Sensing Unsteady Pressure on MAV Wings: A New Method for Turbulence Alleviation

Experiments at low Reynolds numbers were performed on a pressure tapped NACA 2313 wing in a 3 x 2 x 9 meter wind tunnel under nominally smooth (Ti = 1.2%) and turbulent (Ti = 7.2%) flows at a mean flow velocity of 8ms-1(Re ≈120,000). The NACA 2313 wing is a replica of Micro Air Vehicle (MAV) wing of the Flash 3D aircraft used at RMIT University for research purposes. Unsteady surface pressures were measured to understand if the information could be adopted for resolving turbulence-induced perturbations and to furthermore use it in a turbulence mitigation system. Two span-wise locations of chord-wise pressure were acquired when tested under the two different flow conditions. It was discovered that at both span-wise locations, a local Coefficient of Pressure (Cp) held high correlation to the chord-wise Cp integration and allowed for a linear relationship to be formed between the two variables. The defined relationship provided a 95% confidence for angles of attack below stall and was used to estimate the integrated chord-wise pressure coefficient at a particular span wise location. The relationship between a single pressure tap and the integrated Cp of that chord-wise section was valid for the two different span-wise locations with similar defining equations. As one pressure tap is sufficient to adequately estimate the integrated Cp on a chord-wise wing section, a limited amount of pressure taps across the wings span approximates the pressure distribution across the span and eventually approximates the flight perturbations. Being a novel method of sensing aircraft disturbance, applications are not restricted to MAV. The methodology presented could very well be applied to larger aircraft to reduce the effects of turbulence within the terminal area and can provide other means of active stabilization.

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Design and Analysis Software for Propellers

ASME 2013 Gas Turbine India Conference ◽

10.1115/gtindia2013-3681 ◽

2013 ◽

Author(s):

Rajeevalochanam Prathapanayaka ◽

Nanjundaiah Vinod Kumar ◽

Krishnamurthy Settisara Janney ◽

Hari Krishna Nagishetty

Keyword(s):

Performance Analysis ◽

Reynolds Numbers ◽

Performance Comparison ◽

High Lift ◽

Low Reynolds Numbers ◽

Propeller Design ◽

Air Vehicle ◽

Loss Method ◽

Propeller Performance ◽

Air Vehicles

Recent interest in the field of micro and nano scale air vehicles attracted the attention of many researchers all over the world. The challenge associated with these classes of vehicles is to develop efficient miniaturized components. There are different types of micro and nano air vehicles out of which fixed wing micro air vehicle is one of them. Propulsion system for most of the fixed wing MAVs is propeller driven by an electric motor powered by a battery. The endurance of the MAV mainly depends on the performance of these two components. Hence there is a scope to improve the performance of the propeller and motor. Efficient propeller design and its performance analysis are an iterative process and time consuming. In the present study, to ease the process of propeller design and analysis NALPROPELLER code has been developed using MATLAB. This code is based on minimum induced loss theory presented by E.E.Larrabee to generate planform, blade element momentum theory along with Prandtl hub-tip loss model for overall performance analysis and the performance plots could be viewed in the GUI windows. The code consists of three modules namely single airfoil design, multi airfoil design and analysis module. This code is compared with one of the propeller design and analysis code available in the internet JavaProp by Martin Hepperle, which is also based on minimum induced loss method. From literature Eppler 193 airfoil show high lift to drag ratios at low Reynolds numbers [16]. Eppler-193 airfoil is used in the evaluation of propeller performance. A four inch diameter, two bladed, fixed pitch propeller is designed and analysed using this code. The design is compared with one of the design software JavaProp available online as an open source. A poly urethane casting propeller is fabricated based on the design. The performance comparison of the NALPROPELLER code, JavaProp and 3D CFD analysis is presented and discussed.

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A Model for High-Reynolds-Number Flow Past Rough-Walled Circular Cylinders

Journal of Fluids Engineering ◽

10.1115/1.3448822 ◽

1977 ◽

Vol 99 (3) ◽

pp. 486-493 ◽

Cited By ~ 4

Author(s):

O. Gu¨ven ◽

V. C. Patel ◽

C. Farell

Keyword(s):

Boundary Layer ◽

Surface Roughness ◽

Circular Cylinder ◽

Turbulent Boundary Layer ◽

Pressure Coefficient ◽

Empirical Relation ◽

Reynolds Numbers ◽

Boundary Layer Separation ◽

Circular Cylinders ◽

Mean Flow

A simple analytical model for two-dimensional mean flow at very large Reynolds numbers around a circular cylinder with distributed roughness is presented and the results of the theory are compared with experiment. The theory uses the wake-source potential-flow model of Parkinson and Jandali together with an extension to the case of rough-walled circular cylinders of the Stratford-Townsend theory for turbulent boundary-layer separation. In addition, a semi-empirical relation between the base-pressure coefficient and the location of separation is used. Calculation of the boundary-layer development, needed as part of the theory, is accomplished using an integral method, taking into account the influence of surface roughness on the laminar boundary layer and transition as well as on the turbulent boundary layer. Good agreement with experiment is shown by the results of the theory. The significant effects of surface roughness on the mean-pressure distribution on a circular cylinder at large Reynolds numbers and the physical mechanisms giving rise to these effects are demonstrated by the model.

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The effect of waves on subgrid-scale stresses, dissipation and model coefficients in the coastal ocean bottom boundary layer

Journal of Fluid Mechanics ◽

10.1017/s0022112007006118 ◽

2007 ◽

Vol 583 ◽

pp. 133-160 ◽

Cited By ~ 7

Author(s):

W. A. M. NIMMO SMITH ◽

J. KATZ ◽

T. R. OSBORN

Keyword(s):

Dynamic Model ◽

Energy Flux ◽

Correlation Coefficients ◽

Reynolds Numbers ◽

Subgrid Scale ◽

Mean Flow ◽

Low Reynolds Numbers ◽

Induced Motion ◽

Stress Models ◽

Wave Induced

Six sets of particle image velocimetry (PIV) data from the bottom boundary layer of the coastal ocean are examined. The data represent periods of high, moderate and weak mean flow relative to the amplitude of wave-induced motion, which correspond to high, moderate and low Reynolds numbers based on the Taylor microscale (Re). The two-dimensional PIV velocity distributions enable spatial filtering to calculate some of the subgrid-scale (SGS) stresses, from which we can estimate the SGS dissipation, and evaluate the performance of typically used SGS stress models. The previously reported mismatch between the SGS and viscous dissipation at moderate and low Reynolds numbers appears to be related to the sparsity of large vortical structures that dominate energy fluxes.Conditional sampling of SGS stresses and dissipation based on wave phase using Hilbert transforms demonstrate persistent and repeatable direct effects of large-scale but weak straining by the waves on the SGS energy flux at small scales. The SGS energy flux is phase-dependent, peaking when the streamwise-wave-induced velocity is accelerating, and lower when this velocity is decelerating. Combined with strain rate generated by the mean flow, the streamwise wave strain causes negative energy flux (backscatter), whereas the vertical wave strain causes a positive flux. The phase-dependent variations and differences between horizontal and vertical contributions to the cascading process extend to strains that are substantially higher than the wave-induced motion. These trends may explain the measured difference between spatial energy spectra of streamwise velocity fluctuations and spectra of the wall-normal component, i.e. the formation of spectral bumps in the spectra of the streamwise component at the wavenumbers for the transition between inertial and dissipation scales.All the model coefficients of typical SGS stress models measured here are phase dependent and show similar trends. Thus, the variations of measured SGS dissipation with phase are larger than those predicted by the model variables. In addition, the measured coefficients of the static Smagorinsky SGS stress model decrease with decreasing turbulence levels, and increase with filter size. The dynamic model provides higher correlation coefficients than the Smagorinsky model, but the substantial fluctuations in their values indicate that ensemble averaging is required. The ‘global’ dynamic model coefficients indicate that the use of a scale-dependent dynamic model may be appropriate. The structure function model yields poor correlation coefficients and is found to be over-dissipative under all but the highest turbulence levels. The nonlinear model has higher correlations with measured stresses, as expected, but it also does not reproduce the trends with wave phase.

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Steady Flow Through a Double Converging-Diverging Tube Model for Mild Coronary Stenoses

Journal of Biomechanical Engineering ◽

10.1115/1.3168368 ◽

1989 ◽

Vol 111 (3) ◽

pp. 212-221 ◽

Cited By ~ 12

Author(s):

S. C. van Dreumel ◽

G. D. C. Kuiken

Keyword(s):

Pressure Drop ◽

Reynolds Numbers ◽

Velocity Profiles ◽

Tube Model ◽

Mean Flow ◽

Number Range ◽

Low Reynolds Numbers ◽

In Series ◽

Coronary Stenoses ◽

Converging Angle

Velocity profiles and the pressure drop across two mild (62 percent) coronary stenoses in series have been investigated numerically and experimentally in a perspex-tube model. The mean flow rate was varied to correspond to a Reynolds number range of 50–400. The pressure drop across two identical (62 percent) stenoses show that for low Reynolds numbers the total effect of two stenoses equals that of two single stenoses. A reduction of 10 percent is found for the higher Reynolds numbers investigated. Numerical and experimental results obtained for the velocity profiles agree very well. The effect of varying the converging angle of a single mild (62 percent) coronary stenosis on the fluid flow has been determined numerically using a finite element method. Pressure-flow relation, especially with respect to relative short stenoses, is discussed.

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An investigation of turbulent plane Couette flow at low Reynolds numbers

Journal of Fluid Mechanics ◽

10.1017/s0022112095000747 ◽

1995 ◽

Vol 286 ◽

pp. 291-325 ◽

Cited By ~ 123

Author(s):

Knut H. Bech ◽

Nils Tillmark ◽

P. Henrik Alfredsson ◽

Helge I. Andersson

Keyword(s):

Couette Flow ◽

Reynolds Stress ◽

Reynolds Numbers ◽

Wall Turbulence ◽

Turbulence Structure ◽

Plane Couette Flow ◽

Mean Flow ◽

Low Reynolds Numbers ◽

Low Reynolds ◽

Near Wall

The turbulent structure in plane Couette flow at low Reynolds numbers is studied using data obtained both from numerical simulation and physical experiments. It is shown that the near-wall turbulence structure is quite similar to what has earlier been found in plane Poiseuille flow; however, there are also some large differences especially regarding Reynolds stress production. The commonly held view that the maximum in Reynolds stress close to the wall in Poiseuille and boundary layer flows is due to the turbulence-generating events must be modified as plane Couette flow does not exhibit such a maximum, although the near-wall coherent structures are quite similar. For two-dimensional mean flow, turbulence production occurs only for the streamwise fluctuations, and the present study shows the importance of the pressure—strain redistribution in connection with the near-wall coherent events.

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Influence of a Finite Width Micro-Tab on the Spanwise Lift Distribution

Volume 8: Supercritical CO2 Power Cycles; Wind Energy; Honors and Awards ◽

10.1115/gt2013-94381 ◽

2013 ◽

Cited By ~ 5

Author(s):

D. Holst ◽

A. B. Bach ◽

C. N. Nayeri ◽

C. O. Paschereit

Keyword(s):

Pressure Coefficient ◽

Reynolds Numbers ◽

Global Changes ◽

Finite Width ◽

Local Pressure ◽

Low Reynolds Numbers ◽

Pressure Distributions ◽

Coefficient Distribution ◽

Stereo Particle Image Velocimetry ◽

The Impact

The results of surface pressure measurements are presented in this paper to gain further insight into the lift changing influence of finite width micro-tabs, especially in adjacent airfoil sections. Micro-tabs are a promising concept for load control on wind turbines. Local pressure distributions were measured in several rows of pressure taps in the vicinity of the finite width micro-tab attached to a FX 63-137 profile at low Reynolds numbers. The investigation focuses on length dependency, chordwise position, and interaction between two micro-tabs. Additionally, stereo Particle-Image-Velocimetry measurements were conducted to study the structure, sense of rotation, and influence of tab-induced tip vortices, as well as the impact of a finite width micro-tab on the model’s near wake. Experiments reveal relative changes of more than 30 % in the pressure coefficient distribution upstream of several micro-tab configurations. Furthermore, increments of 20 % are recorded in neighbouring sections not directly controlled by micro-tabs. Even higher changes are obtained in the region between two tabs. These improvements are attained due to local and global changes in the effective camber.

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Experimental Investigations of the Influence of Incoming Wakes on the Losses of a Linear Turbine Cascade

Volume 3C: General ◽

10.1115/93-gt-394 ◽

1993 ◽

Cited By ~ 5

Author(s):

M. Ladwig ◽

L. Fottner

Keyword(s):

Suction Side ◽

Reynolds Numbers ◽

Experimental Investigations ◽

Turbine Cascade ◽

Flow Conditions ◽

Inlet Flow ◽

Low Reynolds Numbers ◽

Blade Passage ◽

Inlet Conditions ◽

Hot Film

The objective of this work is to enhance the understanding of the influence of wake induced non-uniform, steady inlet flow conditions on the profile losses of highly-loaded turbines. For different Reynolds numbers wake and profile pressure distribution measurements were carried out on a linear subsonic turbine cascade as well as measurements with a single sensor hot-film probe. The non-uniform inlet flow were simulated with two different cascades of cylindrical bars. The measurements with various circumferential positions of the incoming wakes relative to the turbine cascade show at low Reynolds numbers a decrease of the losses compared to uniform inlet conditions, because no separation of the suction side boundary layer occurs. With increasing Reynolds numbers the non-uniform inlet flow conditions cause an increase in the losses compared to uniform inlet conditions, due to the forward shift of transition. Generally, the smallest influence of the non-uniform incoming flow can be observed when the wakes enter the cascade inlet plane between the pressure-side of the profiles and the middle of the blade passage. Incoming wakes have the highest influence when they enter the blade passage near to the suction side of the profiles.

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Vortex flow aerodynamics behind a symmetric airfoil at low angles of attack and Reynolds numbers

International Journal of Micro Air Vehicles ◽

10.1177/17568293211055653 ◽

2021 ◽

Vol 13 ◽

pp. 175682932110556

Author(s):

D. Funda Kurtulus

Keyword(s):

Vortex Flow ◽

Reynolds Numbers ◽

Low Reynolds Numbers ◽

Vortex Pattern ◽

Air Vehicle ◽

Wake Patterns ◽

The Mean ◽

Low Reynolds ◽

Vortex Patterns ◽

Naca 0012

The low Reynolds number aerodynamics is important to investigate for micro air vehicle applications. The current paper covers numerical simulations to present the downstream development of the wake patterns and detailed analysis of the vortices generated at the downstream of NACA 0012 airfoil around the critical angle of attack where the instantaneous vortex patterns are oscillatory and differ from the mean vortex pattern for low Reynolds numbers ranging from 1000 to 4000. The instantaneous and mean aerodynamic forces, pressure and skin friction coefficients, and vorticity values are compared in addition to the path of the vortex centers, their longitudinal and lateral spacings, Kármán spacing ratios, and distortion ratios at the wake of the airfoil in regard to the different Reynolds numbers investigated. The streamwise and crosswise velocities of the vortex cores and relative velocities at different transverse locations are also discussed and presented in detail. The correlations between different non-dimensional numbers (St, Re, Ro) are obtained at these low Reynolds numbers investigated.

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Unsteady numerical investigation of two different corrugated airfoils

Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering ◽

10.1177/0954410016682539 ◽

2016 ◽

Vol 231 (13) ◽

pp. 2423-2437 ◽

Cited By ~ 5

Author(s):

WH Ho ◽

TH New

Keyword(s):

Large Scale ◽

Numerical Study ◽

Flow Characteristics ◽

Reynolds Numbers ◽

Mean Flow ◽

Airfoil Surface ◽

Low Reynolds Numbers ◽

Corrugated Surfaces ◽

Large Scale Flow ◽

Lift And Drag

An unsteady, two-dimensional numerical study was conducted to investigate the aerodynamic and flow characteristics of two bio-inspired corrugated airfoils at Re = 14,000 and compared with those of a smooth NACA0010 airfoil. Mean aerodynamic results reveal that the corrugated airfoils have better lift performance compared to the NACA0010 airfoil but incur slightly higher drag penalty. Mean flow streamlines indicate that this favourable performance is due to the ability of the corrugated airfoils in mitigating large-scale flow separations and stall. Unsteady flow field results show persistent formations of small recirculating vortices that remain within the corrugations at 10° angle-of-attack or less for one of the corrugated airfoil and below 15° for the other. In contrast, the flow behaviour can be highly turbulent with regular pairings of large-scale flow separation vortices along the upper surface at higher angles-of-attack. This not only disrupts the small recirculating vortices and causes them to detach from the corrugated surfaces, but it gets increasingly dominant at higher angles-of-attack resulting in regular lift and drag oscillations. At the end of each cycle, there is a sudden ejection of flow perpendicular to the airfoil surface and these disruptions manifest themselves as “kinks” in the instantaneous lift and drag of the corrugated airfoils. Therefore instead of regular fluctuations, the lift and drag curves have additional undulations. Despite that, the corrugations are able to produce larger pressure differentials between the upper and lower surfaces than the smooth airfoil. The current study demonstrates the intricate relationships between different sharp surface corrugations and favourable aerodynamic performance. In particular, results from this paper supports earlier investigations that corrugated airfoils may be used to good effects even at low Reynolds numbers, where flow separations are more likely.

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