Wall Corrugation Research Articles

The Effect of U-Bend Zone, Rotation, and Corrugation on Two-Pass Channel Flow

Abstract Further consideration on the two-pass channel flow is still necessary due to the complexity of 180-deg turn, rotation, and wall ribs. Numerical investigations have repeatedly revealed differences from experiments, with the primary focus of the smooth walls. Thus, this work deals with newly added ribs and three-equation variant of the shear stress transport (SST) k–ω model to the current fluid flow and heat transfer depending on an existing experiment as a reference. The adapted turbulence model thought to be more susceptible to U-bend zone, rotation, and wall corrugation is applied using comsolmultiphysics program. A two-pass profile with leafy characteristics, derived from a prior work by the first author, is implemented for the first time and contrasted against alternative corrugation designs. The findings demonstrated that applying the suggested model reduces the percentage error between the computational and experimental data to less than 20%. The Nusselt numbers computed at different leafy-corrugated channel divisions are augmented to 30% with 70% surface temperature reduction; however, the friction penalty rises too.

Inner–outer interaction of unsteady turbulent flow inside duct with wall corrugations: Augmentation and saturation

This study investigates the inner–outer interaction of the unsteady turbulent flow inside a duct with wall corrugations, where “inner” refers to the trapped flow in a corrugation-induced cavity array and “outer” relates to the mainstream flow transporting through a circular duct. Configurations with different pitch–diameter ratios (P/D) are used to demonstrate the effect of the cavity flow pattern on the mainstream flow variations. An improved delayed detached-eddy simulation with dynamic blending function is performed to acquire high-fidelity turbulent flow data, in which dynamic evolution of multi-scale vortex structures containing hairpin vortices and vortex fragments is clearly resolved. The subsequent statistical analysis reveals a nonlinear variation tendency of the inner–outer interaction intensity, experiencing sudden augmentation first and then a gradual attenuation toward the final saturation. Comparatively, a larger pitch ratio results in a stronger interaction under the effect of bicentric recirculation zones within the cavity array. Moreover, a proper orthogonal decomposition analysis allows for the visualization of energetic flow structures, as consistent velocity variations throughout the duct volume are identified for a larger pitch ratio, while discontinuity at the duct termination is found for a smaller pitch ratio. Finally, an advanced elliptical model based on the spatiotemporal cross correlation analysis is proposed to examine the convection velocity and sweeping velocity of the interactive mainstream flow and cavity flow. The results highlighted the presence of first-augmented and then saturated dynamics and kinematics inside the duct with the cavity array.

Effects of corrugation on convective heat transfer and power generation in a wavy walled triangular cavity equipped with inclined elastic fin and piezo-energy harvester assembly

Piezoelectric energy harvesters are one of the energy conversion technologies that can be used to convert a variety of external sources, including wind, fluid motion, and vibrations, into electrical energy. This work suggests a novel wall corrugation design in addition to an elastic fin piezo assembly arrangement for power generation and thermal management in a triangular cavity during turbulent forced convection of air. Using the finite element method with ALE, the analysis is conducted for different values of fin inclination (γ between 0 and 60), corrugation amplitude (Af between 0.01H and 0.06H), corrugation frequency (Nf between 1 and 20) and fin distance from the mid-point of the inclined wall in wall direction. The average Nusselt number (Nu) and generated power (PW) show a non-linear increasing trend with increasing fin tilt. Average Nu increment factor becomes 5.17 with the highest fin inclination while the power increments become 11.6 and 4.46 when rising inclination from 30 to 45 and from 45 to 60. The generated power rises with higher corrugation amplitude and wave number. However, increasing the wave number results in thermal performance degradation. Increment of average Nu becomes 1.17 with highest corrugation amplitude while it declines by a factor of 10.3 at the highest wave number. Power enhancement factors of 5.73 and 2.32 are obtained by increasing the corrugation amplitude from Af = 0.0714H to Af = 0.1786H and from Af = 0.1786H to Af = 0.2143H. When fin positions sf = 0.7143H and sf = -0.7143H are compared with the case of fin location at sf = 0, the power increment factors become 12.27 and 4.76, respectively. For the power produced by the piezo device, a polynomial type correlation is suggested by adjusting the parameters of the corrugated wall.

Suppression of Parasitic Modes in a Cylindrical Gyrotron Beam Tunnel by a Wall Corrugation With Schroeder Diffuser Structures

Suppression of Parasitic Modes in a Cylindrical Gyrotron Beam Tunnel by a Wall Corrugation With Schroeder Diffuser Structures

Electromagnetohydrodynamic (EMHD) flow of Jeffrey fluid through a rough circular microchannel with surface charge-dependent slip.

This research examines the electromagnetohydrodynamic (EMHD) flow of Jeffrey fluid in a rough circular microchannel while considering the effect of surface charge on slip. The channel wall corrugations are described as periodic sinusoidal waves with small amplitudes. The perturbation method is employed to derive solutions for velocity and volumetric flow rate, and a combination of three-dimensional (3D) and two-dimensional (2D) graphical representations is utilized to effectively illustrate the impacts of relevant parameters on them. The significance of the Reynolds number in investigations of EMHD flow is particularly emphasized. Furthermore, the effect of wall roughness and wave number on velocity and the influence of wall roughness and surface charge density on volumetric flow rate are primarily focused on, respectively, at various Reynolds numbers. The results suggest that increasing the wall roughness leads to a reduction in velocity at low Reynolds numbers ( ) and an increment at high Reynolds numbers ( ). For any Reynolds number, a roughness with an odd multiple of wave number ( ) will result in a more stable velocity profile compared to one with an even multiple of wave number ( ). Decreasing the relaxation time while increasing the retardation time and Hartmann number can diminish the impact of wall roughness and surface charge density on volumetric flow rate, independent of the Reynolds number. Interestingly, in the existence of wall roughness, further consideration of the effect of surface charge on slip leads to a 15% drop in volumetric flow rate at and a 32% slippage at . However, in the condition where the effect of surface charge on slip is considered, further examination of the presence of wall roughness only results in a 1.4% decline in volumetric flow rate at and a 1.6% rise at . These findings are crucial for optimizing the EMHD flow models in microchannels.

Collapse behavior of corrugated stiffened pressure shells under external hydrostatic pressure considering actual fabrication imperfections: A reverse modeling technique

The pressure shell is the most critical load-bearing component in submersible vehicles. It is mainly used to withstand the enormous seawater pressure. In this study, a corrugated stiffened pressure shell was proposed to address the problem of low compression performance of the traditional cylindrical pressure shell. Nine corrugated shells made of aluminum alloy with varying corrugation parameters were created using CNC machining. After welding and sealing treatment, hydrostatic pressure tests were conducted on the shells to investigate the impact of parameters such as wall thickness, number of corrugations, and corrugation height on their compression performance. The shells were measured using a 3D scanner, and the resulting data was used for reverse modeling. The analysis focused on the failure behavior of corrugated shells with geometric imperfections under uniform external pressure using nonlinear finite element analysis. The results indicate that increasing the wall thickness or corrugation height can significantly improve the compression performance of the shells. The position of collapse remains consistent with the location of the maximum Mises stress. Furthermore, it was discovered that the corrugated structure also has an additional advantage in retarding the generation and expansion of diamond-shaped defects on the shell surface. The equilibrium paths of all corrugated shells maintained a smooth and continuous state, demonstrating stable buckling behavior. The numerical calculations were in excellent agreement with the experimental results, highlighting the advantages of the reverse modeling technique. This study provides new insights for the structural design of submarine pressure shells and explores more reasonable and feasible stiffening methods.

The effect of the radial heat loss, upper reservoir temperature, and corrugated wall channel on the flooding critical heat flux

This study measured the flooding critical heat flux (flooding CHF) for two vertical annular channels with different channel gaps. The experiments were conducted at atmospheric pressure and with no flow. The effects of the upper reservoir temperature within 30–80 °C and radial heat loss have been studied. It was found that the upper reservoir temperature has a small effect on the flooding CHF values, and it varied in the range of up to 10% compared to the saturated conditions. On the other hand, a significant effect of the radial heat loss was observed on the measured flooding CHF values (up to 100%). The flooding CHF experimental results were compared with numerous empirical correlations from the literature, some initially based on air-water counter-current flow experiments (flooding experiments with no heating). It was found that based on the onset flooding velocity experiments, the flooding CHF results can be successfully predicted. The effect of the wall corrugation on the flooding CHF was also examined in the simple air-water counter-current flow setup. This study shows that the air flooding velocity in a corrugated channel is higher than in a smooth channel with the same cross-section geometry and dimensions. Therefore, using a smooth channel flooding CHF value for a corrugated one guarantees a conservative result.

Influence of uniform wall corrugations on convective heat transfer through a convergent–divergent nozzle by using mono and hybrid nanofluids

Influence of uniform wall corrugations on convective heat transfer through a convergent–divergent nozzle by using mono and hybrid nanofluids

Analysis and Evaluation of the Effects of Uniform and Non-uniform Wall Corrugation in a Pipe Filled with Ternary Hybrid Nanofluid

Analysis and Evaluation of the Effects of Uniform and Non-uniform Wall Corrugation in a Pipe Filled with Ternary Hybrid Nanofluid

Flow dynamics in sinusoidal channels at moderate Reynolds numbers

Pressure-gradient-driven flows through sinusoidal channels have been studied. The analysis was carried out up to the formation of secondary nonlinear states and spanned a range of low and moderate Reynolds numbers. Direct numerical simulations were used to identify and determine the properties of steady as well as non-stationary, two-dimensional (2-D) and three-dimensional secondary flows. Our results indicate the existence of several distinct solution types. Two-dimensional, stationary flows with periodicity determined by the corrugation represent the first type. The second type is associated with the appearance of 2-D oscillatory flows arising from the onset of unstable travelling waves. Such oscillatory solutions are generally out of phase with the wall corrugation but could be in phase in special cases determined by the ratio of the critical disturbance wavelength and the channel corrugation wavelength. Consequently, several distinct types of time-dependent solutions are possible. The third type of solution results from the centrifugal effect caused by wall curvature and leads to three-dimensionalization of the flow through the onset of stationary streamwise vortices. Finally, various states resulting from the interaction of different solution types are possible. We examine those states and present a bifurcation diagram illustrating the formation of some of them. The results presented in this paper might help with the development of small-scale flow measurement and detection devices operating at low and moderate Reynolds numbers, as well as in the use of wall topographies for the intensification of mixing in flows with moderate, subturbulent Reynolds numbers.

Electromagnetohydrodynamic (EMHD) Flow in a Microchannel with Random Surface Roughness.

This study investigates the effect of small random transverse wall roughness on electromagnetohydrodynamic (EMHD) flow is in a microchannel, employing the perturbation method based upon stationary random function theory. An exact solution of a random corrugation function ξ, which is a measure of the flow rate deviated from the case without the roughness of two plates, is obtained by integrating the spectral density. After the sinusoidal, triangular, rectangular, and sawtooth functions that satisfy the Dirichlet condition are expanded into the Fourier sine series, the spectral density of the sine function is used to represent the corrugation function. Interestingly, for sinusoidal roughness, the final expression of the corrugation function is in good agreement with our previous work. Results show that no matter the shape of the wall roughness, the flow rate always decreases due to the existence of wall corrugation. Variations of the corrugation function and the flow rate strongly depend on fluid wavenumber λ and Hartmann number Ha. Finally, the flow resistance is found to become small, and the flow rate increases with roughness that is in phase (θ = 0) compared with the one that is out of phase (θ = π).

Simulation of fluid flow in a lid-driven cavity with different wave lengths corrugated walls using Lattice Boltzmann method

BackgroundThe Lid-driven cavity (LDC) flow is an interesting problem in fluid mechanics. The lattice Boltzmann Method (LBM) is used to simulate fluid flow in a LDC with different wave lengths corrugated walls. MethodsThe D2Q9 model is used for the 2D bounded domain where the analysis of bottom-bounded wall corrugations on the flow features is analyzed. For validation, a square corrugation along the bottom wall with a driven top wall is considered. A lattice size independence study is performed and the LBM code is substantiated with published results for different values of Reynolds number. The code is then modified by using sinusoidal corrugated walls with different wavelengths along the bottom surface. Significant findingThe streamline patterns, vorticity contours and kinetic energy contours are studied for different Reynolds number. Results shown that the position, number and size of vortices depend on the number of corrugations and value of Reynolds number used. The secondary vortices tend to increase in size as the Reynolds number increase. The kinetic energy contours show maximum energy near the top wall which reduces inside the cavity.

Effect of non-uniform wall corrugations on laminar convective heat transfer through rectangular corrugated tube by using graphene nanoplatelets/MWCN hybrid nanofluid

Hybrid nanofluids and non-uniform wall corrugations have been reported to enhance convective heat transfer, which is not yet fully explored. In this study, the heat transfer efficacy of non-uniform wall corrugations on laminar convective heat transfer through a rectangular corrugated tube by using a hybrid nanofluid is investigated. Three different non-uniform wall corrugations; gradually increasing wall corrugation (GIWC), gradually decreasing wall corrugation (GDWC) and periodic wall corrugation (PWC) are investigated and compared with uniform wall corrugation (UWC). The applied hybrid nanofluid is a mixture of graphene nanoplatelets (GnP) and multi-walled carbon nanotubes (MWCN) with water, wherein the volume fractions of nanoparticles are 0.1%, 0.15%, and 0.2%. The computation is conducted under 2000 kW/m2 heat flux conditions on the heated surface of the corrugated wall with the Reynolds number in the range of 500–2000. The heat transfer efficacy and required pumping power are investigated for different wall corrugations and Reynolds numbers. The developed numerical model was validated with experimental studies from the published literature on different corrugated conduits. The computation results indicate that non-uniform wall corrugations GIWC, GDWC, and PWC provided better performance compared to uniform corrugation UWC. The average Nusselt number is the highest for PWC compared to others. At a constant Reynolds number 1000, the heat transfer was enhanced by an overall 15.61% for GDWC, 18.70% for GIWC, and 21.16% for PWC compared to UWC. In addition, PWC provided the highest increase in the pumping power requirement compared to others. At a constant Reynolds number 1000, the pumping power ratio is 1.37 for GDWC, 1.47 for GIWC, and 1.54 for PWC compared to UWC. GnP/MWCN-water hybrid nanofluid with a 0.2% volume fraction provided the highest enhancement in heat transfer compared to pure water. For PWC configuration, mixing nanoparticle volume fractions from 0.1% to 0.2%, the Nusselt number increases from 6.66% to 23.75%,while the pumping power ratio increases from 1.24 to 1.39 compared to water. It can be concluded that further experimental investigation is critical to validate the implementation of non-uniform wall corrugation for enhancing the thermal performance of rectangular corrugated tubes.

Natural-convection heat transfer from regularly ribbed vertical surfaces: Homogenization-based simulations towards a correlation for the Nusselt number

Free-convection heat transfer from vertical surfaces is widely encountered in engineering applications, yet the role played by surface alterations in the heat transfer process and their practical effectiveness are still points of confusion. In this work, buoyancy-driven flows over periodically ribbed vertical plates of different surface micro-textures are investigated, mainly based on an asymptotic homogenization model through which the expensive resolution of the velocity and thermal fields within the inter-rib regions is bypassed, by imposing equivalent effective boundary conditions at a virtual plane surface. Efficiency of the homogenized simulations in detecting macroscopic behavior of the Nusselt number is first assessed, compared with full feature-resolving simulations in which the effects of complex flow patterns, near and within wall corrugations, on the local Nusselt number are captured. Second, the validated model is used to construct a database of numerical results describing deviations of the average Nusselt number over different ribbed surfaces, relative to a corresponding smooth surface. Under the conditions investigated, it is found that surface roughening generally deteriorates heat transfer from vertical surfaces, with slight enhancement for geometries characterized by low thermal slip, for example, rectangular ribs of narrow inter-rib spaces. Finally, a multiple-regression analysis is conducted to formulate a correlation describing effects of the thermal-slip coefficient, the number of ribs, and the Grashof number on the surface-averaged Nusselt number; accuracy of the proposed correlation is attested via further validation. This paper aims to call attention of the heat transfer society to the ability of the homogenization approach to considerably alleviate the computational requirements for relevant simulations and, thus, to significantly accelerate parametric optimization studies.

Laminar flow in epicycloidal corrugated pipes

AbstractDoes longitudinal surface corrugation or roughness affect viscous fluid flow? To answer this question, we study viscous flows through the entire family of pipes with epicycloidal walls, which have n cusps, . We find that the flow becomes insensitive to the longitudinal wall corrugations due to the epicycloidal cusps as : surface roughness of the walls does not affect the flow if it is longitudinal. Exact flows in these corrugated pipes are compared with three ‘rules of thumb’ which give general but approximate formulae for the rate of flow through a pipe of given cross‐sectional shape. Upper and lower bounds on flow, based on circumscribed and inscribed circular boundaries, give even better estimates than the three rules of thumb. All the flow formulae, exact and approximate, apply also to the twisting of solid beams.

Pore wall corrugation effect on the dynamics of adsorbed H2 studied by in situ quasi-elastic neutron scattering: Observation of two timescaled diffusion

The self-diffusion mechanisms for adsorbed H2 in different porous structures are investigated with in situ quasi-elastic neutron scattering method at a temperature range from 50 K to 100 K and at various H2 loadings. The porous structures of the carbon materials have been characterized by sorption analysis with four different gases and the results are correlated with previous in-depth analysis with small-angle neutron scattering method. Thus, an investigation discussing the effect of pore shape and size on the nature of adsorbed H2 self-diffusion is performed. It is shown that H2 adsorbed in nanometer-scale pores is self-diffusing in two distinguishable timescales. The effect of the pore, pore wall shape and corrugation on the fraction of confined and more mobile H2 is determined and analyzed. The increased corrugation of the pore walls is shown to have a stronger confining effect on the H2 motions. The difference of self-diffusional properties of the two H2 components are shown to be smaller when adsorbed in smoother-walled pores. This is attributed to the pore wall corrugation effect on the homogeneity of formed adsorbed layers.

A homogenization approach for buoyancy-induced flows over micro-textured vertical surfaces

Asymptotic homogenization is employed to formulate upscaled effective boundary conditions at a smooth virtual surface for a natural-convection flow over a periodically roughened vertical wall, to bypass the expensive numerical resolution of flow and temperature fields near and within wall corrugations. Microscale problems are found by expanding near-wall variables in terms of a small parameter $\epsilon$ , the ratio between the microscopic and the macroscopic length scales. The expressions of the upscaled velocity and temperature boundary conditions are provided up to second-order accuracy in $\epsilon$ . The case of transverse square ribs is considered as a representative example. The classical Navier-slip condition for the streamwise and the spanwise velocity components is modified at second order by the gradient of the normal stress and the time derivative of the shear stress. The streamwise slip velocity is additionally corrected by a buoyancy term at first order and a temperature-gradient term at second order. The normal velocity at the virtual surface appears only as a second-order transpiration condition. A Robin-like condition for the temperature is found, where the wall temperature is corrected with a temperature-gradient term representing thermal slip. The accuracy levels and the applicability range of the effective conditions to mimic the macroscopic flow behaviour are investigated under laminar flow conditions, in comparison with results of full feature-resolving simulations. A formal validity limit for the approximation is sought in terms of a single accuracy criterion ( $C$ ), which combines the effects of the Grashof number and the ribs’ density. The introduced model is further tested on different rib geometries.

Prevalence of ultrasonographic gastrointestinal wall changes in dogs with acute pancreatitis: A retrospective study (2012-2020).

BackgroundUltrasonographic gastrointestinal wall changes in dogs with acute pancreatitis (AP) are not well characterized in the literature. No detailed studies have described their prevalence, characteristics, distribution, or clinical relevance.Hypothesis/ObjectivesDescribe the prevalence of ultrasonographic gastrointestinal wall changes in a population of dogs with AP and evaluate for associations between the presence of gastrointestinal wall changes and clinical or clinicopathological variables.AnimalsReferral population of 66 client‐owned dogs with AP.MethodsRetrospective search of clinical records to identify dogs with AP. Clinical variables, clinicopathological variables and ultrasonographic findings were reported using descriptive statistics. A binary logistic regression model was used to evaluate for associations between the presence of gastrointestinal wall changes and clinical or clinicopathological variables.ResultsSixty‐six dogs were included. Forty‐seven percent of dogs (95% confidence interval [CI], 35.0%‐59.0%; n = 31) with AP had ultrasonographic gastrointestinal wall changes. Gastrointestinal wall changes were most common in the duodenum and identified in 71% (n = 22) of affected dogs. Of dogs with gastrointestinal wall changes, 74.2% (n = 23) had wall thickening, 61.3% (n = 19) had abnormal wall layering, and 35.5% (n = 11) had wall corrugation. In the multivariable model, only heart rate remained an independent predictor of ultrasonographic gastrointestinal wall changes (P = .02).Conclusions and Clinical ImportanceUltrasonographic gastrointestinal wall changes in this population of dogs with AP were common. Increased heart rate was the only independent predictor of gastrointestinal wall changes, which might imply more severe disease. Additional studies are required to elucidate whether ultrasonographic gastrointestinal wall changes reflect disease severity in AP.

Pore Wall Corrugation Effect on the Two Timescaled Diffusion of Adsorbed H2 Studied by Quasi-Elastic Neutron Scattering

Pore Wall Corrugation Effect on the Two Timescaled Diffusion of Adsorbed H2 Studied by Quasi-Elastic Neutron Scattering

Effect of Non-Uniform Wall Corrugations on Laminar Convective Heat Transfer Through Rectangular Corrugated Tube by Using Graphene Nanoplatelets /Mwcn Hybrid Nanofluid

Effect of Non-Uniform Wall Corrugations on Laminar Convective Heat Transfer Through Rectangular Corrugated Tube by Using Graphene Nanoplatelets /Mwcn Hybrid Nanofluid