Alexis Lefebvre

Numerical simulation of pitching airfoil performance enhancement using Co-Flow Jet Flow control

The two dimensional flow of an oscillating SC1095 airfoil with Co-Flow Jet (CFJ) flow control is simulated using Unsteady Reynolds Average Navier-Stokes (URANS). A 5th order WENO scheme for the inviscid flux, a 4th order central differencing model for the viscous terms and the one equation Spalart-Allmaras model for the turbulence are used to resolve the flow. The Mach number is 0.3 and Reynolds number is 3.93× 10 at reduced frequency from 0.05 to 0.2. The simulated results for the baseline agree reasonably well with the experiments for no-stall, mild-stall and deep-stall cases. The CFJ pitching airfoil is found to increase the airfoil performance for every flow studied. At Cμ = 0.08 the lift is increased by 32% and the drag is decrease by 80%. Considering only the aerodynamic forces applied on the airfoil and not the pumping power, (L/D)ave for this case reach an outstanding 118.3. When Cμ is increased, the average drag becomes negative, proving the feasibility of a CFJ helicopter blade using its pump as the only source of power. Due to the removal of dynamic stall, CFJ airfoil is able to remove the sharp moment drop at high angle of attack. Nomenclature CFJ Co-flow jet AoA Angle of attack LE Leading Edge TE Trailing Edge ZNMF Zero-net mass-flux S Planform area c Profile chord U Flow velocity q Dynamic pressure 0.5 ρU p Static pressure ρ Air density ω Angular velocity of oscillation ṁ Mass flow M Mach number ∞ Free stream conditions j Jet conditions α0 Mean angle of attack ∗ Graduate Student, AIAA Member † Associate Professor, AIAA Senior Member

Design of High Wing Loading Compact Electric Airplane Utilizing Co-Flow Jet Flow Control

This paper presents a conceptual electric airplane design utilizing Co-Flow Jet (CFJ) flow control. The purpose is to design an aircraft with high wing loading and a compact size so that an airplane can carry more battery and reach a longer range. The CFJ Electric Aircraft (CFJ-EA) mission is to carry 4 passengers at a cruise Mach number of 0.15 with a range of about 300nm. The CFJ-EA cruises at a very high CL of 1.3, which produces a wing loading of 182.3kg/m 2 , about 3 times higher than that of a conventional general aviation airplane. The aerodynamic efficiency including the power consumption of the CFJ pump (L/D)c is excellent with a value of 24 at a low momentum coefficient Cµ of 0.04. Takeoff and landing distances are also reasonable due to a very high maximum CL of 4.8, achieved with a high Cµ of 0.28. The wing is designed to pivot around its 1/4 chord axis so that it can achieve high angle of attack (AoA) without rotating the fuselage. A measure of merit defined as PMS=Passengers*Miles/S is introduced, where S is the wing planform area. The PMS of the present EA design is close to that of a conventional reciprocating engine general aviation airplane, and is 2.3 to 3.8 times greater than the PMS of the state of the art EA. The design results suggest that the CFJ-EA has a far greater range than a same size EA using a conventional wing design. Or for the same range, the CFJ-EA has a much smaller size than a conventional design. This design is the first trail with no systematic design optimization. The CFJ-EA concept may open the door to a new class of general aviation EA designs. The same CFJ flow control technology can also be used for other general aviation airplanes with conventional propulsion systems and for high altitude airplanes to reduce size.

Low Drag Automotive Mirrors Using Passive Jet Flow Control

With the increasing public concern on the global environment, reducing fuel consumption and emission pollution becomes more and more pressing. Automotive vehicles consuming fossil fuel is one of the major sources of greenhouse gas emission. Small and light cars become popular for their low fuel consumption. The appearance of electric cars is the consequence of this global trend to push clean technology. Due to the low power density of the current battery technology, the electric cars also tend to be made with small size and weight. With the decreasing car size and weight, wind noise becomes more annoying for the people inside the vehicle. Listening high resolution music on highway driving becomes more difficult. For heavy load trucks of long distance transportation, fossil fuel may remain as the major energy source in a foreseeable future due to its high energy density.

Experimental Investigations of Vehicle Base Drag Reduction Using Passive Jet Boat-Tail Flow Control

This study is focused on the detailed experimental investigation of jet boat-tail (JBT) passive flow control bluff body models to reduce the base pressure drag. The JBT technique is employed through an open inlet at the leading edge of the bluff body along with a circumferential jet at the trailing edge in order to energize the base flow using the high kinetic energy flow from freestream. As a consequence, entrainment of the main flow into base flow region is initiated earlier downstream. A reduction in the turbulent fluctuation of the wake can be observed in addition to a decrease of the recirculation region velocity. Using 2D/3C Particle Image Velocimetry (PIV), two models with different inlet sizes are tested. The large flow rate model is designed with an inlet area 4.7 times greater than the other JBT prototype. The wind tunnel experimental results show a substantial reduction in the wake width and depth for the two models, which indicates a significant drag reduction. Moreover, mean velocity vector plots from PIV measurements at the mid-plane location suggest their flow fields differ significantly due to the nature of the passive jets employed. The Jet1 model initiates the large coherent structures and flow entrainment earlier than the baseline model even though the jet momentum is small. The Jet2 generates paired vortices in the shear layer due to the high jet momentum and entrain main flow to the base region. The experimentation is performed at a Reynolds number of Re = 2.55×105. In order to investigate the effects at higher Reynolds numbers, Computational Fluid Dynamics (CFD) is used to model the flows using Large Eddy Simulation, which shows that the drag reduction is more effective at high Reynolds number.

Performance of a Co-Flow Jet Airfoil with Variation of Mach Number

This paper conducts numerical investigations for a 15% thickness Co-Flow Jet (CFJ) airfoil performance enhancement, which includes the variation of lift, drag, and energy expenditure at Mach number 0.03, 0.3, and 0.4 with jet momentum coefficient Cμ = 0.08. The angle of attack(AoA) varies from 0 ◦ to 30. Two-dimensional simulation is conducted using a Reynolds-averaged Navier-Stokes (RANS) solver. A 5th order WENO scheme for the inviscid flux and a 4th order central differencing for the viscous terms are used to resolve the the Navier-Stokes equations. Turbulence is simulated with the one equation Spalart-Allmaras model. The study shows that at constant Cμ, the maximum lift coefficient is increased with the increasing Mach number due to the compressibility effect. However, at M=0.4, the airfoil stalls with slightly lower AoA due to the appearance of strong λ shock wave that interrupts the jet and trigger boundary layer separation. The drag coefficients vary less with the Mach number, but is substantially increased at Mach 0.4 when the AoA is high due to shock wave-boundary layer interaction and wave drag. The power coefficient is decreased when the Mach number is increased from 0.03 to 0.3. This is again due to the compressibility effect that generates stronger low pressure suction effect at airfoil leading edge, which makes the CFJ pumping easier and require less power. For the same reason of shock appearance at M=0.4 when the AoA is high, the power coefficient is significantly increased due to large entropy increase. Overall, the numerical simulation indicates that the CFJ airfoil is very effective to enhance lift, reduce drag, and increase stall margin with high Mach number up to 0.4 at low energy expenditure.

Co-flow jet airfoil trade study part II: Moment and drag

This paper is Part II of a parametric study on CFJ airfoils. In the first part of the paper, the CFJ airfoil suction surface shape is modified to reduce or overcome the nose-down moment. In the second part of the paper, the injection and suction sizes and Cµ are varied to increase the CFJ airfoil thrust generation. For both parts, the resulting effects on the lift, drag, moment and energy consumption is analyzed. The two dimensional flow is simulated using steady and unsteady Reynolds Average Navier-Stokes (RANS). A 5th order WENO scheme for the inviscid flux, a 4th order central differencing model for the viscous terms and the one equation SpalartAllmaras model for the turbulence are used to resolve the flow. The Mach number is 0.15 and Reynolds number is 6.4 × 10 6 . The nose-down moment of the CFJ airfoils was successfully reduced with the use of reflex camber while negative drag was achieved with a thinner airfoil, and a reduced injection size. Increasing Cµ further reduces the drag, but at the cost of a much higher energy consumption and reduced corrected aerodynamic efficiency. The minimum drag achieved isCD = 0.033 and the highest moment achieved is CM = 0.031.

Mixing Mechanism of a Discrete Co-Flow Jet Airfoil

The flow mechanism leading to the enhanced performance of a discrete co-flow jet (dCFJ) airfoil is investigated. Flow visualization and DPIV are used to analyze the difference between the flow along discrete jets and over the tabs used for discretization of the slot jet. Results show that the entrainment is uniform over the leading jet as long as the tab size is small enough. The jets expand spanwise, inducing downward momentum toward the surface of the airfoil. Combined with the momentum increase due to the CFJ, the dCFJ is shown to dramatically increase lift up to 150% from the baseline airfoil and delay separation up to 10 o angle of attack. More results and analysis will be presented in the final paper.

Pitching Airfoil Performance Enhancement Using Co-Flow Jet Flow Control at High Mach Number

Pitching airfoils with Co-Flow Jet (CFJ) flow control are simulated using Unsteady Reynolds Average Navier-Stokes (URANS) at Mach number 0.4 with reduced frequency of 0.1. The flow is transonic with shock wave boundary layer interaction. A 5th order WENO scheme for the inviscid flux, a 4th order central differencing model for the viscous terms and the one equation SpalartAllmaras model for the turbulence are used to resolve the flow. The airfoil oscillate around its mean AoA of 10 ◦ with amplitude of 5 ◦ , 7.5 ◦ and 10 ◦ . The study demonstrates that the CFJ pitching airfoil is very effective to remove dynamic stall at high Mach number of 0.4. The performance is significantly enhanced with radically increased lift, reduced drag, and decreased moment variation.

Trade study of 3D co-flow jet wing for cruise and takeoff/landing performance

This paper presents a trade study of co-flow jet (CFJ) flow control wings. Several geometry parameters are studied, including injection and suction locations, cavity configurations, airfoil thickness and wing aspect ratio. The simulations are performed at Mach number 0.10 and 0.15 to simulate the takeoff/landing, and cruise condition of a general aviation aircraft. Unlike the conventional flaps and slats systems or other active flow control techniques, CFJ wings contains no moving part and can be used for both cruise and takeoff/landing. A low Cμ with low energy expenditure can be used at cruise and high Cμ with very high lift can be used for takeoff/landing. At cruise, the CFJ wing with a 21% thickness achieves a maximum aerodynamic L/D of 38.8 at a remarkably high CL of 1.22. When the CFJ pumping power P is taken into account, the corrected aerodynamic efficiency defined as L/(D + P/V∞) is 25.2 at AoA = 5 ◦ and Cμ of 0.04. The takeoff/landing performance is also excellent with a maximum CL of 4.7 achieved at Cμ of 0.28 and AoA of 40.0◦. For both cruise and takeoff/landing, the CFJ wing moment is low and hence small tail force is needed for trimming purpose. CFJ is particularly advantageous to be used with thick airfoil such as 21% to achieve high cruise lift coefficient and high aerodynamic efficiency. For the 21% thickness airfoil, the CFJ wing has a drop of peak aerodynamic efficiency of 5.5%, but has the lift coefficient increase by 110%. A thick airfoil also provides higher structure strength, lighter weight, and more inner volume. This study demonstrates that the CFJ airfoil is not only very effective to drastically increase the maximum lift, but also able to achieve high aerodynamic efficiency with very high lift at cruise condition at a small angle of attack due to its low energy expenditure. Overall the CFJ wing is particularly suitable for a light and compact wing with ultra-high wing loading and high efficiency. The extraordinary CFJ wing performance may bring a radically different design philosophy to revolutionize the future aircraft design. The CFJ wing will open a door to a new class of aircraft design.

Parametric trade study for supersonic bi-directional flying wing

This paper conducts a parametric trade study to establish and understand the relationship between the sonic boom/aerodynamic efficiency and the design parameters for supersonic bi-directional flying wing(SBiDir-FW). The mission requirements for this supersonic plane include the cruise Mach number of 1.6, range of 4000 nm, payload of 100 passenger and flight altitude of 50k ft. An advanced geometry model is employed to construct the SBiDir-FW configurations. The geometry model can freely vary airfoil meanline angle distribution to control the expansion and shock waves on the airplane surface in order to mitigate sonic boom and improve aerodynamic efficiency. The trade study has several very important findings: 1) The far field ground sonic boom signature is directly related to the smoothness of the wave distribution on the airplane surface. The meanline angle distribution is a very effective control methodology to mitigate surface shock and expansion wave strength, and mitigate compression wave coalescing by achieving smooth loading distribution chord-wise. Compared with a linear meanline angle distribution, a design using non-monotonic meanline angle distribution with reversed cambering in the mid-chord region is able to reduce the sonic boom ground loudness by over 20PLdB. 2) Decreasing sweep angle within the Mach cone will increase L/D as well as sonic boom. A design with variable sweep from 84◦ at the very leading edge to 68◦ at the tip achieves a very high L/D of 10.4 at Mach number 1.6 due to the low wave drag. If no sonic boom constraint is considered, the L/D can be further increased. 3) The round leading edge and trailing edge under high sweep angle are beneficial to improve aerodynamic performance, sonic boom, and to increase volume of the airplane. The qualitative and quantitative findings in this paper give better understanding of physics and provide the path to achieve the ultimate high performance design. The final ∗ Ph.D. Candidate † Ph.D. Candidate ‡ Ph.D. Candidate § Professor, AIAA Associate Fellow 1 D ow nl oa de d by G ec he ng Z ha o n Ju ly 1 5, 2 01 4 | h ttp :// ar c. ai aa .o rg | D O I: 1 0. 25 14 /6 .2 01 421 06 32nd AIAA Applied Aerodynamics Conference 16-20 June 2014, Atlanta, GA AIAA 2014-2106 Copyright