Diffuser Geometry Research Articles

Discrete strong extremum principles for finite element solutions of advection‐diffusion problems with nonlinear corrections

AbstractA nonlinear correction technique for finite element methods of advection‐diffusion problems on general triangular meshes is introduced. The classic linear finite element method is modified, and the resulting scheme satisfies discrete strong extremum principle unconditionally, which means that it is unnecessary to impose the well‐known restrictions on diffusion coefficients and geometry of mesh‐cell (e.g., “acute angle” condition), and we need not to perform upwind treatment on the advection term separately. Moreover, numerical example shows that when a discrete scheme does not satisfy the strong extremum principle, even if it maintains the global physical bound, non‐physical numerical oscillations may still occur within local regions where no numerical result is beyond the physical bound. Thus, it is worth to point out that our new nonlinear finite element scheme can avoid non‐physical oscillations around sharp layers in advection‐dominate regions, due to maintaining discrete strong extremum principle. Convergence rates are verified by numerical tests for both diffusion‐dominate and advection‐dominate problems.

Diffuse interface modeling of non‐isothermal Stokes‐Darcy flow with immersed transmissibility conditions

AbstractThe coupling between free and porous medium flows has received significant attention since it plays an important role in a wide range of problems from fluid‐soil interactions to biofluid dynamics. However, modeling this coupled process remains a difficult task as it often involves a domain decomposition algorithm in conjunction with a special treatment at the interface. The problem can become more challenging under non‐isothermal conditions because it requires the iterative procedure at every time step to simultaneously meet the transient mass continuity, force equilibrium, and energy balance for the entire system. This article presents a diffuse interface framework for modeling non‐isothermal Stokes‐Darcy flow and the corresponding finite element formulation that bypasses the need for explicitly splitting the domain into two, which enables the unified treatment for distinct regions with different hydrothermal flow regimes. To achieve this goal, we employ the Allen‐Cahn type phase field model to generate the diffuse geometry, where the solution field can be seen as a regularized approximation of the Heaviside indicator function, allowing us to transfer the interface conditions into a set of immersed boundary conditions. Our formulation suggests that the isothermal operator splitting strategy can be adopted without compromising accuracy if the heat and mass transfer processes are decoupled by assuming that the density and viscosity of the phase constituents are independent to the temperature. Numerical examples are also introduced to verify the implementation and to demonstrate the model capacity.

Ground effect of an inverted double element wing diffuser on a sedan car

The diffuser is a critical component in sports cars, enhancing aerodynamics by increasing downforce and reducing drag. Previous studies have focused on its dependence on diffuser incidence, height, and base pressure. The design of the car, particularly the rear end shape and the rear wing's presence, affect base pressure and the diffuser's performance. Previous studies have investigated the effects of diffuser geometry on aerodynamic performance, but the current study is the first to examine the relationship between the diffuser and the rear tires. It also provides specific and quantitative results on the impact of different diffuser design parameters on drag and downforce. The relationship between the rear tires and the double-element inverted wing diffuser using computational fluid dynamics (CFD) was investigated. This is an essential problem because the diffuser is a critical component of sports cars, and its design can significantly impact aerodynamic performance. CFD was used to simulate the flow of air around the car model. The CFD model was based on the Nissan Sunny (Versa) type Almera design, and the diffuser main element and flap wing angles were set at 4 and 15.5°, respectively. The flap gap, overlap distance, and wing ride height above the ground were varied to achieve an optimal aerodynamic design. The study found that the wing's ride height significantly influences the flow through the diffuser. The diffuser significantly impacts base pressure and downforce production. Increasing the ride height decreases base pressure, leading to an increase in downforce until a specific point near the car body, where downforce further increases. The study concluded that the best double-element diffuser design was selected based on lift-to-drag results and the allowable dimensions of the car, wing ride height, element gap, and overlap distances. Ultimately, the best diffuser wing design features a ride height of 154 mm, a gap distance of 10 mm, and an overlap of 5 mm. This design reduces drag by approximately 2.7 % and remarkably increases downforce ten times compared to the baseline car model.

Thermal and dynamic characterization of a multi-jet system with different geometry diffusers

This paper proposed to use the impinging jets mixing process to improve the quality of residential heating and air conditioning. The main objective is to meet the requirements of occupants in terms of thermal comfort and air quality by proposing an optimal solution for the thermal homogenization improvement in the rooms by changing of the diffusers geometry and their arrangement in the ventilation and air-conditioning devices in blowing systems. This study involves both experimental and numerical studies of a three diffusers configurations composed of four peripheral jet with similar geometries and a central jet with a different geometry. All the configurations consist of four equidistant peripheral swirling jets, only the central jet that makes the difference between them. The configuration 1 includes a swirling central jet, on the other hand a circular central jet for the configuration 2 and finally a lobed central jet for configuration 3. The velocity and temperature distributions of the three configurations are investigated experimentally and numerically. Experimentally, the multifunction thermo-anemometer have been used to measure flow temperature and velocity. The dynamic and temperature features are more radially spread and get better homogeneity in configuration 3 and this is due to the energy distribution on the radial plane, which is relatively better than configuration 1 and configuration 2. The second part deals with numerical predictions of the dynamics and thermal fields of the three configurations considered. The study was realized using a RANS-based turbulence model. The numerical results are in reasonable agreement with our experiments for the three configurations. With this study, detailed information on the structure of the resulting flow is very useful to deepen the understanding of the physics of jet interaction and to validate turbulence models. The turbulence simulation is realized by the k-ω-SST model. This model gives a satisfactorily predicts the axial drop in velocity and temperature over the entire study range, demonstrating its ability to handle the interaction between swirling and lobe jets. Our results show that the geometry of the central diffuser is essential. This allows the axial velocity to decrease faster than configurations 1 and 2. This increases lateral diffusion, resulting in better homogenization.

Limitations and generalizations of the first order kinetics reaction expression for modeling diffusion-driven exchange: Implications on NMR exchange measurements.

The study and modeling of water exchange in complex media using different applications of diffusion and relaxation magnetic resonance (MR) have been of interest in recent years. Most models attempt to describe this process using a first order kinetics expression, which is appropriate to describe chemical exchange; however, it may not be suitable to describe diffusion-driven exchange since it has no direct relationship to diffusion dynamics of water molecules. In this paper, these limitations are addressed through a more general exchange expression that does consider such important properties. This exchange fraction expression features a multi-exponential recovery at short times and a mono-exponential decay at long times, both of which are not captured by the first order kinetics expression. Furthermore, simplified exchange expressions containing partial information of the analyzed system's diffusion and relaxation processes and geometry are proposed, which can potentially be employed in already established estimation protocols. Finally, exchange fractions estimated from simulated MR data and derived here were compared, showing qualitative similarities but quantitative differences, suggesting that the features of the derived exchange fraction in this paper can be partially recovered by employing an existing estimation framework.

Comparative analysis of modified jet diffuser geometry for evaluating the impact of rounded edges and chamfered design on cooling efficiency of electronic components in cross flow and impinging jet

Comparative analysis of modified jet diffuser geometry for evaluating the impact of rounded edges and chamfered design on cooling efficiency of electronic components in cross flow and impinging jet

Study of nanofluid flow and heat transfer in a stationary cone-disk system

Rheometric, viscosimetric, bio-medical, and several other pharmaceutical machineries utilize the structural advantages provided by the geometry of a stationary conical diffuser. The problem of the Buongiorno nanofluid flow in the conical gap of a stationary cone-disk system for isothermal boundaries is studied. The governing system, comprising the incompressibility condition, Navier–Stokes equation, energy conservation equation, and conservation of Nanoparticle Volume Fraction (NVF) equation, is analyzed. The Lie-group theory has been used to derive a self-similar model. Solutions of the self-similar equations were computed numerically, and the expressions for the Nusselt number and Sherwood number are obtained. The parametric investigation reveals that the heat and mass transfer rate subside significantly when pre-swirl is introduced to the flow. Furthermore, the nanofluid slip mechanisms enhance the effective temperature of the system.

Enhancing the efficiency of an axial impulse turbine with a diffuser

In oscillating water column wave energy converters, the aerodynamic losses caused by flow misalignment between the rotor outlet and the outlet guide vane of self-rectifying impulse turbines are a significant design problem. The symmetrical positioning of guiding vanes on both sides of the rotor is the reason for it. In comparison to the equivalent Wells turbine, the efficiency of impulse turbines is lower because of these losses in the outlet guide vane. This paper presents a strategy to develop animproved design of an axial impulse turbine to reduce the losses in the outlet guide vane along with the residual kinetic energy loss by integrating a diffuser between the rotor and guide vanes. The proposed model was investigated numerically using RANS simulations. Multiple diffuser geometries were tested against the reference turbine for comparison of the performance characteristics. The results support the hypothesis behind the proposed design. The performance was compared extensively with the reference case in terms of the dimensionless loss coefficients for a better insight into the contribution of all the turbine sectors. The current work shows a possible design path for the performance improvement of the turbine. Results also support the fact that the guide vanes need to beredesigned for obtaining maximizing efficiency with the proposed design. The losses in the outlet guide vane were reduced by approximately 50% with an overall efficiency rise of around 2%.

Effect of Geometrical Parameters on the Exit Pattern Factors Of An Annular Combustor: An Experimental Study

Combustor is an important component of a gas turbine engine and its performance governs the overall performance of the engine. Combustor exit pattern factors are very critical from the consideration of turbine blade and vane life. To achieve the desired goal of pattern factors, the air-management through different zones of combustor is to be carried out very carefully with proper fuel-air mixing followed by complete combustion in the primary zone. During the development stage, extensive studies have been carried out to establish the effect of different geometrical parameters of the combustor on the exit pattern factors. This paper describes the details of the experimental investigations carried out on a full- scale combustor with different geometrical parameters such as diffuser geometry, swiller configuration, atomizer flow passage and dilution zone configurations to study their effect on the exit pattern factors. Dilution zone geometrical parameters and swirler configuration are found to have strong influence in controlling the combustor exit pattern factors and there is an optimum size and spacing of the dilution holes to achieve desired pattern factors at combustor exit.

Effect of Diffuser Geometry on the Performance of an Annular Aero Gas Turbine Combustor

Combustor is an important component of a gas turbine engine and its performance governs the overall performance of the engine. This paper describes the effect of diffuser geometry on the performance parameters of short annular combustors. Full-scale combustors having similar liner configurations but different diffuser geometry were tested in the combustor test facility for this investigation. The combustor aerothermal characteristics such as light-up behavior, exit temperature pattern factors and combustion efficiency are found to be inde- pendent of diffuser geometry. But the major aerodynamic parameters such as diffuser pressure loss, static pressure recoveries etc are significantly affected by the diffuser geometry.

Exhaust condensation through porous bed in the primary zone of novel dump diffuser geometry

The work presented in this article deals with the reduction of air pollution generated by automobiles. It is accomplished through the process of condensation using novel techniques such as utilization of porous metal foams. A modified geometry dump diffuser is used to facilitate flow of exhaust gases slowly around copper coils thereby condensing them. The condensed gases can be collected and stored in a chamber and then can be carried to industries for recycling. This article involves design of the modified geometry dump diffuser using CATIA V5 tool. The computational fluid dynamics (CFD) analysis of the model is carried out using the ANSYS Fluent software. The inlet parameters are obtained as per the exhaust characteristics of a typical 0.8 l 3-cylinder Gasoline Engine. The results are presented for modified geometry dump diffuser models with and without porous bed. Porous bed module is used to simulate the presence of metal foams in the primary zone and inside the inner fluid zone. The results are presented. The results show that the modified geometry dump diffuser model with porous bed can cool the exhaust gases to their condensation temperature. This model can be employed in automobiles to reduce air pollution.

Diffusion-modulated colorimetric sensor for continuous gas detection.

Due to their high sensitivity and selectivity, low cost, and good compatibility for sensor array integration, colorimetric gas sensors are widely used in hazardous gas detection, food freshness assessment, and gaseous biomarker identification. However, colorimetric gas sensors are usually designed for one-time discrete measurement because the sensing materials are entirely exposed to analytes during the sensing process. The fast consumption of sensing materials limits colorimetric sensors' applications in continuous analytes monitoring, increases the operation complexity and brings challenges for calibration. In this work, we reported a novel sensor design to prolong the lifetime of colorimetric gas sensors by engineering the gas diffusion process to preserve the sensing materials. We compared two geometries for gas diffusion control in a sensing matrix through simulation and experiment on an ammonia sensing platform. We found that the 2-dimensional gas diffusion geometry enabled a better sensor performance, including more stable and higher sensitivity and a more linear response to ammonia concentration compared to 1-dimensional gas diffusion geometry. We also demonstrated the usability of this diffusion-modulated colorimetric sensor for continuous environmental ammonia monitoring.

Hydraulic modelling of a catalytic converter for pollutant reduction in atmosphere

Air pollution caused by cars is a major contributor to the greenhouse effect, making it an issue of widespread concern. End-of-combustion of an engine produces pollutants such carbon monoxide (CO), oxides of nitrogen (NOx), oxides of sulphur (SOx), particulate particles and unburned hydrocarbons (HC). The environment, air quality, and human health are all negatively affected by these contaminants. A catalytic converter is a pollution control device for every fuel-operated automobile exhaust system. Increasingly low emission standards and automobile space constraints necessitate optimizing the device geometry. The uniformity index parameter mainly judges a catalytic converter’s smooth working and operational life. In the present study, 16 catalytic converter geometry designs are investigated. Their effects on exhaust flow distribution, i.e., uniformity index, pressure drop, and peak pressure at monolith substrate entry, are identified and visualized through contour plots. A finite volume approach is used to study hydraulic diffusion inside the device with the help of the ANSYS Fluent CFD package. Two-dimensional axisymmetric CFD simulations identify optimum design parameters among the considered geometries. The design of diffuser geometry is crucial in maintaining a uniform flow across monolith honeycomb structures.

Numerical Investigation by Cut-Cell Approach for Turbulent Flow through an Expanded Wall Channel

The expanded wall channel backward-facing step (BFS) and axisymmetric diffuser plays an important role in the society of fluid dynamics. Using a cut-cell technique is an established new method to treat the inclined wall of an axisymmetric diffuser. Cut-cell handle to reach the shape of the inclined wall, an axisymmetric diffuser and complex geometry. It helps treat the boundary condition at the wall in an accurate physical way. The turbulent flow through the geometries is solved by using Reynolds averaged Navier-Stokes equations (RANS) with the standard k-ε model. A self-built FOTRAN code based on the finite volume method with the Semi-Implicit Method for Pressure Linked Equations (SIMPLE) algorithm for pressure velocity coupling is established and examined with published experimental data for two different geometries backward-facing step (BFS) and axisymmetric diffuser. The results of the new technique reflect good agreement between the numerical results and the experimental data. A parametric study of the impact of area ratios (2, 2.5, 3, 3.5) in a backward-facing step on pressure, velocity, and turbulent kinetic energy. The angles (7°, 10°, 14°) and area ratios (2, 2.5, 3, 3.5) effect of an axisymmetric diffuser on the streamlines, local skin friction, pressure, velocity, turbulent kinetic energy, and separation zone.

Modeling spintronic terahertz emitters as a function of spin generation and diffusion geometry

Spintronic THz emitters (STE) are efficient THz sources constructed using thin heavy-metal (HM) and ferromagnetic-metal (FM) layers. To improve the performance of the STE, different structuring methods (trilayers, stacked bilayers) have been experimentally applied. A theoretical description of the overall THz emission process is necessary to optimize the efficiency of STE. In particular, geometry, composition, pump laser frequency, and spin diffusion will be significant in understanding the pathways for further research developments. This work will apply a generalized model based on a modified Transfer Matrix Method (TMM). We will consider the spin generation and diffusion in the FM and HM layers and explain the spintronic THz emission process. This model is suitable for calculating emitted THz signal as a function of FM and HM thicknesses for different geometrical configurations. We will investigate a bilayer geometry as a test case, but the extension to a multi-layer configuration is straightforward. We will show how the different configurations of the sample will influence the THz emission amplitude.

Universal scaling theory of electrochemical immunosensors: An analytical approach to define and compare performance metrics

Electrochemical immunosensors have emerged as a versatile, sensitive, and selective sensor technology of choice for a variety of applications, including detection of proteins, food pathogens, bacteria, viruses, and cancerous molecules. The combination of highly specific biorecognition elements and electrical readout systems facilitates the detection of antigens down to femtomolar concentrations. However, a lack of quantitative theoretical framework has made the design, optimization, and comparison of sensors difficult, without a clear and definitive understanding of the limits of detection, dynamic range, and sensitivity. In this paper, we integrate reaction-diffusion and effective media theories to derive a generalized scaling model for an arbitrary immunosensor that relates the relative change of redox current to the corresponding change in antigen concentration, through scaling exponents related to the geometry of biomolecules diffusion and the measurement resolution. Experimental data from dozens of immunosensors (for a variety of antigens, material systems, and sensor geometry) validate our sensor-agnostic scaling formula. Our results would allow cross-calibration of the emerging and traditional immunosensors reported across the literature and define a physics-based, standardized methodology to compare performance metrics, such as limits of detection, dynamic range, and sensitivity.

Intervertebral disc organ-on-a-chip: an innovative model to study monocyte extravasation during nucleus pulposus degeneration.

Degenerative cascades of the intervertebral disc (IVD) are characterized by the presence of immune cells like monocytes, macrophages, and leukocytes, which contribute to inflammation. Previous in vitro studies on monocyte chemotaxis in the presence of chemical or mechanical stimulation were unable to establish the effects of endogenous stimulating factors from resident IVD cells, or fully understand macrophage and monocyte differentiation pathways in IVD degeneration. Our study simulates monocyte extravasation using a fabricated microfluidic chemotaxis IVD organ-on-a-chip (IVD organ chip), which models the geometry of IVD, chemoattractant diffusion, and infiltration of immune cells. Additionally, the fabricated IVD organ chip mimics stepwise monocyte infiltration and differentiation into macrophages in the degenerative nucleus pulposus (NP) induced by IL-1β. We find that naïve NP cells do not recruit THP-1 monocyte-like cells, but degenerative NP cells recruit and accumulate macrophages through chemo-gradient channels. Furthermore, the differentiated and migrated THP-1 cells show phagocytic activity around inflammatory NP cells. Our in vitro model of monocyte chemotaxis with degenerative NP on an IVD organ chip depicts the sequential processes of monocyte migration/infiltration, monocyte-to-macrophage differentiation, and accumulation. Using this platform to gain a deeper understanding of monocyte infiltration and differentiation processes can provide insights into the pathophysiology of the immune response in degenerative IVD.

VENTILATION SYSTEMS ENHANCEMENT IN SEMICONFINED AND CONFINED ROOMS USING STRAIGHT LOBED GRILLES

This study presents a numerical investigation of flow behavior of a turbulent impinging jet in semiconfined and confined rooms using computing code ANSYS computational fluid dynamics. The lobed grille is proposed as a novel air diffuser design in order to develop air distribution inside the room. A comparison of the different types of diffuser geometry (elliptical, rectangular, and lobed grids) is carried out. Different discharge heights (0.3 m, 0.6 m, and 0.9 m) are taken into account. The effect of jet designs on thermal confort is investigated also. The validation results show a good agreement with the experimental data found in the literature. The flow behavior and thermal characteristics of the three designs are presented. The results show that lobed grilles enhance the ventilation systems for both semiconfined and confined rooms.

Optimal diffuser geometry design and verification for micro-scale high altitude test stand

Optimal diffuser geometry design and verification for micro-scale high altitude test stand

Investigation of Metal Powder Injection into a Combustion Chamber by Large Eddy Simulation for Power to X Studies

AbstractThe numerical modeling and simulation of particle dispersion during the filling process of a tubular combustion chamber are presented. By means of multiphase large eddy simulations (LES) the particle distribution inside a circular diffuser‐reactor chamber is studied to analyze the two‐phase flow dynamics for metal powder combustion in a tubular reactor with flame propagation. Typical particle accumulations are found that form close to the reactor wall and also particles tend to segregate and preferentially concentrate at vortex surfaces in particle bands. Particle segregation and accumulation effects aside vortex structures are analyzed using the LES approach. The causes of particle segregation and inhomogeneities are studied and measures for its reduction by changes in the reactor design are discussed. Alterations of the diffuser geometry are adapted to minimize the central particle jet formation and the particle distribution inhomogeneities during the filling process.