UAV icing: the influence of airspeed and chord length on performance degradation

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Richard Hann ◽  
Tor Arne Johansen
Keyword(s):  
Reynolds Number ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Performance Degradation ◽  
Unmanned Aircraft ◽  
Chord Length ◽  
Ice Accretion ◽  
Content Type ◽  
Ice Accretions ◽  
Ice Shapes

Purpose The main purpose of this paper is to investigate the effects of icing on unmanned aerial vehicles (UAVs) at low Reynolds numbers and to highlight the differences to icing on manned aircraft at high Reynolds numbers. This paper follows existing research on low Reynolds number effects on ice accretion. This study extends the focus to how variations of airspeed and chord length affect the ice accretions, and aerodynamic performance degradation is investigated. Design/methodology/approach A parametric study with independent variations of airspeed and chord lengths was conducted on a typical UAV airfoil (RG-15) using icing computational fluid dynamic methods. FENSAP-ICE was used to simulate ice shapes and aerodynamic performance penalties. Validation was performed with two experimental ice shapes obtained from a low-speed icing wind tunnel. Three meteorological conditions were chosen to represent the icing typologies of rime, glaze and mixed ice. A parameter study with different chord lengths and airspeeds was then conducted for rime, glaze and mixed icing conditions. Findings The simulation results showed that the effect of airspeed variation depended on the ice accretion regime. For rime, it led to a minor increase in ice accretion. For mixed and glaze, the impact on ice geometry and penalties was substantially larger. The variation of chord length had a substantial impact on relative ice thicknesses, ice area, ice limits and performance degradation, independent from the icing regime. Research limitations/implications The implications of this manuscript are relevant for highlighting the differences between icing on manned and unmanned aircraft. Unmanned aircraft are typically smaller and fly slower than manned aircraft. Although previous research has documented the influence of this on the ice accretions, this paper investigates the effect on aerodynamic performance degradation. The findings in this work show that UAVs are more sensitive to icing conditions compared to larger and faster manned aircraft. By consequence, icing conditions are more severe for UAVs. Practical implications Atmospheric in-flight icing is a severe risk for fixed-wing UAVs and significantly limits their operational envelope. As UAVs are typically smaller and operate at lower airspeeds compared to manned aircraft, it is important to understand how the differences in airspeed and size affect ice accretion and aerodynamic performance penalties. Originality/value Earlier work has described the effect of Reynolds number variations on the ice accretion characteristics for UAVs. This work is expanding on those findings by investigating the effect of airspeed and chord length on ice accretion shapes separately. In addition, this study also investigates how these parameters affect aerodynamic performance penalties (lift, drag and stall).

Experimental and computational study of ice accretion effects on aerodynamic performance

2020 ◽  
Vol 92 (6) ◽  
pp. 827-836 ◽  
Author(s):  
Prasad G. ◽  
Bruce Ralphin Rose J.
Keyword(s):  
Wind Tunnel ◽  
Computational Study ◽  
Turbine Blades ◽  
Leading Edge ◽  
Aerodynamic Performance ◽  
Ice Accretion ◽  
Content Type ◽  
Balsa Wood ◽  
Computational Fluid Dynamics Analysis ◽  
Ice Shapes

Purpose The purpose of this paper is to analyse an actual representation of ice accretions, which are important during the certification process. Design/methodology/approach Ice accretion experiments are conducted in a low-speed subsonic wind tunnel testing facility to evaluate the influence of various ice shapes around the airfoil sections. Ice accumulation changes the shapes of local airfoil sections and thereby affects the aerodynamic performance characteristics of the considered NACA 23012 profile. The ice profiles are impregnated using balsa wood with glace, horn and mixed ice accretion cases for the detailed experimental investigation. Findings Computational fluid dynamics analysis is done to compute the influence of different ice shapes on the aerodynamic coefficients (Cl and Cd) while ice accretion occurs at the leading edge of the airfoil sections. It is observed that the Cl and Cd modified immediately more than 40% as compared to the clean wing configuration. In the same fashion, the skin friction coefficient also abruptly changes for different ice shapes that have the potential to induce flutter at the critical speed of the airplane. The computational solutions are further validated through wind tunnel experiments and recent literature concerning certification for flight in icing conditions. Social implications The ice accretion study on the aerodynamic surfaces can also be extended for wind turbine blades installed at different cold regions around the globe. Further, the propeller icing influences the entire rotorcraft aerodynamics at low temperature conditions and the findings of this study are strongly connected with such problems. Originality/value The aerodynamic characteristics of the baseline airfoil are greatly affected by the ice accretion problem. Although flight through icing condition endures for a short duration, the takeoff path and decision speed are determined based on airplane drag as per federal aviation regulations. Hence, the proposed study is focussed on a cost-effective approach to predict the effect of ice accretion to achieve optimum performance.

Heat transfer enhancement using second mode self-oscillating structures

2019 ◽  
Vol 30 (7) ◽  
pp. 3827-3842
Author(s):  
Samer Ali ◽  
Zein Alabidin Shami ◽  
Ali Badran ◽  
Charbel Habchi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Flow Regime ◽  
Vortex Generator ◽  
Reynolds Numbers ◽  
Content Type ◽  
Laminar Flow Regime ◽  
Second Mode

Purpose In this paper, self-sustained second mode oscillations of flexible vortex generator (FVG) are produced to enhance the heat transfer in two-dimensional laminar flow regime. The purpose of this study is to determine the critical Reynolds number at which FVG becomes more efficient than rigid vortex generators (RVGs). Design/methodology/approach Ten cases were studied with different Reynolds numbers varying from 200 to 2,000. The Nusselt number and friction coefficients of the FVG cases are compared to those of RVG and empty channel at the same Reynolds numbers. Findings For Reynolds numbers higher than 800, the FVG oscillates in the second mode causing a significant increase in the velocity gradients generating unsteady coherent flow structures. The highest performance was obtained at the maximum Reynolds number for which the global Nusselt number is improved by 35.3 and 41.4 per cent with respect to empty channel and rigid configuration, respectively. Moreover, the thermal enhancement factor corresponding to FVG is 72 per cent higher than that of RVG. Practical implications The results obtained here can help in the design of novel multifunctional heat exchangers/reactors by using flexible tabs and inserts instead of rigid ones. Originality/value The originality of this paper is the use of second mode oscillations of FVG to enhance heat transfer in laminar flow regime.

A Computational Study on Airfoils at a Low Reynolds Number

2000 ◽  
Author(s):  
Ajit Pal Singh ◽  
S. H. Winoto ◽  
D. A. Shah ◽  
K. G. Lim ◽  
Robert E. K. Goh
Keyword(s):  
Reynolds Number ◽  
Computational Analysis ◽  
Computational Study ◽  
Low Reynolds Number ◽  
Micro Air Vehicles ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Low Reynolds Numbers ◽  
Study Results ◽  
Low Reynolds

Abstract Performance characteristics of some low Reynolds number airfoils for the use in micro air vehicles (MAVs) are computationally studied using XFOIL at a Reynolds number of 80,000. XFOIL, which is based on linear-vorticity stream function panel method coupled with a viscous integral formulation, is used for the analysis. In the first part of the study, results obtained from the XFOIL have been compared with available experimental data at low Reynolds numbers. XFOIL is then used to study relative aerodynamic performance of nine different airfoils. The computational analysis has shown that the S1223 airfoil has a relatively better performance than other airfoils considered for the analysis.

Effect of corrugated skins on the aerodynamic performance of the cambered airfoils

2018 ◽  
Vol 35 (3) ◽  
pp. 1567-1582 ◽  
Author(s):  
Masoud Kharati-koopaee ◽  
Mahmood Fallahzadeh-abarghooee
Keyword(s):  
Drag Coefficient ◽  
Design Methodology ◽  
Reynolds Numbers ◽  
Numerical Approach ◽  
Aerodynamic Performance ◽  
Content Type ◽  
Lift Curve ◽  
Finite Volume Approach ◽  
Naca 0012 ◽  
Relative Curve

Purpose This paper aims to study the effect of corrugated skins on the aerodynamic performance of the cambered NACA 0012 airfoils at different corrugations parameters, maximum cambers, Reynolds numbers and maximum camber locations. Design/methodology/approach In this work, numerical approach is concerned, and results are obtained based on the finite volume approach. To characterize the effect of corrugated skins, the NACA 0012-corrugated airfoil section is chosen as the base airfoil, and different cambered corrugated airfoil sections are obtained by inclusion the camber to the base airfoil. In this research, the corrugation shape is a sinusoidal wave and corrugated skins are in the aft 30 per cent of airfoil chord. To investigate the effect of corrugations on the cambered sections, the drag coefficient and averaged lift curve slope for the corrugated airfoils are compared to those of the corresponding smooth sections. Findings Results indicate that the effect of increase in the maximum camber and also Reynolds number on the relative zero-incidence drag coefficient is of little importance at low corrugation amplitudes, whereas at high corrugation, amplitude results in different behaviors. It is found that as the maximum camber increases, the deterioration in the relative curve slope introduced by corrugated skins is reduced, and reduction in this deterioration is significant for high corrugation amplitudes airfoils. It is shown that an increase in the maximum camber location has nearly no effect on the relative zero-incidence drag coefficient and also relative lift curve slope. Originality/value The outcome of the present research provides the clues for better understanding of the effect of different corrugations parameters on the aerodynamic performance of the unmanned air vehicles to have as high aerodynamic performance as possible in different mission profiles of such vehicles.

A note on the flow coefficients of capillary tube and small orifice restrictors exposed to very low Reynolds number flow

2005 ◽  
Vol 57 (3) ◽  
pp. 116-120 ◽  
Author(s):  
Suat Canbazoğlu ◽  
Fazıl Canbulut
Keyword(s):  
Reynolds Number ◽  
Unsteady Flow ◽  
Capillary Tube ◽  
Low Reynolds Number ◽  
Reynolds Numbers ◽  
Hydraulic Control ◽  
Capillary Tubes ◽  
Content Type ◽  
Control Devices ◽  
Low Reynolds

PurposeThe main objective of this study was to obtain the flow restricting capacity by determining their flow coefficients and to investigate the unsteady flow with low Reynolds number in the flow‐restricting devices such as orifices and capillary tubes having small diameters.Design/methodology/approachThere is an enormous literature on the flow of Newtonian fluids through capillaries and orifices particularly in many application fields of the mechanical and chemical engineering. But most of the experimental results in literature are given for steady flows at moderate and high Reynolds numbers (Re>500). In this study, the unsteady flow at low Reynolds number (10<Re<650) through flow‐restricting devices such as orifices and capillary tubes having very small diameters between 0.35 and 0.70 mm were experimentally investigated.FindingsThe capillary tubes have much more capillarity property with respect to equal diameter orifices. Increasing the ratio of capillary tube length to tube diameter and decreasing the ratio of orifice diameter to pipe diameter before orifice increase the throttling or restricting property of the orifices and the capillary tubes. The orifices can be preferred to the capillary tubes having the same diameter at the same system pressure for the hydraulic systems or circuits requiring small velocity variations. The capillary tubes provide higher pressure losses and they can be also used as hydraulic accumulators in hydraulic control devices to attenuate flow‐induced vibrations because of their large pressure coefficients. An important feature of the results obtained for capillary tubes and small orifices is that as the d/D for orifices increases and the L/d reduces for capillary tubes, higher values C are obtained and the transition from viscous to inertia‐controlled flow appears to take place at lower Reynolds numbers. This may be explained by the fact that for small orifices with high d/D ratios and for capillary tubes with small L/d ratios, the losses due to viscous shear are small. Another important feature of the results is that the least variations in C for small orifices and the higher variations in C for capillary tubes occur when the d/D and L/d ratios are smallest. This has favourable implications in hydraulic control devices since a constant value for the C may be assumed even at relatively low values of Re.Originality/valueTo the authors' knowledge, there is not enough information in the literature about the flow coefficients of unsteady flows through capillary tubes and small orifices at low Reynolds numbers. This paper fulfils this gap.

scholarly journals Aerodynamic Performance of Micro Aerial Wing Structures at Low Reynolds Number

2019 ◽  
Vol 11 (1) ◽  
pp. 107-120 ◽  
Author(s):  
Y. D. DWIVEDI ◽  
Vasishta BHARGAVA ◽  
P. M. V. RAO ◽  
Donepudi JAGADEESH
Keyword(s):  
Reynolds Number ◽  
Low Reynolds Number ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Panel Method ◽  
Experiment Data ◽  
Wing Structures ◽  
Low Reynolds ◽  
Good Agreement

Corrugations are folds on a surface as found on wings of dragon fly insects. Although they fly at relatively lower altitudes its wings are adapted for better aerodynamic and aero-elastic characteristics. In the present work, three airfoil geometries were studied using the 2-D panel method to evaluate the aerodynamic performance for low Reynolds number. The experiments were conducted in wind tunnel for incompressible flow regime to demonstrate the coefficients of lift drag and glide ratio at two Reynolds numbers 1.9x104 and 1.5x105 and for angles of attack ranging between 00 and 160. The panel method results have been validated using the current and existing experiment data as well as with the computational work from cited literature. A good agreement between the experimental and the panel methods were found for low angles of attack. The results showed that till 80 angle of attack higher lift coefficient and lower drag coefficient are obtainable for corrugated airfoils as compared to NACA 0010. The validation of surface pressure coefficients for all three airfoils using the panel method at 40 angles of attack was done. The contours of the non-dimensional pressure and velocity are illustrated from -100 to 200 angles of attack. A good correlation between the experiment data and the computational methods revealed that the corrugated airfoils exhibit better aerodynamic performance than NACA 0010.

Aerodynamics of a Family of Three Highly Loaded Low-Pressure Turbine Airfoils: Measured Effects of Reynolds Number and Turbulence Intensity in Steady Flow

2006 ◽  
Author(s):  
I. Popovic ◽  
J. Zhu ◽  
W. Dai ◽  
S. A. Sjolander ◽  
T. Praisner ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Turbulence Intensity ◽  
Separation Bubble ◽  
Suction Side ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Aerodynamic Performance ◽  
Favourable Effect ◽  
Pressure Probe ◽  
Turbine Airfoils

The steady, midspan aerodynamic performance of a family of three low pressure (LP) turbine airfoils has been investigated in a low-speed cascade wind tunnel. The baseline profile has a Zweifel coefficient of 1.08. To examine the influence of increased loading as well as the loading distribution, two additional airfoils were designed, each with 25% higher loading than the baseline version. All three airfoils have the same design inlet and outlet flow angles. The aerodynamic performance was investigated for Reynolds numbers ranging from 25,000 to 150,000 (based on the axial chord and inlet velocity) and for values of freestream turbulence intensity of 1.5% and 4%. The flow field was measured with a three-hole pressure probe. Also, detailed loading distributions were obtained for all three airfoils using surface static pressure taps. The baseline airfoil and the new aft-loaded airfoil showed a separation bubble on the suction side of the airfoil under most of the conditions examined. In addition, a sudden and intermittent stall was observed at low Reynolds numbers for the new aft-loaded airfoil. The relatively short separation bubble would abruptly “burst” and fail to reattach. As the Reynolds number was decreased over a narrow range, the percentage of time that the flow was fully-separated increased to 100%. By comparison, the separation bubble on the baseline airfoil gradually increased in size in an orderly way as the Reynolds number was decreased. The new front-loaded airfoil provided the most encouraging performance: no separation bubble was present except at the very lowest Reynolds numbers. The absence of a separation bubble also had a favourable effect on the loss behaviour of this airfoil: despite its much higher aerodynamic loading, it exhibited very similar midspan losses to those observed for the baseline airfoil.

Aerodynamic study of corrugated skins for morphing wing applications

2010 ◽  
Vol 114 (1154) ◽  
pp. 237-244 ◽  
Author(s):  
C. Thill ◽  
J. D. Downsborough ◽  
S. J. Lai ◽  
I. P. Bond ◽  
D. P. Jones
Keyword(s):  
Reynolds Number ◽  
Drag Coefficient ◽  
Smooth Surface ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Potential Solution ◽  
Morphing Wing ◽  
Lift Curve ◽  
Length Changes ◽  
Wing Skin

AbstractCorrugated structures offer a potential solution for morphing wing skin applications due to their anisotropic behaviour that allows chordwise camber and length changes. Aerofoils with corrugated skins in the aft 1/3 of the chordwise section have been studied experimentally and computationally using various corrugation shapes and forms (sinusoidal, trapezoidal and triangular) at different Reynolds numbers. The study showed that the aerodynamic performance is highly dependent on corrugation amplitude, wavelength, gradient (combination of amplitude and wavelength) and Reynolds number. Evidence is given highlighting that penalties for having a non-smooth surface in the aft 1/3 of the chordwise section of an aerofoil can be eliminated for the lift curve slope and minimised for the zero lift drag coefficient.

The Effects of Diameter and Rotational Speed on the Aerodynamic Performance of Low Profile Miniature Radial Flow Fans

2007 ◽  
Author(s):  
R. Grimes ◽  
P. Walsh ◽  
E. Walsh ◽  
V. Egan
Keyword(s):  
Reynolds Number ◽  
Power Consumption ◽  
Flow Rate ◽  
Radial Flow ◽  
Pressure Rise ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Low Profile ◽  
And Performance ◽  
High Reynolds

Space constraints in many emerging electronic systems mean that there is a growing demand for heat sinks which are low in profile. As a result, small, low profile fans are necessary. In many instances Radial flow fans are best suited. An understanding of the design and performance of these fans is therefore necessary. For radial flow fans little work has been done to quantify the deviation of aerodynamic performance from that predicted by conventional fan laws. This paper aims to address this situation, by performing measurements of pressure rise, flow rate and power consumption for 3.5mm high radial flow fan rotors ranging in diameter from 20 to 35mm over a range of speeds. Measurements presented show variations of pressure rise and flow rate with Reynolds number to be largely in accordance with trends predicted by high Reynolds number theory, with the exception of flow rates at the lower range of Reynolds numbers which fell below the predicted values. Variations in power consumption show a similar trend to those of flow rate, with power consumption obeying the fan laws for the higher Reynolds numbers investigated, but showing a large increase at the lower Reynolds numbers.

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