In-house Solver Research Articles

Development of heat exchanger modelling capability for a finite volume aeroelasticity solver

Abstract Heat exchangers are frequently used in aero engines and are known to significantly affect the surrounding steady and unsteady flow. In certain applications, they may thereby also influence the aeroelastic stability of upstream or downstream components but there is limited research on this in the public domain. This paper aims to demonstrate the influence of heat exchangers on unsteady flows relevant to aeroelastic problems. This is achieved by developing heat exchanger modelling capability for an in-house finite volume aeroelasticity solver, for which heat exchanger is represented as a porous medium, as this is the established approach in existing aerodynamic studies using commercial CFD software. The governing equations for a Darcy-Forchheimer porous media model suitable for unsteady and compressible flows are presented, which are derived by the application of volume averaging theory to the Navier-Stokes equations. The implementation of this model within the time integration method used for the solver is then described and verified by comparison of results for steady flows against an established commercial CFD solver, where close agreement between both in-house and commercial solvers has been observed. Lastly a preliminary demonstration of the capability to model unsteady heat exchanger flows is presented by application to an aeroacoustic problem, where the interaction of the pressure waves and the heat exchanger is investigated.

Wing–antenna interaction reduces odour fatigue in butterfly odour-tracking flight

Flying insects exhibit remarkable capabilities in coordinating their olfactory sensory system and flapping wings during odour plume-tracking flights. While observations have indicated that their flapping wing motion can ‘sniff’ up the incoming plumes for better odour sampling range, how flapping motion impacts the odour concentration field around the antennae is unknown. Here, we reconstruct the body and wing kinematics of a forwards-flying butterfly based on high-speed images. Using an in-house computational fluid dynamics solver, we simulate the unsteady flow field and odourant transport process by solving the Navier–Stokes and odourant advection-diffusion equations. Our results show that, during flapping flight, the interaction between wing leading-edge vortices and antenna vortices strengthens the circulation of antenna vortices by over two-fold compared with cases without flapping motion, leading to a significant increase in odour intensity fluctuation along the antennae. Specifically, the interaction between the wings and antennae amplifies odour intensity fluctuations on the antennae by up to 8.4 fold. This enhancement is critical in preventing odour fatigue during odour-tracking flights. Further analysis reveals that this interaction is influenced by the inter-antennal angle. Adjusting this angle allows insects to balance between resistance to odour fatigue and the breadth of odour sampling. Narrower inter-antennal angles enhance fatigue resistance, while wider angles extend the sampling range but reduce resistance. Additionally, our findings suggest that while the flexibility of the wings and the thorax's pitching motion in butterflies do influence odour fluctuation, their impact is relatively secondary to that of the wing–antenna interaction.

Design and testing of an innovative electro-dynamic filter for gas turbine intake systems

Abstract Gas turbines require filtered air to preserve the efficiency and the life of the system. Different degradation processes can occur depending on the size and composition of the contaminants. The compressor’s performance can be negatively impacted by fouling and erosion, which alter the shape and roughness of the blades. To limit the effects of the aforementioned phenomena, multistage filtration systems are commonly installed to reduce the contamination at the gas turbine inlet. Traditionally, particle separation is performed through mechanical filtration, which means that the particles are trapped inside cartridges of porous materials. This typology of filter guarantees a high filtration efficiency but on the other hand, generates remarkable pressure drop increasing over time. Inertial filters instead separate contaminants from the flow by utilizing the effect of inertial force acting on solid particles. In recent years, electrostatic filters have become widespread. The fibers of the filters are charged with an electrostatic field before installation and this charge is capable of separating and attracting metallic particles from the airflow. However, the electrostatic field’s effect diminishes with the exposure time with this type of filter. This work presents an innovative electro-dynamic filtration system for gas turbine application. The geometry and electrical features of the devices are designed to keep low-pressure drop and high capturing efficiency over time. To achieve these goals, a numerical campaign is performed using an in-house OpenFOAM solver, which takes into account the effect of the electrostatic force of the Lagrangian phase. After the definition of the optimal geometry, experimental tests are performed to validate the numerical results. Finally, a comprehensive laboratory-scale campaign is carried out to evaluate filtration efficiency under various environmental conditions, including different types of contaminants, concentrations, and exposure times.

Numerical Study of Low Engine Order Excitations due to Manufacturing Variability Part 1: Characterization of the Geometric Scatter and its Effect on Forced Response

Abstract The geometric scatter in the surfaces of blades and vanes due to manufacturing variability has an impact on the dynamics but also on the aerodynamics. The loss of the spatial periodicity of the flow due to the geometric variations generates an aerodynamic forcing with a wave number different from the airfoil count on the adjacent rows. In this paper, deviations from the nominal geometry are obtained from a set of scanned parts. The average manufactured geometry is computed through the point-by-point deviations between the scanned parts and the nominal geometry. Then, Principal Component Analysis is applied to the deviations from the average geometry to find a way to describe them in a simple manner. The cold geometries are reconstructed using the mean geometry and the PCA geometric modes; afterwards, a cold-to-hot process is applied to obtain the hot geometry, and finally the resulting aerodynamics are obtained using an in-house CFD solver. The described method is applied to a representative row constituted by packets of vanes. Firstly, the average packet geometry is used to analyze the aerodynamic forcing associated to the geometric variation of the airfoils inside the vane packet. After that, a conceptual study is carried out under some simplified assumptions in order to relate the geometric variability to random low engine order disturbances, using the geometric modes obtained from the PCA analysis. In both cases, the induced vibrations on the adjacent rotor row are comparable to the excitation due to the nominal blade-passing.

Impact of energy deposition as active flow control on scramjet inlet performance using Immersed Boundary Method

This study investigates the impact of upstream energy deposition as an active flow control method on the performance of a two-dimensional scramjet inlet through numerical simulations. An in-house inviscid finite volume solver was employed for the simulations, with boundary reconstruction of the scramjet achieved using a ghost-cell based immersed boundary method. The effects of different energy spot locations, various energy strengths, and different freestream Mach numbers on the scramjet performance were thoroughly analyzed. Four inlet parameters, namely, mass capture ratio (μ), total pressure ratio (TPR), kinetic energy efficiency (ηKE), and flow distortion index (DI), were used to assess the scramjet performance. The analysis revealed that energy deposition significantly reduced flow distortion, resulting in noticeable improvements in mass flux and total pressure ratio. However, kinetic energy efficiency exhibited minimal change. The study provides comprehensive insights into the impact of energy deposition on scramjet performance, highlighting its potential for enhancing inlet characteristics.

Numerical study of granulation in anelastic thermal convection in spherical shells

The present work investigates granulation or convective flow patterns in density-stratified (or anelastic) convection in spherical shells. The density-stratified thermal convection is typically present in astrophysical systems (such as solar convection); motivated by this, we performed a series of three-dimensional anelastic convection simulations in a spherical shell geometry using an in-house developed hybrid solver. We explored the effect of Rayleigh number and density scale height on the convective flow patterns. The granulation (or cell-like structures) are more prominent at higher density scale height and Rayleigh number. The granulation is further characterized by kinetic energy and helicity spectra. Our results support the argument that the convective flow patterns (or granulation) emerge due to inverse cascade owing to the presence of density stratification. Convective patterns (or granulation) are identified based on length scales, time scales, and flow velocity. The length scale of granules is further verified using a solar granulation model. Our analysis suggests the existence of inverse cascade and supergranulation on the spherical surface due to density-stratified thermal convection in spherical shells.

Implementation of a high-order spatial discretization into a finite volume solver: Applications to turbomachinery test cases using an eddy-viscosity turbulence closure

In this study, the implementation of a high-order spatial discretization method into a Finite Volume solver is presented. Specific emphasis is put on the analysis of the performance over selected turbomachinery test cases. High-order numerical discretization is achieved by adopting the cell-centered Least-Square reconstruction, which is implemented in the in-house solver HybFlow. The validation of the adopted methodology is performed by assessing the solution of a turbulent flat plate with zero pressure gradient, using a eddy-viscosity transitional model. The test case also evidences the effect of the discretization of gradient-based source terms when a high-order reconstruction methodology is used. In the second part of the paper, the solver is used for the solution of relevant two-dimensional turbomachinery test cases, assessing the impact of 2nd and 3rd order reconstruction on the prediction of the aerodynamics and the heat transfer for respectively a low-pressure blade and a high-pressure turbine vane. It is shown how a high-order reconstruction allows for obtaining a better prediction of turbomachinery aerodynamics, with lower number of elements. The benefits over heat transfer predictions in high Reynolds number conditions are instead limited to the reduction of heat transfer coefficient spikes in under-resolved regions of the blade. Eventually, the methodology is validated for a three-dimensional low-pressure turbine cascade with realistic boundary layer inflow conditions.

Two quantum algorithms for solving the one-dimensional advection–diffusion equation

Two quantum algorithms are presented for the numerical solution of a linear one-dimensional advection–diffusion equation with periodic boundary conditions. Their accuracy and performance with increasing qubit number are compared point-by-point with each other. Specifically, we solve the linear partial differential equation with a Quantum Linear Systems Algorithm (QLSA) based on the Harrow–Hassidim–Lloyd method and a Variational Quantum Algorithm (VQA), for resolutions that can be encoded using up to 6 qubits, which corresponds to N=64 grid points on the unit interval. Both algorithms are hybrid in nature, i.e., they involve a combination of classical and quantum computing building blocks. The QLSA and VQA are solved as ideal statevector simulations using the in-house solver QFlowS and open-access Qiskit software, respectively. We discuss several aspects of both algorithms which are crucial for a successful performance in both cases. These are the accurate eigenvalue estimation with the quantum phase estimation for the QLSA and the choice of the algorithm of the minimization of the cost function for the VQA. The latter algorithm is also implemented in the noisy Qiskit framework including measurement noise. We reflect on the current limitations and suggest some possible routes of future research for the numerical simulation of classical fluid flows on a quantum computer.

A mass-momentum consistent THINC-scaling scheme for CLSVOF method on co-located grid

Accurate numerical simulation of practical two-phase flows characterized by high density ratios are indeed challenging as spurious interfacial currents may disrupt the solution. To address such complexities, the present work considers a conservative discretization of the incompressible Navier-Stokes equation that advects the mass and momentum consistently on a co-located grid. An algebraic Coupled Level Set and Volume Of Fluid (CLSVOF) approach, based on THINC (Tangent of the Hyperbola for INterface Capturing)-scaling scheme is used to capture the interface. The numerical methodology relies on a balanced treatment of the pressure and other interfacial forces at the discrete level while emphasizing a compatible calculation of mass and momentum fluxes. Effectiveness of the present Consistent Mass-Momentum Transport (CMMT)-based THINC-scaling method is demonstrated by the thorough numerical analysis of advection of a high density drop. The obtained results signify the requirement of a balanced force CMMT framework for accurate and stable simulation of multiphase flows. Furthermore, performance of the present in-house multiphase solver is evaluated from practical tests like capillary wave, dam break, bubble rise and Rayleigh-Taylor instability. The present work is significant as it presents the capability of the CMMT-based THINC-scaling method to resolve precise interface profiles while preserving close to second order spatial accuracy.

The Evolution of Flow Structures and Coolant Coverage in Double-Row Film Cooling with Upstream Forward Jets and Downstream Backward Jets

The spatiotemporal evolution of the flow structures and coolant coverage of double-row film cooling with upstream forward jets and downstream backward jets, having a significant impact on film-cooling performance, is studied using the simplified thermal lattice Boltzmann method (STLBM). Moreover, the effect of the inclination angle of downstream backward jets is considered. The high-performance simulations of film cooling have been conducted by using our verified in-house solver. Results show that special flow structures, such as a sand dune-shaped protrusion, appear in double-row film cooling with upstream forward jets and downstream backward jets, which is mainly because of the blockage effect resulting from the coolant jet with backward injection. The interaction among structures results in the generation of an anti-counterrotating vortex pair (anti-CVP). The anti-CVP with the downwash motion can result in the attachment of coolant to the bottom wall, which promotes the stability and lateral coverage of coolant film. The momentum and heat transport are strengthened as the backward jet is injected into the boundary layer of the mainstream. Although the downstream evolution of the backward jet is not very smooth, its core attaches closely to the bottom wall due to the downwash motion of anti-CVP. Moreover, there is an obvious backflow zone shown in the trailing edge of the downstream backward jet with a large inclination angle. The obvious backflow makes the coolant attach to the bottom wall well. Therefore, the film cooling effectiveness is improved as the inclination angle of the downstream backward jet varies from αdown=135° to αdown=155°, with a constant blowing ratio of BR=0.5. In addition, the fluctuation of the bottom wall’s temperature is weak due to the stable coverage of the coolant layer under αdown=155°. The film-cooling performance with an inclination angle of αdown=155° is the best among all the cases studied in this work. This work provides essential insights into film cooling with backward coolant injection and contributes to obtaining a complete understanding of film cooling with backward coolant injection.

Comparison Of Full-Scale PIV Measurements With CFD Simulations Of A Ship Propeller Inflow

Flow around the ship's hull and specifically the inflow conditions of the propeller(s) critically influence the propeller efficiency and cavitation behaviour. In a typical single-propeller vessel, the hull of the ship creates a velocity deficit in the top part of the propeller disk. This creates suitable conditions for cavitation, which is the main source of noise and vibration both inside the vessel as well as in the marine environment. Recently, two measurement campaigns were performed using a novel full-scale stereo-PIV device built to measure flows around vessels sailing at sea. During the first campaign, performed in one of MARIN's basins, the device was commissioned. The second campaign was performed during a sea trial; it resulted in propeller inflow data that can be used for validating CFD codes. The uncertainty of the PIV measurements was assessed using both campaigns. In the basin, uncertainty bias could be determined by comparing the PIV results with the carriage speed. At sea, the random part of uncertainty was determined by quantifying the standard deviation of the mean velocity for all three velocity components in the wake peak area of the propeller inflow. Overall, the uncertainty was found to be acceptably small, given the scale of the measurement and the necessity to work with naturally occurring seeding particles in the sea. CFD calculations of the same full-scale flow were performed using an in-house flow solver. The CFD results predicted the propeller RPM and the delivered power measured during the full-scale trial well, which gives confidence in the ability of CFD to predict ship trial performance. The comparison of the flow fields was good, with the PIV results demonstrating that full-scale PIV can be done reliably, and that the CFD is able to capture the major features of the flow in the considered area. For a large part of the flow field, the CFD was within the measurement uncertainty band. The wake peak was slightly underpredicted, which may be related to roughness effects on the boundary layer thickness.

Sidewall influence of varying free stream Mach number in ramp induced shock wave boundary layer interactions

This study investigates the three-dimensional (3D) effects introduced by the end walls for an aspect ratio of 1 in ramp-induced shock wave boundary layer interactions. The simulations are performed using a symmetry boundary condition in the spanwise direction at free-stream Mach numbers in 3D. The simulations are performed using an in-house compressible supersonic solver “OpenSBLIFVM”. Two free stream Mach numbers 2.5, and 3 are used in the current work, and the simulated results are compared with the aspect ratio 1 simulations by Mangalagiri and Jammy. The inflow is initialized with a similarity solution; its Reynolds number based on the boundary layer thickness is adjusted such that the Reynolds number at the start of the ramp is kept at 3×105 for all simulations. From the results, it is evident that the introduction of sidewalls resulted in a shorter centerline separation length when compared with the two-dimensional (2D) simulations. This contradicts the results at Mach 2 by Mangalgiri and Jammy where the vortex observed at Mach 2 in the central separation region disappeared with increasing free-stream Mach number. Additionally, the topology of interaction shifted from owl-like separation of the second kind to the first kind when the freestream Mach number increased from 2 to 2.5. It can be concluded that the interaction topology is crucial to the increase or decrease of the central separation length when compared to 2D simulations.

Numerical Simulations of a Ship’s Maneuverability in Shallow Water

It is necessary to maintain maneuverability for ship navigation in shallow water, such as channels, ports and other confined waters. In this study, a turning circle maneuver with 35° rudder deflection and a 20/5 zigzag maneuver for KVLCC2 in shallow waters are tested numerically to directly predict the maneuverability of the ship in shallow water. A viscous in-house CFD solver is applied with the dynamic overset grid approach. The impacts of the water depth on the ship’s maneuverability in terms of turning and zigzag competence are evaluated, and the underlying mechanism is analyzed. The numerical method is validated by comparing it with experimental data on the turning indices, which shows good agreement. It is demonstrated that the turning capability become worse with a smaller depth–draft ratio, thus resulting in a lower yaw rate and a greater steady turning diameter. However, the drift angle and lateral speed are reduced with a smaller depth–draft ratio for zigzag maneuvers, but the overshoot angle and turn lag vary with the water depth non-monotonically.

CFD stability improvement using dynamic mode decomposition of solution update vectors

We present a novel method for improving the numerical stability of finite volume simulations by optimizing the mesh through dynamic mode decomposition of solution update vectors. Our approach leverages dynamic mode decomposition to approximate the non-linear solution evolution as a linear mapping, enabling us to represent the dynamic system with fewer degrees of freedom. By conducting eigenanalysis on the reduced system, we gain insights into the growth rate and oscillation frequency of dominant solution modes. We then identify the control volumes and vertices that have a significant influence on each dynamic solution mode. We compute the gradients of the Jacobian diagonal elements with respect to the movement of the selected vertices. Based on these gradients, we adjust the positions of the vertices to improve the diagonal dominance of the corresponding Jacobian rows. We utilize this approach in conjunction with our in-house flow solver as well as with Ansys Fluent to test its effectiveness when applied to different types of CFD software architecture. We show that the presented methodology is fully non-invasive to the host flow solver and does not require any modifications or access to the source code. Our approach offers a substantial computational cost reduction compared to existing methods for numerical stability improvement. Various results demonstrate the strength and efficacy of this state-of-the-art approach for improving numerical stability through mesh optimization.

Implementation of the High-Performance Computing Summer Institute at Jackson State University

Between May 25, 2023 and June 21, 2023, we hosted the inaugural four-week High-Performance Computing Summer Institute at Jackson State University. This endeavor was made possible through the support of a three-year NSF CISE-MSI grant. The primary objective of this Summer Institute revolved around the engagement, education, and empowerment of minority and underrepresented students in the realm of High-Performance Computing (HPC) within the field of engineering. Nine undergraduate students with diverse background were recruited to participate in this program. Throughout the program, we immersed these students in a comprehensive curriculum that covered various critical facets of HPC. This curriculum encompassed hands-on instruction in Linux operating system command-line operations, C programming within the Linux environment, fundamental HPC concepts, parallel computing utilizing the Message Passing Interface (MPI) library, and GPU computing through OpenCL. Additionally, we delved into foundational aspects of fluid mechanics, geometric modeling, mesh generation, flow simulation via our in-house flow solvers, and the visualization of solutions. At the end of the program, every participant was tasked with delivering an oral presentation and submitting a written report encapsulating their acquired knowledge and experiences during the program. We are excited to share a detailed overview of our program's implementation with our audience. This includes insights into our utilization of ChatGPT to enhance C programming learning and our suggestion of the NSF ACCESS resources to gain access to HPC systems. We are proud to announce that the program has achieved remarkable success, as evidenced by the positive feedback we received from the participants.

Prediction of the aerodynamic noise of an airfoil via the hybrid methods of aeroacoustics

The accurate prediction of the trailing-edge noise and the determination of its sources are essential to reduce fans and propellers noise. This noise component is due to the scattering of the turbulent boundary layer into acoustic waves by the trailing edge. In this paper, the noise emanating from a CD (Controlled-Diffusion) airfoil is simulated and computed via the hybrid methods of aeroacoustics. In these methods, the aerodynamic and acoustic fields are computed separately. The flow data are obtained using the in-house LES solver SFELES. ACTRAN acoustic solver has been used to solve the acoustics and to provide the near and far fields propagation via Lighthill’s analogy. Curle’s analogy is applied as well in its integral compact formulation which takes the presence of walls into account. Curle’s formulation is applied proposing an approach where the volume and surface integrals have been implemented in SFELES to be calculated simultaneously with the flow in order to avoid the storage of noise sources which requires a huge space. In Lighthill’s analogy, sources and near field maps show that the turbulent boundary layer and wake are the more efficient sources and the center of radiation is the trailing edge. The comparison of the numerical results with the experimental measurements, performed by Moreau and Roger and Moreau et al. , shows an overall excellent agreement confirming the capability of SFELES (LES sources) combined with ACTRAN (Lighthill’s analogy) to predict correctly the noise generated by turbulent flows around airfoils. The acoustic spectrum presents an overprediction up to 5 dB at the frequencies 300 Hz and 550 Hz and an underprediction about 5 dB at the frequencies 1100 Hz and 1750 Hz. The sound pressure level (SPL) obtained using the proposed approach of Curle’s analogy matches very well the experimental results. Thus, Curle’s analogy can be used to obtain a fast, approximated and acceptable results about the noise radiation of airfoils avoiding the storage of noise sources which requires a huge space and time.

Entropy damping and Bulk Viscosity based artificial compressibility methods on dynamically distorting grids

Artificial Compressibility Methods (ACM) rely on an artificial equation that links the pressure and velocity fields to model incompressible flows. These hyperbolic/parabolic equations can rapidly converge to a ‘nearly’ divergence-free flow field in contrast to the methods based on the elliptic pressure Poisson equation. We compare the computational efficacy of two ACMs, namely, the Bulk Viscosity ACM (BVACM) and Entropically Damped Artificial Compressibility (EDAC) recently proposed in the literature. The methods implemented in the in-house high-order finite difference solver, COMPSQUARE, are validated for the test cases of a 2D doubly periodic shear layer (DPSL), a 3D Taylor Green Vortex (TGV), and 2D/3D NACA0012 airfoil pitching about the quarter chord. The efficacy of these methods was also tested on static and dynamic grids using conservative metrics. Although both ACMs yield competitive results, the divergence of the velocity field is found to be more prominent in the highly unsteady regions. BVACM resulted in (a) a superior divergence-free velocity field and (b) 20−38% higher maximum stable time than the EDAC, thereby increasing the computational speed. A higher value of the bulk viscosity coefficient, A, although ensures a stringent divergence-free velocity field, is shown to have minimal effect on the flow statistics and reduce the maximum stable time step. The parabolic–hyperbolic nature of the governing equations and the lack of dual time-stepping in BVACM and EDAC ensures that both these methods are highly scalable on massively parallel architectures. Since the energy equation is no longer required to compute the velocity field, both EDAC and BVACM approaches are found to be 8−10% faster than the weakly compressible Navier–Stokes simulations under the low-Mach number limit.

In-flight anti-icing simulation of electrothermal ice protection systems with inhomogeneous thermal boundary condition

Conventional anti-icing computational solvers calculate the convective heat transfer coefficient using a homogeneous thermal boundary condition, assuming a constant temperature across the surface. However, this approach can lead to inaccuracies in regions with significant temperature variations. To address this limitation, the present study proposes a novel approach that utilizes an inhomogeneous thermal boundary condition, which updates the convective heat transfer coefficient based on the transient wall temperature distribution. We developed a unified finite volume framework that efficiently integrates various in-house solvers, including a compressible Navier-Stokes-Fourier (NSF) airflow solver, a Eulerian droplet impingement solver, a PDE-based ice solver, and a multilayer heat conduction solver. Thermal interaction between the different solvers was modeled using the conjugate heat transfer method. The effects of updating airflow on anti-icing results were investigated by comparing the results obtained by coupled and decoupled solvers. While the decoupled solver computes airflow once and remains unchanged, the coupled solver updates the airflow during the anti-icing simulation. Our findings show that the decoupled solver has the highest deviations from the coupled solver in evaporative anti-icing regimes, where dry regions form within the protection limits. Using coupled solvers in designing ice protection systems in evaporative regimes improves temperature prediction accuracy, enabling designers to reduce safety factors and save energy.

Efficient prediction of tidal turbine fatigue loading using turbulent onset flow from Large Eddy Simulations

To maximise the availability of power extraction from a tidal stream site, tidal turbines need to be able to operate reliably when located within arrays. This requires a thorough understanding of the operating conditions, which include turbulence, velocity shear due to bed proximity and roughness, ocean waves and due to upstream turbine wakes, over the range of flow speeds that contribute to the loading experienced by the devices. High-fidelity models such as Large Eddy Simulation (LES) can be used to represent these complex flow conditions and turbine device models can be embedded to predict loading. However, to inform micro-siting of multiple turbines with an array, the computational cost of performing multiple simulations of this type is impractical. Unsteady onset conditions can be generated from the LES to be used in an offline coupling fashion as input to lower-fidelity load prediction models to enable computationally efficient array design. In this study, an in-house Blade Element Momentum (BEM) method is assessed for prediction of the unsteady loads on the turbines of a floating tidal device with unsteady inflow developed with the in-house LES solver DOFAS. Load predictions are compared to those obtained using the same unsteady inflow to the commercial tool Tidal Bladed and from an Actuator Line Model (ALM) embedded in the LES solver. Estimates of fatigue loads differ by up to 3% for mean thrust and 11% for blade root bending moment for a turbine subject to a turbulent channel flow. When subjected to more complex flows typical of a turbine wake, the predictions of rotor thrust fatigue differ by up to 10%, with loads reduced by the inclusion of a pitch controller.

Study of turbulent wavy annular flow inside a 3.4 mm diameter vertical channel by using the Volume of Fluid method in OpenFOAM

In annular downward flow, an annular liquid film flows at the perimeter of the channel pushed down by the gravity force and by the shear stress that the vapor core exerts on it. Depending on the working conditions, the vapor-liquid interface can be flat or rippled by waves. The knowledge of the liquid film thickness is very important for the study of annular flow condensation because the thermal resistance of the liquid is often the most important parameter controlling the heat transfer. A new approach for the simulation of annular flow is here proposed using an in-house developed transient solver based on the Volume of Fluid (VOF) adiabatic solver interIsoFoam available in OpenFOAM. With the VOF method, in addition to the standard set of equations (continuity and momentum), a transport equation related to the advection of the volume fraction scalar field has to be solved. The numerical setup consists of 2D axisymmetric domain. An adaptive mesh refinement (AMR) method is added to the solver to better capture the interface position. The k-ω SST model is used for turbulence modelling in both the liquid and vapor phases and a source term (whose magnitude is controlled by a model parameter named B) is included in the ω equation to damp the turbulence at the interface.