Unified hydrodynamics study for various types of fishes-like undulating rigid hydrofoil in a free stream flow

2018 ◽  
Vol 30 (7) ◽  
pp. 077107 ◽  
Author(s):  
Namshad Thekkethil ◽  
Atul Sharma ◽  
Amit Agrawal
Keyword(s):  
Stream Flow ◽  
Free Stream

Aspects of Shear Layer Unsteadiness in a Three-Dimensional Supersonic Wake

2005 ◽  
Vol 127 (6) ◽  
pp. 1085-1094 ◽  
Author(s):  
Alan L. Kastengren ◽  
J. Craig Dutton
Keyword(s):  
Shear Layer ◽  
Stream Flow ◽  
Free Stream ◽  
Angle Of Attack ◽  
Three Dimensional ◽  
Base Flow ◽  
Recirculation Region ◽  
Side View ◽  
Near Wake ◽  
Supersonic Wake

The near wake of a blunt-base cylinder at 10° angle-of-attack to a Mach 2.46 free-stream flow is visualized at several locations to study unsteady aspects of its structure. In both side-view and end-view images, the shear layer flapping grows monotonically as the shear layer develops, similar to the trends seen in a corresponding axisymmetric supersonic base flow. The interface convolution, a measure of the tortuousness of the shear layer, peaks for side-view and end-view images during recompression. The high convolution for a septum of fluid seen in the middle of the wake indicates that the septum actively entrains fluid from the recirculation region, which helps to explain the low base pressure for this wake compared to that for a corresponding axisymmetric wake.

scholarly journals Effect of wavelength of fish-like undulation of a hydrofoil in a free-stream flow

Sadhana ◽  
2017 ◽  
Vol 42 (4) ◽  
pp. 585-595 ◽  
Author(s):  
Thekkethil Namshad ◽  
Mukul Shrivastava ◽  
Amit Agrawal ◽  
Atul Sharma
Keyword(s):  
Stream Flow ◽  
Free Stream

A Note Related to the Pressure Inside an Inflating Parachute Canopy

1977 ◽  
Vol 28 (4) ◽  
pp. 271-277
Author(s):  
P R Payne ◽  
E G U Band
Keyword(s):  
Analytic Function ◽  
Stream Flow ◽  
Free Stream ◽  
Internal Flow ◽  
The Other ◽  
Virtual Mass ◽  
Ram Pressure ◽  
Parachute Canopy ◽  
Mass Terms ◽  
Internal Pressures

SummaryIf a canopy is idealised as a cylinder with one end open to the free-stream flow, and the other end closed, then the internal flow during inflation is given by a simple analytic function. In this note the function is derived and then the internal pressures and corresponding forces associated with inflation are determined. It is found that, in addition to ram pressure and the von Kármán “virtual mass” terms in the pressure equations, there are other transient terms associated with radial velocity and acceleration.

An Empirical Formula for Stagnation Point Velocity Gradient for Spheres and Circular Cylinders in Hypersonic Flow

1965 ◽  
Vol 69 (654) ◽  
pp. 407-408 ◽  
Author(s):  
D. R. Topham
Keyword(s):  
Stagnation Point ◽  
Velocity Gradient ◽  
Stream Flow ◽  
Free Stream ◽  
Circular Cylinders ◽  
Stream Velocity ◽  
Flow Properties ◽  
Transfer Rates ◽  
Point Velocity ◽  
Image Position

When stagnation heat transfer rates are expressed in terms of free stream flow properties, the following combination of terms is found to occur: —where ps pressure at the stagnation pointp∞free stream pressureU∞free stream velocityDnose diameterßstagnation point velocity gradient.

Shear Layer Driven Acoustic Modes in a Cylindrical Cavity

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
David B. Stephens ◽  
Francisco R. Verdugo ◽  
Gareth J. Bennett
Keyword(s):  
Shear Layer ◽  
Cylindrical Cavity ◽  
Stream Flow ◽  
Acoustic Pressure ◽  
Free Stream ◽  
Mode Switching ◽  
Stream Velocity ◽  
Azimuthal Mode ◽  
Mode Oscillation ◽  
Cavity Opening

This paper describes the interior acoustic pressure of a cylindrical cavity driven by a shear layer. Existing cavity flow literature is generally focused on rectangular cavities, where the resonance is either longitudinal or the result of excited depth modes inside the cavity. The design of the present circular cavity is such that azimuthal duct modes can be excited in various combinations with depth modes depending on free stream velocity. An acoustic simulation of the system was used to identify the modes as a function of frequency when the system is driven by an acoustic point source. With appropriate manipulation of the free stream flow, abrupt mode switching and mode oscillation were both observed, and a condition with a dominant azimuthal mode was found. The strength of the lock-on was documented for the various resonance conditions, and the effects of the cavity opening size and location were studied.

Four-Fin Bio-Inspired UUV: Modeling and Control Solutions

2011 ◽  
Author(s):  
Jason D. Geder ◽  
Ravi Ramamurti ◽  
John Palmisano ◽  
Marius Pruessner ◽  
Banahalli Ratna ◽  
...  
Keyword(s):  
Stream Flow ◽  
Free Stream ◽  
Open Loop ◽  
Control Algorithms ◽  
Loop Control ◽  
Modeling And Control ◽  
Pectoral Fins ◽  
Flow Speeds ◽  
Computational Fluid Dynamics Cfd ◽  
And Control

This paper describes the modeling and control development of a bio-inspired unmanned underwater vehicle (UUV) propelled by four pectoral fins. Based on both computational fluid dynamics (CFD) and experimental fin data, we develop a UUV model that focuses on an accurate representation of the fin-generated forces. Models of these forces span a range of controllable fin parameters, as well as take into account leading-trailing fin interactions and free stream flow speeds. The vehicle model is validated by comparing open-loop simulated responses with experimentally measured responses to identical fin inputs. Closed-loop control algorithms, which command changes in fin kinematics, are tested on the vehicle. Comparison of experimental and simulation results for various maneuvers validates the fin and vehicle models, and demonstrates the precise maneuvering capabilities enabled by the actively controlled curvature pectoral fins.

Numerical Study of the Laminar Flow Past a Rotating Square Cylinder at Low Spinning Rates

2014 ◽  
Vol 137 (2) ◽  
Author(s):  
Dipankar Chatterjee ◽  
Satish Kumar Gupta
Keyword(s):  
Rotational Speed ◽  
Stream Flow ◽  
Free Stream ◽  
Stokes Equations ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Low Frequency ◽  
Square Cylinder ◽  
Rotating Circular Cylinder ◽  
Critical Rotational Speed

The fluid dynamic interaction between a uniform free stream flow and the rotation induced flow from a sharp edged body is numerically investigated. A two-dimensional (2D) finite volume based computation is performed in this regard to simulate the laminar fluid flow around a rotating square cylinder in an unconfined medium. Body fitted grid system along with moving boundaries is used to obtain the numerical solution of the incompressible Navier–Stokes equations. The Reynolds number based on the free stream flow is kept in the range 10≤Re≤200 with a dimensionless rotational speed of the cylinder in the range 0≤Ω≤5. At low Re=10, the flow field remains steady irrespective of the rotational speed. For 50≤Re≤200, regular low frequency Kármán vortex shedding (VS) is observed up to a critical rate of rotation (Ωcr). Beyond Ωcr, the global flow shows steady nature, although high frequency oscillations in the aerodynamic coefficients are present. The rotating circular cylinder also shows likewise degeneration of Kármán VS at some critical rotational speed. However, significant differences can be seen at higher rotation. Such fluid dynamic transport around a spinning square in an unconfined free stream flow is reported for the first time.

scholarly journals Optimization of wind augmenters for urban power generation

2021 ◽  
Author(s):  
Hans Hamm
Keyword(s):  
Energy Source ◽  
Porous Medium ◽  
Wind Turbine ◽  
Stream Flow ◽  
Power Efficiency ◽  
Free Stream ◽  
Test Case ◽  
High Demand ◽  
Momentum Loss ◽  
Low Costs

Wind power is the most available renewable energy source to date due to the relatively low costs and advances in the field. Consequently, there is a high demand for innovative wind technology. Furthermore, providing energy near consumers, such as in inner city dwellings and urban settings, provides a more efficient and more reliable energy source. The use of architecture to augment wind energy extraction is still unresolved and the area of research is still in its infancy. The few studies conducted have shown substantial benefits by using buildings to collect wind to increase the power efficiency of wind turbines beyond the Betz limit. This study utilized computational fluid dynamics to analyze building shapes to optimize wind turbine power production. Results indicate an increase in power of up to approximately 4-8 times compared with that for the undisturbed free stream flow. Furthermore, a porous medium was used to simulate the momentum loss due to the presence of the wind turbine. The trends remained similar despite the momentum loss caused by the presence of the wind turbine. The porous medium results showed an increase of power approximately 2-3 times. The study extended the geometry to 3D to support the 2D results. The test case indicated the 3D results had a higher performance in comparison to 2D due to the 3D interactions of the vortex shedding dampening the variance of velocity in the gap region. Furthermore, a certain geometry performs better at different angles of attack providing the optimal geometry will be specifically tailored to the typical wind directions associated with the desired building location.

Large-Scale Testing to Validate the Influence of External Crossflow on the Discharge Coefficients of Film Cooling Holes

2000 ◽  
Vol 123 (3) ◽  
pp. 593-600 ◽  
Author(s):  
D. A. Rowbury ◽  
M. L. G. Oldfield ◽  
G. D. Lock
Keyword(s):  
Film Cooling ◽  
Stream Flow ◽  
Large Scale ◽  
Discharge Coefficient ◽  
Static Pressure ◽  
Free Stream ◽  
Discharge Coefficients ◽  
Large Scale Testing ◽  
Cooling Hole ◽  
Film Cooling Holes

This paper discusses large-scale, low-speed experiments that explain unexpected flow-interaction phenomena witnessed during annular cascade studies into the influence of external crossflow on film cooling hole discharge coefficients. More specifically, the experiments throw light on the crossover phenomenon, where the presence of the external crossflow can, under certain circumstances, increase the discharge coefficient. This is contrary to most situations, where the external flow results in a decrease in discharge coefficient. The large-scale testing reported helps to explain this phenomenon through an increased understanding of the interaction between the emerging coolant jet and the free-stream flow. The crossover phenomenon came to light during an investigation into the influence of external crossflow on the discharge coefficients of nozzle guide vane film cooling holes. These experiments were performed in the Cold Heat Transfer Tunnel (CHTT), an annular blowdown cascade of film cooled vanes that models the three-dimensional external flow patterns found in modern aero-engines. (Rowbury et al., 1997, 1998). The variation in static pressure around the exit of film cooling holes under different flow conditions was investigated in the large-scale tests. The study centered on three holes whose geometries were based on those found in the leading edge region of the CHTT vanes, as the crossover phenomenon was witnessed for these rows during the initial testing. The experiments were carried out in a low-speed wind tunnel, with the tunnel free-stream flow velocity set to match the free-stream Reynolds number (based on the local radius of curvature) and the “coolant” flow velocity set to replicate the engine coolant-to-free-stream momentum flux ratio. It was found that the apparent enhancement of film cooling hole discharge coefficients with external crossflow was caused by a reduction in the static pressure around the hole exit, associated with the local acceleration of the free-stream around the emerging coolant jet. When these measured static pressures (rather than the free-stream static pressure) were used to calculate the discharge coefficient, the crossover effect was absent. The improved understanding of the crossover phenomenon and coolant-to-free-stream interactions that has been gained will be valuable in aiding the formulation of predictive discharge coefficient schemes.

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