Edwin A Cowen

• PhD Stanford University
• Professor & Director DeFrees Hydraulics Laboratory at Cornell University

We perform an experimental study to investigate the turbulent boundary layer above a stationary solid glass bed in the absence of mean shear. High Reynolds number (Re_λ ∼ 300) horizontally homogeneous isotropic turbulence is generated via randomly actuated synthetic jet arrays (RASJA - Variano & Cowen 2008). Each of the arrays is controlled by a sp...

Synoptic information on bed shear stress is necessary in predicting the transport of sediments and environmental contaminants in rivers and open channels. Existing methods of estimating bed shear stress typically involve measuring vertical profiles of streamwise velocity or Reynolds stress and taking advantage of the logarithmic or the constant str...

Structural instabilities are often considered a failure state and therefore engineers are trained to avoid them. Recently, flexible buckled structures have gone from merely describing a phenomenon (e.g., twisting of vines, DNA mechanics), to being exploited for novel functionalities (e.g., stretchable electronics, energy harvesting). Herein we pres...

This paper describes a novel velocimetry method we call infrared quantitative image velocimetry (IR-QIV), that uses infrared (IR) images of thermal patterns advecting on water surfaces to calculate time-resolved, instantaneous, two-dimensional surface velocity fields. The method works day or night, and under most weather conditions, by tracking sub...

The use of image based velocimetry methods for field-scale measurements of river surface flow and river discharge have become increasingly widespread in recent years, as these methods have several advantages over more traditional methods. In particular, image based methods are able to measure over large spatial areas at the surface of the flow at h...

As research on wind energy has progressed, it has broadened from a focus on the wind turbine to include the entire wind farm. In particular, methods to mitigate the negative effects of upstream wakes on downstream turbines have received significant attention. One such mitigation method is axial induction control (AIC) in which upstream turbines are...

Stage and discharge are some of the oldest measurements in environmental fluid mechanics and are vital in forecasting water supply and flood safety. These measurements are traditionally manpower intensive, hence expensive, and dangerous under high flow conditions. Considering climate change and the planet’s increasing population there is a critical...

In recent years field-scale applications of image-based velocimetry methods, often referred to as large scale particle image velocimetry (LSPIV), have been increasingly deployed. These velocimetry measurements have several advantages—they allow high resolution, non-contact measurement of surface velocity over a large two dimensional area, from whic...

Controlled in-stream flow manipulations are challenging but necessary to implement to assess the consequences of real-world flow alterations on aquatic ecosystems. We designed a double v-notch weir system, which was first prototype-tested in a laboratory flume and then in the field. The device diverted instantaneous flows proportionally in a robust...

Sediment suspension and bed morphology in a mean shear free turbulent boundary layer - Volume 894 - Blair A. Johnson, Edwin A. Cowen

The open channel flow community has a history of using a set of universal exponential expressions to describe the vertical variation of turbulence intensity in open channel flows. Each of these relationships contain an empirical coefficient that varies with the component direction (Du = 2.3, Dv =1.27, Dw = 1.63). Recent laboratory experiments have...

We experimentally study the transition to large oscillatory motions of a thin elastic plate buckled into a second mode sinusoidal deformation. This deformation, intended to promote the onset of structural instabilities, is created by applying a permanent external net compressive force to the plate through a series of equi-spaced tension lines. Thes...

The design, assembly, use, and analysis of a torque transducer for small-scale wind and hydrokinetic turbines is presented. The new transducer provides a calibration between the torque and electrical current produced by a model turbine that uses a DC motor as a generator. The transducer transfers the torque generated by the turbine's shaft to a sma...

This work is motivated by a case study in which cooling water effluent is discharged from a line‐source diffuser onto the shallow southern shelf of a large lake. The effluent is discharged with high momentum to the north, and the plume influences the surrounding flow for hundreds of meters before becoming a passive tracer. We plan to use a three‐di...

When determining volumetric discharge from surface measurements of currents in a river or open channel, the velocity index is typically used to convert surface velocities to depth-averaged velocities. The velocity index is given by, $k = U_b/U_{surf}$, where $U_b$ is the depth-averaged velocity and $U_{surf}$ is the local surface velocity. The USGS...

Current methods employed by the United States Geological Survey (USGS) to measure river discharge are manpower-intensive, expensive, and during high flow events require field personal to work in dangerous conditions. Indirect methods of estimating river discharge, which involve the use of extrapolated rating curves, can result in gross error during...

The design of water supply infrastructure depends on local conditions such as geophysical features, available technol- ogy, traditions, culture, and available human and economic resources. The costs for designing, building, maintaining, monitoring, and replacing the required infrastructure escalate when any of these factors is inadequate or insuffi...

Setup, testing, and application of a two-dimensional longitudinal-vertical hydrothermal/transport model (the transport submodel of CE-QUAL-W2) is documented for Cayuga Lake, New York, where the Rossby radius is on the order of the lake’s width. The model is supported by long-term monitoring of meteorological and hydrologic drivers and calibrated an...

The shedding and evolution of the vortical structures generated by a solitary wave propagating over a submerged cylindrical structure are investigated ex- perimentally and numerically. The cylindrical structure consists of two con- centric cylinders and represents a simplified model for an offshore submerged intake structure typically used in coast...

A turbulence chamber designed specifically for the laboratory study of environmental scalar fluxes at sediment-water interfaces was developed and fully characterized. The turbulent flow field was documented using particle image velocimetry (PIV), with particular emphasis on turbulence characterization. The chamber is capable of reproducing a wide r...

Traditional methods of directly measuring volumetric discharge are expensive, manpower intensive, and often require technicians to work in hazardous conditions. Here we have developed a reliable, continuous and efficient method of remotely monitoring volumetric flow rate. A series of Largescale Particle Image Velocimetry (LSPIV) and Acoustic Dopple...

We measure solute transport near a turbulent air-water interface at which there is zero mean shear. The interface is stirred by high-Reynolds-number homogeneous isotropic turbulence generated far below the surface, and solute transport into the water is driven by an imposed concentration gradient. The air-water interface is held at a constant conce...

Motivated by the study of drag on plant canopies, a novel non-intrusive drag measurement device was developed—its design, calibration, and validation are presented. The device is based on isolating a region of a test facility, a section of the bed of an open channel flume in the present case, from the facility itself. The drag plate, sufficiently l...

Flow and transport through aquatic vegetation is characterized by a wide range of length scales: water depth (), plant height (), stem diameter (), the inverse of the plant frontal area per unit volume () and the scale(s) over which varies. Turbulence is generated both at the scale(s) of the mean vertical shear, set in part by , and at the scale(s)...

In an effort to develop a reliable, continuous and efficient method of remotely monitoring bathymetry, water column turbulence levels and mean velocities, a surface PIV (particle image velocimetry) experiment is conducted in a wide open channel (B/h > 12) for a range of flow depths. Mean velocity, turbulence intensities, dissipation, divergence, vo...

In environmental flows, we often observe turbulence levels that far exceed those produced by mean boundary shear (e.g., breaking surface waves), contributing to significant sediment resuspension and turbulent boundary layers that differ strikingly from classic turbulent boundary layer characterizations. We choose to study sediment resuspension in t...

Enhancements to the two-dimensional lake and reservoir water quality model W2Tn to simulate the effects of currents and waves on sediment resuspension and turbidity are described. Bed stress attributable to currents was computed by the hydrothermal component of W2Tn, whereas a surface wave component was added to W2Tn to determine bed stress owing t...

Utilizing a commercially available acoustic Doppler velocimeter, the Nortek Vectrino with optional plus (+) firmware, measurements of turbulence are made in a turbulent open channel flow in the 8m Research Flume of the DeFrees Hydraulics Laboratory. The measurements are used to estimate dissipation (ε) from Kolmogorov's 2/3, 5/3 and 4/5 Laws as wel...

Motivated by environmental flows where turbulence levels are set by processes other than mean shear (e.g., breaking surface and internal waves and bores) we choose to study turbulent boundary layers and sediment resuspension in the absence of mean shear using a recently-developed facility designed to generate homogeneous isotropic turbulence with l...

An analysis of limnological and input monitoring data for Cayuga Lake, New York, U.S.A., is presented that addresses differences in trophic state metrics and turbidity between pelagic waters and a shallow (<6 m) near-shore area (shelf) that receives multiple inputs. The effects of tripton (inanimate particles) on the observed patterns, and the cont...

Recent studies on relative dispersion have been exclusively focused on statistics of particle pair separation. Less attention was paid to its application in dispersing contaminant plumes or puffs. Since introduced by Richardson (1926), distance-neighbor function has been used to characterize the detail structure of concentration field in a dispersi...

The velocity field and turbulence structure within the surf and swash zones forced by a laboratory-generated plunging breaking wave were investigated using a particle image velocimetry measurement technique. Two-dimensional velocity fields in the vertical plane from 200 consecutive monochromatic waves were measured at four cross-shore locations, sh...

The design, calibration, and testing of a borescopic quantitative imaging profiler (BQuIP) system, suitable for the insitu measurement of two components of the instantaneous velocity in high sediment concentration flows, are presented. Unlike planar quantitative imaging techniques, BQuIP has a concentration-dependent field of view, requiring detail...

We present laboratory measurements of simultaneous velocity and concentration fields for the transfer of CO2 across a free surface. The interface is subject to the effects of free shear turbulence generated far beneath the surface, exhibiting low mean flow and excellent homogeneity. From measurements of the spatio-temporal mass flux we examine cohe...

We report measurements of the flow above a planar array of synthetic jets, firing upwards in a spatiotemporally random pattern to create turbulence at an air–water interface. The flow generated by this randomly actuated synthetic jet array (RASJA) is turbulent, with a large Reynolds number and a weak secondary (mean) flow. The turbulence is homogen...

Velocity and scalar concentration characteristics of low Reynolds number (Re) neutrally buoyant turbulent round jets were studied using coupled particle image velocimetry and laser induced fluorescence. Experiments were conducted on a jet with a fully developed pipe exit profile at Re=1,500 and Re=4,000. Measurements were made in the far field (60<...

The Cross-shore Sediment Transport Experiment (CROSSTEX) is a multi-investigator, multi-university, multi-phase scientific research project. The experimental phase was conducted at Oregon State University's O.H. Hinsdale Wave Research Laboratory (HWRL) during the summer of 2005. The goal of CROSSTEX is to fill the gap in the study of nearshore proc...

This paper describes the results of laboratory LDV measurements of the bottom boundary layer velocities induced by standing regular wave groups over a constant and fixed bed in the smooth turbulent regime. Using a multiple scale analysis, the Eulerian drift induced by the standing wave group in the weak unsteady and the steady regimes are described...

Liu & Orfila (J. Fluid Mech. vol. 520, 2004, p. 83) derived analytical solutions for viscous boundary layer flows under transient long waves. Their analytical solutions were obtained with the assumption that the nonlinear inertia force was negligible in the momentum equations. In this paper, using Liu & Orfila's solution and the solutions for the n...

In this paper we present mean velocity distributions measured in several different wave flumes. The flows shown involve different types of mechanical wavemakers, channels of differing sizes, and two different end conditions. In all cases, when surface waves, nominally deep-water Stokes waves, are generated, counterflowing Eulerian flows appear that...

We report measurements of the scalar flux field at an air-water interface. The cleaned free surface is subjected to turbulent forcing from below, generated with extremely low mean flow, thus the surface is not subjected to mean shear. The velocity field and temperature fluctuations are resolved in the plane of the free surface from high resolution...

The Cross-shore Sediment Transport Experiment (CROSSTEX) is a multi-investigator, multi-university, multi-phase scientific research project. The experimental phase was conducted at Oregon State University’s O.H. Hinsdale Wave Research Laboratory (HWRL) during the summer of 2005. The goal of CROSSTEX is to fill the gap in the study of nearshore proc...

For those of us who attempt the measurement of water wave induced phenomena, we are constantly reminded of the unique challenges presented to the experimental and observational researcher by the ubiquitous water wave: the dynamic free surface, the phase-to-phase variability due to wave groups and wave–wave interactions, the ongoing struggle to sepa...

The average length of time water remains within the boundaries of an aquatic system is a key parameter controlling the system's biogeochemical behavior. This timescale, generally referred to as the hydraulic residence time, provides a first-order description of multiple and complex processes that drive transport. The procedures to estimate these tr...

A new sub-pixel correlation peak locating algorithm for PIV analysis is introduced. The method is theoretically consistent with the method of continuously shifting interrogation sub-windows by fractional displacements, which has proven to be an effective way to reduce the bias error associated with integer pixel aliasing, or peak-locking. However t...

We analyze the exchange between a weakly forced lacustrine embayment and a large lake through a long, shallow channel. Exchange in the channel is the result of a multiple and subtle balance in which spatial thermal variations (baroclinic forcing), oscillations in the water level (barotropic forcing), bottom friction, diffusion, wind forcing, and th...

We measure the flow above an array of randomly driven, upward-facing synthetic jets used to generate turbulence beneath a free surface. Compared to grid stirred tanks (GSTs), this system offers smaller mean flows at equivalent turbulent Reynolds numbers with fewer moving parts.

Quantitative imaging (QI) techniques are a general class of optically based laboratory measurement techniques used in the field of experimental fluid mechanics, which have seen rapid growth over the last two decades. They are particularly well suited for the study of wavy fluid flows which are characterized by unsteady free surfaces and internal mo...

Using Digital Particle Tracking Velocimetry (DPTV), we measured the oscilla-tory boundary-layer flow motions induced by surface gravity waves propagating over a fixed ripple bed. Spatial and temporal variations of the velocity field were recorded. Two sets of wave parameters, yielding two different Keulegan-Carpenter and Reynolds numbers, were used...

Little Sodus Bay (LSB), a freshwater embayment along the coast of Lake Ontario (LO, North America), is used as a canonical lake-embayment system to investigate the effects of unsteadiness and viscosity on the generally assumed inviscid flow between two reservoirs through a topographic constriction. It is determined, through a scaling analysis based...

The occurrence, features and impacts on oxygen resources of an upwelling event in culturally eutrophic Onondaga Lake, NY, are documented, and recurrence is investigated, based on data collected as part of long-term, robotic, and event monitoring programs. The upwelling event occurred on September 11, 2002, in response to a wind event of average win...

Using a laser induced fluorescence (LIF) technique with a pH-sensitive fluorescent dye we directly visualize CO2 absorption across a free surface and turbulent transport in a free surface facility with bottom-generated turbulence. Coupling this technique with particle image velocimetry (PIV), we investigate the contributions of subsurface turbulenc...

A flourescent tracer is released continuously from a flush bed-mounted source into a fully developed wide open channel flow (width-to-depth ratio is 20:1), generating a passive scalar plume which rapidly mixes across the depth. A two-dimensional coupled particle image velocimetry - laser induced florescence (PIV-LIF) technique is applied to measure...

A particle image velocimetry (PIV) technique is used to make vertically resolved two-dimensional measurements in swash zone flows, which are notoriously recalcitrant to quantitative measurement. The PIV implementation directs the light sheet into the measurement region from beneath the beach thus avoiding issues of free surface diffraction effects....

An autonomous Remote Underwater Sampling Station (RUSS) on Cayuga Lake, New York is described. RUSS is a versatile unit with respect to remote communication, multiparameter measurements, meteorological measurements, and programming. Temperature, wind speed, and wind direction data show the presence of strong nonlinear internal wave dynamics. Turbid...

The mechanism of scale-dependent diffusion of a dispersing cloud of marked fluid was first proposed by Richardson (1926), the so-called '4/3 law'. A more rigorous theoretical analysis was given by Batchelor (1952) based on Kolmogorov's universal similarity hypothesis. Although the theory is based on the assumption of homogeneous and Isotropic turbu...

Mathematical models of aquatic ecosystems in well-mixed laboratory flow reactors suggest that hydraulic residence time is a key variable in determining the extent that ecosystems are self-organized or dominated by outside influence. Our study is part of a larger project "Lake Ontario Biocomplexity Study: Physical, biological, and Human interactions...

A method which combines two nonintrusive imaging techniques, particle tracking velocimetry and laser induced fluorescence, was used to make simultaneous measurements of velocity and concentration in a neutrally buoyant turbulent round jet. The measurements were made at two different Reynolds numbers (R), 360 and 4,210, at a Schmidt number of 1,930....

Boundary layer flows are ubiquitous in the environment, but their study is often complicated by their thinness, geometric irregularity and boundary porosity. In this paper, we present an approach to making laboratory-based particle image velocimetry (PIV) measurements in these complex flow environments. Clear polycarbonate spheres were used to mode...

The ability of many animals and insects to track a plume to its source is a particularly impressive feat when the fluid dynamics is considered. Inspired by this observation this research seeks to identify the information in a passive scalar plume suitable for developing robust and efficient plume tracing algorithms. The subject of this study is a s...

The understanding of many air-sea processes, including the transport of mass, momentum and heat at the air-water interface, is confounded by the lack of highly resolved measurements, in both space and time, of the local near-interface turbulence. Such measurements are necessary to fully understand transport events at an air-water interface and dedu...

This paper presents a particle image velocimetry (PIV) based measurement technique for flow acceleration. Based on the illumination of seeding particles three times over two frames and continuously tracking an individual particle over the three distinct illuminations, two velocity fields and a Lagrangian acceleration are obtained. Subsequently, the...

 A single-camera coupled particle tracking velocimetry–laser-induced fluorescence (PTV–LIF) technique and validation results from an experiment in a neutrally buoyant turbulent round jet are presented. The single-camera implementation allows the use of a 12-bit 60 frame-per-second 1024 × 1024 pixel digital CCD camera capable of streaming images in...

The fundamental activity conducted under this project was to hold a workshop on wave breaking turbulence. The workshop was held October 14-16, 1999, at Cornell University, Ithaca, NY, and organized around laboratory research, field work, numerical modeling, and an integration of these areas. A half day was given to each area, with a format that con...

A method which combines two non-intrusive imaging techniques, particle tracking velocimetry (PTV) and laser induced fluorescence (LIF), was used to make simultaneous measurements of velocity and concentration in a neutrally buoyant turbulent round jet. The measurements were made at two different Reynolds numbers, 360 and 4210, and a Schmidt number...

Experiments on neutrally buoyant turbulent round jets at various Reynolds numbers (Re) are presently being conducted using a single-camera coupled particle tracking velocimetry - laser induced fluorescence (PTV - LIF) technique. Initial measurements of the mean and fluctuating concentration and velocity fields, Reynolds stress, and turbulent scalar...

The scale-dependent growth of a plume, generated by a flush-mounted bottom source in a wide open-channel flow, is investigated using a single-camera coupled PTV-LIF technique. This technique, with excellent spatial and temporal resolution, is capable of determining the turbulent scalar flux (\overlineu_i^' c^'), as well as other turbulent statistic...

A new open-channel experimental facility has been built specifically for the study of coastal plumes. The research perspective is to investigate the physics from the point of view of the identification of contaminant source location. We present the preliminary results of a plume generated by a bottom-mounted source in the presence of lateral meande...

Dispersion of a passive scalar released from a near-bed source is examined in coastal waters, (O(10 m) deep), just off San Clemente Island, California. Rhodamine WT dye was released continuously for several hours from a bottom source on May 8, 1997. Surveys of the hydrodynamic fields (currents and density) are combined with dye concentration measur...

The BASS Rake, a differential travel time, velocity profile sensor with multiple sample volumes, was originally designed for use in thin, oscillatory, bottom boundary layers. Recent proposals have suggested using the instrument to measure full water column and near-surface profiles in the swash and surf zones on a beach. Other technologies cannot r...

Giant kelps (which may reach lengths of 45 m) are a prominent exception to the general rule that wave-swept organisms are small. The ability of these kelps to maintain their large size in the presence of ocean waves has been attributed to their extreme flexibility and the concomitant tendency to 'go with the flow', a tendency that reduces the hydro...

The results of laboratory experiments on the three-dimensional short-crested unsteady breaking waves are reported. Using flow visualization in combination with measurements of the surface displacement and the three-component velocity field, this study explored the generation and subsequent dissipation of vorticity, turbulence and surface-drift in t...

A novel approach to digital particle tracking velocimetry (DPTV) based on cross-correlation digital particle image velocimetry (DPIV) is presented that eliminates the need to interpolate the randomly located velocity vectors (typical of tracking techniques) and results in significantly improved resolution and accuracy. In particular, this approach...

The exchange of momentum, heat, and mass at an air-water interface is generally limited by the aqueous near-interface turbulence structure - where free-surface waves are ubiquitous. A novel measurement technique, digital particle tracking velocimetry (DPTV), was developed and used to make near-surface measurements of the velocity field in wavy and...

Gas transfer at an air-water interface is generally limited by the aqueous near-interface turbulence structure. Wavy open-channel flow is an ideal flow for investigating the effects of free-surface waves on turbulence struc-ture near the free-surface since identical flows with and without waves can easily be compared. We report the preliminary resu...

The formation of longitudinal vortices has been observed in a wavy channel flow and appears to be linked to spilling breaking and/or to vertical vorticity generated by a wave instability at the wave maker. Both conditions were present when the wave slope, ak exceeded 0.25. The wave instability produced velocity jets beneath and just downstream of t...