Flow Attack Angle Research Articles

Laminar Forced Convection and Heat Transfer Characteristics in a Square Channel Equipped with V-Wavy Surface

The numerical investigations on flow pattern and heat transfer characteristic in a heat exchanger channel equipped with V-wavy surface are examined. The influences of the flow attack angles (α = 15°, 20°, 25°, 30°, 35°, 40°, 45°, 50°, 55° and 60°) and wavy surface arrangements (V-tip pointing downstream called V-Downstream, V-tip pointing upstream called V-Upstream) are investigated for laminar regime, Re = 100-1200. The finite volume method with SIMPLE algorithm is used to solve the current research. The numerical result shows that the addition of the wavy surface in the heat exchanger channel can help to develop the heat transfer rate and thermal performance. The wavy surface generates the vortex flow through the test section that disturbs the thermal boundary layer on the heat transfer surface. The insertion of the wavy surface in the heating channel gives higher heat transfer rate around 1.5-10 times above the smooth channel depended on the flow attack angle, Reynolds number and wavy surface arrangement. In addition, the optimum thermal performance is around 3.0 at Re = 1200, α = 40° and V-Upstream.

On some issues in the computational modelling of spacer-filled channels for membrane distillation

This study addresses issues which arise in the computational and experimental modelling of flow and heat/mass transfer in membrane distillation and other processes adopting spacer-filled channels (either planar or spiral wound), but have not been sufficiently clarified in the literature so far. Most of the argumentations presented are based on original computational results obtained by the authors by finite volume simulations; some literature results are also considered. The questions addressed regard the choice of scales for the reduction of data and the definition of dimensionless numbers (Re, f, Nu, Sh); the definition of average heat or mass transfer coefficients; the combined effects of the parameters that characterize the process (spacer pitch to channel height ratio l/H, flow attack angle γ and Reynolds number Re) and the applicability of simple correlations; the influence of the spacer's thermal conductivity. In regard to the influence of the parameters, Re, l/H and γ were found to interact heavily, making a separate-effect analysis impossible and power-law friction or heat/mass transfer correlations of little use. Thermal conduction in the spacer, even for low-conductivity polymeric spacers (λ≈0.15Wm−1K−1), was found to be responsible for up to 10% of the total heat transfer.

Convective Heat Transfer and Thermal Performance in a Circular Tube Heat Exchanger Inserted with U-Shaped Baffle

Numerical investigations on flow structure and heat transfer characteristic in a heat exchanger tube fitted with U-shaped baffle are presented. The U-shaped baffle is created from the concepts of orifice and inclined baffle. The influences of the baffle height (b/D = 0.05, 0.10, 0.15, 0.20 and 0.25) and flow attack angle (α = 20°, 30° and 45°) of the U-shaped baffle on heat transfer, pressure loss and thermal performance are considered. The finite volume method with SIMPLE algorithm is selected to solve the present problem. The numerical results are reported in terms of flow visualization and heat transfer behavior. The performance analysis for the tube heat exchanger inserted with the U-shaped baffle is also reported. As the numerical result, it is found that the insertion of the U-shaped baffle help to improve the heat transfer rate and thermal performance higher than the smooth tube with no baffle. The increments of heat transfer rate and pressure loss are around 1–8.7 and 1–29 times over the smooth tube, respectively. Additionally, it is detected that the 45° U-shaped baffle with the BR = 0.2 gives the highest thermal enhancement factor around 2.9 at the highest Reynolds number, Re = 1200.

Heat Transfer Augmentation in a Divergent Duct with Angled Ribs

Heat transfer characteristics in the rectangular divergent duct with parallel angled ribs are experimentally compared with the straight smooth circular duct. The ribs with four different parallel angles ([Formula: see text], 45[Formula: see text], 60[Formula: see text], and 90[Formula: see text]) are glued on the duct’s two opposite walls as well as on the duct’s one sided wall only, respectively. The 0.72[Formula: see text]-inclined walls are installed at the two opposite walls of the rectangular divergent duct. The test section of 1000[Formula: see text]mm long has the cross section of [Formula: see text][Formula: see text]mm2 at inlet and [Formula: see text][Formula: see text]mm2 at exit. The ribbed walls are manufactured with a rib height [Formula: see text][Formula: see text]mm and the ratio of rib spacing ([Formula: see text]) to height([Formula: see text]) [Formula: see text] 10. The main findings are summarized that the increase in the dimensionless Nusselt number for the flow attack angles can be seen in the order of 90[Formula: see text], 30[Formula: see text], 60[Formula: see text], and 45[Formula: see text] at the two opposite ribbed divergent wall ducts, in addition, the average Nusselt number in the divergent rectangular duct with two opposite ribbed walls is somewhat greater than in the ribbed straight cross-sectional rectangular duct.

Developing heat transfer and pressure loss in an air passage with multi discrete V-blockages

The multi V blockage shapes in discrete type have been evaluated for augmentation in heat transfer and pressure loss in an air flow passage. The data points obtained during experimentation are correlated among different geometrical variations specified as: distance of blockage, width of the blockage, height of the blockage, pitch between the consecutive blockages, width of the discrete region of the blockage, and attack angle of the flow. These variations in the configuration of the multi discrete V-blockage has significant effect on heat transfer and pressure loss in an air flow passage. The aspect ratio of the air flow passage is 10. The flow Reynolds number is varied within the range: 3000–8000. The relative blockage height varied in the range: 0.25–1.0, relative blockage pitch in the range: 8.0–12, relative blockage distance in the range: 0.27–0.77, relative discrete width in the range: 0.50–1.5, flow attack angle in the range: 30–70° and relative blockage width in the range: 1.0–6.0. The investigation affirms the achievement of high thermohydraulic performance, the best achieved at relative blockage height of 0.5, relative blockage pitch of 10, discrete blockage distance of 0.67, relative discrete width of 1.0, flow attack angle of 60° and relative blockage width of 5.0 compared to an air passage without blockages. The investigation has been further carried out to develop Nusselt number and friction factor correlations in terms of flow and geometrical parameters. Further, the performance of different blockage shapes with that of present study has been carried out in terms of thermohydraulic performance parameter.

Laminar Flow and Heat Transfer in a Square Channel Installed with Inclined Wavy Surface

Laminar flow and heat transfer characteristic in a square channel heat exchanger installed with inclined wavy surface are investigated numerically. The inclined wavy surface is designed with the main the aim to help the installation, production and maintenance when using the inclined wavy surface in the heat exchanger. The finite volume method with SIMPLE algorithm is selected to solve the present problem. The effects of flow attack angle (α = 15°-60°) and Reynolds number (Re = 100-1200) on heat transfer, friction loss and thermal performance are considered. The numerical model is validated with the smooth channel. The grid independence of the computational domain is checked. The numerical results show that the heat transfer enhancement is around 1.9-7.5 times above the smooth channel. The optimum thermal performance is found at the flow attack angle of 45° around 2.35 at Re = 1200.

Thermal Hydraulic Performance in a Solar Air Heater Channel with Multi V-Type Perforated Baffles

This article presents heat transfer and fluid flow characteristics in a solar air heater (SAH) channel with multi V-type perforated baffles. The flow passage has an aspect ratio of 10. The relative baffle height, relative pitch, relative baffle hole position, flow attack angle, and baffle open area ratio are 0.6, 8.0, 0.42, 60°, and 12%, respectively. The Reynolds numbers considered in the study was in the range of 3000–10,000. The re-normalization group (RNG) k-ε turbulence model has been used for numerical analysis, and the optimum relative baffle width has been investigated considering relative baffle widths of 1.0–7.0.The numerical results are in good agreement with the experimental data for the range considered in the study. Multi V-type perforated baffles are shown to have better thermal performance as compared to other baffle shapes in a rectangular passage. The overall thermal hydraulic performance shows the maximum value at the relative baffle width of 5.0.

EXPERIMENTAL RESEARCH OF THE CLIFFS AND BANKS WASHAWAY

Vertical and inclined shores washout processes were simulated in the small-scaled water tunnel with curved bed and in the rectangular-sectioned hydraulic flume. Intensity of the washout of lithologically homogeneous material of vertical shore is in direct correlation with the attack angle of flow on the coast: Wa = 349.8(1 + + 3.21sin3 a), where Wa is the intensity of washout at the attack angle a. The power-low relation (Wb = 82 + 1.72b0.71) of underwater river bank washout intensity (Wb) from its incline (b) to the flow surface is fixed. Mathematic simulation results show that the ratio of side erosion to bottom erosion shifts to bottom erosion if flow velocity was increased. Due to their morphometric, timing and hydraulic parameters these models are closest to the processes parameters and morphology of the beds of slope drainage network of shallow waterflows. Sharp river bed curves, high flow velocities and flow turbulence on the top of high water are typical for them. All these features occur in the river drainage networks as well, especially on the mountainous rivers. On the plain rivers the most adequate are the high water processes analogues as long as high water passes in the berm edges of flood-plain coasts.

Experimental investigation of effect of flow attack angle on thermohydraulic performance of air flow in a rectangular channel with discrete V-pattern baffle on the heated plate

In this work, the effect of angle of attack [Formula: see text] of the discrete V-pattern baffle on thermohydraulic performance of rectangular channel has been studied experimentally. The baffle wall was constantly heated and the other three walls of the channel were kept insulated. The experimentations were conducted to collect the data on Nusselt number [Formula: see text] and friction factor [Formula: see text] by varying the Reynolds number ( Re) = 3000–21,000 and angle of attack [Formula: see text] from 30° to 70°, for the kept values of relative baffle height [Formula: see text], relative pitch ratio [Formula: see text], relative discrete width [Formula: see text] and relative discrete distance [Formula: see text]. As compared to the smooth wall, the V-pattern baffle roughened channel enhances the Nusselt number [Formula: see text] and friction factor [Formula: see text] by 4.2 and 5.9 times, respectively. The present discrete V-pattern baffle shapes with angle of attack [Formula: see text] of 60° equivalent to flow Reynolds number of 3000 yields the greatest thermohydraulic performance. Discrete V-pattern baffle has improved thermal performance as compared to other baffle shapes’ rectangular channel.

한면에 리브가 설치된 4면 수축 사각채널에서 리브의 각도가 열전달에 미치는 영향

The local heat transfer and pressure drops of developed turbulent flows in the convergent channels with square cross-sectional areas along the streamwise distance have been investigated experimentally. Four different parallel angled ribs (a = <TEX>$30^{\circ}$</TEX>, <TEX>$45^{\circ}$</TEX>, <TEX>$60^{\circ}$</TEX>, and <TEX>$90^{\circ}$</TEX>) are placed to the one sided wall only, respectively. The ribbed walls are manufactured with a fixed rib height (e)=10 mm and the ratio of rib spacing (p) to height (e) = 10. The measurement was run within the range of Reynolds numbers from 22,000 to 79,000. The result shows that the increases in the Nusselt numbers for the flow attack angles can be seen in the order of <TEX>$30^{\circ}$</TEX>, <TEX>$45^{\circ}$</TEX>, <TEX>$60^{\circ}$</TEX> and <TEX>$90^{\circ}$</TEX>.

Flow topology, heat transfer characteristic and thermal performance in a circular tube heat exchanger inserted with punched delta winglet vortex generators

To improve the heat transfer rate and thermal performance, the punched delta winglet vortex generators, DWVGs, were inserted in the middle of the circular tube heat exchanger. The effects of the flow attack angles and the flow directions were investigated numerically for the Reynolds number Re = 100–2000. The finite volume method and the SIMPLE algorithm were used to study. The results are reported in terms of the flow structure, heat transfer behavior and thermal performance evaluation and also compared with the smooth tube with no vortex generators. As the numerical results, the use of the DWVGs in the tube can improve the heat transfer rate and thermal performance by creating the vortex flow through the tested section. The rise of the flow attack angle results in the increasing strength of the vortex flows. The flow attack angle of 25° performs the highest heat transfer rate and thermal performance, while the flow attack angle of 0o gives the reversed results. The computational results reveal that the optimum thermal enhancement factor is around 2.80 at Re = 2000, α = 25°, with the winglet tip pointing downstream. The correlations on both the Nusselt number ratio and friction factor ratio for the DWVG in the tube heat exchanger are presented.

Trawl-door Shape Optimization by Space-mapping-corrected CFD Models and Kriging Surrogates

Trawl-doors are a large part of the fluid flow resistance of trawlers fishing gear and has considerable effect on the fuel consumption. A key factor in reducing that consumption is by implementing computational models in the design process. This study presents a robust two dimensional computational fluid dynamics models that is able to capture the nonlinear flow past multi-element hydrofoils. Efficient optimization algorithms are applied to the design of trawl-doors using problem formulation that captures true characteristics of the design space where lift-to-drag ratio is maximized. Four design variables are used in the optimization process to control the fluid flow angle of attack, as well as position and orientation of a leading-edge slat. The optimization process involves both multi-point space mapping, and mixed modeling techniques that utilize space mapping to create a physics-based surrogate model. The results demonstrate that lift-to-drag maximization is more appropriate than lift-constraint drag minimization in this case and that local search using multi-point space mapping can yield satisfactory design at low computational cost. By using global search with mixed modeling a solution with higher quality is obtained, but at a higher computational cost than local search.

Numerical Investigation on Turbulent Forced Convection in Heating Channel Inserted with Discrete V-Shaped Baffles

The numerical examinations on flow visualization, heat transfer characteristic and performance improvement in a square duct inserted with discrete V-shaped baffles (DVB) are reported. The DVB is designed to reduce the pressure loss when compared with the V-shaped baffle. The influences of the flow blockage ratios (b/H, BR = 0.05-0.20), V-tip directions (V-Downstream and V-Upstream) are investigated for Reynolds number, Re = 3000-20,000, with a single pitch ratio and flow attack angle of 1 and 30°, respectively. As the results, the DVB can generate the vortex flow and impinging flow through the test section that assists to develop the thermal efficiency. The augmentations on the heat transfer coefficient and pressure drop are around 2.5-5.75 and 4-22.5 times above the smooth duct, respectively. The best thermal efficiency in forms of thermal enhancement factor, TEF, around 2.32 is detected at Re = 3000, BR = 0.10 and V-Upstream.

Hydroacoustic analysis of open cavity subsonic flow based on multiple parameter numerical models

The prediction of the flow-induced noise level is a key issue in the fluid–dynamic acoustics. In the hydroacoustics field, the complicated feedback induced by the flow past open cavities can amplify the convection instability in the shear layer which further leads to important noise radiations. The noise consists of intense narrowband and broadband components. In this paper, the level of the noise radiated by a subsonic cavity flow is calculated by using numerical flow computations based on the large eddy simulation (LES) and by solving the Ffowcs Williams-Hawkings equation. A series of three-dimensional open cavity models with overset grids and appropriate boundary conditions are developed for the hydroacoustic numerical computation. The self-sustained oscillation characteristics of the cavity flow are investigated, together with the mechanisms of the cavity noise generation. The distinguishing features of the flow-induced noise of the underwater structure cavities are studied with respect to the parameters of the cavity models, such as the free stream velocity, the dimensions of the cavity mouth, the angle of the cavity neck, the horizontal and vertical porous cavity models and the actual submarine open cavity model with an incoming flow attack angle. It is shown that it may be feasible to reduce the flow-induced noise by appropriate optimal parameters of the underwater structure cavities.

Flow and mass transfer in spacer-filled channels for reverse electrodialysis: a CFD parametrical study

In reverse electrodialysis (RED) concentration polarization phenomena and pressure drop affect strongly the power output obtainable; therefore the channel geometry has a crucial impact on the system optimization. Both overlapped and woven spacers are commonly commercialised and adopted for RED experiments; the latter exhibit some potential advantages, such as better mixing and lower shadow effect, but they have been poorly investigated in the literature so far.In this work, computational fluid dynamics was used to predict fluid flow and mass transfer in spacer-filled channels for RED applications. A parametric analysis for different spacer geometries was carried out: woven (w) and overlapped (o) spacers with filaments at 90° were simulated, and Reynolds number, pitch to height ratio (l/h) and orientation with respect to the main flow (α=0° and α=45°) were made to vary.The filament arrangement was found to be a crucial feature; for any given pumping power, higher Sherwood numbers were provided by the w-arrangement. The influence of flow attack angle and filament spacing depends on Reynolds number and filament arrangement. Only the configuration w-α45 avoids the presence of poorly mixed zones near the wires. Among the cases investigated here, the configuration that provided the best mixing conditions was w, l/h=2, α=45°.

Influences of the wavy surface inserted in the middle of a circular tube heat exchanger on thermal performance

Numerical investigations on flow topology, heat transfer behavior and performance evaluation in a circular tube inserted with various configurations of wavy surfaces, Inclined wavy surface (IWS), V-downstream wavy surface (VDWS), V-Upstream wavy surface (VUWS) are presented. The effects of the flow attack angles; 20°, 30°, 45° and 60° are studied for the Reynolds numbers, Re = 100-2000. The numerical results are compared with the smooth circular tube with no wavy surface and the previous works. It is found that the IWS, VDWS and VUWS can produce longitudinal vortex flow and impinging jet of the fluid flow like inclined baffle, V-downstream baffle and V-Upstream baffle, respectively, but give lower friction loss. The flow phenomena created by the wavy surfaces help to augment the heat transfer rate and thermal performance in the test tube. In the range studied, the order of enhancement for heat transfer rate is around 1.40-3.75, 1.60-6.25 and 1.30-5.80 times higher than the smooth tube for IWS, VDWS and VUWS, respectively. Moreover, the maximum thermal performance, presented in terms of the Thermal enhancement factor (TEF), is found to be about 1.60, 2.40 and 2.10, respectively, for IWS, VUWS and VDWS.

V 형 rib과 dimple로 구성된 SAH 덕트에서의 총괄 열성능에 대한 수치적 연구

This paper presents the thermal hydraulic performance of a three dimensional rib-roughened solar air heater (SAH) duct with the one principal wall subjected to uniform heat flux. The SAH duct has aspect ratio of 12.0 and the Reynolds number ranges from 2000 to 12000. The roughness has relative rib height of 0.045, ratio of dimple depth to print diameter of 0.5 and rib pitch ratio of 8.0. The flow attack angle is varied from 35° to 70°. Various turbulent flow models are used for the heat transfer and fluid flow analysis and their results are compared with the experimental results for smooth surfaces. The computational fluid dynamics (CFD) results based on the renormalization k-epsilon model are in better outcomes compared with the experimental data. This model is used to calculate heat transfer and fluid flow in SAH duct with the compound roughness of V-shaped ribs and dimples. The overall thermal performance based on equal pumping power is found to be the highest (2.18) for flow attack angle of 55°. The thermo-hydraulic performance for V-pattern shaped ribs combined with dimple ribs is higher than that for dimple rib shape and V-pattern rib shape air duct.

Three-dimensional simulations of flow past two circular cylinders in side-by-side arrangements at right and oblique attacks

The flow past two identical circular cylinders in side-by-side arrangements at right and oblique attack angles is numerically investigated by solving the three-dimensional Navier–Stokes equations using the Petrov–Galerkin finite element method. The study is focused on the effect of flow attack angle and gap ratio between the two cylinders on the vortex shedding flow and the hydrodynamic forces of the cylinders. For an oblique flow attack angle, the Reynolds number based on the velocity component perpendicular to the cylinder span is defined as the normal Reynolds number ReN and that based on the total velocity is defined as the total Reynolds number ReT. Simulations are conducted for two Reynolds numbers of ReN=500 and ReT=500, two flow attack angles of α=0° and 45° and four gap ratios of G/D=0.5, 1, 3 and 5. The biased gap flow for G/D=0.5 and 1 and the flip-flopping bistable gap flow for G/D=1 are observed for both α=0° and 45°. For a constant normal Reynolds number of ReN=500, the mean drag and lift coefficients at α=0° are very close to those at α=45°. The difference between the root mean square (RMS) lift coefficient at α=0° and that at α=45° is about 20% for large gap ratios of 3 and 5. From small gap ratios of 0.5 and 1, the RMS lift coefficients at α=0° and 45° are similar to each other. The present simulations show that the agreement in the force coefficients between the 0° and 45° flow attack angles for a constant normal Reynolds number is better than that for a constant total Reynolds number. This indicates that the normal Reynolds number should be used in the implementation of the independence principle (i.e., the independence of the force coefficients on the flow attack angle). The effect of Reynolds number on the bistable gap flow is investigated by simulating the flow for ReN=100–600, α=0° and 45° and G/D=1. Flow for G/D=1 is found to be two-dimensional at ReN=100 and weak three-dimensional at ReN=200. While well defined biased flow can be identified for ReN=300–600, the gap flow for ReN=100 and 200 changes its biased direction too frequently to allow stable biased flow to develop.

Turbulent forced convection in a heat exchanger square channel with wavy-ribs vortex generator

Turbulent forced convective heat transfer and flow configurations in a square channel with wavy-ribs inserted diagonally are examined numerically. The influences of the 30° and 45° flow attack angles for wavy-ribs, blockage ratio, RB=b/H=0.05–0.25 with single pitch ratio, RP=P/H=1 are investigated for the Reynolds number based on the hydraulic diameter of the square channel, Re=3000–20000. The use of the wavy-ribs, which inserted diagonal in the square channel, is aimed to help to improve the thermal performance in heat exchange systems. The finite volume method and SIMPLE algorithm are applied to the present numerical simulation. The results are presented on the periodic flow and heat transfer profiles, flow configurations, heat transfer characteristics and the performance evaluations. The mathematical results reveal that the use of wavy-ribs leads to a higher heat transfer rate and friction loss over the smooth channel. The heat transfer enhancements are around 1.97–5.14 and 2.04–5.27 times over the smooth channel for 30° and 45° attack angles, respectively. However, the corresponding friction loss values for 30° and 45° are around 4.26–86.55 and 5.03–97.98 times higher than the smooth square channel, respectively. The optimum thermal enhancement factor on both cases is found at RB=0.10 and the lowest Reynolds number, Re=3000, to be about 1.47 and 1.52, respectively, for 30° and 45° wavy-ribs.

Thermal performance assessment in a fin-and-oval-tube heat exchanger with delta winglet vortex generators

Thermal performance assessments, flow configurations and heat transfer characteristics in a fin-and-oval-tube heat exchanger with the delta winglet vortex generators are examined numerically. Delta winglet vortex generators like V-ribs are placed on fin surfaces with V-tip pointing upstream called “V-Upstream”. The effects of the flow attack angles (α = 15°, 30°, 45° and 60°) and the distances between V-tip to the center of the oval tube in transverse line (Transverse pitch, a = 3.77, 4.77 and 5.77 mm) on heat transfer, flow structure and thermal performance are studied for Reynolds number based on the hydraulic diameter of the test channel, Re = 500 − 2500. The numerical results are presented in four parts: validations of the base case, flow configurations, velocity field, heat transfer and thermal performance assessment. It is found that the use of the delta winglet vortex generators can help to improve heat transfer rate in the heating system by creating vortex flow and swirl flow over the test channel. The heat transfer and pressure loss appeared to be higher than the plain fin for all case studies. The augmentation of the flow attack angle results in the rise of heat transfer rate and friction loss, while differences in transverse pitch produced similar values in terms of the Nusselt number and friction loss. In addition, augmentations are found around 1.15 − 1.55 and 1.5 − 3.4 times over the base case for heat transfer and friction factor, respectively. At Re = 2500, a = 5.77 mm and α = 15°, the maximum thermal enhancement factor is found to be around 1.12.