Effect Of Inlet Velocity Profile Research Articles

The effect of inlet velocity profile on entropy generation and hydrothermal performance of a pin-fin heatsink with biologically prepared silver/water nanofluid coolant: Two-phase mixture model

The prediction of heat transfer characteristics numerically depends on several factors such as the numerical method, the boundary and operating conditions, etc. The present paper investigated the influence of using the uniform and non-uniform inlet velocity profiles on the heat transfer coefficient (h), pumping power (W˙p), temperature uniformity (θ), and thermal and frictional entropy generation rates (S˙th and S˙fr) in a pin-fin heatsink with silver/water nanofluid (NF) coolant. The numerical study is conducted utilizing the two-phase mixture scheme. The results proved that h is almost the same for two inlet profiles with the maximum deviation of 0.2%. θ and W˙p, however, for uniform profile is nearly 2.52–1.86% and 15–26% higher than those for the other case at Reynolds numbers of 500–2000, respectively, indicating a lower temperature uniformity and higher power consumption for uniform velocity profile. The figure of merit was obtained as 1.19–1.36 at Re numbers of 500–2000; indicating the better hydrothermal performance of the non-uniform inlet velocity profile over the other case. In addition, S˙th was almost the same for both cases due to same mean temperature and temperature gradients. However, S˙fr for non-uniform profiles was 4.41–8.84% lower than that for other profile at Reynolds numbers of 500–2000.

The influence of inlet velocity profile on predicted flow in type B aortic dissection

In order for computational fluid dynamics to provide quantitative parameters to aid in the clinical assessment of type B aortic dissection, the results must accurately mimic the hemodynamic environment within the aorta. The choice of inlet velocity profile (IVP) therefore is crucial; however, idealised profiles are often adopted, and the effect of IVP on hemodynamics in a dissected aorta is unclear. This study examined two scenarios with respect to the influence of IVP—using (a) patient-specific data in the form of a three-directional (3D), through-plane (TP) or flat IVP; and (b) non-patient-specific flow waveform. The results obtained from nine simulations using patient-specific data showed that all forms of IVP were able to reproduce global flow patterns as observed with 4D flow magnetic resonance imaging. Differences in maximum velocity and time-averaged wall shear stress near the primary entry tear were up to 3% and 6%, respectively, while pressure differences across the true and false lumen differed by up to 6%. More notable variations were found in regions of low wall shear stress when the primary entry tear was close to the left subclavian artery. The results obtained with non-patient-specific waveforms were markedly different. Throughout the aorta, a 25% reduction in stroke volume resulted in up to 28% and 35% reduction in velocity and wall shear stress, respectively, while the shape of flow waveform had a profound influence on the predicted pressure. The results of this study suggest that 3D, TP and flat IVPs all yield reasonably similar velocity and time-averaged wall shear stress results, but TP IVPs should be used where possible for better prediction of pressure. In the absence of patient-specific velocity data, effort should be made to acquire patient’s stroke volume and adjust the applied IVP accordingly.

Effects of inlet velocity profile on flow and heat transfer in the entrance region of a ribbed channel

Due to a complex channel structure, the coolant flow supplied to the internal cooling passage of a gas turbine blade shows an asymmetrical pattern rather than a fully developed or uniform distribution. In this study, the effect of the non-uniform inlet velocity profile of the coolant on the flow and heat transfer in a ribbed channel was investigated using the numerical analysis method. Four inlet velocity profiles were applied to a stationary ribbed channel and three Reynolds numbers of 10,000, 20,000 and 30,000 were considered. The hydraulic diameter of the channel was 24mm and the rib installation angle was 60°. The rib height-to-hydraulic-diameter ratio (e/Dh) and the rib-pitch-to-height-ratio (P/e) were 0.125 and 10, respectively. Numerical analysis results showed that in the entrance region, the location and shape of the reattachment and the recirculation region were altered by the local velocity distribution caused by the different inlet velocity profiles. Therefore, the distribution and the strength of the vorticity in the channel were changed, and the local heat transfer coefficient and pressure drop in the channel were affected by the inlet velocity profile. The overall heat transfer coefficients for all cases showed similar values, however, the fully developed flow profile resulted in the highest thermal performance factor due to the lowest value of friction factor.

Effect of Inlet Velocity Profile on Heat Transfer in a Rotating Channel

The effects of the inlet velocity profile on the heat transfer coefficient in rotating smooth and angle ribbed channels were experimentally investigated. The detailed heat transfer coefficient was measured using the transient liquid crystal technique. Reynolds numbers based on the channel hydraulic diameter of 10,000, 20,000, and 30,000 were tested, and the corresponding rotation number ranged from 0.067 to 0.184. Results showed that the Nusselt number ratio decreased as the Reynolds number increased for both channel cases, and the Nusselt number for the trailing surface is the highest for both channel cases. For the smooth channel case, the Nusselt number for the leading surface is higher than that for the stationary surface, while the reverse trend was observed for the ribbed channel. An inlet velocity profile with a higher centerline velocity resulted in higher heat transfer for the smooth channel, but the skewed inlet velocity profile caused higher heat transfer for the ribbed channel.

입구 속도 분포가 매끈한 회전유로 내 열전달계수에 미치는 영향

The effect of inlet velocity profile on the heat transfer coefficient in a rotating smooth channel was investigated experimentally. Three simulated inlet flow conditions of fully developed, uniform, and distorted inlet conditions were tested. The Reynolds number based on the channel hydraulic diameter was ranged from 10,000 to 30,000 and the transient liquid crystal technique was used to measure the distribution of the heat transfer coefficient in the rotating channel. Results showed that the overall heat transfer coefficient increased as the Reynolds number increased. Also, the distribution of the heat transfer coefficient was strongly affected by the inlet flow condition. Generally, the fully developed flow simulated condition showed the highest heat transfer coefficient.

The effect of inlet velocity profile on the bifurcation COPD airway flow

The effect of inlet velocity profile on the flow features in obstructed airways is investigated in this study. In reality, the inlet velocity distributions on such models, which are extracted from medial branches of natural human lung, should be neither uniform, nor symmetric parabolic, but skewed-parabolic due to having been skewed by the upper carina ridges. Four different three-dimensional three-generation models based on the 23 generations model of Weibel have been considered, respectively. The fully three-dimensional incompressible laminar Navier–Stokes equations and continuity equation have been solved using CFD solver on unstructured tetrahedral meshes. To reduce the complexity of the simulations, only one Reynolds number of 900 was used in this calculation. Four types of inlet boundary conditions, namely uniform, parabolic, positive-skewed parabolic (skewed to the positive x -direction), and negative-skewed parabolic, were imposed on the obstructed airway models, which were considered to be obstructed at either the second generation or the third generation airways, respectively. The results show that the inlet velocity profile has significant influence on the flow patterns, mass distributions, and pressure drops in either the symmetric model, or the three obstructed models. The three generation airways may not be enough to study the bifurcation flow in chronic obstructive pulmonary disease (COPD) airways, and a four-generation or more airway model is necessary to get better predictive results.

Aerodynamic performance of an annular flat plate airfoil cascade with nonuniform inlet velocity

The demand for increased gas turbine engine efficiency with minimum weight is leading to more complex blading designs, in which viscous and three-dimensional effects are significant. As a result, design procedures based on first principle, experimentally verified, three-dimensional aerodynamic analyses are required. This paper describes a series of experiments performed in a large-scale, subsonic, annular cascade facility specifically designed to provide three-dimensional aerodynamic data suitable for code verification. In particular, the effect of inlet velocity profile on the overall three-dimensional performance of a classical flat plate airfoil cascade is investigated over a range of incidence angles including those resulting in airfoil surface flow separation. All of the data are analyzed and correlated with appropriate nonseparated flow predictions.