Uniform Inlet Velocity Profile Research Articles

Physically Realistic Inlet-Velocity Profiles in Duct Flows

A uniform inlet velocity profile is widely used in the numerical simulations of fluid flow and heat transfer in ducts for both incompressible and compressible flows. In incompressible flows, the calculated fluid pressure at the inlet edge is extremely high and affects the calculation of the average pressure. In compressible flows, the fluctuation of pressure in the flow direction results in the fluctuation in the velocity. This has motivated this study to numerically investigate a physically realistic velocity profile at the inlet of a pipe rather than using a uniform velocity profile. The numerical simulations were based on the control volume-based power law scheme and the semi-implicit method for pressure-linked equations (SIMPLE) algorithm. The continuity and momentum equations for a flow in a pipe with the rounded inlet corner were solved to obtain a physically realistic inlet velocity profile. The obtained inlet velocity profile was expressed by a simple expression in the range of Reynolds number from 100 to 2000. Using this velocity profile, both the incompressible and compressible flows in a pipe were numerically investigated. The results resolved the previously observed inconsistencies in the pressure that were previously observed in the numerical simulations with uniform inlet velocity profiles.

Multi-Objective Optimization with Fuzzy Logic Analysis of Confined Flow Characteristics on Circular Cylinder

Two-dimensional, isothermal numerical computations are carried out using Ansys Fluent-18. Here, the flow is unsteady and incompressible past confined circular cylinder in a plane rectangular channel. A uniform inlet velocity profile is preferred; the Reynolds number varies in between 50 and 200. The blockage ratios (width of the channel to circular cylinder diameter) are 5, 10, 15 and 20. Flow characteristics like pressure and frictional drag coefficients, and Strouhal number (flow shedding frequency) are optimized. Fuzzy logic analysis has been used to model and predict the results of confined circular cylinder. A Mamdani fuzzy inference system with triangular membership function is used to be fuzzy sets. The results show that fuzzy model will predict the Strouhal number with 0.45% error. The present study recommends the lowest blockage ratio (highest blockage effect) and the highest Reynolds number combination is more suitable in flow shedding region in real-field applications.

Numerical study of turbulent wall jet over multiple-inclined flat surface

In the present work flow field of a turbulent oblique wall jet with multiple flat inclined wall has been numerically investigated. The Reynolds averaged Navier–Stokes (RANS) equations for incompressible flow are solved in transformed geometry using boundary-fitted coordinate system. The aim of the work is to investigate the influence of three inlet conditions: uniform, parabolic and trapezoidal inlet velocity profiles, on the mean flow and turbulent characteristics of the jet flowing tangentially along a multiple inclined solid wall. The results show that the inlet conditions affect the flow in the vicinity of the nozzle exit area and also the far field region. Mean flow has been presented in terms of evolution of mean velocity profiles, jet spread, decay of streamwise maximum velocity, distribution of wall pressure and skin friction coefficients, and streamwise variations of integrated momentum and energy fluxes. Discontinuities in the boundary slope of the segmented wall produces oscillations in distribution of skin friction and pressure coefficients. Reduced pressure in the region of wall discontinuity appeared to be causing the deflected jet to remain attached to the wall. The growth of the inner layer of the jet is relatively high with uniform inlet velocity profiles in the near-field region, but in the far-field region the inner layer grows with higher rate for the trapezoidal and the parabolic profiles. The rate of decay of maximum streamwise velocity for oblique wall jet on segmented wall is higher than that of plane wall jet. The jet with parabolic and trapezoidal inlet profiles show higher rate of decay than that with a uniform inlet profile. Similarity of streamwise velocity and velocity component parallel to the oblique wall has been observed in the developed region of flow. The volume flow rate of the jet varies linearly along the flow direction due to entrainment of the fluid from the surrounding. Sudden change in slope of the wall causes a sharp rise in entrained volume of fluid. The distribution of near wall velocity in the inner coordinates of the boundary layer is grossly altered and the profiles do not conform to the universal velocity profiles in the form of the law of the wall. Relatively higher position of defect law data signifies comparatively lower turbulence in the outer mixing layer. Cross-stream distribution of Reynolds stresses shows that the effect of inlet velocity profiles is more pronounced in the near field region of flow. Self-similarity is observed in the normalized turbulent shear stress profiles whereas considerable scatter can be noticed in the profiles of turbulent normal stresses for all the inlet velocity conditions. Two distinct peaks in the normalized turbulent kinetic energy profiles characterize the two shear layers of the jet and shifting of the outer peak toward the wall suggests a strong interaction of the outer layer with the inner layer as the jet develops.

Effect of spatial inlet velocity profiles on the vortex formation pattern in a dilated left ventricle

Despite the advancement of cardiac imaging technologies, these have traditionally been limited to global geometrical measurements. Computational fluid dynamics (CFD) has emerged as a reliable tool that provides flow field information and other variables essential for the assessment of the cardiac function. Extensive studies have shown that vortex formation and propagation during the filling phase acts as a promising indicator for the diagnosis of the cardiac health condition. Proper setting of the boundary conditions is crucial in a CFD study as they are important determinants, that affect the simulation results. In this article, the effect of different transmitral velocity profiles (parabolic and uniform profile) on the vortex formation patterns during diastole was studied in a ventricle with dilated cardiomyopathy (DCM). The resulting vortex evolution pattern using the uniform inlet velocity profile agreed with that reported in the literature, which revealed an increase in thrombus risk in a ventricle with DCM. However the application of a parabolic velocity profile at the inlet yields a deviated vortical flow pattern and overestimates the propagation velocity of the vortex ring towards the apex of the ventricle. This study highlighted that uniform inlet velocity profile should be applied in the study of the filling dynamics in a left ventricle because it produces results closer to that observed experimentally.

Particle inhalation and deposition in a human nasal cavity from the external surrounding environment

CFD computations of particle flows in a human nasal cavity were conducted, using two types of inlet velocity profiles at the nostril openings respectively. One type is the widely used uniform inlet velocity profile while the other is a realistic inlet velocity profile extracted from the external environment that is influenced by facial features. The latter type of inlet velocity profiles were obtained through CFD computations of indoor gas-particle flows around a human head geometry containing detailed facial features in an enclosed space. Comparisons were made between the predicted results of airflow field, particle tracks and particle deposition efficiency in the nasal cavity. It was revealed that although the effects of facial features exist only in a small region (10–20 mm) in front of the face, they lead to complicated, and non-uniform velocity profiles at the nostril openings. This discrepancy leads to different predictions of airflow fields and local particle deposition efficiency in the nasal cavity, especially in the anterior regions such as the vestibule and nasal valve. The results may further lead to discrepant health-risk assessments associated with particle inhalation. Therefore, for CFD simulations of particle deposition in the nasal cavity, the inlet velocity profiles induced by facial features are important for more realistic results.

Numerical Investigation for Net Enhancement in Thermal-Hydraulic Performance of Compact Fin-Tube Heat Exchangers with Vortex Generators

Systematic numerical simulations are carried out for a steady-state, laminar and constant-property air flow through a passage of a compact fin-tube heat exchanger specified with a constant wall temperature distribution and a uniform inlet velocity profile. A pair of delta winglet-type vortex generators (VGs) is punched out of the plain fin surface near the tube as a heat transfer enhancement device. A variety of VG configurations are investigated and their effects on the thermal-hydraulic (heat transfer) performance of the compact fin-tube heat exchanger are presented in terms of the Colburn factor j and the friction factor f for a specific Reynolds number (Re=400). In addition, the highest net enhancement in the thermal-hydraulic performance, defined as the ratio of the heat transfer enhancement to the pressure loss penalty, is sought. It is found that a moderate degree of the upstream shifting and the spanwise shifting of VG toward the tube contribute to the net enhancement. Nearly 9% of the net enhancement is achieved with an optimum configuration investigated presently.

Prediction of the flow structure in a turbulent rectangular free jet

A numerical analysis is conducted for turbulent flow of a rectangular free jet with an aspect ratio of 2:1. The computations were performed using two standard two-equation turbulence models (the k–ε and the k–ω models). Two inflow boundary conditions were evaluated with each model: a uniform inlet velocity profile and a profiled inlet velocity fitted to experimental data. The results show that the k–ε model with the profiled inlet velocity succeeded in predicting the main features of the flow, including the vena contracta and the saddle-shaped velocity profiles in the near-field region, and the rate of velocity decay in the far-field region.

The entrance effect of laminar flow over a backward-facing step geometry

The study investigates the entrance effect for flow over a backward-facing step by comparing predictions that set the inlet boundary at various locations upstream of the sudden expansion. Differences are most significant in the sudden expansion region. If the geometry has an inlet channel, then shorter reattachment and separation lengths are predicted. Comparisons with experimental data indicate that better agreement is found using a long inlet channel, but only for low Reynolds numbers where the experimental error is less significant. For certain cases, predictions with a high expansion number are perturbed by the entrance effect more than low-expansion-number predictions; however, the effect is localized in the sudden expansion region. Channels with low expansion numbers always experience a greater entrance effect after some distance upstream and downstream of the sudden expansion. The boundary layer growth in the inlet channel was examined using a uniform inlet velocity profile. © 1997 John Wiley & Sons, Ltd.

The upstream scale of flow development in curved circular pipes

For steady airflows at moderate Dean number (100 [les ] κ [les ] 500) axial- and transversevelocity profiles were delineated by anemometry in the entry region of curved circular pipes, having curvature ratios R/a of 4.66 or 8. Uniform inlet velocity profiles were found to evolve downstream over two inviscid length scales. Axial profiles develop on the lengthscale a, the pipe radius. The upstream influence extends at least 6a into a bend. Within this region axial development is largely inviscid and apparently independent of the radius of curvature R. Secondary currents develop on the scale (aR)½. Their initial growth is consistent with a model of vorticity transport based on streamline curvature, but instead of progressing monotonically to an asymptotic value, this swirl first overshoots, then subsides approximately 2(aR)½ downstream from the inlet. Hawthorne's model of streamline twist appears to account qualitatively for this dampening.

Steady flow in a sudden expansion at high Reynolds numbers

The sudden expansion of a laminar flow in a two-dimensional channel is examined theoretically in the limit of large Reynolds number R. Previous investigators found, from experiment and from numerical solutions of the equations of motion, that a region of closed streamlines is formed whose streamwise length is linearly related to R for R = O(102). It is desired to determine if the steady solutions to the Navier–Stokes equations continue to exhibit this relationship indefinitely for increasing R. Since solutions are sought for which the longitudinal length scale is O(R) and that in the tranvserse direction is O(1), the equations of motion reduce to the boundary-layer equations as R→∞. These equations are solved numerically using a finite difference technique for selected values of λ, the ratio of the upstream channel half-width to the step height. Steady solutions are found for all values of λ when the inlet velocity profile is parabolic. However, a uniform inlet velocity profile yields steady solutions with an O(R) wake length only for λ⩽λc = 1.54. Analogous results apply in the axisymmetric case for which λc is found to be equal 3.67.

Flow of the Entrance Region in a Porous Pipe : 2nd Report, Uniform Inlet Velocity Profile

Flow of the Entrance Region in a Porous Pipe : 2nd Report, Uniform Inlet Velocity Profile

Flow of the Entrance Region in a Porous Pipe : 2nd Report, uniform Inlet Velocity Profile

Flow of the Entrance Region in a Porous Pipe : 2nd Report, uniform Inlet Velocity Profile

Symmetrical Laminar Channel Flow With Wall Suction

Entrance region solutions of the two-dimensional boundary layer equations are presented in terms of a convergent power series for steady, laminar, incompressible channel flow with uniform mass suction at the walls. The entrance solutions obtained using both uniform and parabolic velocity profiles at the inlet to the channel are compared to the solutions obtained from the similarity equations for a wide range of non-dimensional suction velocities (0 ≤ Rew ≤ 30). With a parabolic inlet velocity profile, the flow does not become fully developed for Rew > 7, except right at the downstream end of the channel (x = L). The similarity solutions are in good agreement with the entrance solutions over a reasonable length of the channel only for very small values of Rew. With a uniform inlet velocity profile, the flow does not become fully developed in the range 7 < Rew < 13, except right at x = L. In this case, the similarity equations should not be used to predict overall axial pressure variations except for very large values of Rew.

Effect of Non-Uniform Inlet Velocity Profile on the Development of a Laminar Flow between Parallel Plates

This paper describes a theoretical analysis of a laminar developing flow in the entrance region between parallel plates, when the inlet flow has a constant velocity gradient normal to the channel axis. The analysis is performed within the framework of the boundary layer theory, and governing equations are solved by a finite-difference method. The following results are obtained from the analysis : (1) If the flow rate through the channel is constant, the additional pressure drop in the entrance region is considerably decreased as the normal velocity gradient at the entrance section is increased. (2) As is physically expected, when isothermal walls of the channel are considered, the mean heat transfer rate is much larger at the wall of higher inlet velocity side than at the smaller inlet velocity side. However, an average value of the heat transfer rate on the two walls as a whole is smaller by a few percent than that for the case of a uniform inlet velocity profile. (3) The entrance length shows a significant reduction with the increase of the transverse velocity gradient at the inlet section.