Insights and lessons learned from the aerodynamic analysis of the High Wing Transport (HWT) high-lift configuration are presented. Three-dimensional Navier-Stokes CFD simulations using the OVERFLOW flow solver are compared with high Reynolds test data obtained in the NASA Ames 12 Foot Pressure Wind Tunnel (PWT) facility. Computational analysis of the baseline HWT high-lift configuration with and without Externally Blown Flap (EBF) jet effects is highlighted. Several additional aerodynamic investigations, such as nacelle strake effectiveness and wake vortex studies, are presented. Technical capabilities and shortcomings of the computational method are discussed and summarized

An, Michael Y.

Baker, M.David

Mysko, Stephen J.

Nash, S.

Rogers, Stuart E.

Roth, Karlin

Slotnick, Jeffrey P.

Yeh, David T.

NASA Technical Reports Server

Source of Acquisition 
NASA Ames Research Center 
Navier-Stokes Analysis of a High Wing Transpo~~  
High-Lift Configuration With Externally Blown Haps 
Jeffrey P. Slotnick, Michael Y. An, Stephen J. Mysko, and David T. Yeh 
The Boeing Cornpu~zy 
Stuart E. Rogers and Karlin Roth 
NASA Ames Research Center 
M. David Baker and S. Nash 
MCAT, Inc. 
Abstract 
Insights and lessons learned from the aerodynamic analysis of the High Wing Transport 
(HWT) high-lift configuration are presented. Three-dimensional Navier-Stokes CFD simulations 
using the OVERFLOW flow solver are compared with high Reynolds test data obtained in the 
NASA Ames 12 Foot Pressure Wind Tunnel (PWT) facility. Computational analysis of the 
baseline HWT high-lift configuration with and without Externally Blown Flap (EBF) jet effects 
is highlighted. Several additional aerodynamic investigations, such as nacelle strake 
effectiveness and wake vortex studies, are presented. Technical capabilities and shortcomings of 
the computational method are discussed and summarized. 
Introduction 1 
To reduce the costs associated with the design, development, and manufacturing of 
modern transport aircraft, major improvements in both aircraft development cycle (time-to- 
market) and affordability (flyaway cost) must be achieved in order to make new concepts 
commercially viable. The major driver in reducing aircraft development cycle time and total 
system cost is the reduction of aerodynamic design cycle time. 
To enable these improvements, significant efforts to utilize CFD for high-lift system 
design are underway in order to greatly reduce the amount of wind tunnel testing required in the 
design process. Emerging Navier-Stokes methods that model the viscous-dominated flow 
physics associated with advanced transport aircraft aerodynamics have the potential to reduce 
aerodynamic design cycle time. However, to be successful, CFD methods must be easy to use, 
fast, and accurate. 
High-lift analysis is particularly challenging, and remains the pacing item in reducing 
aerodynamic cycle time mainly due to geometric complexity, and the wide range of flow 
phenomena typically present in high-lift flowfields. High-lift aerodynamics is extremely 
complex, and is dominated by viscous flow phenomena, such as separation, shock-boundary 
layer interactions, and multiple element merging confluent wakes. A significant body of work 
has been performed in 2D to characterize high-lift flow physics'12. However, since high lift flows 
are inherently three-dimensional, testing and simulation of complete transport configurations are 
required to accurately predict high lift system performance. 
Computing the three-dimensional subsonic flow over a complete transport high lift 
configuration is one of the most difficult challenges of modern CFD~. Inclusion of engine jet 
impingement effects in the simulation of EBF-powered high lift systems remains a pacing item 
for emerging CFD technology. Under the Integrated Wing Design (IWD) element of the NASA 
https://ntrs.nasa.gov/search.jsp?R=20090013841 2019-08-30T06:29:55+00:00Z
Advanced Subsonic Technology (AST) program, a significant efforl was focused on developing 
the CFD software tools required to do production level C;FiD analysis of 3 0  high-liA systems on 
complete transport configurations. As a result of these efforts, the CFD analysis time associated 
with generating a CFD simulation from geometry to final solution on a complete high-lift 
transpoa configuration was reduced by an order of magnitude. This technology was used 
extensively to analyze the aerodynamic performance of the EBF-powered high-lift 
configuration. 
This paper discusses some of the successes and shortcomings involved in the numerical 
simulation of the complete HWT configuration high-lift configuration using modern Navier- 
Stokes methods. Outstanding issues include facility wall interference effects, jet modeling 
adequacy, and grid density effects. 
Experimental Data and Computational Analysis 
Under the AST-IWD program, extensive high Reynolds number powered test data was 
obtained for the semispan HWT model in the NASA Ames Research Center's 12 Foot Pressure 
Wind Tunnel (PWT) facility. Turbine Powered Simulator (TPS) units were used to simulate the 
engine exhaust flow. Data collected included standard force and moments, and a vast array of 
surface pressure transducer measurements on the fuselage, the main wing, the high lift elements 
(slat, vane, and flap), and winglet. Also, flowfield pressure and temperature measurements were 
obtained using the Boeing Quantitative Wake Survey System (QWSS). An additional test entry, 
designed for TPS calibration, was used to collect jet flow QWSS flowfield data. 
The Chimera overset grid method was employed to discretize the HWT surface and 
volume domain. The OVERFLOW Navier-Stokes flow solver, with multigrid convergence 
acceleration, was used to solve the viscous HWT high-lift flowfield. All computations are fully 
turbulent, and employ the Spalart-Allmaras one-equation turbulence model. The computational 
model of the baseline HWT high-lift configuration at forty degrees flap deflection installed in a 
computational model of the NASA Ames 12 Foot PWT facility is shown in Fig. 1. The HWT 
overset grid system is composed of 153 grids and 35.2 million grid points. The grid model 
contains all geometry detail except the empennage, slat brackets, and vane brackets. 
Figure 1. HWT computational geometry model. 
Baseline HWT High-Lift Configuration Results 
To evaluate the capability of the OVERPLOW code to accurately predict the 
aerodynamic performance of the HWT high-lift configuration, several simulations with and 
without EBF power effects at a range of angle-of-attack were computed. Comparison of the lift 
curve slope between experimental data and CFD simulations is shown in Fig. 2. This data is for 
the baseline vane-flap configuration deflected 40 degrees, with wind tunnel walls modeled in 
both unpowered (cp=0.03) and powered (cp0.5) modes, where cp is the engine thrust coefficient. 
The difference between the experimental and CFD data at each CFD flow condition is given in 
percent. Also, the linear portion of each experimental lift curve has been extrapolated and is 
plotted with black, dashed lines. In general, CFD results compare very well with unpowered test 
data up to Clrnax. However, the powered computational results differ from the experimental 
results. The primary reasons for these differences are thought to come from at least two different 
sources. The first of these is the inaccuracies in the computation of the engine jets. Evidence of 
this is presented below. The second factor is the effect of the wind tunnel test section. In this 
flowfield, the EBF jet exhaust is deflected down due to the presence of the flap, but is forced to 
bend downstream (upward) prematurely at the wall. As a result, the large wall interference effect 
effectively pushes the jet up closer to the flap surface. With more of the jet impinging on the flap 
at higher angles-of-attack in the experiment than is experienced in free-air, the lift increases 
nonlinearly up to stall. This explains the non-linear bending of the powered lift curve at the high, 
pre-stall angles of attack. The computational geometry does include an inviscid, simplified 
model of the wind tunnel test section, but it neglects the effects of viscosity of the test section 
splitter plate and semispan mounting apparatus, and the divergence of the wind tunnel walls. The 
current CFD results predict the trend of the nqn-linear lift curve, but not to the same magnitude 
as found in the experimental results. 
+ Run 612 (CmrsO.03) 
L Run 614 (CrneO.5) 
, Alpha (degrees) 
I\ 
Figure 2. Comparison of'total configuration lift. 
Surface pressures also show good agreement between CFD and test data for the baseline HWT 
configuration at zero degrees angle-of-attack. Figure 3 shows the slat, main wing, vane, and flap 
element surface pressure comparisons between CFD and test data at five spanwise rows of 
pressure taps. For the unpowered case, pressure comparisons between CFD and test data at the 
pressure rows that bracket the engine jet streams are excellent. For the poweied case, however, 
OVERFLOW does not predict the large pressure rise due to the jet exhaust impingement on the 
flap at 34% and 60% span. These differences are attributed not only to wall interference effects, 
but also lack of adequate CFD jet modeling. 
X Location 
(a) Power-off 
X Location 
(b) dower-on 
All prernwetap. L p  h h w l a t ~ .  acd nadle 
IDcatlcnrsre4Ppmxmste 
Figure 3. Comparison of surface pressures, a=O degrees. 
To illustrate the jet modeling capability of the OVERFLOW code, comparisons of QWSS 
jet flowfield data collected during the isolated TPS calibration experiment with Cm) results are 
presented. Fig. 4 shows the computational model and representative OVERFLOW Mach 
contours for the TPS calibration configuration. The CFD model contains 2.6 million points in 32 
grids. Also shown are the three streamwise plane stations where flowfield data was collected. 
Fig. 5 shows the comparison of test data (top) with OVERFLOW computational results (bottom) 
using the S-A turbulence model. The experimental data clearly shows an asymmetric distortion 
of the jet at all three QWSS stations. This is likely caused by flow swirl in the TPS unit, and 
perhaps influenced by the presence of total pressure rakes inside the fan and core ducts. For the 
OVERFLOW simulations, jet boundary conditions are defined as average, radially-constant flow 
without swirl. Even with this approximation, the basic magnitude of the jet flow is modeled well 
with CFD. However, in these cases using the 1-equation S-A turbulence model, the jet stream 
mixing and spreading are underpredicted. Since OVERFLOW does not accurately predict the 
proper spreading of the jet at the HWT flap (very near station 3), there is less jet impingement on 
the flap, resulting in lower total configuration lift relative to test data. 
Figure 4. TPS calibration model grid system and representative OVERn,OW solution. 
. GWSS Plane #l QWSS Plane # 2  . QWSS Plane #3 
lare&t- 6a;redt-  12 amedt&~vz@m 
d c w m s - o f ~  danstiEan0foore drirrstrean of axe 
d t  @.= =it @== &t. @.= 
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'rest mta '&st I)ata mst mta 
MW*.912 . Md=0.901  Mm=O. 846 
I - I h- . 
I I ' . 
. . 
- I. . 
. .  
OVERFLO OVERFLOW 
S-A Model S-A Model 
M - 4 . 9 3 7  
/,', 
,,, , 
m \-Z_. 
VIEW L O O K S  FORWARD 
Figure 5. QWSS Mach number comparisons. 
Nacelle Strake Effectiveness Studies , 
, x1 
In addition to the analysis of the baseline HWT high-lift flowfield, CFD has been used 
with much success to study specific, Petailed aspects of HWT aerodynamic performance. 
Increased understanding of nacelle strak& effectiveness on maximum lift, for example, is critical 
to properly optimize strake size and location. Moreover, determining the computational 
requirements to predict these strake effects is equally as important. For these purposes, the ability 
of Navier-Stokes CFD methods to capture nacelle strake effects was evaluated. 
OVERFLOW solutions at an angle-of-attack near stall were obtained both with all strakes 
on and with all strakes off. Nacelle strakes are designed to increase Clmax' through two flow 
mechanisms. First, nacelle strakes relieve the adverse flow effects at the wing-pylon intersection 
by reducing nacelle upwash. Fig. 6 clears shows the reduction of upwash with strakes on. As a 
result, cross-flow separation on the nacelle near the pylon juncture is reduced (Fig. 7). 
Figure 6. Nacelle surface oilflow. 
Figure 7. OVERFXOW nacelle strake particle traces. 
Second, the presence of the strake vortices provides downwash on the wing upper surface that 
serves to energize the boundary layer. Fig. 8 depicts total pressure contours at two streamwise 
locations on the wing aft of the outboard,nacelle/pylon. For the strake-off configuration, the flow 
tends pull away from the surface. The strake vortices provide downwash that effectively 
eliminates this flow behavior. As a result, the health of the boundary layer is improved, and flow 
separation is delayed. In general, OVERFLOW CFD analysis has greatly increased our 
understanding of the flow physics mechanism associated with how the presence of nacelle 
strakes increases configuration maximum lift. 
X=52.75 Inches X-55.25 Inches 
Outboard 
STRAKE-OFF 
Outbolrd 
STRAKE-ON 
Wake Vortex Studies 
To evaluate the capability of the OVERFLOW code to predict near-field wake vortex 
structure (to ultimately assess vortex alleviation concepts), several CFD simulations for a variety 
of flap configurations were obtained, and compared with QWSS flowfield data collected during 
the HWT model test. The constant streamwise QWSS measurement plane is located 
approximately one tip chord downstream of the wing trailing edge. Fig. 9 shows the Mach 
number contour comparison for the baseline 40 degree vane-flap configuration at a 
representative approach power condition. 
VIEW LOOKING FORWARD 
I I 
I '  
(a) Test data. 
(b) Computation result. 
Figure 9. Comparison of Mach number contours in QWSS wake vortex survey plane. 
In general, the CF'D results and experimental data agree quite well. The distortion of both the 
inboard and outboard engine jet exhaust downstream of the flap is well predicted by 
OVERFLOW. However, due to a significantly greater wall interference effect seen in the test 
data relative to the CF'D simulations, the overall experimental wake flowfield is shifted up 
vertically, so that the jet exhaust stream is closer to the wing. Subsequently, OVERFXOW has 
been used to analyze the wake vortex structure of several alternate flap configurations. These 
alternate flap configurations are designed to minimize wake vortex strength. 
Conclusions 
The OVERFLOW code has been applied to the aerodynamic analysis of the complete 
HWT high-lift configuration. Power-off simulations compare well with experimental data. 
However, power-on simulations underpredict the total configuration lift relative to the test data, 
due to wind tunnel wall interference effects and inadequate turbulence modeling for jet flows. 
Even with these shortcomings, OVERFLOW CFD results have been successfully used to gain 
valuable insights into the flow physics associated with nacelle strake effectiveness and wake 
vortex formation. 
References 
[I] Rogers. S. E., "Progress in High-Lift Aerodynamic Calculations," AIAA Paper 93-0194, 
Jan. 1993. Also published in the Journal of Aircraft, Vol31, No. 6, Nov. 1994, pp 1244- 
1251. 
[2] Cao, H. V. and Kusunose, K., "Grid Generation and Navier-Stokes Analysis for Multi- 
Element Airfoils," AIAA Paper 94-0748, January, 1994. 
131 Cao, H. V., Su, T. Y., and kogers, S. E., "Navier-Stokes Analysis of a 747 High Lift - -
Configuration," AIAA Paper 9812623, July 1998. 
1 


Navier-Stokes Analysis of a High Wing Transport High-Lift Configuration with Externally Blown Flaps

Navier-Stokes Analysis of a High Wing Transport High-Lift Configuration with Externally Blown Flaps

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