Numerical Investigations of a Rotating Wire-Wrapped Cylinder

2018 ◽  
Author(s):  
Assma Begum ◽  
Komal Gada ◽  
Hamid Rahai
Keyword(s):  
Rotation Rate ◽  
Free Stream ◽  
Tangential Velocity ◽  
Rotating Cylinder ◽  
Trailing Edge ◽  
Mean Velocity ◽  
Numerical Investigations ◽  
Cylinder Diameter ◽  
Smooth Cylinder ◽  
The Wire

Previous investigations [1–3] on the effects of rotating cylinder with either a smooth surface or cylinders with different surface geometries, placed at either the leading or the trailing edge of a symmetric airfoil on its aerodynamic parameters have shown that rotation at the leading edge does not provide significant lift, while placing the rotating cylinder at the training edge results in more than 20% increase in lift at all angles of attack (AOA) investigated. Increasing the rotation rate (α), the ratio of tangential velocity at the surface of the cylinders (Uτ) to the free stream mean velocity (U∞), increases the lift and grooved cylinders produced more lift than the smooth cylinder. There is an increase in drag when the rotating cylinder is placed at the trailing edge of the airfoil. Here we performed unsteady numerical investigations of a rotating wire-wrapped cylinder, placed in steady flow with α varied between 0 and 2. The free stream mean velocity was constant at 10 m/sec. and the smooth cylinder diameter was 5 cm, which corresponds to an approximate Reynolds number of 3.2 × 104. The wire wrapped had a wire diameter of 5 mm and the ratio of pitch spacing to the cylinder diameter was 1. The wire was wrapped tightly around the entire cylinder. The cylinder has a length to diameter ratio of 20. The rotation rate (α) ranged from 0.5 to 2.0. Results indicate wire-wrapped rotating cylinder produce higher lift than the rotating smooth cylinder and at α equal to 2, the lift for the wire-wrapped cylinder is nearly 150% of the lift of the smooth cylinder. However, wire-wrapped cylinder has higher drag force at higher rotation rate. At α = 2, the lift to drag ratio for the smooth rotating cylinder is 3.89, while the corresponding value for the rotating wire-wrapped cylinder is 3.54. Details of the flow indicates wire-wrapping reduces coherency and increases phase angle of vortices, resulting in increased lift.

scholarly journals Numerical Analysis of Effect of Leading-Edge Rotating Cylinder on NACA0021 Symmetric Airfoil

2019 ◽  
Vol 4 (7) ◽  
pp. 11-17
Author(s):  
Md. Abdus Salam ◽  
Vikram Deshpande ◽  
Nafiz Ahmed Khan ◽  
M. A. Taher Ali
Keyword(s):  
Free Stream ◽  
Numerical Study ◽  
Tangential Velocity ◽  
Leading Edge ◽  
Rotating Cylinder ◽  
Aerodynamic Performance ◽  
Stream Velocity ◽  
Surface Boundary ◽  
Lower Velocity ◽  
Numerical Studies

The moving surface boundary control (MSBC) has been a Centre stage study for last 2-3 decades. The preliminary aim of the study was to ascertain whether the concept can improve the airfoil characteristics. Number of experimental and numerical studies pointed out that the MSBC can superiorly enhance the airfoil performance albeit for higher velocity ratios (i.e. cylinder tangential velocity to free stream velocity). Although abundant research has been undertaken in this area on different airfoil performances but no attempt was seen to study effect of MSBC on NACA0021 airfoil for and also effects of lower velocity ratios. Thus, present paper focusses on numerical study of modified NACA 0021 airfoil with leading edge rotating cylinder for velocity ratios (i.e.) between 1 to 1.78 at different angles of attack. The numerical study indicates that the modified airfoil possess better aerodynamic performance than the base airfoil even at lower velocity ratios (i.e. for velocity ratios 0.356 and beyond). The study also focusses on reason for improvement in aerodynamic performance by close look at various parameters.

Three-dimensionality in the wake of a rapidly rotating cylinder in uniform flow

2013 ◽  
Vol 730 ◽  
pp. 379-391 ◽  
Author(s):  
A. Rao ◽  
J. S. Leontini ◽  
M. C. Thompson ◽  
K. Hourigan
Keyword(s):  
Steady State ◽  
Rotation Rate ◽  
Free Stream ◽  
Three Dimensional ◽  
Rotating Cylinder ◽  
Marginal Stability ◽  
Cylinder Surface ◽  
Rotation Rates ◽  
Centrifugal Instability ◽  
The Stability

AbstractThe flow around an isolated cylinder spinning at high rotation rates in free stream is investigated. The existence of two steady two-dimensional states is confirmed, as is the existence of a secondary mode of vortex shedding. The stability of the two steady states to three-dimensional perturbations is established using linear stability analysis. At lower rotation rates on the first steady state, two three-dimensional modes are confirmed, and their structure and curves of marginal stability as a function of rotation rate and Reynolds number are determined. One mode (named mode $E$) appears consistent with a hyperbolic instability in the wake, while the second (named mode $F$) appears to be a centrifugal instability of the flow very close to the cylinder surface. At higher rotation rates on the second steady state, a single three-dimensional mode due to centrifugal instability (named mode ${F}^{\prime } $) is found. This mode becomes increasingly difficult to excite as the rotation rate is increased.

Flexibility in flapping foil suppresses meandering of induced jet in absence of free stream

2014 ◽  
Vol 757 ◽  
pp. 231-250 ◽  
Author(s):  
Sachin Y. Shinde ◽  
Jaywant H. Arakeri
Keyword(s):  
Free Stream ◽  
Fluid Dynamic ◽  
Maximum Velocity ◽  
Extreme Case ◽  
Chord Length ◽  
Stream Velocity ◽  
Trailing Edge ◽  
Mean Velocity ◽  
Coherent Jet ◽  
Flap Deflection

AbstractThrust-generating flapping foils are known to produce jets inclined to the free stream at high Strouhal numbers $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}\mathit{St} = fA/U_{\infty }$, where $f$ is the frequency and $A$ is the amplitude of flapping and $U_{\infty }$ is the free-stream velocity. Our experiments, in the limiting case of $\mathit{St} \rightarrow \infty $ (zero free-stream speed), show that a purely oscillatory pitching motion of a chordwise flexible foil produces a coherent jet composed of a reverse Bénard–Kármán vortex street along the centreline, albeit over a specific range of effective flap stiffnesses. We obtain flexibility by attaching a thin flap to the trailing edge of a rigid NACA0015 foil; length of flap is $0.79\, c$ where $c$ is rigid foil chord length. It is the time-varying deflections of the flexible flap that suppress the meandering found in the jets produced by a pitching rigid foil for zero free-stream condition. Recent experiments (Marais et al., J. Fluid Mech., vol. 710, 2012, p. 659) have also shown that the flexibility increases the $\mathit{St}$ at which non-deflected jets are obtained. Analysing the near-wake vortex dynamics from flow visualization and particle image velocimetry (PIV) measurements, we identify the mechanisms by which flexibility suppresses jet deflection and meandering. A convenient characterization of flap deformation, caused by fluid–flap interaction, is through a non-dimensional ‘effective stiffness’, $EI^{*} = 8 \, EI/(\rho \, V_{{{TE_{{max}}}}}^2 \, s_{{{f}}} \, c_{{{f}}}^3/2)$, representing the inverse of the flap deflection due to the fluid-dynamic loading; here, $EI$ is the bending stiffness of flap, $\rho $ is fluid density, $V_{{{TE_{{max}}}}}$ is the maximum velocity of rigid foil trailing edge, $s_{{{f}}}$ is span and $c_{{{f}}}$ is chord length of the flexible flap. By varying the amplitude and frequency of pitching, we obtain a variation in $EI^{*}$ over nearly two orders of magnitude and show that only moderate $EI^{*}\ (0.1 \lesssim EI^{*} \lesssim 1)$ generates a sustained, coherent, orderly jet. Relatively ‘stiff’ flaps ($EI^{*} \gtrsim 1$), including the extreme case of no flap, produce meandering jets, whereas highly ‘flexible’ flaps ($EI^{*} \lesssim 0.1$) produce spread-out jets. Obtained from the measured mean velocity fields, we present values of thrust coefficients for the cases for which orderly jets are observed.

Lift and Drag Forces of a High Efficiency Airfoil With an Embedded Rotating Cylinder

2016 ◽  
Author(s):  
Komal Gada ◽  
Hamid Rahai
Keyword(s):  
Flow Separation ◽  
High Efficiency ◽  
Active Flow Control ◽  
Tangential Velocity ◽  
Axial Flow ◽  
Flow Simulation ◽  
Leading Edge ◽  
Rotating Cylinder ◽  
Chord Length ◽  
Mean Velocity

Numerical investigations of an optimized thin airfoil with an active flow control device (rotating cylinder) embedded into the airfoil have been performed. The objective of the study was to investigate the possibility of using a rotating cylinder to maintain performance of micro aerial vehicles, MAVs, when significant and sudden variation in wind speed (example: gust) is present. The airfoil has a chord length of 19.66 cm and a span of 25 cm. The free stream mean velocity was 20 m/s which corresponds to a chord length Reynolds number of 2.54×105. Simulations were performed at 17 degrees angle of attack which include the initial angle that the cambered leading edge makes with the incoming axial flow. Simulation results for the airfoil without the embedded cylinder have shown flow separation at approximately 85% chord length. Then, a rotating cylinder with a 0.51 cm diameter was embedded into the airfoil, spanning the width of the airfoil at slightly downstream of the location of flow separation, i.e. at x/c = 0.848. There was 1 mm spacing between the cylinder and the airfoil, to allow cylinder’s rotation. Investigations were performed at different rotation speeds, corresponding to corresponding tangential velocities being higher than, equal to and less than the local axial freestream mean velocity. Results showed approximately 10% improvement in lift to drag ratio (L/D), when the tangential velocity was the same or higher than the local axial mean velocity.

Experimental investigation on the momentumless wake using trailing edge blowing

2008 ◽  
Vol 222 (8) ◽  
pp. 1477-1486 ◽  
Author(s):  
Y Wu ◽  
X Zhu ◽  
Z Du
Keyword(s):  
Three Dimensional ◽  
Velocity Profiles ◽  
Axial Fan ◽  
Trailing Edge ◽  
Mean Velocity ◽  
Piv Measurement ◽  
Image Velocimetry ◽  
Velocity Spectra ◽  
Momentumless Wake ◽  
Wake Characteristics

A developed plate stator model with and without trailing edge blowing (TEB) is studied using experimental methods. Wake characteristics of flow over the stator in the three-dimensional wake regimes are studied using hot-wire anemometry (HWA) and particle image velocimetry (PIV) techniques. First, the mean velocity profiles have been measured in the wake of the stator using HWA. Four wake characteristics have been obtained through momentum thickness judgments: pure wake, weak wake, momentumless wake, and jet. These velocity profiles show some differences in momentum deficit for the four cases. Then, the velocity spectra of the pure wake and momentumless wake obtained through the HWA measurements showed that TEB can eliminate the shedding vortex of the stator. Characteristic length scales based on the wake turbulent intensity profiles showed that the momentumless wake can reduce the wake width and depth. PIV measurement is carried out to measure the flow field of the four wakes. Finally, the application of TEB approaching momentumless wake status is used on an industrial ventilation low-pressure axial fan to assess noise reduction. The results show that TEB can make the outlet of the stator uniform, reduce velocity fluctuation, destroy the vorticity structure downstream of the stator, and reduce interaction noise level of the stator and rotor.

Direct numerical simulation of flow past a transversely rotating sphere up to a Reynolds number of 300 in compressible flow

2018 ◽  
Vol 857 ◽  
pp. 878-906 ◽  
Author(s):  
T. Nagata ◽  
T. Nonomura ◽  
S. Takahashi ◽  
Y. Mizuno ◽  
K. Fukuda
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Mach Number ◽  
Direct Numerical Simulation ◽  
Drag Coefficient ◽  
Rotation Rate ◽  
Free Stream ◽  
Rotating Sphere ◽  
Free Stream Mach Number ◽  
Low Reynolds

In this study, direct numerical simulation of the flow around a rotating sphere at high Mach and low Reynolds numbers is conducted to investigate the effects of rotation rate and Mach number upon aerodynamic force coefficients and wake structures. The simulation is carried out by solving the three-dimensional compressible Navier–Stokes equations. A free-stream Reynolds number (based on the free-stream velocity, density and viscosity coefficient and the diameter of the sphere) is set to be between 100 and 300, the free-stream Mach number is set to be between 0.2 and 2.0, and the dimensionless rotation rate defined by the ratio of the free-stream and surface velocities above the equator is set between 0.0 and 1.0. Thus, we have clarified the following points: (1) as free-stream Mach number increased, the increment of the lift coefficient due to rotation was reduced; (2) under subsonic conditions, the drag coefficient increased with increase of the rotation rate, whereas under supersonic conditions, the increment of the drag coefficient was reduced with increasing Mach number; and (3) the mode of the wake structure becomes low-Reynolds-number-like as the Mach number is increased.

LES and Hybrid RANS/LES of a Fundamental Trailing Edge Slot

2014 ◽  
Author(s):  
Elizaveta Ivanova ◽  
Gregory M. Laskowski
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Numerical Study ◽  
Mixing Layer ◽  
Detached Eddy Simulation ◽  
Trailing Edge ◽  
Adiabatic Wall ◽  
Mean Velocity ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation

This paper presents the results of a numerical study on the predictive capabilities of Large Eddy Simulation (LES) and hybrid RANS/LES methods for heat transfer, mean velocity, and turbulence in a fundamental trailing edge slot. The geometry represents a landless slot (two-dimensional wall jet) with adjustable slot lip thickness. The reference experimental data taken from the publications of Kacker and Whitelaw [1] [2] [3] [4] contains the adiabatic wall effectiveness together with the velocity and the Reynolds-stress profiles for various blowing ratios and slot lip thicknesses. The simulations were conducted at three different lip thickness and several blowing ratio values. The comparison with the experimental data shows a general advantage of LES and hybrid RANS/LES methods against unsteady RANS. The predictive capability of the tested LES models (dynamic ksgs-equation [5] and WALE [6]) was comparable. The Improved Delayed Detached Eddy Simulation (IDDES) hybrid method [7] also shows satisfactory agreement with the experimental data. In addition to the described baseline investigations, the influence of the inlet turbulence boundary conditions and their implication for the initial mixing layer and heat transfer development were studied for both LES and IDDES.

Paper 20. Improvement of Control by Special Devices

1972 ◽  
Vol 14 (7) ◽  
pp. 150-154
Author(s):  
H. Ritter
Keyword(s):  
Large Angle ◽  
Leading Edge ◽  
Rotating Cylinder ◽  
Practical Significance ◽  
Trailing Edge ◽  
Stall Angle ◽  
Lift Control ◽  
And Control

The paper discusses hydrodynamic devices for improving manoeuvring and control. Two hydrodynamic concepts are shown to be of practical significance for large craft: control of hydrofoil lift independent of incidence, and deflection of the propulsion jet through a large angle by means of a simple hydrofoil. Lift control independent of incidence is illustrated by the jet flap and the trailing edge rotating cylinder. Improved deflection of the propeller slipstream involves extending the rudder stall angle, and it is shown how this may be achieved by fitting the rudder with a leading edge rotating cylinder.

scholarly journals Numerical Analysis of an Instrumented Turbine Blade Cascade

2018 ◽  
Author(s):  
Bryn N. Ubald ◽  
Jiahuan Cui ◽  
Rob Watson ◽  
Paul G. Tucker ◽  
Shahrokh Shahpar
Keyword(s):  
Numerical Analysis ◽  
Measurement Accuracy ◽  
Free Stream ◽  
Separation Bubble ◽  
Leading Edge ◽  
Pressure Probe ◽  
Mean Flow ◽  
Trailing Edge ◽  
Free Stream Turbulence ◽  
Jet Trajectory

The measurement accuracy of the temperature/pressure probe mounted at the leading edge of a turbine/compressor blade is crucial for estimating the fuel consumption of a turbo-fan engine. Apart from the measurement error itself, the probe also introduces extra losses. This again would compromise the measurement accuracy of the overall engine efficiency. This paper utilizes high-fidelity numerical analysis to understand the complex flow around the probe and quantify the loss sources due to the interaction between the blade and its instrumentation. With the inclusion of leading edge probes, three dimensional flow phenomena develop, with some flow features acting in a similar manner to a jet in cross flow. The separated flow formed at the leading edge of the probe blocks a large area of the probe bleed-hole, which is one of the reasons why the probe accuracy can be sensitive to Mach and Reynolds numbers. The addition of 4% free stream turbulence is shown to have a marginal impact on the jet trajectory originated from the probe bleedhole. However, a slight reduction is observed in the size of the separation bubble formed at the leading edge of the probe, preceding the two bleedhole exits. The free stream turbulence also has a significant impact on the size of the separation bubble near the trailing edge of the blade. With the addition of the free stream turbulence, the loss observed within the trailing edge wake is reduced. More than 50% of the losses at the cascade exit are generated by the leading edge probe. A breakdown of the dissipation terms from the mean flow kinetic energy equation demonstrates that the Reynolds stresses are the key terms in dissipating the counter rotating vortex pairs with the viscous stresses responsible for the boundary layer.

Exploring the Presence of Pressure Waves in Axial Compressor Cascades

2020 ◽  
Author(s):  
John Leggett ◽  
Richard Sandberg
Keyword(s):  
Free Stream ◽  
Axial Compressor ◽  
Pressure Waves ◽  
Compressor Cascade ◽  
Suction Surface ◽  
Trailing Edge ◽  
Surface Transition

Abstract The presence of pressure waves in an axial compressor cascade are ubiquitous and have been known and investigated for some time. Much of the work to date focuses on compressor acoustics and vibration, which is largely due to wake blade interactions and trailing edge shedding. However, it has been shown on free aerofoils that pressure waves can be produced from volume sources, such as separation, at non-negligible amplitudes. The work presented here highlights the presence of pressure waves emanating from the suction surface transition of a NACA 65 axial compressor cascade, and briefly investigates and details the influence different free-stream disturbances have on the frequency of the pressure waves produced.

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