In this paper, wind tunnel experiments are combined with Computational

Fluid Dynamics (CFD) aiming to analyze the aerodynamics of

realistic fuselage con¦gurations. A development model of the ANSAT

aircraft and an early model of the AKTAI light helicopter were employed.

Both models were tested at the subsonic wind tunnel of KNRTU-KAI

for a range of Reynolds numbers and pitch and yaw angles. The force

balance measurements were complemented by particle image velocimetry

(PIV) investigations for the cases where the experimental force measurements

showed substantial unsteadiness. The CFD results were found to

be in fair agreement with the test data and revealed some §ow separation

at the rear of the fuselages. Once con¦dence on the CFD method was

established, further modi¦cations were introduced to the ANSAT-like

fuselage model to demonstrate drag reduction via small shape changes

Barakos, G.

Batrakov, A.

Kusyumov, A.

Mikhailov, S.

Pakhov, V.

Sungatullin, A.

Valeev, M.

Zherekhov, V.

English

In this paper, wind tunnel experiments are combined with Computational Fluid Dynamics (CFD) aiming to analyze the aerodynamics of realistic fuselage configurations. A development model of the ANSAT aircraft and an early model of the AKTAI light helicopter were employed. Both models were tested at the subsonic wind tunnel of KNRTU-KAI for a range of Reynolds numbers and pitch and yaw angles. The force balance measurements were complemented by particle image velocimetry (PIV) investigations for the cases where the experimental force measurements showed substantial unsteadiness. The CFD results were found to be in fair agreement with the test data and revealed some flow separation at the rear of the fuselages. Once confidence on the CFD method was established, further modifications were introduced to the ANSAT-like fuselage model to demonstrate drag reduction via small shape changes

A. Batrakov

A. Kusyumov

S. Mikhailov

V. Pakhov

A. Sungatullin

M. Valeev

V. Zherekhov

G. Barakos

EDP Sciences OAI-PMH repository (1.2.0)

Helicopter fuselage drag ─ combined computational fluid dynamics and experimental studies

In this paper, wind tunnel experiments are combined with Computa-tional Fluid Dynamics (CFD) aiming to analyze the aerodynamics of realistic fuselage con¦gurations. A development model of the ANSAT aircraft and an early model of the AKTAI light helicopter were employed. Both models were tested at the subsonic wind tunnel of KNRTU-KAI for a range of Reynolds numbers and pitch and yaw angles. The force balance measurements were complemented by particle image velocimetry (PIV) investigations for the cases where the experimental force measure-ments showed substantial unsteadiness. The CFD results were found to be in fair agreement with the test data and revealed some §ow separation at the rear of the fuselages. Once con¦dence on the CFD method was established, further modi¦cations were introduced to the ANSAT-like fuselage model to demonstrate drag reduction via small shape changes. 

CiteSeerX

HELICOPTER FUSELAGE DRAG ¡ COMBINED COMPUTATIONAL FLUID DYNAMICS AND EXPERIMENTAL STUDIES

Crossref

Enlighten

HELICOPTER FUSELAGE DRAG ¡ COMBINEDCOMPUTATIONAL FLUID DYNAMICSAND EXPERIMENTAL STUDIESA. Batrakov1, A. Kusyumov1, S. Mikhailov1, V. Pakhov1,A. Sungatullin1, M. Valeev1, V. Zherekhov1,and G. Barakos21Kazan National Research Technical University10 K. Marx Str., Kazan 424011, Russia2School of Engineering, University of LiverpoolLiverpool L69 3GH, U.K.In this paper, wind tunnel experiments are combined with Computa-tional Fluid Dynamics (CFD) aiming to analyze the aerodynamics ofrealistic fuselage con¦gurations. A development model of the ANSATaircraft and an early model of the AKTAI light helicopter were employed.Both models were tested at the subsonic wind tunnel of KNRTU-KAIfor a range of Reynolds numbers and pitch and yaw angles. The forcebalance measurements were complemented by particle image velocimetry(PIV) investigations for the cases where the experimental force measure-ments showed substantial unsteadiness. The CFD results were found tobe in fair agreement with the test data and revealed some §ow separationat the rear of the fuselages. Once con¦dence on the CFD method wasestablished, further modi¦cations were introduced to the ANSAT-likefuselage model to demonstrate drag reduction via small shape changes.1 INTRODUCTIONThe use of CFD for the prediction of helicopter aerodynamics is a complex taskbecause of the transient and three-dimensional (3D) nature of the §ow aroundthe main and tail rotors. Additional complexity arises due to the requirement tomodel the §ow around the fuselage that in many cases behaves as a blu¨ bodywith §ow separation at its rear part and around the engine exhausts, fuel tanks,skids, etc. The §ow separation is partially responsible for an excess amount ofdrag on such bodies. Further, the inherent §ow unsteadiness makes experimen-tation harder and calls for repeatable sets of measurements to result in data withProgress in Flight Physics 7 (2015) ??-?? DOI: 10.1051/eucass/201507??? © Owned by the authors, published by EDP Sciences, 2015This is an Open Access article distributed under the terms of the Creative Commons Attribution License ?.0,  which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Article available at http://www.eucass-proceedings.eu or http://dx.doi.org/10.1051/eucass/201507021PROGRESS IN FLIGHT PHYSICSFigure 1 Photograph of ANSAT heli-copterFigure 2 Wind tunnel model of theANSAT-M2 helicopter fuselagegood con¦dence intervals. The focus of the present work is the CFD prediction ofthe helicopter fuselage aerodynamics. This topic has been the subject of severalinvestigations and a good summary is provided in [13].A key aspect of the present workFigure 3 Wind tunnel model of the AK-TAY helicopter fuselageis the use of realistic fuselages withthe main characteristics encounteredin modern designs. For this reason,instead of idealized bodies, early de-velopment models of real helicopterswere used. In order to have a fuselagerepresentative of modern designs, anapproximation to the ANSAT heli-copter produced by the JSC KazanHelicopters (Fig. 1) was ¦rst consid-ered. A variant of this baseline fuse-lage referred to as ANSAT-M2 andshown in Fig. 2 was the ¦rst modelconsidered. The ANSAT-M2 is oneof many initial designs employed during the development of the ANSAT air-craft and was used for preliminary aerodynamic studies conducted in the windtunnel T-1K of KNRTU. The fuselage is not the exact shape of the ANSAThelicopter body with di¨erences concentrated near the engine housing and ex-hausts.The second case considered in this paper is an early model of the AKTAI lighthelicopter (Fig. 3). It is an asymmetric fuselage shape due to the requirementsto house the engine and other equipment. The aerodynamics of several earlymodels of the ANSAT helicopter has also been investigated and these results arepresented in [47].22AERODYNAMICSThe numerical computations were performed using the in-house CFD toolHMB (helicopter multiblock), developed at Liverpool University. The CFD gridswere constructed using the ANSYS ICEM commercial mesh generator. Thecomputational domains were resolved using hexahedral grids and the 3D steadyReynolds-averaged NavierStokes (RANS) equations. The computation of theintegral and distributed loads on an isolated helicopter fuselage was the ¦rst aimof the present investigation.2 COMPUTATIONAL FLUID DYNAMICSMESH GENERATIONFor the CFD grids around the ANSAT-M2 and AKTAY fuselages, theICEM-Hexa tool has been used. The length of the ANSAT-M2 fuselage wasLF = 1.57 m, and a reference area of SF = 0.0694 m2 was used for computingthe aerodynamic coe©cients of lift and drag. The computational domain wasdivided in 764 blocks. For the AKTAY wind tunnel model, the geometric pa-rameters were LF = 1.64 m and SF = 0.1075 m2, while the CFD grid required1342 blocks. The grid was re¦ned near the fuselage surface (and the resultingy+ values were near 1) to resolve the laminar sublayer for better predictions ofthe friction drag coe©cients.Figure 4a presents a part of the multiblock topology of the grid as well asthe surface mesh on the ANSAT-2M fuselage. The surface grid for the AKTAYfuselage is shown in Fig. 4b. A mesh convergence study was ¦rst conducted withrespect to the number of surface cells and their spatial distribution.For all fuselages, the results presented in this work are nearly mesh indepen-dent for the employed Re and turbulence model.Figure 4 Surface mesh and multiblock topology for the ANSAT-2M fuselage (a) andsurface mesh on the AKTAY model (b)23PROGRESS IN FLIGHT PHYSICS3 PREDICTION OF AERODYNAMIC FORCECOEFFICIENTSThe open test section (of a 2.25-meter diameter) closed circuit, low speed, windtunnel T-1K of KNRTU-KAI is equipped with a six-component Prandtl balance.Eight-times measurements were conducted to reduce random experimental errors(system errors, mounting of model, model manufacturing errors, etc.) and forplotting error bars around the obtained results.The standard kω turbulence model was used for computations due to itspopularity within the CFD [8,9]. The CFD validation was conducted at Reynoldsnumber of Re = 3,2 ·106 and at a free-stream Mach number of M∞ = 0.1. Theseconditions correspond to the experimental investigations. Figure 5a presentsthe CFD predictions of the lift and drag coe©cients for the ANSAT-M2 modelin comparison with the wind tunnel experiment data. The error bars shownon the graphs correspond to the experimental con¦dence intervals. Figure 5bpresents the corresponding CD for the AKTAY model. Figures 5a and 5b suggestFigure 5 Experimental (1) and CFD (2) lift and drag coe©cients vs. pitch angle forthe ANSAT-M2 (a) and AKTAY (b) models24AERODYNAMICSa good agreement between CFD and experimental results for the lift and dragcoe©cients in the considered range of pitch angles. For all models, the dragcoe©cient values are overpredicted in comparison with the experimental dataunlike the underpredicted lift coe©cient data. The level of agreement with theexperiments is satisfactory for a simple RANS model used for computations.4 DISTRIBUTED FLOW PARAMETERSThe integrated loads are complemented by comparisons of distributed §ow pa-rameters that allow for a better understanding of the in§uence of the fuselagegeometry on the §ow structure. For postprocessing of the CFD results, theTECPLOT360 commercial visualization tool was used.4.1 Experimental and Computational Fluid DynamicsPredicted Vector Fields ComparisonFigures 6a and 6b present a comparison of experimental and CFD-predictedvector ¦elds for ANSAT-M2 and AKTAY models.The experimental vector ¦eld was obtained using a two-dimensional (2D)PIV system. Figure 6 suggests a good qualitative agreement between CFD andexperiments for the considered range of pitch angles. Both CFD and wind tunneltests revealed a §ow separation area although the extend of separation is di¨erentbetween the two models.4.2 Velocity FieldsFigure 7 presents velocity distributions around the mid-plane of the fuselage,and shows the evolution of the separated §ow regions with the pitch angle.For the ANSAT-M2 model, increasing the pitch angle leads to growth ofthe separation area at rear part of fuselage, but it does not cause the samegrowth in the drag force (see also Fig. 5a). Moreover, according to the CFDand experimental data, the drag coe©cient is monotonically decreasing with thepitch angle. For the AKTAY fuselage, the drag coe©cient has approximatelyconstant values within the considered range of pitch angles. Figure 8 presentsthe velocity ¦elds at a horizontal plane under the tail boom of the ANSAT-M2and AKTAY fuselages.At α = 8◦, a separation area centered in the considered section is locatedat the symmetry plane of ANSAT-M2 fuselage (see Fig. 8b). For α = −8◦,Fig. 8a reveals the presence of two separation cores near the horizontal plane.25PROGRESS IN FLIGHT PHYSICSFigure 6 The PIV (left column) and CFD (right column) velocity vector ¦elds at themid plane of the ANSAT-M2 (a) and AKTAY (b) fuselages for α = 0◦. Comparisonaround the rear fuselage part is shownThe ANSAT-M2 geometry is more streamlined in comparison to the AKTAYmodel. For the AKTAY model, the topology of the separated area is the samefor α = −8◦ and 8◦. For this reason, the drag coe©cient value for α = −8◦ isclose to the drag coe©cient for α = 8◦. This behavior was expected for a body26AERODYNAMICSFigure 7 The CFD predictions of mid-plane velocity for the ANSAT-M2 (left column)and AKTAY (right column) fuselages at α = −8◦ (a), 0◦ (b), and 8◦ (c)shaped like the AKTAY that has always separated the §ow near the fuselagejunction with the tail-boom.4.3 Further Flow VisualizationIsosurfaces corresponding to velocity magnitude of V = 0.2V∞ are used for visu-alization where V∞ is the free-stream velocity. For areas without §ow separation,27PROGRESS IN FLIGHT PHYSICSFigure 8 The CFD prediction of horizontal plane velocity for the ANSAT-M2 (leftcolumn) and AKTAY (right column) fuselages at α = −8◦ (a) and 8◦ (b)the isosurfaces of V = const are close to the fuselage surface and the geometry ofthe isosurfaces corresponds to the fuselage geometry. In the separation zones, theisosurfaces detach from the fuselage surface and this shows the §ow separationzones. Figure 9 presents the isosurfaces for di¨erent pitch angles.Figure 9 shows the di¨erent character of the separation areas for the stream-lined (ANSAT-M2) and the blu¨ (AKTAY) fuselages. In general, the shape ofthe isosurfaces corresponds to the §ow ¦elds presented in Fig. 8.For the ANSAT-M2 model, there are two areas of separation with di¨erentcharacter of development with respect to the pitch angle. Both areas of separa-tion are located symmetrically to the fuselage mid-plane. This separation regionis maximized for negative pitch angles and it maintains the same structure withtwo contra-rotating vortices. The intensity of the separation is maximum fora negative pitch angle of −8◦ and monotonically decreases with respect to thepitch angle. A di¨erent separated §ow region with a single core of separation islocated at the back of the fuselage, near the tail boom junction. The intensityof this separated §ow region is maximum for a positive pitch angle of 8◦. At28AERODYNAMICSFigure 9 Isosurfaces corresponding to V = 0.2V∞ for the ANSAT-M2 (left column)and the AKTAY (right column) fuselages for α = −8◦ (a); 0◦ (b); and 8◦ (c)a pitch of −8◦, this separation region almost disappears. The §ow structure forthe AKTAY model is di¨erent because of the blu¨ rear fuselage. For the AKTAYmodel, the §ow at the rear part of fuselage has a more unsteady character andis less sensitive to the pitch angle.29PROGRESS IN FLIGHT PHYSICSFigure 10 Stream functions for ANSAT-M2 (left column) and AKTAY (right col-umn) fuselages for α = −8◦ (a), 0◦ (b), and 8◦ (c)30AERODYNAMICS4.4 Flow Stream LinesFigure 10 shows the stream lines on the ZY plane that is normal to the free-stream velocity vector. For the ANSAT-M2 model, the location of vortices atthe rear part of fuselage shows two cores of separation present at −8◦. At 0◦and 8◦ of pitch, the §ow is more attached. The §ow structure at the rear part ofAKTAY fuselage appears to be separated regardless of the pitch angle and thesize of the separated §ow region is independent of the pitch angle.5 CONCLUDING REMARKS AND FUTURE WORKThe §ows around the simpli¦ed ANSAT and AKTAY helicopter fuselages wereanalyzed. The experimental values of drag and lift coe©cients were comparedwith CFD data with good agreement. The structure of the separated §ow regionat the rear of both fuselages was also analyzed at di¨erent pitch angles. It isshown that for the streamlined shape of the ANSAT-M2 model, the §ow at rearpart of fuselage has two main separation regions. This is not the case for theAKTAY where the §ow separation covers a single large area, and is presentregardless of the pitch angle. In the future, the e¨ect of the helicopter rotor onthe fuselage drag will be considered along with further investigations to designthe rear fuselage for drag reduction in an optimal way.ACKNOWLEDGMENTSThis work is supported by the ¤Leading Scientist¥ grant of the Russian Federa-tion, under order 220 of the Russian Ministry of Education. The authors wouldlike to acknowledge the Kazan Helicopter Plant for providing the initial fuselageshapes for this research.REFERENCES1. D£Alascio, A., K. Pahlke, and F. Le Chuiton. 2004. Application of a structured andan unstructured CFD method to the fuselage aerodynamics of the EC145 helicopter,prediction of the time averaged in§uence of the main rotor. ECCOMAS EuropeanCongress on Computational Methods in Applied Sciences and Engineering.2. Le Chuiton, F., A. D£Alascio, G.N. Barakos, R. Steijl, D. Schwamborn, andH. Ludeke. 2009. EC145 helicopter fuselage ¡ an industrial case. DESider ¡A European e¨ort on hybrid RANS-LES modelling. Eds. W. Haase, M. Braza,31PROGRESS IN FLIGHT PHYSICSand A. Revell. Notes on numerical §uid mechanics and multidisciplinary designser. Springer Verlag. 103:250260.3. Bridgeman, J.O., and G.T. Lancaster. 2010. Predicting hub drag on realistic ge-ometries. American Helicopter Society Aeromechanics Specialists£ Conference. SanFrancisco, CA, USA.4. Kusyumov, A.N., S.A. Mikhailov, E. I. Nikolaev, N.A. Shilova, and A.O. Garipov.2011. Simulation of §ow around the fuselage of ¤ANSAT¥ helicopter. ASME 2011 In-ternational Mechanical Engineering Congress & Exposition (IMECE2011). Denver,Colorado, USA.5. Pahov, V., M. Valiev, V. Zherekhov, L. Makarova, A. Kusuymov, and G. Barakos.2012. Creating a database for validation of predictive methods for rotorcraft. 47thSymposium (International) of Applied Aerodynamics. Paris, France.6. Kusyumov, A.N., S.A. Mikhailov, E. V. Romanova, A.O. Garipov, E. I. Nikolaev,and G. Barakos. 2012. Simulation of §ow around isolated helicopter fuselage. EFM2012 Conference. Hradec Kralove, Czech Republic.7. Kusyumov, A., S. Mikhailov, A. Garipov, E. Nikolaev, and G. Barakos. 2012. CFDsimulation of fuselage aerodynamics of the ¤ANSAT¥ helicopter prototype. Trans.Control Mech. Syst. 1(7):318324.8. Lienard, C., A. Le Pape, and C. Verbeke. 2012. Numerical and experimental inves-tigation of helicopter fuselage drag reduction using active §ow control. AmericanHelicopter Society 68th Annual Forum. Fort Worth, TX, USA.9. Dietz, M., T. Kneisch, G. Roth, A. D£Alascio, and D. Schimke. 2012. EC145 T2:Comprehensive and challenging industrial CFD applications. American HelicopterSociety 68th Annual Forum. Fort Worth, TX, USA.32

Helicopter Fuselage Drag ─ Combined Computational Fluid Dynamics and Experimental Studies

Enlighten: Publications

HELICOPTER FUSELAGE DRAG ¡ COMBINED
COMPUTATIONAL FLUID DYNAMICS
AND EXPERIMENTAL STUDIES
A. Batrakov1, A. Kusyumov1, S. Mikhailov1, V. Pakhov1,
A. Sungatullin1, M. Valeev1, V. Zherekhov1,
and G. Barakos2
1Kazan National Research Technical University
10 K. Marx Str., Kazan 424011, Russia
2School of Engineering, University of Liverpool
Liverpool L69 3GH, U.K.
In this paper, wind tunnel experiments are combined with Computa-
tional Fluid Dynamics (CFD) aiming to analyze the aerodynamics of
realistic fuselage con¦gurations. A development model of the ANSAT
aircraft and an early model of the AKTAI light helicopter were employed.
Both models were tested at the subsonic wind tunnel of KNRTU-KAI
for a range of Reynolds numbers and pitch and yaw angles. The force
balance measurements were complemented by particle image velocimetry
(PIV) investigations for the cases where the experimental force measure-
ments showed substantial unsteadiness. The CFD results were found to
be in fair agreement with the test data and revealed some §ow separation
at the rear of the fuselages. Once con¦dence on the CFD method was
established, further modi¦cations were introduced to the ANSAT-like
fuselage model to demonstrate drag reduction via small shape changes.
1 INTRODUCTION
The use of CFD for the prediction of helicopter aerodynamics is a complex task
because of the transient and three-dimensional (3D) nature of the §ow around
the main and tail rotors. Additional complexity arises due to the requirement to
model the §ow around the fuselage that in many cases behaves as a blu¨ body
with §ow separation at its rear part and around the engine exhausts, fuel tanks,
skids, etc. The §ow separation is partially responsible for an excess amount of
drag on such bodies. Further, the inherent §ow unsteadiness makes experimen-
tation harder and calls for repeatable sets of measurements to result in data with
Progress in Flight Physics 7 (2015) ??-?? 
DOI: 10.1051/eucass/201507??? 
© Owned by the authors, published by EDP Sciences, 2015
This is an Open Access article distributed under the terms of the Creative Commons Attribution License ?.0,  which 
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Article available at http://www.eucass-proceedings.eu or http://dx.doi.org/10.1051/eucass/201507021
PROGRESS IN FLIGHT PHYSICS
Figure 1 Photograph of ANSAT heli-
copter
Figure 2 Wind tunnel model of the
ANSAT-M2 helicopter fuselage
good con¦dence intervals. The focus of the present work is the CFD prediction of
the helicopter fuselage aerodynamics. This topic has been the subject of several
investigations and a good summary is provided in [13].
A key aspect of the present work
Figure 3 Wind tunnel model of the AK-
TAY helicopter fuselage
is the use of realistic fuselages with
the main characteristics encountered
in modern designs. For this reason,
instead of idealized bodies, early de-
velopment models of real helicopters
were used. In order to have a fuselage
representative of modern designs, an
approximation to the ANSAT heli-
copter produced by the JSC Kazan
Helicopters (Fig. 1) was ¦rst consid-
ered. A variant of this baseline fuse-
lage referred to as ANSAT-M2 and
shown in Fig. 2 was the ¦rst model
considered. The ANSAT-M2 is one
of many initial designs employed during the development of the ANSAT air-
craft and was used for preliminary aerodynamic studies conducted in the wind
tunnel T-1K of KNRTU. The fuselage is not the exact shape of the ANSAT
helicopter body with di¨erences concentrated near the engine housing and ex-
hausts.
The second case considered in this paper is an early model of the AKTAI light
helicopter (Fig. 3). It is an asymmetric fuselage shape due to the requirements
to house the engine and other equipment. The aerodynamics of several early
models of the ANSAT helicopter has also been investigated and these results are
presented in [47].
22
AERODYNAMICS
The numerical computations were performed using the in-house CFD tool
HMB (helicopter multiblock), developed at Liverpool University. The CFD grids
were constructed using the ANSYS ICEM commercial mesh generator. The
computational domains were resolved using hexahedral grids and the 3D steady
Reynolds-averaged NavierStokes (RANS) equations. The computation of the
integral and distributed loads on an isolated helicopter fuselage was the ¦rst aim
of the present investigation.
2 COMPUTATIONAL FLUID DYNAMICS
MESH GENERATION
For the CFD grids around the ANSAT-M2 and AKTAY fuselages, the
ICEM-Hexa tool has been used. The length of the ANSAT-M2 fuselage was
LF = 1.57 m, and a reference area of SF = 0.0694 m
2 was used for computing
the aerodynamic coe©cients of lift and drag. The computational domain was
divided in 764 blocks. For the AKTAY wind tunnel model, the geometric pa-
rameters were LF = 1.64 m and SF = 0.1075 m
2, while the CFD grid required
1342 blocks. The grid was re¦ned near the fuselage surface (and the resulting
y+ values were near 1) to resolve the laminar sublayer for better predictions of
the friction drag coe©cients.
Figure 4a presents a part of the multiblock topology of the grid as well as
the surface mesh on the ANSAT-2M fuselage. The surface grid for the AKTAY
fuselage is shown in Fig. 4b. A mesh convergence study was ¦rst conducted with
respect to the number of surface cells and their spatial distribution.
For all fuselages, the results presented in this work are nearly mesh indepen-
dent for the employed Re and turbulence model.
Figure 4 Surface mesh and multiblock topology for the ANSAT-2M fuselage (a) and
surface mesh on the AKTAY model (b)
23
PROGRESS IN FLIGHT PHYSICS
3 PREDICTION OF AERODYNAMIC FORCE
COEFFICIENTS
The open test section (of a 2.25-meter diameter) closed circuit, low speed, wind
tunnel T-1K of KNRTU-KAI is equipped with a six-component Prandtl balance.
Eight-times measurements were conducted to reduce random experimental errors
(system errors, mounting of model, model manufacturing errors, etc.) and for
plotting error bars around the obtained results.
The standard kω turbulence model was used for computations due to its
popularity within the CFD [8,9]. The CFD validation was conducted at Reynolds
number of Re = 3,2 ·106 and at a free-stream Mach number of M∞ = 0.1. These
conditions correspond to the experimental investigations. Figure 5a presents
the CFD predictions of the lift and drag coe©cients for the ANSAT-M2 model
in comparison with the wind tunnel experiment data. The error bars shown
on the graphs correspond to the experimental con¦dence intervals. Figure 5b
presents the corresponding CD for the AKTAY model. Figures 5a and 5b suggest
Figure 5 Experimental (1) and CFD (2) lift and drag coe©cients vs. pitch angle for
the ANSAT-M2 (a) and AKTAY (b) models
24
AERODYNAMICS
a good agreement between CFD and experimental results for the lift and drag
coe©cients in the considered range of pitch angles. For all models, the drag
coe©cient values are overpredicted in comparison with the experimental data
unlike the underpredicted lift coe©cient data. The level of agreement with the
experiments is satisfactory for a simple RANS model used for computations.
4 DISTRIBUTED FLOW PARAMETERS
The integrated loads are complemented by comparisons of distributed §ow pa-
rameters that allow for a better understanding of the in§uence of the fuselage
geometry on the §ow structure. For postprocessing of the CFD results, the
TECPLOT360 commercial visualization tool was used.
4.1 Experimental and Computational Fluid Dynamics
Predicted Vector Fields Comparison
Figures 6a and 6b present a comparison of experimental and CFD-predicted
vector ¦elds for ANSAT-M2 and AKTAY models.
The experimental vector ¦eld was obtained using a two-dimensional (2D)
PIV system. Figure 6 suggests a good qualitative agreement between CFD and
experiments for the considered range of pitch angles. Both CFD and wind tunnel
tests revealed a §ow separation area although the extend of separation is di¨erent
between the two models.
4.2 Velocity Fields
Figure 7 presents velocity distributions around the mid-plane of the fuselage,
and shows the evolution of the separated §ow regions with the pitch angle.
For the ANSAT-M2 model, increasing the pitch angle leads to growth of
the separation area at rear part of fuselage, but it does not cause the same
growth in the drag force (see also Fig. 5a). Moreover, according to the CFD
and experimental data, the drag coe©cient is monotonically decreasing with the
pitch angle. For the AKTAY fuselage, the drag coe©cient has approximately
constant values within the considered range of pitch angles. Figure 8 presents
the velocity ¦elds at a horizontal plane under the tail boom of the ANSAT-M2
and AKTAY fuselages.
At α = 8◦, a separation area centered in the considered section is located
at the symmetry plane of ANSAT-M2 fuselage (see Fig. 8b). For α = −8◦,
Fig. 8a reveals the presence of two separation cores near the horizontal plane.
25
PROGRESS IN FLIGHT PHYSICS
Figure 6 The PIV (left column) and CFD (right column) velocity vector ¦elds at the
mid plane of the ANSAT-M2 (a) and AKTAY (b) fuselages for α = 0◦. Comparison
around the rear fuselage part is shown
The ANSAT-M2 geometry is more streamlined in comparison to the AKTAY
model. For the AKTAY model, the topology of the separated area is the same
for α = −8◦ and 8◦. For this reason, the drag coe©cient value for α = −8◦ is
close to the drag coe©cient for α = 8◦. This behavior was expected for a body
26
AERODYNAMICS
Figure 7 The CFD predictions of mid-plane velocity for the ANSAT-M2 (left column)
and AKTAY (right column) fuselages at α = −8◦ (a), 0◦ (b), and 8◦ (c)
shaped like the AKTAY that has always separated the §ow near the fuselage
junction with the tail-boom.
4.3 Further Flow Visualization
Isosurfaces corresponding to velocity magnitude of V = 0.2V∞ are used for visu-
alization where V∞ is the free-stream velocity. For areas without §ow separation,
27
PROGRESS IN FLIGHT PHYSICS
Figure 8 The CFD prediction of horizontal plane velocity for the ANSAT-M2 (left
column) and AKTAY (right column) fuselages at α = −8◦ (a) and 8◦ (b)
the isosurfaces of V = const are close to the fuselage surface and the geometry of
the isosurfaces corresponds to the fuselage geometry. In the separation zones, the
isosurfaces detach from the fuselage surface and this shows the §ow separation
zones. Figure 9 presents the isosurfaces for di¨erent pitch angles.
Figure 9 shows the di¨erent character of the separation areas for the stream-
lined (ANSAT-M2) and the blu¨ (AKTAY) fuselages. In general, the shape of
the isosurfaces corresponds to the §ow ¦elds presented in Fig. 8.
For the ANSAT-M2 model, there are two areas of separation with di¨erent
character of development with respect to the pitch angle. Both areas of separa-
tion are located symmetrically to the fuselage mid-plane. This separation region
is maximized for negative pitch angles and it maintains the same structure with
two contra-rotating vortices. The intensity of the separation is maximum for
a negative pitch angle of −8◦ and monotonically decreases with respect to the
pitch angle. A di¨erent separated §ow region with a single core of separation is
located at the back of the fuselage, near the tail boom junction. The intensity
of this separated §ow region is maximum for a positive pitch angle of 8◦. At
28
AERODYNAMICS
Figure 9 Isosurfaces corresponding to V = 0.2V∞ for the ANSAT-M2 (left column)
and the AKTAY (right column) fuselages for α = −8◦ (a); 0◦ (b); and 8◦ (c)
a pitch of −8◦, this separation region almost disappears. The §ow structure for
the AKTAY model is di¨erent because of the blu¨ rear fuselage. For the AKTAY
model, the §ow at the rear part of fuselage has a more unsteady character and
is less sensitive to the pitch angle.
29
PROGRESS IN FLIGHT PHYSICS
Figure 10 Stream functions for ANSAT-M2 (left column) and AKTAY (right col-
umn) fuselages for α = −8◦ (a), 0◦ (b), and 8◦ (c)
30
AERODYNAMICS
4.4 Flow Stream Lines
Figure 10 shows the stream lines on the ZY plane that is normal to the free-
stream velocity vector. For the ANSAT-M2 model, the location of vortices at
the rear part of fuselage shows two cores of separation present at −8◦. At 0◦
and 8◦ of pitch, the §ow is more attached. The §ow structure at the rear part of
AKTAY fuselage appears to be separated regardless of the pitch angle and the
size of the separated §ow region is independent of the pitch angle.
5 CONCLUDING REMARKS AND FUTURE WORK
The §ows around the simpli¦ed ANSAT and AKTAY helicopter fuselages were
analyzed. The experimental values of drag and lift coe©cients were compared
with CFD data with good agreement. The structure of the separated §ow region
at the rear of both fuselages was also analyzed at di¨erent pitch angles. It is
shown that for the streamlined shape of the ANSAT-M2 model, the §ow at rear
part of fuselage has two main separation regions. This is not the case for the
AKTAY where the §ow separation covers a single large area, and is present
regardless of the pitch angle. In the future, the e¨ect of the helicopter rotor on
the fuselage drag will be considered along with further investigations to design
the rear fuselage for drag reduction in an optimal way.
ACKNOWLEDGMENTS
This work is supported by the ¤Leading Scientist¥ grant of the Russian Federa-
tion, under order 220 of the Russian Ministry of Education. The authors would
like to acknowledge the Kazan Helicopter Plant for providing the initial fuselage
shapes for this research.
REFERENCES
1. D£Alascio, A., K. Pahlke, and F. Le Chuiton. 2004. Application of a structured and
an unstructured CFD method to the fuselage aerodynamics of the EC145 helicopter,
prediction of the time averaged in§uence of the main rotor. ECCOMAS European
Congress on Computational Methods in Applied Sciences and Engineering.
2. Le Chuiton, F., A. D£Alascio, G.N. Barakos, R. Steijl, D. Schwamborn, and
H. Ludeke. 2009. EC145 helicopter fuselage ¡ an industrial case. DESider ¡
A European e¨ort on hybrid RANS-LES modelling. Eds. W. Haase, M. Braza,
31
PROGRESS IN FLIGHT PHYSICS
and A. Revell. Notes on numerical §uid mechanics and multidisciplinary design
ser. Springer Verlag. 103:250260.
3. Bridgeman, J.O., and G.T. Lancaster. 2010. Predicting hub drag on realistic ge-
ometries. American Helicopter Society Aeromechanics Specialists£ Conference. San
Francisco, CA, USA.
4. Kusyumov, A.N., S.A. Mikhailov, E. I. Nikolaev, N.A. Shilova, and A.O. Garipov.
2011. Simulation of §ow around the fuselage of ¤ANSAT¥ helicopter. ASME 2011 In-
ternational Mechanical Engineering Congress & Exposition (IMECE2011). Denver,
Colorado, USA.
5. Pahov, V., M. Valiev, V. Zherekhov, L. Makarova, A. Kusuymov, and G. Barakos.
2012. Creating a database for validation of predictive methods for rotorcraft. 47th
Symposium (International) of Applied Aerodynamics. Paris, France.
6. Kusyumov, A.N., S.A. Mikhailov, E. V. Romanova, A.O. Garipov, E. I. Nikolaev,
and G. Barakos. 2012. Simulation of §ow around isolated helicopter fuselage. EFM
2012 Conference. Hradec Kralove, Czech Republic.
7. Kusyumov, A., S. Mikhailov, A. Garipov, E. Nikolaev, and G. Barakos. 2012. CFD
simulation of fuselage aerodynamics of the ¤ANSAT¥ helicopter prototype. Trans.
Control Mech. Syst. 1(7):318324.
8. Lienard, C., A. Le Pape, and C. Verbeke. 2012. Numerical and experimental inves-
tigation of helicopter fuselage drag reduction using active §ow control. American
Helicopter Society 68th Annual Forum. Fort Worth, TX, USA.
9. Dietz, M., T. Kneisch, G. Roth, A. D£Alascio, and D. Schimke. 2012. EC145 T2:
Comprehensive and challenging industrial CFD applications. American Helicopter
Society 68th Annual Forum. Fort Worth, TX, USA.
32


https://www.eucass-proceedings.eu/articles/eucass/pdf/2015/01/eucass7p21.pdf

Helicopter Fuselage Drag ─ Combined Computational Fluid Dynamics and Experimental Studies

Abstract

Similar works

Full text

Available Versions

EDP Sciences OAI-PMH repository (1.2.0)

CiteSeerX

Crossref

Enlighten

Enlighten: Publications