Computational Fluid Dynamics As A Tool For Visualizing Hemodynamic Flow Patterns

Floodways, where a road embankment is permitted to be overtopped by flood water, are usually designed as broad-crested weirs. Determination of the water level above the floodway is crucial and related to road safety. Hydraulic performance of floodways can be assessed numerically using 1-D modelling or 3-D simulation using computational fluid dynamics (CFD) packages. Turbulence modelling is one of the key elements in CFD simulations. A wide variety of turbulence models are utilized in CFD packages; in order to identify the most relevant turbulence model for the case in question, 96 3-D CFD simulations were conducted using Flow-3D package, for 24 broad-crested weir configurations selected based on experimental data from a previous study. Four turbulence models (one-equation, k-ε, RNG k-ε, and k-ω) ere examined for each configuration. The volume of fluid (VOF) algorithm was adopted for free water surface determination. In addition, 24 1-D simulations using HEC-RAS-1-D were conducted for comparison with CFD results and experimental data. Validation of the simulated water free surface profiles versus the experimental measurements was carried out by the evaluation of the mean absolute error, the mean relative error percentage, and the root mean square error. It was concluded that the minimum error in simulating the full upstream to downstream free surface profile is achieved by using one-equation turbulence model with mixing length equal to 7% of the smallest domain dimension. Nevertheless, for the broad-crested weir upstream section, no significant difference in accuracy was found between all turbulence models and the one-dimensional analysis results, due to the low turbulence intensity at this part. For engineering design purposes, in which the water level is the main concern at the location of the flood way, the one-dimensional analysis has sufficient accuracy to determine the water level.

Auxiliary Power Units (APU’s) are gas turbine engines which are located in the tail of most commercial and business aircraft. They are designed to provide electrical and pneumatic power to the aircraft on the ground while the main propulsion engines are turned off. They can also be operated in flight, when there is a desire to reduce the load on the propulsion engines, such as during an engine-out situation. Given an APU’s typical position in the back of an airplane, the intake systems for APU’s can be very complex. They are designed to provide sufficient airflow to both the APU and the cooling system while minimizing the pressure losses and the flow distortion. These systems must perform efficiently during static operation on the ground and during flight at very high altitudes and flight speeds. An APU intake system has been designed for a new commercial aircraft. This intake system was designed using the latest Computational Fluid Dynamics (CFD) techniques. Several iterations were performed between the APU supplier and the aircraft manufacturer since each of their components affects the performance of the other. For example, the aircraft boundary layer impacts APU intake performance and an open APU flap impacts aircraft drag. To validate the effectiveness of the CFD analysis, a full scale intake rig was designed and built to simulate the tailcone of the aircraft on the ground. This rig was very large and very detailed. It included a portion of the tailcone and rudder, plus the entire APU and cooling intake systems. The hardware was manufactured out of fiberglass shells, stereolithogrophy components and machined plastic parts. Three different airflows for the load compressor, engine compressor and cooling system had to be measured and throttled. Fixed instrumentation rakes were located to measure intake induced pressure losses and distortion at the APU plenum and cooling ducts. Rotating pressure and swirl survey rakes were located at the load compressor and engine compressor eyes to measure plenum pressure losses and distortion. Static pressure taps measured the flow pattern along the intake and flap surfaces. The intake rig was designed to be flexible so that the impact of rudder position, intake flap position, APU plenum baffle position and compressor airflow levels could be evaluated. This paper describes in detail the different components of the intake rig and discusses the complexity of conducting a rig test on such a large scale. It also presents the impact of the different component positions on intake performance. These results were compared to CFD predicted values and were used to calibrate our CFD techniques. The effectiveness of using CFD for APU intake design and its limitations are also discussed.

In this paper, multi-objective optimization (MOO) of Al2O3-water nanofluid flow in microchannel heat sinks (MCHS) with triangular ribs is performed using Computational Fluid Dynamics (CFD) techniques and Non-dominated Sorting Genetic Algorithms (NSGA II). At first, nanofluid flow is solved numerically in various MCHS with triangular ribs using CFD techniques. Finally, the CFD data will be used for Pareto based multi-objective optimization of nanofluid flow in MCHS with triangular ribs using NSGA II algorithm. In the MOO process there are seven geometrical and non-geometrical parameters and the conflicting objective functions are to simultaneously maximize the amount of heat transfer and minimize the pressure drop. Five optimum designs are determined and discussed for both nanofluid and base fluid flows. Details of design variables for each of five optimum points are deeply discussed. It is shown that the achieved Pareto solution includes important design information on nanofluid flow in MCHS with triangular ribs.

The droplet drift during aerial spraying process of oilseed rape, which is induced by complex flow field including random lateral wind, is difficult to predict and suppress. In this study, the high-fidelity computational fluid dynamics (CFD) technique is employed to simulate the two-phase flow of droplets in the rotor flow field, and the influence of main operation parameters on spraying effect is investigated numerically. Furthermore, the mechanism of droplet deposition in various operation conditions is discussed according to the analysis of unsteady flow field characteristics. However, the simulation via CFD technique is time-consuming, and it is not suitable for multidisciplinary work and optimization design. To address such issue, a filter white Gaussian noise signal is used to mimic the random lateral wind, and the droplet drift distance is obtained numerically. Based on the input and output dataset of CFD, the recursive algorithm including nonlinear autoregressive exogenous model and surrogate-based recurrence framework and the deep learning method for time-series prediction called long short-term memory neural network are used to build the efficient reduced-order model, respectively. Numerical simulations show that the droplet drift distance can be predicted by measurable lateral wind speed via the reduced-order model approach, which agreed well with the results obtained via the CFD method. In addition, the reduced-order model could decrease computation cost by 6 orders of magnitude with an acceptable accuracy, which indicates that the proposed method could be used for the design of off-line closed-loop controller of a variable spraying system.

A multi-objective optimization design framework integrated with CFD for the design of AUVs

Papers published in Engineering and Computational Mechanics are eligible for awards from the Institution of Civil Engineers. Papers from any of the ICE journals can be nominated for several awards. In addition, each journal has awards dedicated to their specific subject area.On Friday 13 October 2023, ICE president Keith Howells presented awards to the following papers published in Engineering and Computational Mechanics in 2022. The editorial panel nominated their best papers and an awards committee chaired by Tim Broyd allocated the awards.The George Stephenson Medal, awarded to the second best overall paper, was awarded to Daniels and Xie (2022).Understanding and predicting the effects of wind loading on a structure is necessary for safe, effective, and economical engineering design. Wind tunnel techniques often provide data that is not sufficient for the structural engineer. With increasing advances in computational capabilities, Computational Fluid Dynamics techniques have recently become feasible to complement experiments. Of these, one of the most effective is Large-Eddy Simulation (LES). The application of LES to analyse wind loading, and aeroelastic effects on structures are only a recent venture in the field. This paper reviews the progress made over the last few decades for the analysis of wind flow around slender structures, and the more recent analysis incorporating the effects of freestream turbulence. First, a review of the literature is carried out for generating freestream turbulence approaches, of which many are used for the analysis of surface pressures on an isolated object. Subsequently, a review is made on wind tunnel experiment and LES for aeroelastic analysis of bridge sections. The recent advances in the understanding of turbulence effects on the aerostatic responses are summarised. Finally, the future of LES and its relationship with wind tunnel experiment for wind loading analysis are discussed.The Telford Premium Prize, presented to the best paper published in Engineering and Computational Mechanics, was awarded to Cannon et al. (2022). ‘Long-duration’ blast waves can exert damaging drag loads on finite structural columns that are complex to characterise. In the absence of suitable drag coefficients, computational fluid dynamics (CFD) can be the only satisfactory approach for calculating blast loading. Commercially available CFD software with shockwave modelling capabilities require solving the Euler equations that assume inviscid flow. Two Eulerian solver types are generally used: Godunov and flux-corrected transport, the latter of which is commonly perceived as more accurate for shockwave problems. This study investigates the capability of both solvers for calculating drag loading from long-duration blast interaction with an I-section, verified through comparison to experimental measurements. No solver sensitivity was observed for pressures on exposed geometry surfaces, although discrepancies were observed for shielded surfaces, particularly during later stage interaction. The Godunov scheme demonstrated increased computational efficiency and reliability in comparison to the flux-corrected transport solver type, generating results in better agreement to experimental data. The results provided new understanding of solver sensitivity for modelling long-duration blast drag loading on finite targets using Eulerian CFD analyses.

ABSTRACTWith rapid advancements in computer hardware and numerical modeling methods, Computational Fluid Dynamics (CFD) has gained prominence in simulating complex flows. As parallel computation becomes an industry standard, the computational efficiency of simulations has become critical. The flow around a Vertical Axis Wind Turbine (VAWT), characterized by complex dynamics and challenging rotating geometry, serves as an intriguing case for CFD studies. This study employs the open‐source CFD solvers SU2 and OpenFOAM to simulate the incompressible, unsteady, and turbulent flow around an H‐type Darrieus VAWT in two dimensions. Spatial and temporal discretization parameters are examined to balance computational cost and accuracy, revealing notable effects on power predictions. Simulations conducted under identical conditions allow for a comparison of the predictions and parallel performances of SU2 and OpenFOAM across three distinct tip speed ratios (TSRs). The findings show that discretization parameters behave differently at various TSRs. While power predictions from SU2 and OpenFOAM generally align with experimental data and with each other, discrepancies arise at lower TSRs, with thrust predictions showing better consistency. Although OpenFOAM provides a faster solution across all parallel configurations, SU2 demonstrates superior parallel scalability, achieving higher speedup and efficiency.

A “credible” computational fluid dynamics (CFD) model has the potential to provide a meaningful evaluation of safety in medical devices. One major challenge in establishing “model credibility” is to determine the required degree of similarity between the model and experimental results for the model to be considered sufficiently validated. This study proposes a “threshold-based” validation approach that provides a well-defined acceptance criteria, which is a function of how close the simulation and experimental results are to the safety threshold, for establishing the model validity. The validation criteria developed following the threshold approach is not only a function of Comparison Error, E (which is the difference between experiments and simulations) but also takes in to account the risk to patient safety because of E. The method is applicable for scenarios in which a safety threshold can be clearly defined (e.g., the viscous shear-stress threshold for hemolysis in blood contacting devices). The applicability of the new validation approach was tested on the FDA nozzle geometry. The context of use (COU) was to evaluate if the instantaneous viscous shear stress in the nozzle geometry at Reynolds numbers (Re) of 3500 and 6500 was below the commonly accepted threshold for hemolysis. The CFD results (“S”) of velocity and viscous shear stress were compared with inter-laboratory experimental measurements (“D”). The uncertainties in the CFD and experimental results due to input parameter uncertainties were quantified following the ASME V&V 20 standard. The CFD models for both Re = 3500 and 6500 could not be sufficiently validated by performing a direct comparison between CFD and experimental results using the Student’s t-test. However, following the threshold-based approach, a Student’s t-test comparing |S-D| and |Threshold-S| showed that relative to the threshold, the CFD and experimental datasets for Re = 3500 were statistically similar and the model could be considered sufficiently validated for the COU. However, for Re = 6500, at certain locations where the shear stress is close the hemolysis threshold, the CFD model could not be considered sufficiently validated for the COU. Our analysis showed that the model could be sufficiently validated either by reducing the uncertainties in experiments, simulations, and the threshold or by increasing the sample size for the experiments and simulations. The threshold approach can be applied to all types of computational models and provides an objective way of determining model credibility and for evaluating medical devices.

Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to calculate, analyze, and visualize fluid (liquids, gases, and dissolved gases) flows. This document provides general introductions to best practices for CFD modeling in water infrastructure for practitioners, particularly those new to CFD modeling, which is becoming a widely used tool in the design and retrofitting of water, wastewater, and stormwater infrastructure. The method serves as an alternative, or complement, to physical modeling. In recent years, CFD has often been used in evaluating and troubleshooting existing water systems as well as improving future designs. As with the applications in other fields, the popularity of CFD in the water industry has been propelled by a multitude of factors including, but not limited to, the maturity achieved by CFD techniques, the development of stable and reliable numerical schemes, and the ever-improving computer-aided design (CAD) and meshing technologies for real-world complex geometries. This has been accompanied by many commercial and open-source CFD packages that can be run on increasingly more powerful computing hardware. Despite the visible progress in the application of CFD in water infrastructure projects achieved to date, there are still many challenges that hinder the widespread use of CFD techniques in water treatment design. Perhaps more important is that many of these challenges may result in misuse of the tool with dire consequences. It is imperative that CFD practitioners appropriately apply this tool without overpromising capability or accuracy and that reviewers of CFD model results know what to look for in ensuring proper methods have been applied and that results are representative of reality.

This article describes an optimization design of a sugar evaporative crystallizer using numerical simulation experiments. Computational fluid dynamics (CFD) is used to simulate the circulation flow of sugar juice in the crystallizer, and the numerical experiments are designed according to orthogonal experiment matrix. First, based on the specific working characteristics of sugar evaporative crystallizer, major factors influencing the cane sugar evaporative crystallization process were identified. Then CFD software was utilized to establish various three‐dimensional CFD models of the sugar evaporative crystallization with different factors and levels. Statistics software (IBM SPSS) is used to analyze the CFD simulation results. In order to measure circulation velocity under different conditions, physical experiments were conducted in the experiment platform in our laboratory. The circulation velocity measured under the optimal condition was increased by 128%, and the crystallization efficiency could be guaranteed.Practical ApplicationsComputation fluid dynamics (CFD) enables studying the details within the crystallizer, making the invisible become visible. The orthogonal test replaces all tests with partial tests. The orthogonal test coupled CFD technique can hugely decrease the cost of optimization design. The application of this method will benefit the optimization design of food engineering.

Flows around a swimmer's body in a prone glide position are computed with a Computational Fluid Dynamics (CFD) technique in order to understand the effect of a body shape on flow characteristics. A human model which consists of artificial bones, joints and an overlying skin is used to model the body shape in the consistent form via manipulation of the joints. A finite-volume based Navier-Stokes solver is used with unstructured tetra, prism and hexahedral grids for the flow computation to cope with the complicated geometry of a human body. The computed results of the underwater swimming show that the pressure drag is more than six times larger than the frictional drag. Various types of longitudinal vortices, flow separations and reattachments are observed due to the concave and convex geometry of the body. The parameter study for the gliding depth is conducted to evaluate the free-surface effects and the wave making resistance. The deformation of free-surface is computed reasonably well and it is shown that the wave making resistance can be estimated by the CFD technique.

본 연구는 스프링클러 헤드 근처에서 형성되는 액막의 자유표면 유동에 대해 CFD 모델을 적용하여 해석하고 스프링클러의 초기분무 특성 예측을 위한 기존 이론식의 결과와 비교를 통해 이론 모델의 타당성을 검토하였다. CFD 해석은 상용 해석프로그램인 CFX 14.0을 이용하였으며 노즐과 디플렉터로 이루어진 단순형상에 대해 표준난류모델과 VOF법을 적용하여 해석을 수행하였다. 평판부의 디플렉터 끝단에서 속도분포는 CFD 해석과 경험식이 매우 잘 일치된 결과를 보였으나 기하학적 형상이 복잡한 부분에서는 속도분포의 차이를 보였다. 이론모델에서 예측된 평균액적크기는 실제 스프링클러 헤드에서 측정된 평균액적크기에 대한 이전 연구결과와 큰 차이를 보였다. 그러나 이론 모델은 스프링클러 헤드의 초기 액적형성과정의 메커니즘을 이해하고 실험적 접근이 용이하지 않은 상황에서 분무 액적의 특성을 예측하는데 유동한 도구로 활용될 수 있다. The present study examined the free surface flow of a liquid sheet near a sprinkler head using a Computational Fluid Dynamics (CFD) model and considered the feasibility of the empirical model for predicting the initial spray characteristics of the sprinkler head through a comparison of the CFD results. The CFD calculation for a simplified sprinkler geometry considering the nozzle and deflector were performed using the commercially available CFD package, CFX 14.0 with the standard <TEX>$k-{\varepsilon}$</TEX> turbulence model and theVolume of Fluid (VOF) method. The predicted velocity of the empirical model at the edge of deflector were in good agreement with that of the CFD model for the flat plate region but there was a certain discrepancy between the two models for the complex geometry region. The mean droplet diameter predicted by the empirical model differed significantly from the measured value of the real sprinkler head. On the other hand, the empirical model can be used to understand the mechanism of droplet formation near the sprinkler head and predict the initial spray characteristics for cases without experimental data.

Thermal performance modeling and performance prediction of a solar still which is single basin single slope (SBSS) for the typical climatic condition of India at Jalandhar (31.3260° N, 75.5762° E) is analyzed in the present work. A numerical investigation of an SBSS solar still is conducted during the month of June 2022 using the ANSYS Fluent 2021 computational fluid dynamics (CFD) package and artificial neural network (ANN) prediction model. A user define function is written and used in fluent to formulate the problem with 9‐h solar radiation flux, on solar still glass surface. The simulation outcomes for surface temperature at three different water depths were compared with the existing experimental study. Water temperature and productivity of freshwater were well aligned with experimental results. Three‐dimensional domain is used with a two‐phase volume of fluid model for the condensation and evaporation processes in a solar still. The performance evaluation parameters, that is, coefficients of convective, evaporative, and radiative heat transfer, different temperature values, distillation output, and system efficiency were calculated numerically. The parametric analysis is expanded, and an ANN model in MATLAB R2020a is utilized to estimate yearly performance and reduce the high computational cost of numerical analysis. The data for solar radiation, design, and operational parameters are fed into the ANN model, and as a result, the water temperature at various depths is computed. The ANN model was trained using numerical results computed for the month of June and tested, showing 99.7% accuracy with CFD results. The annual performance of the solar still was evaluated using ANN models for 9 h of the day and with different boundary conditions. To decrease computational and experimental costs, the recommended technique of combined CFD and ANN models for computing the annual performance of (SBSS) solar still is the most effective option.

PS206. Use of Computational Fluid Dynamics Studies in Predicting Aneurysmal Degeneration of Acute Type B Aortic Dissections

Hydrodynamic force coefficients are important parameters in design and assessment of marine risers. The hydrodynamic coefficients are widely used for assessing marine riser responses due to floater motion excitation and vortex-induced vibrations (VIV). Traditionally, the hydrodynamic coefficients have been obtained from physical model tests on short rigid riser sections. Recently, the offshore industry has started to use computational fluid dynamics (CFD) analysis for predicting the hydrodynamic coefficients due to the recent advancement of CFD software and high-performance computing capabilities, but a reliable CFD modeling practice is requested for CFD analysis to be a more widely accepted prediction tool in the industry. A joint industry effort has been made for developing and verifying the reliable CFD modeling practice through a working group of the Reproducible Offshore CFD JIP. In the working group, a CFD modeling practice document was written based on existing practices already validated for model test data, and verified by blind validations with three CFD practitioners. The first year works are focused on the bare riser with circular cross-section, and the second year work will be extended to the other riser sections such as staggered buoyancy module and straked riser. This paper presents the working group’s first-year verification activities for a bare riser with circular cross-section. The verification works covers three test problems: 1) stationary simulation in steady current, 2) forced-oscillation in calm water, 3) forced-oscillation in steady current. In the stationary simulation, mean drag coefficient, standard deviation of lift coefficient, and Strouhal numbers are compared. In the forced-oscillation simulation in calm water, the fully-submerged riser section oscillates with a sinusoidal motion, and damping and added mass coefficients are compared. In the forced-oscillation simulation in current, the riser section oscillates in cross-flow direction to the steady current, and lift coefficient and added mass coefficient are compared. By following the modeling practice, the CFD predictions are consistent with each other and close to the model test data for a majority of test cases.