Upstream Flow Conditions Research Articles

Simulation of flow through dam foundation by isogeometric method

This research introduces a numerical approach called IsoGeometric Analysis (IGA) to solve the Laplace equation. Non-Uniform Rational B-Splines (NURBS) basis function is applied for approximation of the anisotropic saturated porous media of dam foundation field, as for description of the geometry. The discretized form of the governing Laplace equation is obtained using the standard Galerkin method. The present results consist of uplift pressure, seepage discharge and exit gradient which are validated with existing experimental data based on a physical model. The obtained data are also compared with empirical data. The computed results show a satisfactory agreement with the experimental measurements in the wide ranges of upstream flow conditions. In addition, it was found that the mentioned numerical method improves the convergency and accuracy of parameters compared to traditional methods.

The role of initial flow conditions for sibilant fricative production.

Sibilant fricative sound production depends on the geometric and flow properties of the production system. Nevertheless, few studies deal with the potential impact of flow properties other than the inlet volume flow rate on the noise produced. In this work, an experimental study is presented using a replica based on a reconstructed oral cavity for the phoneme /s/. Initial flow conditions upstream from the sibilant groove are altered by varying the method of air supply. Statistical moments of the initial velocity distribution are characterized using hot-film anemometry and related to spectral features of the radiated acoustic pressure. Discrepancies in the dynamic amplitude (≤25%) and negative spectral slope (≤35%) observed at a constant Reynolds number but different initial upstream flow conditions are of the same order of magnitude as those previously reported in humans. This suggests that consideration of the upstream flow conditions is important in the study of sibilant fricative sound production.

The Influence of Upstream Flow Angle Variation on Intermediate Turbine Duct

Intermediate turbine duct represent the flow path between the high pressure and low pressure turbine. Caused by the complex flow mechanism, the outlet flow condition of the high pressure turbine is easily changed. Since the upstream flow condition from the high pressure turbine has a significant effect on the internal flow field of intermediate turbine duct, the study in the upstream condition is of high value. Through numerical simulation, the influence of upstream flow angle variation on intermediate turbine duct is observed. It is found that the main influence of the flow angle variation is near the hub side of the duct, and the quantitative result shows that a larger flow angle has a positive effect on the flow field and can reduce loss.

Impact of upstream flow conditions on the initiation of moist convection over the island of Corsica

The influence of upstream flow on the initiation of moist convection over Corsica is investigated using semi-idealized simulations. The simulations, performed with the Consortium for Small-scale Modeling (COSMO) model, are initialized with one vertical profile at all grid points and under constant boundary conditions. The upstream wind velocity and wind direction, as well as the saturation deficit and stability, are systematically varied to estimate the impact of the individual factors on the initiation and strength of moist convection. Also, the influence of radiation is evaluated. It is found that deep convection can only develop with high solar radiation. With lower radiation, thermal wind systems are weak, and only shallow convection is triggered. Results show that with strong solar radiation, a strong upstream wind velocity is less efficient in triggering deep convection than a weaker one. This is due to the dynamic effects on the flow field. A low upstream wind velocity enables thermal wind systems to become dominant and the preconvective conditions for deep convection are more favorable. This leads to more events with deep convection and precipitation. The wind direction can be the determining factor for the initiation of deep convection and also controls the location of precipitation. A change of just 15° can decide on whether deep convection occurs or not. With a high upstream wind velocity, the location is always on the lee side of the island. With a lower upstream wind velocity, two hot spots for convection initiation, one in the northern central part and one in the western part of the island, are identified. It is further found that the impact of saturation deficit is higher than the impact of stability. With increased instability, the atmospheric conditions are more favorable for the development of convection, but the high saturation deficit in the middle troposphere prevents the formation of deep convection. Through reduction of the saturation deficit, multiple convective cells can develop in the more humid atmosphere. Additionally, the integrated water vapor is larger, which means that more precipitable water is available allowing larger amounts of precipitation.

Effect of uneven red cell influx on formation of cell-free layer in small venules

This study examined how the uneven influx of red blood cells (RBCs) from feeding vessels influences formation of cell-free layer (CFL) in the downstream vessel of a venular bifurcation. Spatio-temporal variations of the CFL width along the downstream vessel (19–41-μm inner diameter, D) were determined at 0.5D intervals from 0.5D to 3.0D away from the bifurcation. Upstream flow conditions were quantified by the ratio of volume flow rates (Q⁎=QHigh/QLow) between high flow (QHigh) and low flow feeding (QLow) vessels. The RBC aggregation level in the rats was adjusted to be at healthy human levels by infusing Dextran 500. Our results suggested that the CFL formation process could be seen only from 2.0D away from the bifurcating point. The mean CFL width at the wall adjacent to the feeding vessel with a higher flow rate was consistently greater than that at the opposite wall, leading to an asymmetric CFL formation in the vessel. A positive relation (P<0.05) between the asymmetry of the CFL width and the volume flow rate ratio (Q⁎) was found. Our numerical prediction showed that flow resistance in the venular network could be significantly increased by the asymmetric formation of CFL downstream and this effect might become more pronounced under pathological flow conditions such as hyper-aggregating and/or low shear conditions.

Development of Empirical Formulas for Effect of Circular Pier and Abutment on Local Scour Depth

This study based on laboratory experiments for computing depth of local scour around abutment and bridge pier neighboring abutment considering the study of the effects of upstream flow conditions , pier and abutment sizes , median size of bed material and spacing between pier and abutment on the maximum scour depth and scour pattern around a pier and abutment. The study was conducted using a physical hydraulic model of pier and abutment operated under subcritical flow , clear-water condition and using uniform cohesionless sand as bed material . Three different size models of pier and abutment were used to show the effect of the size on the local scour and two different median size (d50) of sand were used in this study. Dimensional analysis techniques and statistical analysis were used to find new formulas with help of the experimental data . One of these formula was to compute the maximum scour depth at pier neighboring abutment and the other to find the maximum scour depth at abutment. There formula were derived to predict the maximum scour depth in terms of Froude number , diameter of pier and abutment , median size of sand , flow depth , flow velocity and spacing between pier and abutment.

Computational fluid dynamics based assessment of discharge-water depth relationships for combined sewer overflows

This article describes a general method to assess discharge-water depth relationships for combined sewer overflow (CSO) chambers. This method is particularly suitable for: complex geometries, unavailable univoc relationship between upstream and downstream flow and complex downstream hydraulic conditions. The methodology presented in this article is based on computational fluid dynamics. Its aim is to propose a relationship between the water depths in the CSO chamber and the overflow discharge. This study focuses on the evaluation and integration of the uncertainties in the determination of the most suitable depth-overflow relationship. Uncertainties related to numerical model, boundary conditions and water depth have been taken into account in order to elaborate water depth-overflow rate relationship. This approach is illustrated through the example of the ‘Milan’ CSO of Mulhouse city, France.

Iterative Solution for Ideal Fluid Jets

AbstractFree jets are important flow phenomena from outflow structures of dams and reservoirs. The basic case of jet flow originates from a free overfall with upstream critical flow conditions and a fully ventilated nappe. In this paper, a two-dimensional potential flow model has been developed. Semiinverse mapping of the Laplace equation has been employed in conjunction with an analytical solution of the Boussinesq equations to initiate iterations for locating the free streamlines under atmospheric pressure. A systematic iteration method is proposed using the squaring technique for solving the Laplacian field, a computation of the free streamlines using the curvilinear formulation of velocity at boundary streamlines in the energy equation, and an iteration of the position of the terminal jet section versus the brink section conditions. The model permits a convergent numerical solution, which was verified against experimental data, thereby indicating that the proposed ideal fluid flow model can be applied...

Observations of the atmospheric boundary layer height under marine upstream flow conditions at a coastal site

AbstractWe investigate several lidar‐type instruments and methodologies for boundary layer height (BLH) estimation during 2 days at a coastal site for winds that experience marine upstream flow conditions. Wavelet and profile fitting procedures on the aerosol backscatter signals from a ceilometer and an aerosol lidar reveal similar BLHs, but their agreement depends on the presence of clouds and the instrument signal, among others. BLHs derived by a threshold on the carrier‐to‐noise profiles of a wind lidar agree well with those derived by using a threshold on the backscatter profile of the ceilometer and are used as reference for a 10 day BLH intercomparison. Furthermore, the BLHs from the aerosol analysis are comparable to those derived from wind speed and direction profiles from combined mast/wind lidar measurements. The BLH derived from simulations performed with the Weather Research and Forecasting (WRF) model shows similar behavior compared to the lidar observations. The seasonal diurnal variation of the BLH for 2010, derived from the wind lidar and ceilometer thresholds, shows similar BLHs but generally higher values compared to that from WRF. No clear BLH diurnal variation is observed neither from the observations nor from the WRF model outputs, except in summer for the latter. Both observations and WRF model simulations reveal higher BLHs during autumn compared to spring time. These BLHs are used to evaluate the intra‐annual variation and show high peaks in September, November, and February.

Numerical Investigation on the Effect of Inlet Conditions on the Oblique Shock System in a High-Speed Wind Tunnel

The Present study is conducted to find out the best inlet conditions for designing process of a high-speed wind tunnel. The inlet conditions are appropriate for the cases that the real nozzle has not been calculated and downstream parts designers (such as test section and diffuser designers) need a reasonable upstream flow condition for their calculations. Inlet boundary condition of each case has been specified by User-Defined Function. The process of User-Defined Function (UDF) specification is time-consuming and is based on a try and error method. Several cases of inlet conditions have been designed and examined. The comparison of results is shown in terms of cross-sectional and axial distributions of parameters and contours of Mach number and static pressure. Finally, the 1.2 m-length Ogive curve with 0.5 degree initial angle and after that, the case of 1.2 m-length ducthave been chosen as the equivalent nozzles.

Shear-induced demixing in polymeric membrane dopes

One of the critical challenges in producing hollow fiber membranes is controlling fiber microstructure. The dope solutions involved possess (by design) an inherent thermodynamic sensitivity to phase separation, and are therefore susceptible to shear-induced microstructural changes when they are subjected to the complicated flow conditions that accompany spinning. This study demonstrates that shear-induced demixing is relevant in polymeric membrane dopes, and that it can affect macrovoid formation. Furthermore, we find that surprisingly subtle changes in shear history can affect demixing. Our investigation consisted of a two-tier approach. First, we used shear-small-angle light scattering (shear-SALS) to observe the microstructural evolution in liquid dope solutions before, during, and after shear flow. By varying the speed at which samples were syringe-loaded into the rheometer, we found that the pattern (and hence, the microstructure) observed after demixing varied based on shear history. In the second set of experiments, dopes with varying shear histories were extruded into a non-solvent bath to form solid fibers. Despite the fact that the fibers were all extruded under identical conditions, scanning electron microscopy (SEM) showed that the number of macrovoids observed varied widely between fibers. A comparison of the shear-SALS and extrusion results showed that shear-demixing is strongly linked to macrovoid formation. Our findings suggest that low-shear, upstream flow conditions (e.g., in supply tubing) could be just as important for fiber microstructure as the high-shear flow within the actual spinneret.

Correction of flow metering coefficients by using multi-dimensional non-linear curve fitting

Flow disturbances can significantly affect flow metering because the downstream flow of flow disturbances can become unstable and asymmetric, thus resulting in measurement errors in the flow meter. A clamp-on type ultrasonic flow meter is an example of a flow meter that is susceptible to flow disturbances given its diametrical configuration of ultrasonic paths. Several flow rate correction formulas have been suggested to mitigate the effect of flow disturbance for improved flow metering. As a novel method, a multi-dimensional non-linear correction formula is suggested to overcome limitations in flow metering that are attributed to the non-linearity of flow disturbances. The non-linear correction formula comprises n-th order polynomials with multiple variables. To validate the usefulness of the non-linear correction formula, the standard error of estimate (SEE) is introduced. Four types of flow configurations, namely, downstream of a contraction pipe, an expansion pipe, a single elbow joint, and a tee joint, are used to show the effect of the non-linear correction formula. The expanded uncertainty based on the SEE indicates estimated values of 1.29%, 11.14%, 1.07%, and 6.31% for the four upstream flow configurations, respectively. Thus, the effect of the non-linear correction formula is limited according to the upstream flow conditions. In the downstream flow of the contraction pipe and of the single elbow joint, the non-linear correction formula not only harmonizes the distribution of the flow rate deviations but also removes the biases of flow rate deviations with respect to the flow velocity, the installation location, and the diameter ratio.

Group method of data handling to predict scour depth around bridge piers

In this study, group method of data handling network with quadratic polynomial was used to predict scour depth around bridge piers. Effective parameters on scour phenomena include sediment size, geometry of bridge pier, and upstream flow conditions. Different shapes of piers have been utilized to develop the GMDH network. Back propagation algorithm was performed to train the GHMD network which updated weighting coefficients of quadratic polynomial in each iteration of the training stage. The GMDH performed with the lowest errors of training and testing stages for cylindrical pier. Also, Richardson and Davis, Johnson’s equations produced relatively good performances for different types of piers. Finally, the results indicated that GMDH could be provided more accurate prediction than those obtained using traditional equations.

Simplified procedure for design of long-throated flumes and weirs

An appropriate critical-depth measuring device should match the flume to approach channel conditions to provide a suitable Froude number in the approach channel to pass the sediment and for producing a stable and readable water surface at the gauging station. In current research, area ratio is explicitly expressed via an elegant equation. This equation is used to design the rectangular-throated flumes and weirs based on the upstream Froude number (upstream flow conditions). Introducing a correction factor, Cf, the proposed equation can be also used with high accuracy for nonrectangular control sections such as triangular (Cf=0.979) and parabolic/trapezoidal (Cf=0.987) sections. Moreover explicit equations for approach velocity coefficient of the long broad-crested weirs (long-throated flumes) are also presented. These relationships facilitate the discharge computation of the broad-crested weirs and long-throated flumes. The relations presented in this study will be useful in the design and analysis of the long-throated flumes and weirs, and reduce computation time and effort.

Distribution of mean velocity in turbulent boundary layer over permeable surface with air blowing

In the present article, we investigate the possibility of using simple physical models for predicting properties of incompressible turbulent boundary layer on permeable wall at various values of air-microblowing mass flow rate. It is shown that the velocity scaling U∞*/δ99 can be successfully used to approximate the distribution of mean velocity in the outer region of the boundary layer. The use of this scaling makes the velocity profiles invariant with respect to Reynolds-number variation; this circumstance largely facilitates the analysis of experimental data, making it independent of upstream flow conditions. The distribution of mean velocity in the logarithmic flow region of the boundary layer over permeable surface can be described with a modified law of the wall involving a constant C0 equal to the same constant for canonical boundary layer, and a quantity K being a weak function of blowing ratio.

Simulating 2D open-channel flows through an SPH model

The present work deals with the development and application of a 2D Smoothed Particle Hydrodynamics (SPH) model to simulate a broad range of open-channel flows. Although in the last decades the SPH modelling has been widely used to simulate free-surface flows, few applications have been performed for free-surface channels. For this reason, an appropriate algorithm is developed to enforce different upstream and downstream flow conditions and simulate uniform, non-uniform and unsteady flows. First, the proposed algorithm is validated for a viscous laminar flow in open channel characterized by Reynolds numbers of order O(102). The second test case deals with a hydraulic jump for which different upstream and downstream conditions are needed. Varying the Froude number, several types of jumps are investigated with specific focus on the velocity field, pressure forces, water depths and location of the jump. Comparisons between numerical results, theory and experimental data are provided. Finally, the interaction between a flash flood generated by an unsteady inflow condition and a bridge is shown as an example of an engineering application.

Comparison of Aortic Flow Patterns Before and After Transcatheter Aortic Valve Implantation

Little is known of the likely changes in blood flow velocity profiles and aortic wall shear stress (WSS) following transcatheter aortic valve implantation (TAVI). The objective of this study was to investigate the effects of TAVI on flow patterns in the thoracic aorta by using cardiovascular magnetic resonance imaging (CMR) and computational fluid dynamics (CFD). An elderly patient with aortic stenosis was examined using MRI pre- and post-TAVI, and CFD simulations were carried out incorporating MRI-derived patient-specific anatomy and upstream flow conditions. Pre-TAVI velocity profiles demonstrated the highly disturbed turbulent flow and jet impacting the wall of the arch owing to the partial opening of the stenosed aortic valve, with likely pathological effects. In the Post-TAVI aorta, velocity profiles were similar to those of healthy aortas with spatially more uniform WSS and lower turbulence levels, demonstrating the favourable effects of the TAVI procedure in restoring normal aortic flow. This study has shown both the effectiveness of TAVI on an individual patient and the advantage of the combined CMR and CFD method for a comprehensive patient-specific assessment of pre- and post-TAVI aortic flow patterns and WSS over CMR alone.

Experimental Study on Flow Coefficient of Broad-Crest Ridge-Free Weir of Gudi Hydroelectric Power Station

The flow coefficient is an important factor in analyzing and computing the flow capacity of broad-crested ridge-free weir of low head hydroelectric key position. For determine the flow coefficient of the broad-crested ridge-free weir of low head dam accurately, this paper study on the rule of the flow coefficient change base on the Gudi hydroelectric station model test. The test show in the condition of the high submergence and complex upstream and downstream flow condition, the flow coefficient value that use empirical formula compute is big. The author proposes the correction formula according the empirical formula and the test result.

Choke-free flow in trapezoidal channels

is very suitable to design a channel transition from the point of view of a no-choke condition. In this study, the condition of choke-free flow for two types of transitions in trapezoidal channels subject to a rise in bed elevation is considered. Based on the critical flow occurring downstream of the transition zone, the energy equation is solved with the aid of numerical methods to determine explicit equations for the maximum permitted bed rise under a given approaching regime. The presented procedure herein can also be used to determine end sill height in triangular and trapezoidal channel sections to assure hydraulic jump occurrence in stilling basins. Moreover, to determine the limits of upstream-flow depths (the choke-free regions) a suitable dimensionless specific energy equation is presented. This equation can be utilised to choose the operating ranges of upstream flow depths for choke-free flow in subcritical and supercritical upstream flow conditions. Finally energy loss in the transition zone is considered by applying it in the proposed equations.

Choke-free flow in circular and ovoidal channels

A comprehensive solution for circular and ovoidal channel sections is obtained under the condition of choke-free flow owing to a gradual and smooth rise in bed elevation. Generally, two practical cases of channel transition are considered: (a) rising bed elevation caused by a change in the position of the channel centreline; and (b) rising bed elevation caused by a decrease in the channel diameter. Considering the critical flow occurring downstream of the transition zone, the energy equation is solved with the aid of a numerical technique to determine the explicit equations for the maximum allowable bed rise under a given approaching regime. Moreover, to determine the limits of upstream flow depths (the choke-free regions) from the information on upstream channel geometry, rise in bed elevation and discharge, suitable graphical solutions are presented using dimensionless specific energy equations. These graphs can be utilised to choose the operating ranges of upstream flow depths for choke-free flow in both subcritical and supercritical upstream flow conditions. Since the downstream critical depth is required to determine the upstream operating range, the direct solutions for critical depths in circular and ovoidal channels are also presented. Finally, energy loss in the transition zone is considered by applying it in the proposed equations.