Flow Attack Angle Research Articles

Numerical and experimental investigations of thermohydraulic performance enhancement of triangular duct solar air heaters using circular wing vortex generators

AbstractThis study presents the thermohydraulic performance enhancement in a triangular duct solar air heater (TSAH) using circular wing vortex generators (CWVGs) on the absorber plate using computational fluid dynamics (CFD) methodology for the Reynolds number (Re) range of 6000–21,000. The use of wing vortex generators offers relatively lower interference with the core flow region, while the circular geometry offers a smooth curved edge, which reduces multiple vortex interactions in the wake region, thereby limiting the pressure drop. This study explores the impact of flow attack angle, longitudinal pitch, transverse pitch, and diameter of CWVG on the thermohydraulic performance of TSAH. The results reveal that a lower flow attack angle exhibits enhanced heat transfer with a lower friction factor penalty. The nondimensional diameter greater than d/Dh = 0.325 tends to limit heat transfer and exhibits an increased friction factor. The transverse pitch parameter also exhibits a similar trend where the threshold nondimensional pitch is found to be 1.5. The highest improvement in Nu is 4.37 times that of smooth duct for d/Dh = 0.433, Pl/d = 1, Pt/d = 1.5 and α = 20° at Re = 6000. The highest rise in friction factor is about 10.23 times that of smooth duct for d/Dh = 0.433, Pl/d = 1.0, Pt/d = 1.5, and α = 20° at Re = 21,000. The highest thermohydraulic performance parameter (THPP) value is about 2.23 at Re = 6000, with THPP values ranging from 1.69 to 2.23 across different CWVG configurations. Finally, mathematical correlations are developed for Nu and friction factors which are in close agreement with CFD results, with deviations averaging 5.03% and 3.69%, respectively.

Investigations on thermal profiles and flow structures in a square channel equipped with staggered vortex turbulators

Given the escalating energy demands today, improving the efficiency of engineering equipment is crucial for optimizing energy use. This study focuses on enhancing heat exchanger performance through passive methods, particularly by installing vortex turbulators. Passive techniques can effectively manage energy costs while enhancing efficiency.The research examines thermal profiles and airflow structures within a square channel heat exchanger (SCHE) equipped with staggered vortex turbulators (SVTs). SVTs feature a unique design combining rectangular winglets and V-pattern baffles. The installation of SVTs aims to intensify vortex strength, thereby increasing SCHE efficiency, convective heat transfer coefficients, and overall heat transfer potential. The study investigates the effects of SVT dimensions (b1/H and b2/H), airflow directions (+x and -x), installation patterns (pattern no. 1 and 2), pitch to height ratios (P/H = 1, 1.5, and 2), and flow attack angles (α = 20°, 30°, and 45°). Computational simulations using the finite volume method with a commercial code (FLUENT) under laminar flow conditions (Reynolds number of 100–2000) provide insights into thermal profiles, fluid temperature distributions, and flow configurations within the SCHE. Staggered arrangement and gap spacing are employed to reduce pressure loss and enhance airflow strength. The results highlight flow structures and heat transfer characteristics in the heat exchanger channels, elucidating the underlying mechanisms of the heat exchange process. Understanding these behaviors is crucial for developing more efficient heat exchangers and vortex generators in the future. Simulation findings demonstrate that SVTs significantly enhance convective heat transfer over smooth channels due to increased vortex strength. Notably, pattern no. 2 SVTs (b1/H = b2/H = 0.20) achieve the highest Nu/Nu0 of 19.21 in the +x flow direction at Re = 2000, α = 30°, and P/H = 1. In conclusion, the study identifies a maximum thermal enhancement factor of 4.38. It underscores the potential of pattern no. 2 SVTs for optimizing heat exchanger performance, offering valuable insights for future developments in thermal management technologies.

Aerodynamic interference effects of bridge-train-like bluff bodies with small flow attack angle

Aerodynamic interference effects of bridge-train-like bluff bodies with small flow attack angle

Effect of Chamfered Turbulators on Performance of Solar Air Heater - Numerical Study

This paper presents a numerical analysis of the thermal performance improvement in a flat plate solar air heater equipped with chamfered turbulators attached below the absorber plate for evaluating performance for Reynolds numbers ranging from 3,000 to 21,000. According to the research, chamfered turbulators caused the flow to become highly turbulent. This flow behaviour with flow separation around the turbulators positively affects performance. This paper attempts to explain the complex flow behaviour found during the analysis. The turbulator diameter varies in 1 mm increments from 3 to 7 mm at a constant longitudinal pitch of 200 mm. The number of turbulator rows in the transverse direction is kept constant at three. The chamfer is represented by the flow attack angle, which can be 30°, 45°, or 60° facing the direction of flow and opposing the direction of flow. The results showed that a 7mm diameter turbulator with a 30° chamfer angle placed against the flow of air yielded a considerably more significant thermal enhancement factor of 1.15 over the spectrum of flow Reynolds number studied

Koopman mode analysis on discovering distributed energy transfer of post-transient flutter of a bluff body

The flutter response of a rectangular cylinder model with an aspect ratio of 5 is investigated by direct numerical simulation for various Reynolds numbers (Re) and flow angles of attack (α). The results show that the lower α and Re, the larger the torsional amplitude at the critical reduced flow velocity (Ur) corresponding to the occurrence of flutter. High-order Koopman mode analysis method (HOKM) was developed to synchronously capture the inherent flow and structural modes. The element-mode-based energy transfer between cylinders and flow modes was used to reveal the underlying mechanism. HOKM analysis shows that only odd-order modes contribute to the occurrence of flutter, with an augmentation in Ur enhancing this phenomenon. By analyzing the work done in odd-order modes, it is found that the primary mode always occupies the main contribution to the work done. The leading-edge endpoint portion is always where the maximum work is done. An escalation in Re and α notably influences both the spatially relevant part (WΦ) and the temporally relevant part (Wc), while an increase in Ur predominantly impacts WΦ. This study offers universal guidance on the safety and protection of ocean engineering structures and flow control strategies.

Thermohydraulic performance augmentation of triangular duct solar air heater using semi‐conical vortex generators: Numerical and experimental study

AbstractThermohydraulic performance augmentation using turbulence promotors is a commonly adopted technique in solar air heater (SAH) applications. This article presents the thermohydraulic performance augmentation of triangular duct SAH using semi‐conical vortex generators (SCVG) using computational fluid dynamics and experimental methodology for various flow Reynolds numbers ranging from 6000 to 21,000. An in‐depth parametric analysis is undertaken to establish the influence of flow attack angle, relative longitudinal pitch, relative transverse pitch and cone diameter of SCVG on the thermohydraulic performance as indicated by the thermohydraulic performance parameter (THPP). The results reveal that the SCVG generates longitudinal vortices and introduces flow impingement zones which significantly affects the flow and heat transfer characteristics of air heaters. Correlations for Nusselt number and friction factor are established, which predicts the performance outcomes with an average error of 6.74% and 4.46%, respectively. The optimal THPP is determined to be 1.74 using artificial neural network model and Bonobo Optimization algorithm. The SCVG produces THPP values well above unity for the entire flow Reynolds number range of 6000–21,000.

A zero-net-mass-flux wake stabilization method for blunt bodies via global linear instability

A rectangular cylinder, with an aspect ratio of 5, is a widely used bluff body in engineering practice. It undergoes intricate dynamical behavior in response to minute alterations in the flow angle of attack (α). These modifications invariably precipitate the failure of wake control for classical flow control methods with various α values. In this study, global linear instability, adjoint method, and sensitivity analysis are employed to identify the optimal position for flow control. It is found that the sensitive region gradually transitions from the leeward side to the downwind side of the model as α and Reynolds number (Re) increase. So, we set up airflow orifices for flow control in both positions. Jet flow control on the leeward side effectively inhibits vortex shedding (α ≤ 2°). High-order dynamic mode decomposition is employed to reveal the inherent mechanism of control. Suction control on the downside effectively mitigates the shear layer separation phenomenon induced by the altered spatial structure associated with higher α. A novel zero-net-mass-flux wake control, bionics-based breathe-valve control (BVC), is proposed to optimize the control effect. BVC is applicable for various α and Re, with optimal effectiveness achievable through jet velocity adjustments. The prediction-control approach in this investigation provides a targeted method to mitigate flow-induced vibration.

Study of local scour around rectangular and square subsea caissons under steady current condition

Numerical simulations were conducted to investigate steady current scour around rectangular and square subsea caissons. The caissons, which are representative of subsea structures, have a submerged height ranging from 0.5 to several times their longest base dimension. The flow model used is based on the Reynolds Averaged Navier-Stokes equations, and the scour model simulates bed load and suspended load transport to predict the evolution of the seabed profile. The aim of this study is to investigate the mechanisms of local scour, specifically the contribution of the horseshoe vortex and the local streamline contraction near the caisson corners to local scour. The model is validated through comparisons with experimental measurements, indicating reasonable agreement. Based on the numerical model results, the mechanisms of local scour around square and rectangular caissons are found to be qualitatively similar. If the flow is directed perpendicular to one of the caisson faces, both the horseshoe vortex and the local streamline contraction contribute to scour. The maximum scour depth is located at the two upstream corners of the caisson due to the combined effects of the horseshoe vortex and streamline contraction. When the flow approaches the caisson with a diagonal attack angle of 45°, the two upstream faces act like a streamlined wedge that splits the incoming flow. The study found that the horseshoe vortex almost disappears and the scour is primarily caused by the local velocity amplification at the two side corners. If the flow attack angle is 45°, the scour does not initiate near the upstream corner without the contribution from the horseshoe vortex. These findings are expected to serve as a valuable theoretical foundation for the design of scour protection.

Flow pattern- and forces-susceptibility to small attack angles for a rectangular cylinder

This study employs numerical simulation to investigate the two-dimensional flow of a rectangular cylinder with an aspect ratio of 5, under various flow attack angles (α) and Reynolds numbers. The lift and drag coefficients, surface pressure distributions, and flow structures are analyzed using the HODMD method. The findings suggest that a rise in flow attack angle increases the lift and drag coefficients of rectangular cylinders, but the turning point of the Reynolds number leads to an opposite trend in the increase of drag coefficients. The sensitivity of the flow field is intricately related to the Reynolds number and flow attack angle. Additionally, the increase in both Reynolds number and flow attack angle enhances the complexity of the flow structure, particularly at the trailing edge, which is a sensitive part of applying flow control. HODMD analysis shows that the first three modes dominate dynamics. Odd-order modes contribute significantly to lift at low α, while even-order modes cancel each other. As α increases, the contributing modes of lift gradually shift from odd to even order. This study provides valuable insights for prospective flow control strategies and addresses vibration concerns in associated submerged structures.

Straight fiber bundles with non-uniform porosity: Shell-side hydrodynamics and mass transfer in cross flow

This study explores fully developed shell-side hydrodynamics and mass transfer past straight fiber bundles with non-uniform porosity in cross-flow. Simplified geometries made up by checkerboard arrays of alternately high and low porosity regions are considered. Simulations are performed for two domain sizes: a small geometry (26 fibers) and a large geometry (104 fibers). In the small geometry, the Darcy friction coefficient (fT) exhibits hydraulic isotropy at low transverse flow Reynolds numbers (ReT) but becomes dependent on the flow attack angle (θ) at higher ReT. In the large geometry, this dependency is observed at lower ReT. A non-uniform porosity reduces fT at almost all ReT and θ in the small geometry, with the large geometry exhibiting a more complex behavior. Regarding mass transfer, up to ReT≈1-10 (depending on θ), a non-uniform porosity leads to lower Sherwood numbers compared to regular square arrays. However, at higher ReT, it enhances mass transfer.

Hydrodynamic effects of the elliptical spacer filament on the flow and mass transfer in a desalination membrane channel

This study numerically investigates the impacts of an elliptical spacer on the flow and mass transfer within a desalination membrane channel. We consider the effects of the fluid Reynolds number, the elliptical spacer position yin/H, the flow attack angle θ and the aspect ratio B of spacer on the fluid flow, concentration polarization, and permeation flux. Our findings reveal that the elliptical spacers can improve both the mass transfer and permeation flux compared with the traditional circular spacers. Placing the spacer near the membrane surface effectively disrupts the concentration boundary layer, thereby amplifying the local concentration polarization surrounding the spacer. A single recirculation vortex behind the spacer induces numerous large vortices around the membrane, resulting in a significant increment in freshwater production. By changing θ and B, the system's stability can be reduced, potentially leading to a 16.0% increment in permeation flux when compared with the traditional circular spacers. Furthermore, the drag and lift coefficients acting on the elliptical spacer are greater than those of circular spacers, which is the main reason for the transition of flow condition. Our findings provide a reference for the design of the efficient structures in reverse osmosis membranes.

Heavy-duty gas turbine 3D blade modelling and flow field analysis

Hydrogen-fuelled heavy-duty gas turbine is an important trend of gas turbine due to its low emission characteristics. Due to the change of components and thermodynamic properties of the fuel, the physical properties of the working fluid of the turbine will change and affect the performance of the gas turbine. In this study, through 3D scanning and inverse modelling, the parametric models of the turbine blades were obtained. CFD analysis was conducted to analyse the change of thermodynamic performance and flow field under different fuel, which is natural gas, 50% natural gas and 50% hydrogen and hydrogen. The result of the CFD indicated that the efficiency of natural gas fuelled working flux is 92.86%, and decreased by 0.19% and 0.83% with hydrogen doped in. It is analysed that though the increased magnitude of relative velocity with hydrogen doped in, the increased flow attack angle of the rotor, from -4.74°, to -3,61°, to -1.88° with hydrogen doped in, caused the split of rotor leading edge cooling air and decreased the efficiency of the turbine stage. Modification of blade metal angle could boost the efficiency of the turbine stage under hydrogen-doped fuel.

Exergy and sustainability analysis of a solar heat collector with wavy delta winglets as turbulent promoters: A numerical analysis

This numerical study aims to determine the exergy analysis for a modified solar heat collector (SHC) having wavy delta winglets as turbulent promoters. These winglets disrupt the viscous layer to improve the heat transfer rate from the heat-absorbing surface to the fluid medium in the rectangular channel. The analysis considers following parameters: the relative longitudinal pitch (P/H), number of waves (φ), and flow angle of attack (α0) and flow Reynolds number range of 4000–18000. The maximum exergy efficiency of 29.18% is achieved with a longitudinal pitch of 5, an angle of attack of 60°, and a relative number of waves of 5. To evaluate the system's feasibility and sustainability, the study uses a Sustainability Index (SI), which reflects the system's Waste Energy Ratio (WER) and Improvement Potential (IP). This assessment helps identify opportunities for improvement in the thermal system.

Optimization and correlations development for heat transfer and fluid flow characteristics of ZnO/H2O-ethylene glycol-based nanofluid flow through an inclined ribbed square duct

One simple technique to improve the heat transfer rate is to roughen a square duct’s heated plate. This work is concerned with the heat transfer () and friction factor () of //ethylene glycol nanofluid flowing in ribbed square duct were optimized, and correlations have been developed. Design parameters include nanoparticle concentration (φ) 1–4%, relative angled rib pitch 2.18–3.25, relative angled rib height 0.10–0.25, flow attack angle of inclination rib and Reynolds number (Re) 4000–19,000. The response surface method (RSM) was utilized for optimization. Varying the roughness parameters improves the heat transfer performance of inclined ribbed, but it increases the pumping power of the square duct. RSM results indicated that the maximum heat transfer enhancement belongs to φ of 4%, of 2.50, of 0.20, and of 60°. In addition, a generalized quadratic correlation for Nu and f is constructed based on the analysis of variance, with percentage deviations of and respectively, in contrast to empirically obtained values of Nusselt number and friction factor.

Influence of bundle porosity on shell-side hydrodynamics and mass transfer in regular fiber arrays: A computational study

CFD predictions of the effects of a fiber bundle porosity on shell-side hydrodynamics and mass transfer under conditions of steady laminar flow were obtained. Fluid was assumed to flow around regular hexagonal or square arrays of cylindrical fibers of different pitch to diameter ratios, yielding bundle porosities ranging from the theoretical minimum up to ∼1. A large number of axial, transverse and mixed flow combinations were simulated by letting the axial and transverse flow Reynolds numbers and the transverse flow attack angle vary. Both fully developed and developing conditions (entrance effects) were considered. The continuity and momentum equations, along with a transport equation for the concentration of a high-Schmidt number solute, were solved by a finite volume CFD code. Fully developed conditions were simulated by the well-established “unit cell” approach, in which the computational domain is two-dimensional and includes a single fiber with the associated fluid, periodic boundary conditions are imposed between all opposite sides and compensative terms are introduced to account for large-scale longitudinal or transversal gradients. Developing flow was studied by using a fully three-dimensional computational domain. Predictions were validated against experimental, computational and analytic literature results. The simulations showed that lattices with different porosities exhibit a qualitatively similar behavior, but differ significantly in important quantities such as the Darcy permeability, the Sherwood number and the hydrodynamic and mass transfer development length.

Friction and Heat Transfer in Membrane Distillation Channels: An Experimental Study on Conventional and Novel Spacers.

The results of an experimental investigation on pressure drop and heat transfer in spacer-filled plane channels, which are representative of Membrane Distillation units, are presented and discussed. Local and mean heat transfer coefficients were obtained by using Thermochromic Liquid Crystals and Digital Image Processing. The performances of a novel spacer geometry, consisting of spheres that are connected by cylindrical rods, and are hereafter named spheres spacers, were compared with those of more conventional woven and overlapped spacers at equal values of the Reynolds number Re (in the range ~150 to ~2500), the pitch-to-channel height ratio, the flow attack angle and the thermal boundary conditions (two-side heat transfer). For any flow rate, the novel spacer geometry provided the least friction coefficient and a mean Nusselt number intermediate between those of the overlapped and the woven spacers. For any pressure drop and for any pumping power, the novel spacer provided the highest mean Nusselt number over the whole Reynolds number range that was investigated. The influence of buoyancy was also assessed for the case of the horizontal channels. Under the experimental conditions (channel height H ≈ 1 cm, ΔT ≈ 10 °C), it was found to be large in empty (spacer-less) channels that were up to Re ≈ 1200 (corresponding to a Richardson number Ri of ~0.1), but it was much smaller and limited to the range Re < ~500 (Ri < ~0.5) in the spacer-filled channels.

Investigation of Offshore Wind Turbine Structure Deflection Using Experimental Work, Numerical, and Theoretical Approach

Electrical energy from offshore wind turbines is an important source of clean, renewable energy production. One of the reasons for the low efficiency of wind turbines is the change in the flow angle of attack, denoted by the symbol (α), as a result of the deflection of the structure. The study aims to know the values of the maximum deflection of the proposed structure under the environmental conditions of the Arabian Gulf water area. Our research adopted a novel approach to extracting results; the characteristics of sea waves were extracted from the experimental work after fixing five sea waves, knowing the displacement of the top of the structure, and using the numerical approach in the ANSYS-Fluent program to know the average wind and wave forces. Two simulations were performed. The first included the five cases of sea wave characteristics without rotating wind turbine blades. The second was for the fifth case only with the wind turbine blades rotating at a speed of (20.5 rpm), assuming that the structure was exposed to a constant wind speed (12 m/s) for the two simulations. The study also included obtaining the maximum deflection value of the structure. Then, the equations of the theoretical approach were developed based on the Euler-Bernoulli bending moment equation, and the forces extracted from the simulations were entered into the theoretical equations to extract the maximum deflection values of the structure. Reading the experimental work resulted in the highest displacement of the top of the structure in the fifth case (0.178 m). The result of the second simulation had the highest value of the structure deflection (0.201 m). In comparison, its value came in the theoretical approach (0.160 m), which adopted the forces of the second simulation.

Experimental investigation of two-side heat transfer in spacer-filled channels representative of membrane distillation

Heat transfer in spacer-filled plane channels was investigated by using thermochromic liquid crystals and digital image processing. A novel test section allowed the establishment of two-side cooling, closely representative of the conditions existing in real plane or spiral-wound membrane distillation (MD) modules. Several spacer configurations were investigated, differing in design (overlapped or woven filaments), pitch-to-height ratio and orientation with respect to the main flow direction. The Reynolds number Re ranged from 160 to 2500, as is typical in MD. At all flow rates investigated, symmetric two-side cooling provided significantly higher (25–35%) local and mean heat transfer coefficients hh than one-side cooling. The mean heat transfer coefficient increased when the pitch-to-height ratio increased from 2 to 4, and was much higher for woven than for overlapped spacers. Overlapped spacers with a flow attack angle ϕ of 0°-90° with respect to the two layers of spacer filaments exhibited significantly different distributions and mean values of hh on the two sides, the larger values occurring where the flow was orthogonal to the filaments. In all cases, the dependence of hh on Re could not be described by a simple power law.

Heat transfer augmentation in a solar air heater with conical roughness elements on the absorber

Adding flow-disturbing components to the absorber plate's effective heat transfer zone is the most efficient Thermo-hydraulic performance enhancement approach for a solar air heater (SAH). Researchers are attempting to decide the best geometrical parameters for a SAH when the turbulent flow has fully established with fabricated roughness protrusions on the absorber surface plate in a cone-shaped contour. The Thermo-hydraulic performance of the proposed SAH design is taken into account throughout the optimization process. Air flow rate and geometrical variables such as the Reynolds number R e = 3000 to 8000 , relative rib pitch p / e = 10 to 20 , and relative rib gap w / e = 4 to 8 are varied in a series of experiments to assess the SAH's performance. Flow angle of attack ( α = 90°), relative roughness height ( e / D h = 0.08), and rectangular flow passage aspect ratio ( W / H = 5) are maintained constant in all the trials for inline and staggered configurations. Series of tests are carried out to establish statistical correlations between the average Nusselt number and the average friction factor. Thermo-hydraulic performance is affected by the Reynolds number (Re) as well as relative roughness gaps ( w / e ) and relative roughness pitch ( p / e ) of the conical protrusions. There was a 64.5% increase in Nusselt number and a 153.3% increase in friction factor at Re = 8000, p / e = 10 and w / e = 4. Cone-shaped roughness, as suggested, has a Thermo-hydraulic efficiency index of 0.8233, which ocuurs at p / e = 20 and w / e = 8 at Re = 3000.

Signal-to-noise ratio analysis on saw-tooth vortex generator in vehicle radiators

Fin-and-flat tube heat exchangers are widely applied to construction vehicles due to native advantages. An elementary unit out of such one was numerically compared with the corresponding experimental validation to secure accuracy, then, saw-tooth vortex generators were introduced to the rear of the tube, and further analyzed under the same configuration. JF factors from two models were utilized to confirm the initial expectation for a higher comprehensive performance, which also encouraged the following L18(36) orthogonal test on wing width ( ww), wing height ( sw), blade height ( sb), flow attack angle ( Gf), installation angle ( Gi), and saw-tooth number ( Ns) for signal-to-noise ratio and contribution rate (CR). The results stated that the numerical implementation could be capable of the following analyses with the maximum errors of 5.00% for heat transfer coefficient and 5.33% for pressure loss, and also corroborate performance enhancement with a JF increment of 29.9% in the following comparison. The CRs of Gi, Ns, sw, ww, Gf, and sb are 30.39%, 19.61%, 15.69%, 13.73%, 10.78%, and 9.80%, respectively.