Tyler Van Buren

• PhD
• Professor (Assistant) at University of Delaware

Rectangular orifice steady jets impinging into a laminar crossflow are experimentally studied using particle image velocimetry. Jets with multiple orifice geometries, including orifice orientation, aspect ratio, and jet velocities were tested. We primarily focus on the (1) jet vortex structure and velocity field characterization, (2) theoretical sc...

We use small-amplitude inviscid theory to study the swimming performance of a flexible flapping plate with time-varying flexibility. The stiffness of the plate oscillates at twice the frequency of the kinematics in order to maintain a symmetric motion. Plates with constant and time-periodic stiffness are compared over a range of mean plate stiffnes...

The foundational differences of steady and unsteady jets issued into a laminar boundary layer crossflow are considered. Jets have been used widely for flow control applications, due to their ability to enhance mixing and mitigate separation, but it is unclear what role jet steadiness plays in flow control effectiveness. Here we compare experimental...

In this work, direct numerical simulation (DNS) is used to investigate how airfoil shape affects wake structure and performance during a pitching-heaving motion. First, a class-shape transformation (CST) method is used to generate airfoil shapes. CST coefficients are then varied in a parametric study to create geometries that are simulated in a pit...

Pipe flow responds to strong perturbations in ways that are fundamentally different from the response exhibited by boundary layers undergoing a similar perturbation, primarily because of the confinement offered by the pipe wall, and the need to satisfy continuity. We review such differences by examining previous literature, with a particular focus...

Bioinspired Structures and Design - edited by Wole Soboyejo September 2020

Cambridge Core - Materials Science - Bioinspired Structures and Design - edited by Wole Soboyejo

Blood damage (hemolysis) can occur during clinical procedures, e.g. dialysis, due to human error or faulty equipment, and it can cause significant harm to the patient or even death. We propose a simple technique to monitor changes in hemolysis levels continuously and in real time. As red blood cells rupture, the overall conductivity of the blood in...

The structure of swimmers’ wakes is often assumed to be an indicator of swimming performance, that is, how momentum is produced and energy is consumed. Here, we discuss three cases where this assumption fails. In general, great care should be taken in deriving any conclusions about swimming performance from the wake flow pattern.

For wall-bounded turbulent flows, Townsend's attached eddy hypothesis proposes that the logarithmic layer is populated by a set of energetic and geometrically self-similar eddies. These eddies scale with a single length scale, their distance to the wall, while their velocity scale remains constant across their size range. To investigate the existen...

Large-amplitude oscillations of foils have been observed to yield greater propulsive efficiency than small-amplitude oscillations. Using scaling relations and experiments on foils with peak-to-peak trailing edge amplitudes of up to two chord lengths, we explain why this is so. In the process, we reveal the importance of drag, specifically how it ca...

Large-amplitude oscillations of foils have been observed to yield greater propulsive efficiency than small-amplitude oscillations. Using scaling relations and experiments on foils with peak-to-peak trailing edge amplitudes of up to two chord lengths, we explain why this is so. In the process, we reveal the importance of drag, specifically how it ca...

The structure of swimmers' wakes is often assumed to be an indicator of swimming performance. Here, we discuss three cases where this assumption fails. In general, great care should be taken in deriving any conclusions about swimming performance from the wake flow pattern.

Many swimming and flying animals are observed to cruise in a narrow range of Strouhal numbers, where the Strouhal number ${St = 2fA/U}$ is a dimensionless parameter that relates stroke frequency $f$, amplitude $A$, and forward speed $U$. Dolphins, sharks, bony fish, birds, bats, and insects typically cruise in the range $0.2 < St < 0.4$, which coin...

The effects of trailing edge shape on the vortex dynamics and surface pressure distributions on pitching foils are examined using direct numerical simulation. Results are presented for a Reynolds number of 1×104 and a Strouhal number of 0.5, which corresponds to the Strouhal number for maximum efficiency as found by experiment [Van Buren et al., Ph...

Significance Almost 30 y ago, researchers discovered that a great variety of efficient swimmers cruise in a narrow range of Strouhal numbers, a dimensionless number describing the kinematics of swimming. Almost 15 y later, separate researchers discovered that fliers (bats, birds, and insects) also cruise in the same narrow range of Strouhal numbers...

Here we present a general overview of bio-inspired propulsion. We identify the major types of aquatic swimmers (oscillatory, undulatory, pulsatile, and drag-based) and break down their mechanisms for thrust production (drag-based, lift-based, added mass, and momentum injection). For each swimmer, we (1) discuss wake characteristics; (2) derive expr...

We consider the propulsive performance of an unsteady heaving and pitching foil, experimentally studying an extensive parameter space of motion amplitudes, frequencies, and phase offsets between the heave and pitch motions. The phase offset $\phi$ between the heaving and pitching motions proves to be a critical parameter in determining the dynamics...

We consider the propulsive performance of an unsteady heaving and pitching foil, experimentally studying an extensive parameter space of motion amplitudes, frequencies, and phase offsets between the heave and pitch motions. The phase offset $\phi$ between the heaving and pitching motions proves to be a critical parameter in determining the dynamics...

Experiments are reported on the performance of a pitching and heaving two-dimensional foil in a water channel in either continuous or intermittent motion. We find that the thrust and power are independent of the mean freestream velocity for two-fold changes in the mean velocity (four-fold in the dynamic pressure), and for oscillations in the veloci...

Experiments are reported on the performance of a pitching and heaving two-dimensional foil in a water channel in either continuous or intermittent motion. We find that the thrust and power are independent of the mean freestream velocity for two-fold changes in the mean velocity (four-fold in the dynamic pressure), and for oscillations in the veloci...

We present an experimental study on the response of turbulent pipe flow at Re τ = 3486 to rapid changes in pipe shape that are designed to manipulate the Large Scale and Very Large Scale Motions in wall-bounded turbulence. Stereo PIV measurements were taken 5 pipe diameters downstream of 3D printed pipe inserts designed to target specific azimuthal...

We report the benchmark results of a new Immersed Boundary Method (IBM) incorporated into Direct Numerical Simulation (DNS) of a pitching panel, representing fish-like swimming, using foam-extend-3.2. The panel is flat and thin, and it has a triangular (convex) trailing edge, similar to that seen in the caudal fin of some fish. The accuracy of the...

Scaling laws are presented for the propulsive performance of rigid foils undergoing oscillatory motion in water. Water tunnel experiments on a nominally two-dimensional foil show that the scaling laws provide an excellent description of the data for thrust, power, and efficiency. The scaling laws are then extended to account for the effects of non-...

Experiments are presented that demonstrate how liquid-infused surfaces can reduce turbulent drag significantly in Taylor-Couette flow. The test liquid was water, and the test surface was composed of square microscopic grooves measuring 100 $\mu$m to 800 $\mu$m, filled with alkane liquids with viscosities from 0.3 to 1.4 times that of water. We achi...

Experiments are presented that demonstrate how liquid-infused surfaces can reduce turbulent drag significantly in Taylor-Couette flow. The test liquid was water, and the test surface was composed of square microscopic grooves measuring 100 $\mu$m to 800 $\mu$m, filled with alkane liquids with viscosities from 0.3 to 1.4 times that of water. We achi...

The flow field generated by suction through a rectangular orifice within a laminar boundary layer is investigated using stereoscopic particle image velocimetry. For orifice aspect ratios of 6, 12, and 18, the impact of suction on the surrounding flow field appears to be self-similar, scaling with aspect ratio and suction velocity. Changing the orif...

The impact of wave-form shape on the wake and propulsive performance of a pitching and heaving two-dimensional foil is explored experimentally. Jacobi elliptic functions are used to define wave-form shapes that are approximately triangular, sinusoidal, or square. The triangular-like and sinusoidal waves produce qualitatively similar wakes, with a t...

Scaling laws for the propulsive performance of rigid foils undergoing oscillatory heaving and pitching motions are presented. Water tunnel experiments on a nominally two-dimensional flow validate the scaling laws, with the scaled data for thrust, power, and efficiency all showing excellent collapse. The analysis indicates that the behaviour of the...

Scaling laws for the propulsive performance of rigid foils undergoing oscillatory heaving and pitching motions are presented. Water tunnel experiments on a nominally two-dimensional flow validate the scaling laws, with the scaled data for thrust, power, and efficiency all showing excellent collapse. The analysis indicates that the behaviour of the...

Experiments are reported on intermittent swimming motions. Water tunnel experiments on a nominally two-dimensional pitching foil show that the mean thrust and power scale linearly with the duty cycle, from a value of 0.1 all the way up to continuous motions, indicating that individual bursts of activity in intermittent motions are independent of ea...

Experiments are reported on intermittent swimming motions. Water tunnel experiments on a nominally two-dimensional pitching foil show that the mean thrust and power scale linearly with the duty cycle, from a value of 0.2 all the way up to continuous motions, indicating that individual bursts of activity in intermittent motions are independent of ea...

The effects of stable thermal stratification on turbulent boundary layers are experimentally investigated for smooth and rough walls. For weak to moderate stability, the turbulent stresses are seen to scale with the wall shear stress, compensating for changes in fluid density in the same manner as done for compressible flows. This suggests little c...

The response of an initially neutral rough-wall turbulent boundary layer to a change in wall temperature is investigated experimentally. The change causes a localized peak in stable stratification that diffuses and moves away from the wall with downstream distance. The streamwise and wall-normal components of turbulent velocity fluctuations are dam...

Using only quasi-steady lift-based and added mass forces, new scaling laws for thrust coefficients, power coefficients, and efficiencies were derived for a rigid foil undergoing oscillatory heaving and pitching motions.

The effects of changing the trailing edge shape on the wake and propulsive performance of a pitching rigid panel are examined experimentally. The panel aspect ratio is AR=1, and the trailing edges are symmetric chevron shapes with convex and concave orientations of varying degree. Concave trailing edges delay the natural vortex bending and compress...

High-Reynolds number flows are very common in technological applications and in nature, and hot-wire anemometry is the preferred method for measuring the time-series of fluctuating velocity in such flows. However, measurement of very high-Reynolds number flows requires hot-wires with higher temporal and spatial resolution than is available with con...

The formation and evolution of flow structures due to the interaction of a finite-span synthetic jet with a zero-pressure gradient laminar boundary layer were experimentally investigated using stereoscopic particle image velocimetry. A synthetic jet with three orifice aspect ratios of AR = 6, 12, and 18 was issued into a free-stream velocity of U∞...

The formation and evolution of flow structures associated with a finite-span synthetic jet issued into a zero-pressure gradient boundary layer were investigated experimentally using stereoscopic particle image velocimetry. A synthetic jet with an aspect ratio of AR = 18 was mounted on a flat plate and its interaction with a free stream, having a ve...

Results on turbulent skin friction reduction over air- and liquid-impregnatedsurfaces are presented for aqueous Taylor-Couette flow. The surfaces are fabricated by mechanically texturing the inner cylinder and chemically modifying the features to make them either non-wetting with respect to water (air-infused, or superhydrophobic case), or wetting...

A poster presented at the Princeton E-ffiliates Partnership Fourth Annual Meeting. Funded by the Princeton E-ffiliates Partnership with The Southern Company

We aim to generate an artificially thickened boundary layer in a wind tunnel with properties similar to the neutral atmospheric boundary layer. We implement a variant of Counihan's technique which uses a combination of a castellated barrier, elliptical vortex generators, and surface roughness to create a thick boundary layer in a relatively short w...

The interaction of a combined vortex generator and a finite-span synthetic jet, i.e., a hybrid actuator, with a zero pressure gradient laminar boundary layer over a flat plate was explored experimentally using Stereoscopic Particle Image Velocimetry (SPIV). The free stream velocity was U∞ = 10 m/s corresponding to a Reynolds number based on the loc...

The impact of cavity geometry on the source of acoustic resonance (Helmholtz or quarter-wave) for synthetic jet type cavities is presented. The cavity resonance was measured through externally excited microphone measurements. It was found that, for pancake-shaped cavities, the Helmholtz resonance equation was inadequate (off by more than 130%) at p...

A detailed analysis of a finite-span synthetic jet in a quiescent fluid is presented, with the goal of achieving a high speed and momentum synthetic jet, with a peak velocity exceeding 200 m/s. A total of two scales of actuator apparatuses having either 40- or 80-mm-diameter piezoelectric discs were used. A temperature-compensated hot wire, laser d...

A new method for measuring turbulent heat fluxes using a combination of particle image velocimetry and a nanoscale fast-response cold-wire is tested by examining a rough-wall turbulent boundary layer subject to weakly stable stratification. The method has the advantages of simple calibration and setup, as well as providing spatial correlations of v...

Detailed velocity measurements in the wake of a body of revolution are reported for pitch angles up to $12^{\circ }$ , over an unprecedented range of Reynolds numbers ( $2.4\times 10^{6}\leqslant \mathit{Re}_{L}\leqslant 30\times 10^{6}$ ). The body of revolution, an idealized submarine shape (DARPA SUBOFF), is mounted using a support that mimi...

A collection of nanoscale sensing devices developed specifically for high-frequency turbulence measurements is presented. The new sensors are all derived from the nanoscale thermal anemometry probe (NSTAP), which uses a free-standing platinum wire as active sensing element. Each sensor is designed and fabricated to measure a specific quantity and c...

The turbulent wake of a submarine model in yaw was investigated using stereoscopic particle image velocimetry at \(Re_{L} = 2.4 \times 10^{6}.\) The model (DARPA SUBOFF idealized submarine geometry) is mounted in a low-speed wind tunnel using a support that mimics the sail, and it is yawed so that the body moves in the plane normal to the support....

The formation and evolution of flow structures of a finite-span synthetic jet issuing into a quiescent flow were investigated experimentally using stereoscopic particle image velocimetry (SPIV). The effect of two geometrical parameters, the orifice aspect ratio and the neck length, were explored at a Strouhal number of 0.115 and a Reynolds number o...

The formation and evolution of a finite-span synthetic jet within a zero pressure gradient laminar boundary layer were analyzed utilizing Stereoscopic Particle Image Velocimetry (SPIV). The effect of the orifice orientation, including the pitch and skew angles, was studied at a free stream velocity of U∞ = 10 m/s and a fixed aspect ratio and blowin...

The formation and evolution of flow structures of a high-speed, finite-span synthetic jet issued into a quiescent flow were investigated experimentally using Stereoscopic Particle Image Velocimetry for jet peak velocities up to 150 m/s. The effect of high jet Reynolds number (Re○ = 1150, 3450, and 5750, with corresponding Strouhal numbers of St = 0...

Micro air vehicles (MAV) are a major focus of aerodynamics today with many military as well as civilian applications. MAV flight is dominated by the unsteady characteristics of low Reynolds number flows. Three-dimensional separations may occur at random on different parts of the wing, causing highly unsteady forces and moments, as well as full wing...

The effects of different geometries and input parameters on the flow structures of a finite span synthetic jet are explored in quiescent flow experiments using stereoscopic PIV. Common geometrical parameters, such as neck height, and orifice aspect ratio are varied along with the jet performance characteristics such as Strouhal numbers and Reynolds...