Extracting energy from unsteady flows through vortex control

Streitlien, Knut

doi:10.1575/1912/5563

Cited by 8 publications

(6 citation statements)

References 54 publications

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“…In this latter case, the interaction between the foil and vortex can lead to substantially increased or decreased lift, affecting the performance of the foil. This has been demonstrated theoretically by the work of Streitlien [72] and experimentally by Gopalkrishnan [30] where the relative positions were altered via the phase between foil oscillation and vortex shedding. In this case, identifying the relative location of the external vortex to the foil is critically important for predicting the type of affect that will result from the interaction [30].…”

Section: Discussionmentioning

confidence: 86%

“…These results are shown in Table 5 The response of a foil to a vortex passing nearby can be modeled using a potential flow model in which the wake of the foil is simulated by a series of discrete vortices, satisfying the Kutta condition at the trailing edge each timestep. This model was implemented according to the work by Streitlien et al [73,72]. For this analysis, the pressure sensor array will be simulated over the front half of the upper foil, as for any practical purposes, the vortex would need to be located early in the interaction in order to extract the maximum Figure 5-35: Simulated setup for a pressure sensor array similar to the one on a streamlined body being applied to a foil in order to track an external vortex.…”

Section: Discussionmentioning

confidence: 99%

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Performance analysis for lateral-line-inspired sensor arrays

Fernández¹

2011

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The lateral line is a critical component of the fish sensory system, found to affect numerous aspects of behavior including maneuvering in complex fluid environments, schooling, prey tracking, and environment mapping. This sensory organ has no analog in modern ocean vehicles, despite its utility and ubiquity in nature, and could fill the gap left by sonar and vision systems in turbid cluttered environments. Yet, while the biological sensory system suggests the broad possibilities associated with such a sensor array, nearly nothing is known of the input processing and what information is available via the real lateral line. This thesis demonstrates and characterizes the ability of lateral-line-inspired linear pressure sensor arrays to perform two sensory tasks of relevance to biological and man-made underwater navigation systems, namely shape identification and vortex tracking.The ability of pressure sensor arrays to emulate the "touch at a distance" feature of the lateral line, corresponding to the latter's capability of identifying the shape of objects remotely, is examined with respect to moving cylinders of different cross sections. Using the pressure distribution on a small linear array, the position and size of a cylinder is tracked at various distances. The classification of cylinder shape is considered separately, using a large database of trials to identify two classification approaches: One based on differences in the mean flow, and one trained on a subset which utilizes information from the wake. The results indicate that it is in general possible to extract specific shape information from measurements on a linear pressure sensor array, and characterize the classes of shapes which are not distinguishable via this method.Identifying the vortices in a flow makes it possible to predict and optimize the performance of flapping foils, and to identify imminent stall in a control surface. Vortices in wakes also provide information about the object that generated the wake at distances much larger than the near-field pressure perturbations. Experimental studies in tracking a vortex pair and an individual vortex interacting with a flat plate demonstrate the ability to track vortices with a linear pressure sensor array from both small streamlined bodies and large flat bodies. Based on a theoretical analysis, the relationship between the necessary array parameters and the range of vortices of interest is established.

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Section: Discussionmentioning

confidence: 86%

Section: Discussionmentioning

confidence: 99%

Performance analysis for lateral-line-inspired sensor arrays

Fernández¹

2011

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“…The above equation describes the entire flow field, except at the vortex locations, which are singular points and thus undefined. Using Routh's rule [13], the k th vortex conjugate velocity…”

Section: Vortex-shedding Flow Modelmentioning

confidence: 99%

“…The position of the shed vortex z k may be modeled using one of several existing approaches. This paper adopts the "1/3 arclength" method introduced by Streitlien and Triantafyllou [13], which places the shed vortex at the one-third point of the arc tangent to the camber line at the trailing edge and passing through the previous vortex point. Thus,…”

Section: Vortex-shedding Flow Modelmentioning

confidence: 99%

“…Although the vortex-shedding model (18) is a reliable model for describing flow field, the discrete-time vortex addition is not suitable for real-time estimation. A more tractable model is needed to approximate the flow field and to help estimate the motion of the robot, so we adopt the quasi-steady potential-flow model (13). Let Λ Λ Λ = [U, α, H] T represent the flow parameter vector.…”

Section: Flow Estimation Using Bayesian Filter With Distributed Pressmentioning

confidence: 99%

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Distributed Flow Sensing Using Bayesian Estimation for a Flexible Fish Robot

Zhang

Lagor

Yeo

et al. 2015

Volume 2: Diagnostics and Detection; Drilling; Dynamics and Control of Wind Energy Systems; Energy Harvesting; Estimation and I

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Flexibility plays an important role in fish behaviors by enabling high maneuverability for predator avoidance and swimming in turbulence. In this paper, we present a novel, flexible fish robot equipped with distributed pressure sensors for flow sensing. The body of the robot is made of a soft, hyperelastic material that provides flexibility. The fish robot features a Joukowski-foil shape conducive to modeling the fluid analytically. A quasisteady potential-flow model is adopted for real-time flow estimation, whereas a discrete-time vortex-shedding flow model is used for higher-fidelity simulation. The dynamics for the flexible fish robot are presented, and a reduced model for one-dimensional swimming is derived. A recursive Bayesian filter assimilates pressure measurements for estimating the flow speed, angle of attack, and foil camber. Simulation and experimental results are presented to show the effectiveness of the flow estimation algorithm.

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