ratio on the transient response of upstream gas and liquid flow rates, upstream pressure and exit Mach number to the lowering of pressure downstream of the convergent nozzle. Results are presented both for flows that remained in the bubbly regime and for flows that transitioned to an annular flow regime during a trial.
Capstone Design Sequence in Engineering Education
Authors: Taghavi R. , Farokhi S.
Published: October 2020

The Capstone design requirements have become an integral part of the most engineering curricula in the United States. They all share the goal of developing multidisciplinary designs for real-world problems/applications, often with industry sponsorship. In this paper, the three-capstone design options required by the aerospace engineering department at the University of Kansas are discussed. The aerospace engineering seniors have three design options based on their career interests. These are aircraft design, propulsion system design, and spacecraft system design options. In the aircraft design, our students may select individual or team design for their competitions. In the latter two, the propulsion and spacecraft system designs, the students are grouped in a number of teams, based on the class and team size requirements. The individuals and teams participate and compete in the respective American Institute of Aeronautics and Astronautics (AIAA) Design Competitions at the end of their senior year. Participation in the AIAA Design Competition is one of the course requirements. Written and oral communication is assessed throughout the semester. In this paper, the methodology used in the aerospace engineering propulsion system capstone design is presented.
Experimental and Numerical Analysis of Fluid Flow Through a Micromixer With the Presence of Electric Field
Authors: Rubby Md Fazlay , Parvez Mohammad Salman , Biswas Prosanto , Huq Hasina , Islam Nazmul
Published: October 2020

Fluid flows in a microchannel with highly ordered laminar fashion. For this reason, two different fluid streams cannot mix easily, or it takes a very long time. The problem becomes intense for large molecules such as peptides, proteins, and nucleic acids during rapid mixing for biochemical applications in a microfluidic device. Many researchers tried to solve this problem by applying an electric potential. In this work, a numerical simulation was performed on a 2D micromixer. Four symmetric electrodes were placed on the wall of a straight microchannel of width 19 μm. The electroosmotic slip velocity boundary condition was used to create the turbulence on the laminar fluid stream. It was found that this model creates a well-mixed flow at the channel outlet. Then the input parameters were changed to compare the mixing performance in terms of concentration distribution at the channel outlet. Channel width, inter-electrodes gap, the magnitude of electric potential, frequency of the electric potential and asymmetricity of the electrodes were changed and results were compared. An experimental micromixer like the numerical model was fabricated by dc magnetron sputtering machine. Four gold electrodes (thickness, 120 nm) were sputtered on top of a silicon substrate. The value of the input parameters was chosen based on the results obtained from the numerical simulation. To test the mixing functionality of our device the movement of tracer particles was tracked down on the zone surrounded by four electrodes. The micro-PIV (Particulate Image Velocimetry) system was used to analyze the movement of the tracer particles and visualize the flow field in the mixing zone. The magnitude of the AC electric potential and frequency was changed to find out the optimum input parameters for the micromixer. These results could play an important role to design and improve a micromixer design using an AC electric field. A micromixer has many potential applications in biology (DNA analysis, enzyme Screening), chemistry (synthesis, polymerization) and detection (drug discovery, diagnosis).
Comparison of Turbulent Boundary Layer Profiles Modified With Injection or Uniform Concentration of Drag-Reducing Polymer Solution
Authors: Elbing Brian R.
Published: October 2020

The current study explores the influence of polymer drag reduction on the near-wall velocity distribution in a turbulent boundary layer. The classical view is that the polymers modify the intercept constant within the log-region without impacting the von Kármán coefficient, which results in the log-region being unaltered though shifted outward from the wall. However, it has been recently shown that this is not accurate, especially at high drag reduction (> 40%). Past work examining the von Kármán coefficient and intercept constant has shown that polymer properties must impact the deviations, but without any quantification of the dependence. This work reviews the literature to make estimates of the local polymer properties and then demonstrates that the scatter at HDR can be attributed to variations in the Weissenberg number. In addition, new polymer ocean results are incorporated and shown to be quite consistent with polymer injection results using the maximum polymer concentration to define the polymer properties.