Increase In Wall Shear Stress Research Articles

Computational Fluid Dynamics as an Indicator of Offending Vessel in Trigeminal Neuralgia and Hemifacial Spasms

Abstract Context: Newer Imaging tool for diagnosing offending vessel in trigeminal neuralgia (TN) and Hemifacial spasms (HFS). Aim: To find out if Computational FluidDynamics (CFD) can correctly predict the offending vessel in HFS and TN & thus improving the outcome of Microvascular Decompression) MVD. Settings and Design: CFD is a relatively new mode of imaging. Its application to indicate offending vessel in TN & HFS was tested. Materials & Methods: Retrospectively we studied 13 consecutive patients operated in 2017 for either HFS or TN. Preoperatively MRI & Computed Tomography Angiogram (CTA) were done and the offending vessel identified along with its point of contact with the concerned nerve. CFD was done using Hemoscope 2015 software and wall pressure, wall shear stress, vector & streamline flow were obtained in the offending vessel (test) & contralateral vessel (control). Results of these were charted on an excel sheet & results analyzed. The postoperativeoutcome were assessed and compared with CFD results. Statistical analysis used: Small study group hence statistical analysis couldn’t be applied. Results: Of the 13 patients, offending artery had high wall pressure in 12 and increased wall shear stress innine. Among the controls six had high wall pressure and only two had high wall shear stress. Conclusion: CFD can be used to determine offending vessel and can predict good outcome following microvascular decompression.

Effect of swirl flow on whey protein fouling and cleaning in a straight duct

Whey protein fouling is a complex phenomenon involving several mechanisms. Product, surface properties and process parameters interact simultaneously. This experimental work focuses on the effect of a swirl flow on whey protein fouling and cleaning in a straight tube, independently of any other factors. In a holding section after a heating zone composed of a plate heat exchanger, the dry deposit mass obtained from a straight tube was compared with that obtained in the presence of a swirl flow. For varying conditions, namely two protein concentrations, two processing temperatures and two fouling durations, the dry deposit mass increases despite the wall shear stress increase induced by the swirl device. Nevertheless, the cleaning time was found to be significantly shorter in presence of swirl flow in laminar and turbulent conditions. These results reveal that cleaning efficiency can be improved by such a swirl insert, which is seldom used in the food process industry.

A numerical study on hemodynamics in the left coronary bifurcation with normal and hypertension conditions.

In this study, a three-dimensional analysis of the non-Newtonian blood flow was carried out in the left coronary bifurcation. The Casson model and hyperelastic and rigid models were used as the constitutive equation for blood flow and vessel wall model, respectively. Physiological conditions were considered first normal and then compliant with hypertension disease with the aim of evaluating hemodynamic parameters and a better understanding of the onset and progression of atherosclerosis plaques in the coronary artery bifurcation. Two-way fluid-structure interaction method applying a fully implicit second-order backward Euler differencing scheme has been used which is performed in the commercial code ANSYS and ANSYS CFX (version 15.0). When artery deformations and blood pressure are associated, arbitrary Lagrangian-Eulerian formulation is employed to calculate the artery domain response using the temporal blood response. As a result of bifurcation, noticeable velocity reduction and backflow formation decrease shear stress and made it oscillatory at the starting point of the LCx branch which caused the shear stress to be less than 1 and 2Pa in the LCx and the LAD branches, respectively. Oscillatory shear index (OSI) as a hemodynamic parameter represents the increase in residence time and oscillatory wall shear stress. Because of using the ideal 3D geometry and realistic physiological conditions, the values obtained for shear stress are more accurate than the previous studies. Comparing the results of this study with previous clinical investigations shows that the regions with low wall shear stress less than 1.20Pa and with high OSI value more than 0.3 are in more potential risk to the atherosclerosis plaque development, especially in the posterior after the bifurcation.

Measurements of skin-friction of systematically generated surface roughness

The flow conditions at which a given surface will begin to show the effects of roughness in the form of increased wall shear stress above that of the hydraulically-smooth wall and the behavior of frictional drag in the transitionally-rough regime are still poorly understood. From a practical standpoint, the engineering correlations to predict this behavior should be based on information that can be obtained solely from the surface topography, thus excluding any information that requires hydrodynamic testing. The goal of this work is to take a systematic approach when generating surface roughness where the roughness parameters can be controlled. Three surfaces with fixed amplitude and varying power-law spectral slope (E(κ) ∼ κP; P=−0.5,−1.0,−1.5) were generated and replicated using high-resolution 3D printing. Results show that the surface with the shallower spectral slope, P=−0.5, produces the highest drag, whereas the surface with the steeper spectral slope, P=−1.5 produces the least drag. This highlights that some roughness scales do not contribute significantly to the drag. In fact, the effective slopes, ES of the investigated surfaces were less than 0.35, which indicates that the surfaces are in the so-called “wavy” regime (Schultz and Flack, 2009). A high-pass filter of 1 mm (corresponding to ∼ 10 times of the roughness height) was applied. By removing the long-wavelength roughness scales, the correlation between the filtered roughness amplitude and the frictional drag showed the correct trend.

Momentum balance and stresses in a suspension of spherical particles in a plane Couette flow

Non-Brownian suspension of monodisperse spherical particles, with volume fractions ranging between ϕ = 0.05 and 0.38 and particle Reynolds numbers ranging between Rep = 0.002 and 20, in plane Couette shear flows is investigated using three-dimensional particle-resolved numerical simulations. We examine the effects of volume fraction and particle Reynolds number on the macroscopic and microscopic stresses in the fluid phase. The effective viscosity of the suspension is in a good agreement with the previous empirical and experimental studies. At Rep = 20, however, the effective viscosity increases significantly compared to the lower particle Reynolds number simulations in the Stokes flow regime. Examining the stresses over the depth of the Couette gap reveals that this increase in wall shear stresses at high particle Reynolds numbers is mainly due to the significantly higher particle phase stress contributions. Next, we examine the momentum balance in the fluid and particle phase for different regimes to assess the significance of particle/particle interaction and fluid and particle inertia. At the highest particle Reynolds number and volume fraction, the particle inertia plays a dominant role in the momentum balance and the fluid inertia is non-negligible, while the short-lived contact forces are negligible compared to these effects. For all other regimes, the fluid inertia is negligible, but the particle inertia and contact forces are important in the momentum balance. Reynolds stresses originated from velocity fluctuations do not contribute significantly to the suspension stresses in any of the regimes we have studied, while the reduction in the shear-induced particle rotation can be a reason for higher wall shear stress at Rep = 20. Finally, we study the kinematics of particles, including their velocity fluctuations, rotation, and diffusion over the depth of the Couette gap. The particle diffusion coefficients in the cross flow direction exhibit an abrupt increase at Rep = 20.

Abstract No. 482 Morphological comparison before and after coil embolization of pulmonary arteriovenous malformations on computed tomographs

To examine morphological changes of pulmonary arteriovenous malformations (PAVMs) before and after coil embolization on computed tomographs (CT). Between October 2012 and October 2016, 7 patients (1 male, 6 females, median age 70 years) with 10 PAVMs who improved clinically after coil embolization (CE) of sac PAVMs were enrolled. Pre- and post-CE morphological comparisons included the diameter of the feeders and drainers, the sac volume, and the shrinkage rate the feeding and draining vessels. Computational fluid dynamics (CFD) analysis was performed in 3 patients. The median follow-up was 360 days (range, 26-1376 days). The average diameter before and after CE of the feeding vessel was 4.4- and 2.8 mm, of the drainage vessel it was 3.7- and 2.5 mm. The average pre- and post-CE sac volume was 211.49 mm3 (median 200.63 mm3). The average shrinkage rate of the feeders and drainers was 37.2% and 33.7%, respectively; the pre- and post-CE diameter of the feeders and drainers was significantly different (p = 0.0001). There was no statistically significant correlation between the sac volume and the shrinkage rate of the feeding- (r = -0.3108, p = 0.3820) and the draining vessels (r = 0.09978, p = 0.7839). CFD analysis showed that most of the blood flow from the feeders passed through the PAVM sac. CDF analysis of virtual CE of PAVMs indicated that feeders and drainers were subject to increased wall shear stress (WSS) and that their oscillating shear index (OSI) was increased. Comparison of pre- and post-CE CT images of PAVMs showed that after the procedure, the diameter of the feeders and drainers was significantly smaller. We think that the absence of a correlation between the sac volume and the shrinkage rate of the feeding and draining vessels is attributable to a post-CE increase in the WSS and OSI.

Self-Similar Solution of Radial Stagnation Point Flow and Heat Transfer of a Viscous, Compressible Fluid Impinging on a Rotating Cylinder

In this study, the radial stagnation point flow of strain rate $$\bar{k}$$ impinging on a cylinder rotating at constant angular velocity ω and its heat transfer are investigated. Reduction in the Navier–Stokes equations and energy equation to primary nonlinear ordinary differential equation systems is obtained by use of appropriate transformations when the angular velocity and wall temperature or wall heat flux all are constant. The impinging free stream is steady and normal to the surface from all sides, and the range of Reynolds number variation ( $$Re = \bar{k}a^{2} /2\upsilon$$ ) is 0.1–1000 in which a and υ are cylinder radius and kinematic viscosity, respectively. Flow results are presented for selected values of compressibility factor and different values of Prandtl numbers along with shear stress and Nusselt number. For all values of Reynolds numbers and surface temperature or surface heat flux, as compressibility factor increases the radial velocity field, the heat transfer coefficient and the wall shear stress increase, whereas the angular velocity field decreases. The rotating movement of the cylinder does not have any effect on the radial component of the velocity, but its increase increases the angular component of the fluid velocity field and the surface shear stress.

Aortic valve stenosis and aortic diameters determine the extent of increased wall shear stress in bicuspid aortic valve disease.

BackgroundUse of 4‐dimensional flow magnetic resonance imaging (4D‐flow MRI) derived wall shear stress (WSS) heat maps enables identification of regions in the ascending aorta with increased WSS. These regions are subject to dysregulation of the extracellular matrix and elastic fiber degeneration, which is associated with aortic dilatation and dissection.PurposeTo evaluate the effect of the presence of aortic valve stenosis and the aortic diameter on the peak WSS and surface area of increased WSS in the ascending aorta.Study TypeProspective.SubjectsIn all, 48 bicuspid aortic valve (BAV) patients (38.1 ± 12.4 years) and 25 age‐ and gender‐matched healthy individuals.Field Strength/SequenceTime‐resolved 3D phase contrast MRI with three‐directional velocity encoding at 3.0T.AssessmentPeak systolic velocity, WSS, and aortic diameters were assessed in the ascending aorta and 3D heat maps were used to identify regions with elevated WSS.Statistical TestsComparisons between groups were performed by t‐tests. Correlations were investigated by univariate and multivariate regression analysis.ResultsElevated WSS was present in 15 ± 11% (range; 1–35%) of the surface area of the ascending aorta of BAV patients with aortic valve stenosis (AS) (n = 10) and in 6 ± 8% (range; 0–31%) of the ascending aorta of BAV patients without AS (P = 0.005). The mid‐ascending aortic diameter negatively correlated with the peak ascending aortic WSS (R = –0.413, P = 0.004) and the surface area of elevated WSS (R = –0.419, P = 0.003). Multivariate linear regression analysis yielded that the height of peak WSS and the amount of elevated WSS depended individually on the presence of aortic valve stenosis and the diameter of the ascending aorta.Data ConclusionThe extent of increased WSS in the ascending aorta of BAV patients depends on the presence of aortic valve stenosis and aortic dilatation and is most pronounced in the presence of AS and a nondilated ascending aorta. Level of Evidence: 2 Technical Efficacy: Stage 2J. MAGN. RESON. IMAGING 2018;48:522–530.

The quaternary state of polymerized human hemoglobin regulates oxygenation of breast cancer solid tumors: A theoretical and experimental study.

A major constraint in the treatment of cancer is inadequate oxygenation of the tumor mass, which can reduce chemotherapeutic efficacy. We hypothesize that polymerized human hemoglobin (PolyhHb) can be transfused into the systemic circulation to increase solid tumor oxygenation, and improve chemotherapeutic outcomes. By locking PolyhHb in the relaxed (R) quaternary state, oxygen (O2) offloading at low O2 tensions (<20 mm Hg) may be increased, while O2 offloading at high O2 tensions (>20 mm Hg) is facilitated with tense (T) state PolyhHb. Therefore, R-state PolyhHb may deliver significantly more O2 to hypoxic tissues. Biophysical parameters of T and R-state PolyhHb were used to populate a modified Krogh tissue cylinder model to assess O2 transport in a tumor. In general, we found that increasing the volume of transfused PolyhHb decreased the apparent viscosity of blood in the arteriole. In addition, we found that PolyhHb transfusion decreased the wall shear stress at large arteriole diameters (>20 μm), but increased wall shear stress for small arteriole diameters (<10 μm). Therefore, transfusion of PolyhHb may lead to elevated O2 delivery at low pO2. In addition, transfusion of R-state PolyhHb may be more effective than T-state PolyhHb for O2 delivery at similar transfusion volumes. Reduction in the apparent viscosity resulting from PolyhHb transfusion may result in significant changes in flow distributions throughout the tumor microcirculatory network. The difference in wall shear stress implies that PolyhHb may have a more significant effect in capillary beds through mechano-transduction. Periodic top-load transfusions of PolyhHb into mice bearing breast tumors confirmed the oxygenation potential of both PolyhHbs via reduced hypoxic volume, vascular density, tumor growth, and increased expression of hypoxia inducible genes. Tissue section analysis demonstrated primary PolyhHb clearance occurred in the liver and spleen indicating a minimal risk for renal damage.

Simulations of Slot Film-Cooling With Freestream Acceleration and Turbulence

Slot film cooling in an accelerating boundary layer with high freestream turbulence is studied numerically using large eddy simulations (LES). Calculations are done for a symmetrical leading edge geometry with the slot fed by a plenum populated with pin fins. The synthetic eddy method is used to generate different levels of turbulence and length scales at the inflow cross-plane. Calculations are done for a Reynolds number of 250,000 and freestream turbulence levels of 0.7%, 3.5%, 7.8%, and 13.7% to predict both film cooling effectiveness and heat transfer coefficient over the test surface. These conditions correspond to the experimental measurements of (Busche, M. L., Kingery, J. E., and Ames, F. E., 2014, “Slot Film Cooling in an Accelerating Boundary Layer With High Free-Stream Turbulence,” ASME Paper No. GT2014-25360.) Numerical results show good agreement with measurements and show the observed decay of thermal effectiveness and increase of Stanton number with turbulence intensity. Velocity and turbulence exiting the slot are nonuniform laterally due to the presence of pin fins in the plenum feeding the slot which creates a nonuniform surface temperature distribution. No transition to fully turbulent boundary layer is observed throughout the numerical domain. However, freestream turbulence increases wall shear stress downstream driving the velocity profiles toward the turbulent profile and counteracts the laminarizing effects of the favorable pressure gradient. The effective Prandtl number decreases with freestream turbulence. The temperature profiles deviate from the self-similar profile measured under low freestream turbulence condition, reflecting the role of the increased diffusivity in the boundary layer at higher freestream turbulence.

An unsteady flow of magnetic nanoparticles as drug carrier suspended in micropolar fluid through a porous tapered arterial stenosis under non-uniform magnetic field and periodic body acceleration

A mathematical model has been developed for pulsatile flow of blood through a tapered arterial stenosis in a porous medium under the influence of non-uniform magnetic field and periodic body acceleration treating blood as micropolar fluid carrying iron oxide nanoparticles. The governing equations of the system are solved numerically using finite difference schemes. The effects of stenotic height, taper angle, micropolar parameters, magnetic field, porosity, pulsatility, and magnetic nanoparticles on the flow of blood are analysed, and the results are represented graphically. It is significant to note that the flow parameters such as wall shear stress and flow resistance increase with increase in stenotic height, tapering parameter, magnetic field, pulsatile Reynolds number, time period, particle concentration, and particle mass parameters. Wall shear stress decreases with the increasing values of coupling number and it shows opposite behaviour in the case of flow resistance. Also increase in Darcy number leads to decrease in wall shear stress and flow resistance. The significance of treating blood as micropolar fluid is that the rotation of particles is taken into account. Cardiovascular diseases occur mainly due to abnormal blood flow in the arteries. To normalize the blood flow in the arteries, analysis of parameters involved in the study is essential. Hence, the present study has various applications in biomedical sciences. The effects of nanoparticles on blood flow analysed in the study have significant applications in delivery of drugs for treating cancer.

The influence of flow velocity on electrochemical reaction of metal surface

In order to find out the effect of fluid flow velocity on electrochemical reaction, the electrochemical parameters of super 13Cr stainless steel in 3.5% NaCl aqueous solution were measured by a jet flow system at different flow velocities. The electrochemical characters such as open-circuit potential and polarization curve were monitored online using a three-electrode electrochemical system. The results show that the increase of wall shear stress caused by the high flow velocity leads to the rupture of passive films and the exposure of fresh metal in the corrosive media, which causes the increase of corrosion rate. Meanwhile, the corrosion rate shows a significant growth when the flow velocity is less than 0∼10.0 m/s. But it gradually decreases after reaching a maximum value.

Role of Wall Shear Stress in Cryptosporidium parvum Oocyst Attachment to Environmental Biofilms.

This study investigated Cryptosporidium parvum oocyst deposition onto biofilms as a function of shear stress under laminar or turbulent flow. Annular rotating bioreactors were used to grow stabilized stream biofilms at shear stresses ranging from 0.038 to 0.46 Pa. These steady-state biofilms were then used to assess the impact of hydrodynamic conditions on C. parvum oocyst attachment. C. parvum deposition onto biofilms followed a pseudo-second-order model under both laminar (after a lag phase) and turbulent flows. The total number of oocysts attached to the biofilm at steady state decreased as the hydrodynamic wall shear stress increased. The oocyst deposition rate constant increased with shear stress but decreased at high shear, suggesting that increasing wall shear stress results in faster attachment of Cryptosporidium due to higher mass transport until the shear forces exceed a critical limit that prevents oocyst attachment. These data show that oocyst attachment in the short and long term are impacted differently by shear: higher shear (to a certain limit) may be associated with faster initial oocyst attachment, but lower shear is associated with greater numbers of oocysts attached at equilibrium.IMPORTANCE This research provides experimental evidence to demonstrate that shear stress plays a critical role in protozoan-pathogen transport and deposition in environmental waters. The data presented in this work expand scientific understanding of Cryptosporidium attachment and fate, which will further influence the development of timely and accurate sampling strategies, as well as advanced water treatment technologies, to target protozoan pathogens in surface waters that serve as municipal drinking water sources.

Pulsatile Non-Newtonian Fluid Flows in a Model Aneurysm with Oscillating Wall

This research presents a numerical simulation of an unsteady two-dimensional channel flow of Newtonian, and some non-Newtonian fluids using the finite volume method. The walls of the geometry oscillate sinusoidally with time. We have used the Cartesian curvilinear coordinates to handle complex geometries, i.e., arterial stents and bulges and the governing Navier-Stokes equations have been modified accordingly. Physiological pulsatile flow has been used at the inlet to characterize four different non-Newtonian models, i.e., the (i) Carreau, (ii) Cross, (iii) Modified-Casson and (iv) Quemada. We have presented the numerical results in terms of wall shear stress (WSS), pressure distribution as well as the streamlines and discussed the hemodynamic behaviors for laminar and laminar to turbulent transitional flow conditions. An increase of wall shear stress and a decrease in wall pressure are significantly observed at the stenosis throat for high Reynolds number and highly stenosed arteries. Likewise, the flow recirculation also increases if the narrowing level and the Reynolds number increases in the dilated region which eventually leads the stream to experience a transition to turbulence at $Re= 750$. The results for the fluid flow through an aneurysm just after a stenosis with oscillating wall are novel in the literature.

The Influence of Critical Flow Velocity on Corrosion of Stainless Steel

In order to find out the effect of fluid flow velocity on electrochemical reaction, the electrochemical parameters of super 13Cr stainless steel in 3.5% NaCl aqueous solution were measured by a jet flow system at different flow velocities. The electrochemical characters such as open-circuit potential and polarization curve were monitored online using a three-electrode electrochemical system. The results show that the increase in wall shear stress caused by the high flow velocity leads to the rupture of passive films and the exposure of fresh metal in the corrosive media, which cause the increase in corrosion rate. Meanwhile, the corrosion rate shows a significant growth when the flow velocity is less than 0–10.0 m/s. But it gradually decreases after reaching a maximum value.

Prediction of fouling tendency in PHE by data of on-site monitoring. Case study at sugar factory

The fouling deposition on heat transfer surfaces can have significant detrimental effect on heat recuperation and jeopardise the efficiency of energy usage, increasing fossil fuels consumption and harmful environmental effects. The data of plate heat exchanger (PHE) thermal performance monitoring in fouling conditions are presented. PHE is installed at sugar factory for preheating purified thin juice before evaporation. The character of deposits on plate heat transfer surface is examined by opening PHE after the tests. It reviled the scaling and particulate fouling mechanism. Mathematical model for prediction of fouling deposition development in time is proposed, which accounts for shear stress at the channel walls and surface temperature. The model parameters are determined according to industrial tests data. The ways of fouling mitigation in PHE are discussed using the model predictions. It is shown that fouling mitigation in PHE is possible by increasing wall shear stress at the same pressure drop in heat exchanger. It requires to eliminate additional pressure loss in connections and to optimize the number of plates and their arrangement adding some plates with higher corrugation angle. These recommendations are discussed and some are implemented at the factory conditions. That allowed increase the operation time between stops for PHE cleaning maintenance. The proposed model can be directly used for design and maintenance scheduling at the specific factory. It can also be used asa preliminary guidance for energy saving reconstructions in other sugar factories. But the direct model application requires data of fouling formation monitoring to identify its parameters for work with specific media streams prone to fouling.

Bicuspid Aortic Valve, Bovine Aortic Arch and early Atherosclerosis: When one plus one equals three

Despite that even normally functioning bicuspid aortic valves can have abnormal transvalvular-flow patterns, resulting in regional increases in wall shear stress and aortic dilatation, most often are preserved during ascending aorta replacement.

Characterization of complex flow patterns in the ascending aorta in patients with aortic regurgitation using conventional phase-contrast velocity MRI

Ascending aorta (AA) flow displacement (FD) is a surrogate for increased wall shear stress. We prospectively studied the flow profile in the AA in patients with aortic regurgitation (AR), to identify predictors of FD and investigate whether magnetic resonance imaging (MRI) phase-contrast flow rate curves (PC-FRC) contain quantitative information related to FD. Forty patients with chronic moderate (n = 14) or severe (n = 26) AR (21 (53%) with bicuspid aortic valve) and 22 controls were investigated. FD was determined from phase-contrast velocity profiles and defined as the distance between the center of the lumen and the “center of velocity” of the peak systolic forward flow or the peak diastolic negative flow, normalized to the lumen radius. Forward and backward volume flow was determined separately for systole and diastole. Seventy percent had systolic backward flow and 45% had diastolic forward flow in large areas of the vessel. AA dimension was an independent predictor of systolic FD while AA dimension and regurgitant volume were independent predictors of diastolic FD. Valve phenotype was not an independent predictor of systolic or diastolic FD. The linear relationships between systolic backward flow and systolic FD and diastolic forward flow and diastolic FD were strong (R = 0.77 and R = 0.76 respectively). Systolic backward flow and diastolic forward flow identified marked systolic and diastolic FD (≥0.35) with a positive likelihood ratio of 6.0 and 10.8, respectively. In conclusion, conventional PC-FRC data can detect and quantify FD in patients with AR suggesting the curves as a research and screening tool in larger patient populations.

Mathematical modelling for pulsatile flow of Casson fluid along with magnetic nanoparticles in a stenosed artery under external magnetic field and body acceleration

In the present paper, the magnetohydrodynamics effects on flow parameters of blood carrying magnetic nanoparticles flowing through a stenosed artery under the influence of periodic body acceleration are investigated. Blood is assumed to behave as a Casson fluid. The governing equations are nonlinear and solved numerically using finite difference schemes. The effects of stenotic height, yield stress, magnetic field, particle concentration and mass parameters on wall shear stress, flow resistance and velocity distribution are analysed. It is found that wall shear stress and flow resistance values are considerably enhanced when an external magnetic field is applied. The velocity values of fluid and particles are appreciably reduced when a magnetic field is applied on the model. It is significant to note that the presence of nanoparticles, magnetic field and yield stress tend to increase the plug core radius. Increased wall shear stress and flow resistance affects the circulation of blood in the human cardiovascular system. The results obtained from the study can be used in normalizing the values of the model parameters and hence can be used for medical applications. The presence of magnetic field helps to slow down the flow of fluid and magnetic particles associated with it. The magnetic particles of nanosize developed in recent days are biodegradable and used in biomedical applications. Biomagnetic principles and biomagnetic particles as drug carriers are used in cancer treatments.

Large-eddy simulations of flow and heat transfer in heated concentric annulus with inner cylinder rotation

Results from large-eddy simulations are reported for the flow and heat transfer in the annular gap between two concentric cylinders with the outer cylinder stationary and the inner cylinder rotating about its longitudinal axis. The objective of the study was to document the effects of destabilizing rotation on the turbulent transport of heat and momentum. The inner cylinder was heated by applying a constant heat flux while the conditions at the outer wall were adiabatic. Results were obtained for a stationary inner cylinder to serve as baseline for isolating the effects of rotation, and for the inner cylinder rotated at two different rotation numbers viz. 0.21 and 0.86. The Reynolds number was set at 9000 for all cases. With the outer cylinder stationary and the inner cylinder rotating, the effects of rotation are to destabilize the turbulence leading to enhanced mixing and significant increase in wall shear stress and Nusselt number. Additional effects include the displacement from each other of the points where the Reynolds stresses and the corresponding rates of strain are zero, and the non-alignment of their respective directions. These and other results reported herein provide a useful contribution to the very limited literature on heated turbulent flows destabilized by rotation, and can serve as benchmark to aid in the development and validation of turbulence closures for engineering applications.