Prashanth Reddy Hanmaiahgari

Turbulence characteristics of flow in an open channel with temporally varying mobile bedforms

Abstract Turbulence of flow over mobile bedforms in natural open channels is not yet clearly understood. An attempt is made in this paper to determine the effect of naturally formed mobile bedforms on velocities, turbulent intensities and turbulent stresses. Instantaneous velocities are measured using a two-dimensional particle image velocimetry (PIV) to evaluate the turbulence structure of free surface flow over a fixed (immobile) bed, a weakly mobile bed and a temporally varying mobile bed with different stages of bedform development. This paper documents the vertical distribution of velocity, turbulence intensities, Reynolds shear stress and higher-order moments including skewness and turbulent diffusion factors. Analysis of the velocity distributions shows a substantial decrease of velocity near the bed with increasing bedform mobility due to increased friction. A modified logarithmic law with a reduced von Kármán constant and increased velocity shift is proposed for the case of the mobile bedforms. A significant increase in the Reynolds shear stress is observed in the mobile bedforms experiments accompanied by changes over the entire flow depth compared to an immobile bed. The skewness factor distribution was found to be different in the case of the flow over the mobile bedforms. All higher-order turbulence descriptors are found to be significantly affected by the formation of temporally varying and non-equilibrium mobile bedforms. Quadrant analysis indicates that sweep and outward events are found to be dominant in strongly mobile bedforms and govern the bedform mobility.

Time Variation of Scour at Downstream Pier for Two Piers in Tandem Arrangement

A semi-empirical model is presented to estimate the time variation of scour depth at downstream of pier when two piers are arranged in tandem arrangement under clear water scour condition with uniform sediments. The methodology developed for computing the time variation of scour depth is based on the concept of the conservation of mass of sediment, considering the primary horseshoe vortex system to be the main agent of scouring and assuming a layer-by-layer scouring process. The proposed model agrees closely with the reported experimental data of time variation of scour depth at downstream piers in tandem pier arrangements under clear water condition with uniform sediments.

Dominant features in three-dimensional turbulence structure: comparison of non-uniform accelerating and decelerating flows

The results are presented from an experimental study to investigate three-dimensional turbulence structure profiles, including turbulence intensity and Reynolds stress, of different non-uniform open channel flows over smooth bed in subcritical flow regime. In the analysis, the uniform flow profiles have been used to compare with those of the non-uniform flows to investigate their time-averaged spatial flow turbulence structure characteristics. The measured non-uniform velocity profiles are used to verify the von Karman constant κ and to estimate sets of log-law integration constant Br and wake parameter П, where their findings are also compared with values from previous studies. From κ, Br and П findings, it has been found that the log-wake law can sufficiently represent the non-uniform flow in its non-modified form, and all κ, Br and П follow universal rules for different bed roughness conditions. The non-uniform flow experiments also show that both the turbulence intensity and Reynolds stress are governed well by exponential pressure gradient parameter β equations. Their exponential constants are described by quadratic functions in the investigated β range. Through this experimental study, it has been observed that the decelerating flow shows higher empirical constants, in both the turbulence intensity and Reynolds stress compared to the accelerating flow. The decelerating flow also has stronger dominance to determine the flow non-uniformity, because it presents higher Reynolds stress profile than uniform flow, whereas the accelerating flow does not.

Identification of partial blockages in pipelines using genetic algorithms

A methodology to identify the partial blockages in a simple pipeline using genetic algorithms for non-harmonic flows is presented in this paper. A sinusoidal flow generated by the periodic on-and-off operation of a valve at the outlet is investigated in the time domain and it is observed that pressure variation at the valve is influenced by the opening size of blockage and its location. In this technique, the unsteady (steady oscillatory) pressure time series at only one location is required to identify two blockages. In the proposed methodology, the solution of the governing hyperbolic PDEs of pipe flow is obtained using the method of characteristics. For any piping system similar to the hypothetical pipe system used in the simulations, generalized best amplitude and best frequency of the valve operation are determined, which give maximum deviation in pressure responses for a specific blockage at different locations for a given constant-head reservoir. The generalized best amplitude and best frequency of the valve operation are also obtained for two blockages. Accuracy of the proposed methodology in identifying blockages in a hypothetical simple pipe system with increased noise in the simulated measurements is studied. A non-dimensional variable is proposed to determine whether the proposed methodology is applicable to isolate partial blockages in a piping system. Finally, the proposed methodology is experimentally validated on a laboratory piping system for a single blockage and two blockages.

The United Nations

The organization of United Nations is reviewed in the present chapter. Chronological development and current status of Non-Proliferation Treaty (NPT) of nuclear arsenal is presented. The Geneva Protocol (1925), Biological Weapon Convention (1972), and Chemical Weapon Convention (1993), as adopted by the United Nations General Assembly, in order to prohibit the use of bacterial and toxic weapons against other member countries are also discussed.

Turbulent Hydrodynamics Along Lateral Direction in and Around Emergent and Sparse Vegetated Open-Channel Flow

Jute plantation is one of the important crops in India and Bangladesh region. The vegetation density of Jute plantations is usually sparse. No comprehensive experimental study has been carried out till date to investigate turbulent characteristics in the lateral direction at interior and exterior of sparse and emergent vegetation patch. The proposed study investigates important turbulent characteristics at different cross sections at upstream, interior and downstream of emergent and sparsely vegetated open-channel flow. An array of seventy uniform rigid acrylic cylindrical rods with regular spacing was used to represent the emergent sparse vegetation patch. Three-dimensional instantaneous velocities were measured by a Nortek VectrinoPlus ADV. From this study, it was evident that time-averaged streamwise velocities were decreasing in interior of the vegetation along the streamwise direction. Inside the vegetation patch, time-averaged lateral velocities were directed towards the nearest sidewall. Time-averaged vertical velocities were negative throughout the cross section at upstream of the vegetation patch. But absolute magnitudes are decreasing in interior and downstream of the vegetation patch. Turbulent kinetic energy was decreasing inside the vegetation patch, and the peak values were located far from the channel bed in interior and downstream cross sections through the vegetation.

Comparison of Turbulent Hydrodynamics with and without Emergent and Sparse Vegetation Patch in Free Surface Flow

In the present study, we have compared the turbulent hydrodynamics in open turbulent flow with and without an emergent and sparse vegetation patch. The rigid patch, located at the middle cross-sectional region, was made by acrylic cylindrical rods with regular spacing between them along streamwise and transverse directions. The measurements of flow velocity components were taken by a Nortek Vectrino Plus acoustic Doppler velocimeter, and experimental data were collected along cross section for vegetation-free fully developed flow and along the cross section which is located at the middle of the streamwise length of the vegetation patch. Inside the vegetation patch, we have observed decreased value of time-averaged streamwise velocity in comparison with those of the vegetation-free fully developed flow. The time-averaged values of transverse and vertical velocities show increased magnitude with respect to the corresponding values in the vegetation-free fully developed flow. Inside the vegetation patch, with increasing transverse length from right-hand sidewall to left-hand sidewall, the magnitudes of normal stresses gradually increase and exceed the corresponding magnitudes of normal stresses in the vegetation-free fully developed flow. Along the cross section inside the patch, the magnitudes of governing Reynolds shear stress are smaller than the corresponding values of Reynolds shear stress without the vegetation. Along the cross section inside the patch, the vectors of secondary current follow are directed towards the left-hand sidewall together with zigzag pattern in vertical direction. In the interior of the vegetation, the strength of anticlockwise vortex in terms of the magnitude of moment of momentum is greater than that of the vegetation-free fully developed flow.

Experimental Investigation of Turbulent Hydrodynamics in Developing Narrow Open Channel Flow

In the present study, a detailed experimental investigation of turbulent hydrodynamics is carried out on developing flow along the centreline of a narrow open channel. The characteristics of flow velocity, normal stresses and Reynolds stresses have been investigated. At the beginning of the modelled region, the time-averaged streamwise velocity increases up to 20% of the flow depth from the channel bed and decreases with further increase in vertical height. With increasing streamwise length, vertical location of the maximum time-averaged streamwise velocity is shifting away from the bed. The time-averaged lateral velocities are positive along the midsection in the modelling region, whereas the time-averaged vertical velocities exhibit negative value. In the modelled region, the maximum value of time-averaged lateral velocity occurs either near the channel bed or in the vicinity of the free surface; however, the peak value of time-averaged vertical velocity appears in the neighbourhood of the channel bed. In the developing flow region, the values of normal stresses in streamwise and lateral directions are maximum near the bed and decrease with vertical distance up to 40% of the flow depth from the channel bed and after that normal stresses increase with further increase in vertical distance from the channel bed. Moreover, the observed magnitudes of streamwise normal stresses are greater than the corresponding values of lateral normal stress. The normal stress in vertical direction increases with increasing vertical height from the channel bed; however, the increasing trend decreases with increasing streamwise distance. Before attaining the fully developed profile, the Reynolds shear stress exhibits a decreasing trend with increasing vertical height up to 60% of the flow depth from the channel bed, and with further increase in vertical distance, the Reynolds shear stress trend starts increasing. An important finding is that in the modelled region, the developing flow zone, the transition zone from developing flow to fully developed flow and the fully developed flow zone are detected. The present study provides a good quality data for further investigations of developing flow in a narrow open channel.

Lateral Variation of Turbulent Features in Developing and Developed Narrow Open-Channel Flow

In the present study, a detailed experimental investigation of lateral variation of turbulent characteristics is carried out in developing and fully developed flow over a fixed rough bed. Experiments are conducted in a rectangular flume of aspect ratio \((b/h = 3.05)\) and bed roughness \(d_{50} = 2.5\,{\text{mm}}\). Instantaneous three-dimensional velocities were measured using a Nortek Vectrino plus downlooking ADV. The characteristics of normalized flow velocity, turbulent intensities, Reynolds shear stresses and TKE distribution have been investigated. Raw velocity data have been filtered as prescribed in the recent literature. From the experimental data, it is observed that boundary-layer thickness increases along the streamwise distance in the developing flow region and reaches maximum in fully developed flow. On the contrary, boundary-layer thickness decreases in the lateral direction from the centreline of the channel towards sidewalls in both developing flow and fully developed flow. Local shear velocities are estimated from the Reynolds shear stress distribution in intermediate layer. Lateral variation of shear velocity shows decreasing trend in both developing and fully developed flow from the centreline towards sidewalls. Velocity dip phenomenon due to secondary current is observed in both the vertical distribution of normalized streamwise velocity profiles and RSS distribution along the lateral direction near to the side wall in both the developing flow and fully developed flow. Normalized Reynolds shear stress decreases in the lateral direction from the centreline of the channel towards the side wall in the developing flow with retardation of flow in the outer layer.

Hydrodynamics and turbulence in emergent and sparsely vegetated open channel flow

This present study reports the results of an experimental study characterizing thorough variation of turbulent hydrodynamics and flow distribution in emergent and sparsely vegetated open channel flow. An emergent and rigid sparse vegetation patch with regular spacing between stems along the flow and transverse directions was fixed in the central region of the cross-section of open channel. Experiments were conducted in subcritical flow conditions and velocity measurements were obtained with an acoustic Doppler Velocimetry system. Large variations of the turbulence intensities, Reynolds shear stress, turbulent kinetic energy and vortical motions are found in and around the vegetation patch. At any cross-section through the interior of the vegetation patch, streamwise velocity decreases with increase in streamwise length and the velocity profiles converge from the log-law to a linear profile with increasing slope. Time-averaged lateral and vertical velocities inside the vegetation patch increase with increasing streamwise distance and converge from negative values to positive values. Turbulence intensities interior of the sparse vegetation patch are more than those of without the vegetation patch. Similar to the trend of streamwise velocity profiles inside the vegetation, turbulence intensities and longitudinal-normal Reynolds shear stress profile decreases with streamwise direction. In the interior of the vegetation patch and downstream of the trailing edge, turbulent kinetic energy profiles are exhibiting irregular fluctuations and the maximum values are occurring in the outer layer. Analysis of flow distribution confirms sparse vegetation patch is inducing a serpentine flow pattern in its vicinity. At the leading edge, flow is rushing towards the right hand sidewall, and at the trailing edge, flow is turning to the left hand sidewall. In between the leading and trailing edges, the streamlines are following a zig-zag fashion at varied degree along the streamwise and lateral directions. Immediate upstream of the leading edge and in the interior of the vegetation patch, vortex motion is clearly visible and the vortices are stretched along the width of the channel with streamwise direction.