Matahel Ansar

Numerical simulations of inviscid three-dimensional flows at single- and dual-pump intakes

Three-dimensional inviscid solutions for pump-approach flow distributions within both a single-pump and a dual-pump sump model were developed. The single-pump sump model consisted of a rectangular pump bay with a vertical circular pipe located at the downstream end of the bay. The two-pump sump model consisted of a wider rectangular pump bay with two vertical circular pipes located at the downstream end of the bay. The equations of motions were solved in generalized curvilinear coordinates on a non-staggered grid. For the single-pump model, the simulations were carried out for two cases, cross-flow and no-cross-flow. The results are in good agreement with laboratory flow measurements obtained from a 1:10-scale model using an Acoustic Doppler Velocimeter. For the two-pump sump model, simulations were also carried out for two cases. In Case 1, an equal pumping discharge was delivered through the two pipes, and in Case 2 the total discharge was split in a 7-to-3 ratio between the two pipes. The results for the two cases were compared with a focus on the formation of free-surface and subsurface vortices surrounding the pumps.

Applicability of Hydraulic Performance Graph for Flow Estimation in Open Channels

The hydraulic performance graph (HPG) is an efficient means for summarizing the backwater profiles of all possible gradually varied flow conditions in an open-channel reach, expressed in the form of water surface elevations (stages) or depths at the ends of the channel reach for different constant discharges. HPGs have been used for determining the flow carrying capacity of channel systems (Yen and Gonzalez, 1994, 2000). Further, Gonzalez and Yen (2000) have also carefully assessed the applicability of HPG for unsteady flow routing. Theoretically, the HPG for a channel reach is a graphical representation of the relation between discharge and the downstream and upstream stages in the reach according to gradually varied flow. In this paper we explore the applicability of HPGs for estimating the flow in an openchannel reach from observed water stages at its two end stations. We describe the methodology for developing the HPG for a site in South Florida based on actual channel geometric and roughness properties and compare the discharges estimated with the reach’s HPG for actual observations of upstream and downstream stages with field-flow measurements concurrently collected with an acoustic Doppler current profiler. This comparison shows that the HPG of channel reach is a plausible and reliable alternative for estimating flows in open channels. It is also shown that the accuracy of the HPG for flow rating is a function of Sf L / H, where Sf = friction slope, L = length of the channel reach and H is the error in estimating the water stages. HPG ratings are found relatively accurate for Sf L / H >> 1, but their accuracy decreases as Sf L / H 1.

Submerged Weir Flow at Prototype Gated Spillways

Submerged weir flow is one of the most difficult flow conditions to accurately predict at gated spillways. Previous research work has mostly focused on submerged weir flow measured in small-scale laboratory models. In this paper, we develop a submerged weir flow equation based on field measurements collected with an Acoustic Doppler Current Profiler at several prototype gated spillways in southern Florida. The proposed method is developed using dimensional analysis. This method is compared with field measurements and several previously published submerged weir equations.

Applications of Computational Fluid Dynamics to Flow Ratings at Prototype Spillways and Weirs. I: Data Generation and Validation

AbstractAccurate flow ratings at water-control structures are essential for water-resource management. This paper presents an approach to obtain numerically generated data using computational fluid dynamics (CFD) to complement field measurements needed to improve spillway flow-rating formulas. The procedure to generate CFD flow data described herein is based on solving Reynolds-Averaged Navier-Stokes equations using the κ-e turbulence closure model with the free surface resolved by the volume of fluid (VOF) method. The steps for setting the computational domain, generating the mesh, selecting the boundary conditions, and choosing a convergence criteria for the simulations are discussed. The turbulence closure model and VOF method for the present application are verified with data from laboratory measurements of submerged jet flow below a gate and in a sharp open-channel bend. CFD flow data generation is validated with laboratory and field measurements for gated ogee spillways in south Florida. The results...

Applications of Computational Fluid Dynamics to Flow Ratings at Prototype Spillways and Weirs. II: Framework for Planning, Data Assessment, and Flow Rating

AbstractTraditionally, flow-rating formulas for hydraulic structures are calibrated and validated with data comprising field measurements of discharge, water stages, and operational settings monitored in near real time. Lack of sufficient field measurements that include all flow types and cover the full operational ranges has been a major constraint in developing reliable flow ratings for prototype hydraulic structures. A companion paper introduced a plausible method that relies on computational fluid dynamics (CFD) simulations to generate accurate flow data that complements field measurements for flow rating analysis. In this paper, a general framework for applying CFD in flow rating is proposed, which includes planning of CFD simulations, assessing CFD flow data, and improving existing flow ratings using a hybrid data set of field-measured and CFD-simulated flows. Finally, two case studies of flow rating for spillways and weirs carried out to demonstrate the proposed framework are presented. Results sho...

A new flow calculation algorithm for weir box culverts

In this paper, a new algorithm is presented for flow rating of weir box culverts. Weir box culverts are compound culverts, which consist of a weir box in the front, and a traditional culvert in the back. This configuration makes it quite difficult to obtain accurate flow rating with traditional culvert flow equations. In the new algorithm, flow through weir and culvert is first calculated separately, then iteration method is used to systematically adjust water elevation inside the weir-box and recalculate the flow. This loop keeps on going until the discharge continuity is satisfied with certain convergence criteria. This algorithm has been validated at various weir box culverts. The results show reasonable agreement with field flow measurements. 1. Introduction

RECENT APPLICATIONS OF HYDROACOUSTIC-BASED FIELD FLOW MEASUREMENTS IN UNDERSTANDING THE HYDRAULICS OF WATER CONTROL STRUCTURES

Hydroacoustic-based field flow measurements have been applied at the South Florida Water Management District (SFWMD) for the last ten years for rating validation and calibration of water control structures, such as spillways, weirs, pumps and culverts. This paper summarizes recent applications of these types of measurements in calibrating flow rating equations at hydraulic structures maintained and operated by SFWMD for real-time flow monitoring. Selected recent research findings on complex physical processes related to the hydraulics of flow through water control structures are then discussed. The findings include improved rating equations for free and submerged orifice flow at radial gate spillways.