Assumption Of Incompressible Flow Research Articles

Interactive Airfoil Optimization Using Parsec Parametrization and Adjoint Method

In the development of interactive aerodynamic optimization tools, the need to reduce the computational complexity of flow calculations has arisen. Computational complexity can be reduced by estimating the flow variables using machine learning, but that approach has a number of hindrances. Avoiding these hindrances through lowering the computational complexity by stating the assumptions of inviscid incompressible potential flow is the focus of this article. The assumptions used restrict the applicability of this approach to only specific cases, but in engineering practice, these cases are quite widespread. The assumptions allowed the coupling of the adjoint method with parsec parametrization and the panel method, yielding a highly computationally efficient and robust tool for optimizing an airfoil’s lift coefficient (Cy). The optimization of the NREL S809 airfoil was carried out, and the results were verified using the Xfoil 6.99 software. The Xfoil verification showed that by making minimal changes to the airfoil’s shape, the Cy and lift-to-drag ratios were significantly improved. The improvement magnitude was over 94% for a 0 deg angle of attack (AoA) and over 16% for 6.2 deg AoA. This indicates an improvement in performance that is similar to that of some genetic algorithms, but with computational costs that are many orders of magnitude lower.

Characteristics and evolution of ground vortex under heaving ground conditions: Insights from large eddy simulation (LES) analysis

When an aircraft engine operates near the ground, the ambient vortices generated by the freestream velocity boundary layer and engine suction will gather and lift, forming ground vortices which may result in intake distortion, consequently affecting the engine operation stability. To develop a shipborne test platform, this study conducted large eddy simulation calculations using the ANSYS Fluent and based on the assumption of incompressible flow. The 3-D unsteady Navier-Stokes (N-S) equations were solved using the WALE sub-grid model. The analysis focused on the characteristics and evolution of ground vortices under heaving ground conditions within 1 s. The results indicate that the ground vortex exhibits strong unsteady characteristics. During the descending phase of the platform, the quantity of vortex formed beneath the intake duct would decrease while the trailing vortex becomes more pronounced. However, the structure of the inlet vortex remains relatively unchanged at each time step. The intensity of the vortex and pressure distortion coefficient exhibit significant fluctuations over time, and their temporal variations approximately follow a sinusoidal function, which is also the heaving motion of the platform. Generally, when the velocity of the platform reaches its maximum downward vertical value, the average vortex intensity of the ground vortex tends to be minimal while the pressure distortion coefficient approaches its maximum value. Conversely, when the velocity of the platform reaches its maximum upward vertical value, the opposite trend can be observed.

A novel order-separated generalized feedforward design for motion control in energy-efficient electrohydraulic system with proportional and integral feedback

Existing feedforward, or FF, controllers are based on differentially flat models. For double-acting single-rod cylinders, more compact than the double-rod ones, flat models could be constructed either under an incompressible-flow assumption for low-pressure, slow-response applications or for a matched valve-cylinder combination. Contrasting the existing models tackling only a single nonlinear aspect like valve leakage, oil compressibility or friction, a novel FF controller, generalized for different types of valve-cylinder-pump combinations, has been developed here. It is based on the highest-order assumption of incompressible flow that sustains the piston motion. An FFPI controller has been implemented in a laboratory setup for displacement tracking against sinusoidal demands up to 9 Hz frequency. The FF parameters has been estimated by minimizing the deviation of simulation prediction from an offline experimental time-varying response. The PI gains have been selected through a stability analysis by extending Routh criteria for linearized time-variant error dynamics. Comparison against a PI-only controller with identical gains has established the energy-saving potential of the FFPI controller both working with the same variable-displacement pump. In comparison to existing nonlinear adaptive controllers, more precise and smoother responses have been obtained over wider frequency range at lower control expenses, admittedly with occasional marginal penalty in the phase variation. The FFPI controller has exhibited the shortest transient and the highest resilience against measurement noise.

Numerical analysis of the binder angle effect on convective heat transfer and pressure drop in drilled-hollow sphere architected foams

Due to their capability of generating customized microstructures, additive manufactured cellular materials are promising to being employed in heat transfer devices. To this aim, among printable cellular materials Drilled-Hollow Spheres Architected (DHSA) foams are investigated. However, at the present status, limited data on pressure drop and heat transfer in DHSAs are available. Starting from hollow spheres, a metal DHSA foam is generated with CAD software in this study. Forced air convective heat transfer in the foam is investigated numerically, under the assumptions of air incompressible laminar flow and uniform wall heat flux from the solid to the fluid phase. Mass, momentum and energy equations in the fluid region are written and solved numerically, for various values of the foam binder angle and the velocity of the inlet air. The convective heat transfer coefficients, the pressure drop and the friction factor are predicted. The effects of the binder angle and the air inlet velocity on heat transfer and pressure drop are highlighted.

Extension of the delayed equilibrium model to flashing flows of organic fluids in converging-diverging nozzles

Flashing flows of organic fluids find application in various energy systems, but the available modelling approaches rely on semi-empirical correlations calibrated for other fluids and operating conditions. This paper extends the state-of-the-art one-dimensional models developed for water to flashing of organic fluids, using R134a as a reference. First, the delayed equilibrium model combined with Grönnerud's friction correlation is identified as the most appropriate approach, reducing the error on mass flow rate with respect to experimental results from 48.3 %, obtained with the homogeneous equilibrium model, to 10.3 %. Then, the traditionally adopted incompressible flow assumption for the metastable liquid phase is replaced by a dedicated thermodynamic model, preventing the appearance of unphysical metastable phase temperatures. Moreover, the delayed equilibrium model is tailored to R134a by tuning the semi-empirical coefficients of the constitutive law. The proposed modifications to the state-of-the-art delayed equilibrium model result in an improvement in the prediction of the pressure profiles and the mass flow rate for flashing flows of R134a, with a decrease in the error on mass flow rate from 10.3 % to 6.1 % with respect to the original formulation.

A numerical study of gas focused non-Newtonian micro-jets

The present numerical study assesses the jet length, diameter and velocity of various non-Newtonian power-law fluids of a gas dynamic virtual nozzle. A related two-phase flow problem is formulated within the mixture framework and solved with the finite volume method and volume of fluid interface treatment in axisymmetry. The process parametric range allows the incompressible laminar flow assumption. A comprehensive jet characteristics analysis is carried out in a typical micro-nozzle configuration for a range of shear-thinning to shear-thickening fluids with power law indices 0.5 ≤ n < 1.5, gas mass flow rate of 10 mg/min and liquid volumetric flow rate of 43 µl/min, resulting in a gas Reynolds number of 130 with Reynolds and Weber numbers for a reference water jet being 90 and 10, respectively. It is observed that jets from shear-thinning fluids (0.5 ≤ n < 1.0) tend to be thicker, longer, and slower when compared with the shear-thickening fluids (1.0 < n ≤ 1.5). A dripping-jetting phase diagram of the nozzle is constructed by varying the power law index, gas and liquid flow rates in the range 0.9–1.1, 5–15 mg/min and 5–50 µl/min, respectively. It is observed that the area of stable jetting decreases with the increase of the power law index. The obtained novel information on the behaviour of non-Newtonian gas-focused micro-jets provides a possible new dimension for tailoring the serial crystallography sample delivery systems where the micro-jets carry dispersed crystals into an X-ray beam.

Design and optimization of an integrated novel desalination system based on the temperature difference between the sea and mountain

As the world’s population and increasing urbanization continue to grow, freshwater needs have risen dramatically. A desalination process based on a natural vacuum and pipeline desalination method that can produce freshwater and transfer it simultaneously is designed and modeled comprehensively in this research. It has been demonstrated that the effect of compressibility is negligible for pressure and temperature ranges of the system, indicating that the first system model using incompressible flow assumption is valid. Solar thermal energy was also utilized to improve the system’s efficiency. The results are investigated for three scenarios for Bandar-Abbas and the adjacent mountain, Genu. The first, second, and third scenarios are associated with the initial model based on pipeline desalination, the model utilizing solar cooling to reduce the temperature in the condensation section, and the model using solar energy to increase the temperature in the evaporation section, respectively. The results show that the highest freshwater production is estimated at 125,842,962 and 21,101,132 kg per year for a tube diameter of 2 and 1 m, respectively. Furthermore, the annual production rate of distilled water in scenarios #2 and #3 increased by 13.85% and 139.1% compared to scenario #1, with a tube diameter of 2 m.

CFD analysis on blood flow inside a symmetric stenosed artery: Physiology of a coronary artery disease.

This research article interprets the computational fluid dynamics analysis on blood flow inside a symmetric stenosed artery. The current problem models the blood flow inside the left coronary artery as having a symmetric stenosis in the central region. A comprehensive physiological examination of coronary artery disease is numerically evaluated by using the computational fluid dynamics toolbox Open-Field Operation And Manipulation. There are no assumptions of mild stenosis taken into account since the considered stenosis has an exactly measured length, height and position, etc. The blood flow problem is modeled for the non-Newtonian Casson fluid with unsteady, laminar, and incompressible flow assumptions. The underlying problem is solved numerically in its dimensional form. A thorough graphical analysis is provided on the blood flow simulations, pressure profile, velocity line graphs, pressure line graphs, and streamlines for the left coronary artery having a symmetric stenosis formation. The considered artery is divided into three sections, i.e. pre-stenosis, post-stenosis, and stenosis region, and the velocity and pressure line graphs are plotted for these considered regions. The graphical illustrations provide a detailed analysis of how the blood flow is affected inside the left coronary artery due to coronary artery disease. These pre- and post-stenosis velocity line graphs reveal two intriguing results: In the pre-stenosis zone, the velocity increases with increasing axial coordinate length, whereas in the post-stenosis region, the velocity decreases with rising axial coordinate length. It is evident that as the flow moves toward the stenosis region, the flow profile rises; yet, after passing through the stenosis zone, the flow profile begins to fall as the flow moves away from the stenosis region.

Hybrid nanofluid turbulent transportation through a tube with an innovative twisted tape combined with helical fins heat sink

To ameliorate the convective flow of testing fluid inside the absorber pipe of solar water heater, new design of twisted tape combined with helical fins heat sink has been suggested in current article. While there are benefits in existence of turbulator, the greater pressure drop stems from this too. To consider the main efficacy of mounting such device, numerical simulation based on finite volume approach was presented considering assumptions of incompressible steady turbulent flow. Besides, to ameliorate the thermal features of water it was mixed with hybrid alumina-grapheme nanoparticles with ϕ = 0.035 which is reasonable range for approximation of homogeneous mixture. Different simulations were simulated to detect the efficacy of Re (ranging from 4500 to 18000), distance between fins (b = 0.33R, 0.5R) and fraction of hybrid nanomaterial (ϕ = 0, 0.035). Nu enhances around 2.61 % with rise of ϕ because of augmentation of convective flow when b = 0.33R, Re = 4500. As five helical fins were mounted and Nu has been augment around 70.52 % while Darcy factor has been increased around 692.08 %. As Re rises from 4500 to 9000, Darcy factor declines around 22.72 % while Nu increases around 76.31 % in absence of helical fins. The same change in Re when b = 0.33R, leads to augmentation of Nu about 63.21 % and reduction of Darcy factor about 24.53 %.

Measurements of the relative permeability to CO2‐and‐brine multiphase fluid of Paaratte formation at near‐reservoir conditions

AbstractCO2 sequestration in deep saline aquifers is a promising method to reduce atmospheric CO2. The on‐going CO2CRC Otway project aims to demonstrate the effectiveness of large‐scale CO2 storage in deep saline formations and to develop new monitoring technologies in Australia. The relative permeability curves are essential for predicting the movements of CO2 and estimate residual trapping in the aquifer during and after injection through numerical simulations. However, studies of relative permeability curves for the Paaratte sandstone at the in situ conditions are limited. In addition, different rock types in the Paaratte formation can behave differently when CO2 displaces brine. This work reports four relative permeability experiments of CO2/brine systems using the unsteady‐state core flooding method for different types of rock collected from various depths of Paaratte formations at near‐reservoir conditions. The relative permeability results calculated from the analytical Johnson, Bossler, and Naumann (JBN) method and the numerical history matching method are compared. The JBN method does not calculate the relative permeability accurately for CO2/brine systems due to the assumptions of incompressible flow, since the CO2 relative permeability results calculated from the JBN method are similar for all the cases. The history matching results show that the brine (water) relative permeability of the core samples with a high fraction of macropores is similar to the measurements for Paaratte formation reported in the literature over a large range of brine (water) saturation. In contrast, the brine relative permeability of the core samples with a high fraction of micropores is considerably higher than that of the core samples with macropores, suggesting better connectivity for the samples with a high fraction of micropores. The new findings will be useful in reservoir‐scale numerical modelings of the Paaratte formation to more accurately predict the movement of CO2 during and after the injection. © 2021 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Simulation of aeroacoustics of low Mach number flow with the use of wave equation model

Results of simulations of the noise generated by a turbulent flow around a simplified rain gutter of a car windshield are presented. The hybrid approach of ANSYS FLUENT used the scale-resolving SBES model for calculating a turbulent flow under an incompressible flow assumption, and the wave equation model for the propagation of acoustic perturbations. The mean static pressure and the sound intensity obtained in the simulations were compared with experimental data and were found to be well predicted.

Reconstructing the Velocity and Deformation of a Rapid Landslide Using Multiview Video

AbstractNoncontact measurements of spatially varied ground surface deformation during landslide motion can provide important constraints on landslide mechanics. Here, we present and test a new method for extracting measurements of rapid landslide surface displacement and velocity (accelerations of approximately 1 m/s2) using sequences of stereo images obtained from a pair of inexpensive, stationary 4K video cameras with nominal frame rates of 29.97 Hz. The method combines elements of Structure from Motion with those of optical flow to extract data on 3‐D evolution of the ground surface during slope failure. We apply the method to an experiment at the U.S. Geological Survey debris‐flow flume in which a high‐speed, liquefying landslide was triggered by gradually adding water to a 6‐m3 prism of loosely packed sediment on a 31° slope. Strip‐scanning lidar measurements made during the experiment corroborate our video‐based measurements, but the latter encompassed the entire landslide surface and were much lower in cost. Our video‐based measurements enabled computation of depth‐integrated landslide dilation/contraction rates. The range of computed rates was within the ranges inferred from independent measurements of evolving pore water pressures and reasonable estimates of the hydraulic permeability of the sediment. Dilation and contraction rates play a crucial role in landslide mechanics. The dilation and contraction we observe contradict the incompressible flow assumption used in many studies that have employed noncontact methods to infer landslide properties.

Incompressible flow assumption in hydroacoustic predictions of marine propellers

Incompressible flow assumption is an essential step that simplifies numerical simulations for objects inside flowing water. However, incompressibility assumption creates a conflicting situation for sound propagation as the propagation speed is given by c0=dp/dρ where p denotes the pressure and ρ denotes the density. When dρ=0 is assumed to relieve simulations, speed of sound theoretically becomes infinite and therefore, induced pressures should be corrected with the acoustic analogy. This approach is called the “hybrid method” that combines hydrodynamic solver with hydroacoustic solver. Hydroacoustic solver adds compressibility effects to the incompressible hydrodynamic solver and uses hydrodynamic pressure to calculate acoustic pressure. Time step size is an important parameter to calculate acoustic pressure field in the fluid domain and an approach to determine the minimum value (for at least capturing the first blade passage frequency) is presented in this study. Another purpose of this paper is to investigate the effect of incompressibility on hydroacoustics and to analyze the necessity of utilising the famous Ffowcs Williams-Hawkings (FWH) equation for predicting marine propeller noise; both for cavitating and non-cavitating cases. Our results are in line with other researchers; hydrodynamic pressure is sufficient to assess the hydroacoustic performance of marine propellers in the near-field due to having very low acoustic Mach numbers. Near-field results from the hydrodynamic solver are then extrapolated to the far-field by adopting ITTC distance normalization equation. However; this equation, which is actually the inverse distance law, is only valid for point noise sources in stationary flow. It is found out that eliminating FWH equation by coupling the incompressible hydrodynamic solver with ITTC distance normalization equation fails to produce satisfactory results. For cavitating cases, numerical results in this study show that implementation of FWH is required even in the near-field.

Numerical study on the fluid dynamical aspects of atomic layer deposition process

Computational fluid dynamics investigations on the mixing process of gases inside an atomic layer deposition (ALD) reactor are carried out. A test case involving a real ALD reactor geometry is investigated under nonreacting, incompressible flow assumption. The relatively low Reynolds number (Re) of the test reactor, often being in the laminar regime, advocates the usage of scale-resolving simulations. The authors investigate mixing of two precursors in two different injection configurations for 40 &amp;lt; Re &amp;lt; 2400. The feasibility of the approach is shown and discussed. The results illustrate how both Reynolds number and injection configurations influence the precursor distribution in the ALD reactor. The authors also carry out a set of experiments in the same ALD reactor and discuss them in light of the simulations.

Aerodynamic Modelling and Analysis of a Novel Mechanism for Chord and Camber Morphing Wing

This paper presents the aerodynamic modelling and analysis of surfaces created by a novel deployable mechanism, which is composed of a four-bar linkage and a scissor-structural mechanism (SSM) which contains several scissor-like elements (SLEs). With the help of that mechanism, which is located inside the trailing portion of wing section, continuous adjustment of the airfoil is possible. In order to highlight the advantageous aerodynamic characteristics of newly created airfoil geometries via proposed SSM, several aerodynamic analyses have been performed. The flow characteristics used for the analyses are determined by the flight envelope of an intended generic UAV. Since the maximum speed range of the sample aircraft is well below Mach 0.3, incompressible flow assumption is made throughout the solutions and conservation laws of Reynolds Transport Theorem are employed.

Numerical investigation of fluid flow and heat transfer characteristics in a helically-finned tube

In order to investigate the characteristics of flow and heat transfer rate in a Helically-finned tub (HFT), we used continuity, momentum and energy equations under a steady, three-dimensional and incompressible fluid flow assumptions. For the performance metrics, we considered the Darcy friction factor, Colburn j-factor, volume goodness factor and area goodness factor of the HFT. We could also evaluate the effect of geometry parameters on the results of local pressure coefficient, fluid vorticity and Nusselt number of the HFT. We carried out the CFD calculation for a range of laminar flow (Re = 100) and turbulent flow (Re = 2000 and 10000). In a laminar and turbulent flow regime, the friction factor increases with increasing the each geometric parameter. While the Colburn j-factor decreases as increasing these geometric parameters. Consequently, the thermal performance of HFT is poorer than that of single straight circular tube type because of having a small volume and area goodness factor as increasing the Reynolds numbers.

Computational analysis of blood flow and wall mechanics in a model of early atherosclerotic artery

In this paper, the model of the early atherosclerotic artery was introduced to investigate the blood flow and wall mechanics and the effects of atherosclerosis on neighboring healthy arteries. Under the assumptions of unsteady, laminar, Newtonian, viscous, and incompressible blood flow and linear-elastic, isotropic, and incompressible vessel wall, the finite element method was used to construct the fluid-structure interaction scheme. Results show that wall shear stress is lower, and cyclic strain is higher in the neighboring healthy arteries than those in the atherosclerotic artery. The hemodynamic and wall mechanical factors are disadvantageous to the healthy arteries and have negative effects. The mechanical changes induced by early atherosclerosis may cause the disease to spread to the healthy arteries. This work proves that early diagnosis and treatment are important in preventing the further development and propagation of atherosclerosis.

Design of a Kaplan turbine for a wide range of operating head -Curved draft tube design and model test verification-

As for turbomachine off-design performance improvement is challenging but critical for maximising the performing area. In this paper, a curved draft tube for a medium head Kaplan type hydro turbine is introduced and discussed for its significant effect on expanding operating head range. Without adding any extra structure and working fluid for swirl destruction and damping, a carefully designed outline shape of draft tube with the selected placement of center-piers successfully supresses the growth of turbulence eddy and the transport of the swirl to the outlet. Also, more kinetic energy is recovered and the head lost is improved. Finally, the model test results are also presented. The obvious performance improvement was found in the lower net head area, where the maximum efficiency improvement was measured up to 20% without compromising the best efficiency point. Additionally, this design results in a new draft tube more compact in size and so leads to better construction and manufacturing cost performance for prototype.The draft tube geometry parameter designing process was concerning the best efficiency point together with the off-design points covering various water net heads and discharges. The hydraulic performance and flow behavior was numerically previewed and visualized by solving Reynolds-Averaged Navier-Stokes equations with Shear Stress Transport turbulence model. The simulation was under the assumption of steady-state incompressible turbulence flow inside the flow passage, and the inlet boundary condition was the carefully simulated flow pattern from the runner outlet. For confirmation, the corresponding turbine efficiency performance of the entire operating area was verified by model test.

Computational analysis of erosion in a radial inflow steam turbine

Abstract In the present work, the erosion of the blades of a radial inflow turbine due to the ingested steam flow containing solid particles was investigated in detail. The study has been conducted by designing and modeling the 3D geometry of the turbine using the CFturbo tool and by carrying out a series of CFD simulations using the software package ANSYS CFX 15.0. As compressibility effects may affect the output results, a study was conducted to ensure the validity of the incompressible flow assumption. Furthermore, the erosion simulation results indicated that there are three main surface areas where significant erosion occurs. The first and by far the most affected part of the studied radial steam turbine is the trailing edge of the stator blade, where a relatively huge number of particles with sharp angles strike the surface. This surface area is found to be affected by a concentration effect, where a high number of particles impinge on a small surface area continuously. The second but less affected part is the leading edge of the suction side of the rotor blade, where the particles strike the blade surface many times. The particles are trapped in a vortex area between the trailing edge of the stator blades and the leading edge of the rotor blades. The third surface area which is eroded significantly is the central region of the pressure side of the rotor blade. However, the blade erosion in this area is less than the other two areas. Additionally, the effects of several factors such as the rotor rotational speed, input mass flow and particle size on the erosion have been studied in detail. The relations between these factors and the erosion rate density have been determined.

Characterisation of sheet cavity noise of a hydrofoil using the Ffowcs Williams–Hawkings acoustic analogy

Concerns about pollution of the marine environment with ship-induced noise and the scarcity of available numerical methods have recently stimulated significant amounts of research in hydroacoustic modelling. In this work, Large Eddy Simulation (LES) is used with Schnerr–Sauer mass-transfer cavitation model and a porous Ffowcs Williams–Hawkings (FW-H) acoustic analogy in order to simulate sheet cavitation on a NACA0009 hydrofoil. The aim is to investigate how well the proposed method captures the dominant noise sources associated with periodic sheet cavitation. The study further focuses on practical aspects, such as the importance of the non-linear FW-H term and convergence of the acoustic solution depending on the choice of the integration surface. This is done by correlating the radiated noise with integral and local flow quantities, such as cavity volume, lift coefficient and local vapour content. A key finding of the study is that the simulation framework is capable of correctly capturing the monopole nature of the sound generated by an oscillating cavity sheet. Results indicate that the numerical method is incapable of accurately resolving the flow during the final collapse stages of smaller cavity clouds, mainly due to mesh density limitations and the use of an incompressible flow assumption. Lack of small-scale bubble structures also causes the high-frequency range of the noise spectra to be under-predicted. Despite certain limitations the presented method offers a significant insight into the nature of cavitation-dominated noise and allows for some of the dominant sound generating mechanisms to be categorised.