Department of Civil & Infrastructure Engineering

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IIT Jodhpur

A notable universal feature of wall-bounded turbulent flows is the universal logarithmic law of the wall deduced by Theodore von Kármán. This law of the wall describes how time-averaged streamwise velocity changes with distance from the wall. Despite the law of the wall having a universal von Kármán constant κ = 0.41 that governs the slope of the log-law velocity profile, as commonly known over a period of about 80 years, in fluvial streams there are a number of instances of the non-universality of κ. To be specific, it behaves as a variable in flows with low relative submergence, or where there is bed-load and/or suspended-load sediment transport. This article focuses on the aspect of non-universality of κ by inviting various open questions relating to future research directions.© Springer-Verlag Berlin Heidelberg 2013.

World University root node

GeoPlanet: Earth and Planetary Sciences

Evidence of Non-Universality of von Kármán's κ

When an unsteady free surface flow encounters an adverse slope, it results in a decelerating flow up the adverse slope. The time dependent turbulent flow is treated here by appropriately reducing the two-dimensional Reynolds averaged Navier-Stokes equation along with the equation of continuity considering turbulence closure. With suitable choice of parameters, the resulting differential equations are numerically solved to compute free surface and streamwise velocity profiles with time. It is found that initially the advancing free surface is convex upwards for a short time, followed by a jump of the free surface with a negative streamwise velocity that is a backwater rolling breaker due to deceleration of flow. At later time, however, the velocity becomes positive, that is, the breakers roll forward. This dual feature of motion, that is a surge followed by rolling breakers, is repeated for sometime before the jumps stop. The theoretical analysis presented here is motivated by tidal bores propagating upstream in an estuarine river. © 2012 Versita Warsaw and Springer-Verlag Wien.

Acta Geophysica

Turbulent unsteady flow profiles over an adverse slope

Water Science and Technology

Potential of zerovalent iron nanoparticles for remediation of environmental organic contaminants in water: a review

In this study, the hydrodynamics of three types of steady undular free surface flow problems are theoretically analyzed. These flows are governed by the steady-state equations of conservation of mass and momentum developed by Bose and Dey in 2007 (J Hydraul Eng 133:1074-1079) and 2009 (Phys Rev E 80:036304). The first type of flow is an undular hydraulic jump on a plane smooth boundary when the approach flow Froude number marginally exceeds its critical value of unity. Here, it is established that the undular hydraulic jump phenomenon can be treated as an instability of the free surface flow being described by the instability principle. The results reveal that the threshold of an undular hydraulic jump is represented by a monotonic increase of approach flow Froude number with boundary inclination. The elevation of the undular free surface increases, as the boundary inclination increases. However, the amplitude of the free surface waves decreases with downstream distance. The second type of flow is that over a submerged hemi-cylindrical boss (inverted semi-circular section) placed on the channel bottom with its horizontal diameter lateral to the flow direction. The steady-state flow analysis shows that there is a drop in the free surface elevation on the downstream end of the cylinder with an undular free surface profile. The third type of flow is that over a continuous sinusoidal boundary of a channel. A numerical experiment shows that there exists a phase lag between the free surface profile and the boundary profile. Also, it is revealed that if the flow depth is reduced, an accumulation of heaved wave occurs indicating an onset of chocking.© Springer-Verlag Berlin Heidelberg 2013.

Hydrodynamics of Undular Free Surface Flows

EGU General Assembly Conference Abstracts, EGU

Potential of iron nanoparticles for remediation of organic contaminants in groundwater

In-situ aircraft measurements of cloud condensation nuclei (CCN) and aerosol size distribution were carried out over the region spanning from 24.78 °N to 29.5 °N and 78.1 °E to 85.0 °E from June 29 to July 3, 2009 during the Indian Continental Tropical Convergence Zone (CTCZ) campaign, consisting of total 9 flight sorties. CCN measurements were conducted at a constant supersaturation (SS) of 0.84%. It was found that at higher altitudes (4.7-6.7km), 30nm sized particles were dominating while at lower altitudes (0.6-3.7km), 50nm particles. Overall, CCN closure ratio (CCNpredicted/CCNmeasured) at different altitudes using Köhler theory and assuming pure ammonium sulfate was 1.375 (R2=0.80). For each sortie, the closure ratio varied with height and depended greatly on measured CN concentrations. A case study of Khajuraho sortie showed that the closure ratio increased from 1.07 to 1.40 as the CCN concentration increased from 1000cm-3 to 4000cm-3. Results of CCN closure improved significantly (overprediction improved by 37.5% and 34.6% for Pantnagar and Gaya, respectively) with the assumption of internally mixed aerosols composed of ammonium sulfate and insoluble organics. Hygroscopicity parameter calculated for these two sorties (κ=0.51 and 0.5) indicates the presence of moderately hygroscopic organic species along with some inorganic content. © 2013 Elsevier B.V.

Atmospheric Research

CCN closure results from Indian Continental Tropical Convergence Zone (CTCZ) aircraft experiment

Submerged sluice gates may be used as discharge measuring structures in irrigation channels. One commonly used model to predict discharge under submerged gates is based on the simultaneous solution of the energy and momentum equations (EM method). The conventional assumption for the solution is that the roller forming downstream of the gate is a static bubble of water with zero net flux of both momentum and kinetic energy. Energy losses along the submerged gate flow are commonly neglected. In this study, rational analysis of the EM method shows that the roller momentum flux and the energy loss may be considerable. A novel formulation of the EM method accounting for these two phenomena is proposed. Although it yields results similar to those of the conventional method, the new method introduces rationality in the application of the EM equations for submerged gate flow and helped to critically revise the assumptions in which the conventional EM method is based. © 2013 American Society of Civil Engineers.

Journal of Irrigation and Drainage Engineering

Revisiting the energy-momentum method for rating vertical sluice gates under submerged flow conditions

A one-dimensional depth-averaged velocity deformation model is developed to study the characteristics of the unsteady flows in open channels. The vertical profile of the streamwise velocity is expressed in a power series, and the coefficients of the velocity are evaluated by using the unsteady equation of motion. A concise form of the friction velocity for unsteady nonuniform flow is then proposed by utilizing the coefficients of the power series. The applicability of the model is validated with experimental data, producing reasonably good agreement between the model results and the observed data. Finally, the deformation of velocity at the surface is assured by comparing velocity distribution of numerical model with the computational results from a previous model. © 2013 American Society of Civil Engineers.

Journal of Hydraulic Engineering

Velocity deformation model for unsteady open-channel flows over smooth and rough beds

Scour at piers embedded in a bed of cohesive sediment mixture is investigated to quantify the effects of bed compaction. Experiments were conducted in a large rectangular laboratory flume with natural clay sediment collected from a stream located at the Chilean coastal range. Nonintrusive and high-resolution topographic measurements of scoured bed in the vicinity of piers were performed during the experimental runs with an installation of a laser distance sensor (LDS) that was traversed by the precision step motors. Measurements were taken by the LDS in different azimuthal half-planes to study the spatiotemporal variation of the topography of evolving scour holes. Experiments were conducted over 40 h, until an advanced stage of scour was reached, with the approaching flow having a bed shear stress equaling 95% of the Shields critical condition for the initiation of motion of sand in a sand-clay mixture. Results show that the bed is successively scoured in three different forms, chunks of aggregates, aggregate by aggregate, and particle by particle, when increasing the ratio of actual to Proctor's optimum molding water content, w̌ .Maximum scour depth was mainly observed at the wake region (downstream of the pier) and ranged from 10 to 58% of that in the sand alone case for mixtures with the same size of the sand fraction. For a given compaction energy, scour depths first decrease with w̌ , up to a value of w̌ 1/4 2.5, as fine clay particles are flocculated and increasingly dispersed with water content. For values of w̌ >2.5, the sediment matrix behaves as a fluid mud. In the latter case, scour depths increase with water content as the sediment bed becomes increasingly liquid. ©2013 American Society of Civil Engineers.