Comparative Analysis of Aerodynamic Lift and Drag of Commercially Used Air-foil Incorporated with Co-flow Jet

In this research, a baseline airfoil is modified by incorporating a Co-flow Jet into the airfoil. Co-flow jet is also called zero net mass flux as the same amount of highly pressurized air is injected towards the streamlines of an airfoil from the leading edge and sucks this air without changing the amount in the trailing edge using an air pump. A performance boost is expected for the use of the Co-flow Jet. An airplane’s performance is based on a few parameters such as the coefficient of lift, coefficient of drag, boundary layer separation, and many others. In this research, a comparative analysis is run between a baseline airfoil and a CFJ airfoil. NACA-4412 is chosen as the target airfoil. The research shows how the incorporation of CFJ in an airfoil increases the coefficient of lift (CL) and decreases the coefficient of drag (CD). Thus, it is possible to maintain a better CL/CL ratio by using CFJ. The research also mentions the increase in stall angle due to the use of CFJ. It is a computational analysis performed in the software Ansys. For simplicity, the analysis is limited to two-dimensional analysis. This research may bring a better improvement in the aircraft and aerodynamic sectors. Though the results obtained from the research may not fully be similar to the hypothesis, it has been tried to maintain that the results of the simulation hardly differ from the theoretical analysis.


Introduction
The airfoil constitutes a pivotal and indispensable component of aircraft wings, serving as the fundamental structure responsible for generating lift as it interacts with the surrounding air.Its meticulously crafted curved surfaces are designed to achieve an optimal lift-to-drag ratio, thereby imparting superior performance characteristics to the aircraft.As the primary source of lift production, the airfoil's efficiency significantly influences the overall performance of the aircraft, making an enhanced lift-to-drag ratio a crucial aspect of aeronautical engineering.The generation of drag, attributed to boundary layer separation, poses a prominent challenge in aviation.This phenomenon arises due to adverse pressure gradients encountered during airflow expansion, leading to the formation of extended regions of separated flow.Consequently, a reverse flow, commonly known as backflow, becomes prevalent.The most critical juncture in this process occurs when the aircraft surpasses the critical angle of attack, resulting in an abrupt increase in drag.This pivotal angle is commonly referred to as the stall angle.Effectively overcoming the stall angle and reducing backflow becomes imperative to achieve optimal aerodynamic performance, particularly at higher angles of attack.To address this challenge, this research 1305 (2024) 012009 IOP Publishing doi:10.1088/1757-899X/1305/1/012009 2 endeavors to implement a Co-Flow jet within the widely used NACA 4412 airfoil.The introduction of the Co-Flow jet aims to elevate lift production, extend the stall angle, and mitigate backflow phenomena, ultimately leading to a significantly improved lift-to-drag ratio.This paper seeks to investigate the effects of the Co-Flow jet on the NACA 4412 airfoil's aerodynamic performance, with a specific emphasis on lift enhancement and drag reduction at greater angles of attack.The comprehensive analysis and experimental validation presented herein endeavor to establish the efficacy of this innovative approach in augmenting the airfoil's aerodynamic capabilities.By shedding light on the potential advantages of Co-Flow jet induction, this research contributes to the advancement of airfoil design and optimization techniques, thereby promising to revolutionize aeronautical engineering.The envisioned superior lift-to-drag ratio at higher angles of attack holds significant implications for enhancing aircraft efficiency and performance, thereby propelling the future of aviation technology.

Background
Aircraft performance enhancement has been an interesting research topic for many decades to the researchers.Normally an airfoil produces a lift force when it moves relative to air.This lift force makes an airplane fly.Techniques of increasing lift force are 1) high speed by increasing thrust in the engine, 2) high angle of attack, 3) use of flap & slat, and 4) decreasing drag force.By using four of them an airplane starts to take off.Usually, 15 15-degree angle of attack is used to take off.As long as the engine's thrust is more than the drag, the speed of the airplane will keep on increasing.The greater the speed, the higher will be the lift force.This causes the airplane to go up.There won't be any acceleration or change in altitude when the airplane reaches level flight.In this case, the thrust should be exactly equal to the drag force and the lift should be exactly equal to the weight of the airplane.For landing, pilots decrease the engine's thrust and keep the nose of the airplane down.It is the opposite of the climb operation.Reverse thrust and low speed make the airplane stop.This research aims to maintain the lift when an aircraft takes off.There are some drawbacks and that's why some flow control methods are used.CFJ is one of them.It generates greater lift comparatively than others and less drag by increasing the stall angle.In this analysis, CFJ is induced in NACA 4412 airfoil and it is simulated in CFD simulation.This analysis makes a more efficient lift-producing airfoil rather than reducing the drag coefficient.CFJ or co-flow jet is used in flow control methods which has an injection slot in the leading edge and suction in the trailing edge.It is called zero net mass flux (ZNMF) because a high-energy jet is injected tangentially through an injection slot in the leading edge and goes through an air pump to the suction port without any loss in mass flow, the same amount of fluid is sucked by the suction in trailing edge.This configuration demonstrates the better lift coefficient by inducing in NACA 4412 airfoil.

Problem Statement
The wing is the main portion of the aircraft which helps in the takeoff, landing, cruise position, and stall speed, increasing the aerodynamic efficiency of the flight.When a wing is generating lift, the upper surface of the wing has reduced pressure and the lower surface gets an increased pressure.This increased pressure with a lower velocity than the upper surface higher velocity remains the aircraft fly.But besides lift force, drag force is also produced due to aerodynamic force and wingtip vortices.And that is the major problem of an aircraft flying.This research is about reducing the coefficient of drag and enhancing the coefficient of lift of commercially used airfoil NACA 4412 at different angles of attack to get a better stall margin.This can be done by reducing the boundary layer separation that minimizes the backflow of the airfoil.In an airfoil, drag and lift both increase with the increase of the angle of attack.At a certain angle of attack, the drag suddenly increases very high and the lift begins to decrease.This angle is called the stall angle or critical angle of attack.This is because the adverse pressure gradient increases and thus the boundary line separation increases.In that case, by using CFJ we can reduce the drag and increase the lift of the CFJ airfoil by increasing the stall angle that prevents the boundary layer separation compared to the basic airfoil.
In this analysis, 2D airfoil simulation is chosen instead of 3D because of its simplicity.For this reason, here both pressure drag and skin friction drag are considered.Pressure drag or form drag is part of the air resistance that is created due to the size and shape of the airfoil.It increases with the square of the airspeed.The skin friction drag arises from the frictional forces that exist between the airfoil body and the air through which it is moving.It increases with the surface area of the airfoil and the square of the airspeed.But there wasn't considered the lift-induced drag or wave drag because they are applicable to the 3D airfoil.Wave drag is mainly produced in transonic and supersonic flow due to the presence of shock waves.Here we only simulated the subsonic flow.And the highest velocity experimented with was 70 m/s.So, the Mach Number obtained from the calculation is 0.21084 which is less than 1.

Objectives
• To show the comparative performance analysis of the CFJ airfoil with the conventional NACA 4412 airfoil.• To determine the CL/CD ratio with different angles and velocities.
• To investigate the performance enhancements in terms of CL, CD, and boundary layer separation.

Geometry of Co-Flow Jet
Yan Ren and Gecheng Zha describe the suction and injection ducts are mathematically modeled as a super ellipse.The duct inlet and outlet have different shapes.The inlet of the suction duct and outlet of the injection duct has a rectangular shape, whereas the outlet of the suction duct and inlet of the injection duct has a circular shape.The diameter of the injection port is smaller than the diameter of the suction port.The ports are designed to provide enough velocity heads in the injection port, maintaining the continuity equation.[2] Baibhav Tilak and Professor T.K. Jindal researched the positioning of the suction and injection port.They have discovered setting the injection port at the maximum thickness of the airfoil gives the best performance of the co-flow jet airfoil.The maximum performance includes better lift augmentation, higher stall angle, and reduction of drag.[5] 2.2 Velocity of Suction and Injection V. Yamini Anoosha, Dr. Dilip. A. Shah, and R. Murali researched the ratio of the suction velocity of CFJ to the free stream velocity.They have introduced a dimensionless factor , which is the ratio of suction velocity to the free stream velocity.The research results that, the best performance of the coflow can be obtained when >1.[4] Yan Ren and Gecheng Zha also describe the mass conservation of co-flow jets.The rate of mass of air sucked in by the suction port is equal to the rate of mass injected from the injection port.The suction velocity is significantly lower than the injection velocity.According to the velocity of injection and suction, the diameter of the suction and injection port is set taking mass conservation under consideration.[2] 2.3 Computational Analysis Ge-Cheng Zha, Wei Gao, and Craig D. Paxton run computational analysis on NACA 0025 using the coflow jet.The name convention of CFJ is very important to build a CFJ geometry.The grid meshing is shown for the CFJ0025-065-000 and CFJ0025-065-196.By the process of meshing, ideas are generated to mesh our NACA 4412.[6] 2.4 Free-Stream Conditions R. Abinav, Nandu R. Nair, P. Sravan, Pradeesh Kumar, and S. R. Nagaraja conducted some experiments on NACA 6409 CFJ in different Mach numbers.The research shows that, the less the free stream Mach number, the better the L/D ratio.Again, a higher free-stream Mach number provides a higher stall angle and less L/D ratio.[1]

Research Methodology
The research is about the comparative analysis of aerodynamic properties between baseline NACA 4412, and CFJ NACA 4412.The main target of the research is to find out the performance enhancement of NACA 4412 by modifying it with a co-flow jet.We use a 2D computational approach to verify the characteristics.We will not consider 3D airfoil for this purpose.So, there will be a slight difference in the practical result.

Geometry
Both 3D and 2D geometry are built to understand the shape properly.But during simulation, only 2D geometry is used.The 3D Geometry of the actual co-flow jet was built to show the actual shape of CFJ NACA 4412.It is not taken into consideration during analysis.Only the 2D geometry is taken under consideration during analysis.The slotted portion of the Co-flow jet has been designed following the naming convention.Our chord length is 1 meter.By making the ratio, we can get the size of the suction port, and injection port.The size of the suction port, and injection port plays a vital role in CFJ airfoils.The suction port is bigger than the injection port.If we consider the continuity equation, the velocity of air at the suction port is significantly lower than at the injection port.Still, we make sure the velocity of air at the injection port doesn't reach the supersonic MACH number.The position of the injection port is very important.It is found that, for the best performance of CFJ, the injection port is to be set at the maximum thickness of the airfoil.Applying the concept of NACA 4412, we have found that the maximum thickness of NACA 4412 is 12% of the chord length.Also, the location of maximum thickness is found at its maximum camber.By locating the points, we can get the maximum camber.[8] Similar split line features are used in the CFJ airfoil geometry.They are done for meshing simplicity.
Here the whole geometry is split into 8 sections.

Setup and Boundary Conditions
The model, and the environment are complete.After this, we had to define different considerations, assumptions, and states to Ansys to simulate the whole thing.Our research is limited to 2D computational fluid model analysis.So, we have chosen only the fluid model, and boundary conditions.The Spalart-Allmaras model has been chosen for the analysis.It is described in the overview section.
• Model = Viscous (Spalart-Allmaras 1 equation model) No-Slip Wall As our free-stream velocity is 43.9 m/s, we assume that there is a stationary airfoil wall cross-section.The air is flowing through the cross-section with a velocity of 43.9 m/s.The velocity-specified method is chosen for both magnitude and direction.The magnitude of the velocity is 43.9 m/s.The direction of the free-stream air can be defined by the x, and y components.As the analysis is a 2D analysis, there will be no velocity component for the z-axis.If the angle of attack is denoted as .The directions of the flow of injection, and suction is defined by Normal to the boundary.So, the flow direction is perpendicular to the axis of suction, and injection boundaries.The negative sign in the suction velocity shows that the flow is going inside the suction port.

Mesh Sensitivity for Baseline NACA 4412 Model
A series of Iterations has run to the baseline NACA 4412 model at an angle of attack 13 degrees using various numbers of mesh elements (from 98210 to 800600).A slight increase in CL and a slight decrease in CD can be noticed with each incremental step of mesh size.However, after simulating the model in element number 338390, the difference in results -by a gradual increase in mesh size -has shown a significant decrease (less than 1%).Thus, an element size of 338390 can be considered as the optimal mesh size for the model.All of the simulations of the baseline airfoil have been performed in 338390 elements mesh.

Mesh Sensitivity for Co-Flow Jet NACA 4412 Model
A series of Iterations has run to Co-Flow Jet NACA 4412 model at an angle of attack of 13 degrees using various numbers of mesh elements (from 69650 to 6244525).Unlike baseline airfoil, A slight increase in CL and a slight decrease in CD can be noticed by each incremental step of mesh size.However, after simulating the model in element number 400680, the difference in results -by a gradual increase in mesh size -has shown a significant decrease (less than 1%).Thus, an element size of 400680 can be considered as the optimal mesh size for the model.All of the simulations of the CFJ airfoil have been performed in 400680 elements mesh.

Comparison of Base Line Airfoil Model with Official NACA 4412 Data
A series of iterations run to the baseline airfoil model.The CL vs. AOA and CL vs. CD curve is generated from the data in different free-stream velocities.The curves are compared to the official data of NACA 4412.The similarities between our computational data from CFD and the official data from NACA are visible in the following graphs.The official data of NACA 4412 is experimented in a large range of angles of attack.The computational data generated by us is matched according to our used range.[7]

Decreasing of CD by the Use of Co-Flow Jet
For 0° angle of attack, it gives a coefficient of drag of 0.1078.It keeps rising exponentially with the increase of the angle of attack.The stall angle is at 15.5° and this, the CD is 0.0499.After the stall angle, the CD keeps increasing even more drastically.The values of CD from both the baseline airfoil and the CFJ-incorporated airfoil are plotted against AOA on the same graph and shown below.This is the turning point as the value of CD is decreased by 5-15% in the CFJ incorporated airfoil compared to the baseline airfoil.This helps because, if CD also increased just as much as CL increased, then the point of incorporating would have been useless.As the CD dropped down for every specific AOA, it proves that the CFJ is successfully working to redirect the backflows into smooth forward flows.

Enhancement of CL by the Use of Co-Flow Jet
For angles of attack ranging from 0° to 20°, simulations were completed and data were extracted.For 0° angle of attack, it gives a coefficient of lift of 0.4454.It keeps rising with the increase of the angle of attack up to the stall angle.The stall angle is at 15.5° and this, the CL is 1.743755839.After the stall angle, the CL keeps decreasing drastically.The values of CL from both the baseline airfoil and the CFJ-incorporated airfoil are plotted against AOA on the same graph and shown below.The results are phenomenal and as expected.The stall angle increased significantly from 15.5° on the baseline airfoil to 25° on the CFJ-incorporated airfoil.This also means, the highest CL is increased.Therefore, for 25° AOA of the CFJ incorporated airfoil, the highest CL is achieved and that is 3.68.

Comparison of Boundary Layer Separation between Baseline Airfoil and CFJ Incorpoted Airfoil
The boundary layer separation in this is noticeably far away from the upper surface of the airfoil.It can be observed by following the separation line of green and blue indicated velocities.It means, it has a lot more flow being generated into the vortex.But the formation of a vortex occurs due to the 'Adverse Pressure Gradient' which ultimately yields a lot of Drag force.That is why the coefficient of drag (CD) is generated in the baseline airfoil.As a bonus observation of this simulation, it can be noticed that the velocity of wind right above the upper surface of the leading edge is much higher than any region of the airfoil.According to the basic aerodynamics of an airfoil, it happens due to the shape of the airfoil.This higher velocity in this region gives out less pressure than the lower surface according to Bernoulli's equation as mentioned previously.This ultimately generates the lift force.The more this is, the more coefficient of lift (CL) is generated.

Figure 12: Velocity contour of Baseline airfoil
The velocity contour of the CFJ airfoil is generated following the same method.Analyzing this gives the easiest understanding of how the CFJ is assisting to reduce drag and thereafter increase lift.Two main additions to the geometry of the CFJ are the suction port and the injection port.The suction port is sucking air in at 63.66 m/s which is higher than the free stream velocity of 43.9 m/s.This is indicated by the green portion near the suction port.The injection port is injecting air out at 340 m/s.This is indicated by the red portion right after the injection port.Red indicates the highest velocity here, which is only observed at the injection port.
As the air pump sucks air in through the suction port, it creates an addition of velocity magnitude to the air which is near the wall.The air in this region is normally subjected to adverse pressure gradients.However, this gradient can be minimized by adding the flow of air to the desired direction.This is why, the flow near the wall which would have normally formed vortices, is now using that extra velocity magnitude to flow smoothly even when they are near the wall.The viscous effect is still there, but it is affecting them a lot less because of the added velocity magnitude.
Comparing this to the contour of the baseline airfoil, it can be seen that the region over which adverse pressure is active, or the region where the vortices are formed, is much smaller in the CFJ-incorporated airfoil.Thus the simulation shows the effect of CFJ. 12

Conclusion
• From comparative analysis between baseline airfoil NACA 4412 and Co-flow Jet injected airfoil CFJ 4412-196-010, it can be seen that the boundary layer separation is reduced for using the coflow jet.According to velocity contour, backflow is reduced with the increase of angle of attack and velocity and decrease of boundary layer separation for using the co-flow jet.• Co-flow jet airfoil can reduce the drag and convert the streamlined vortices into usable thrust that increases the efficiency of an aircraft.From the coefficient of lift (CL) and drag (CD) graph, it is seen that the lift coefficient is increased by 60-90% and the drag coefficient is decreased by 20-30% after using the co-flow jet.So, the ratio of lift to drag coefficient (CL/CD) increases which reduces the required thrust.And the performance of the aircraft is enhanced.• For baseline NACA 4412 airfoils, the stall angle is found 15.5° whereas in co-flow jet injected airfoils, it is found about 24°.So, the stall angle increases with the increase of the angle of attack, and for this higher lift can be gained.• Above all, this comparative analysis discusses the enhancement of the aircraft performance and gives a better understanding of the co-flow jet airfoil which enhances the efficiency of the airfoil wing.

Figure 1 :
Figure 1: L/D Ratio with Free Stream Mach Number

Figure 4 :
Figure 4: Geometry of the Baseline NACA 4412 Airfoil in Ansys Workbench

Figure 6 :
Figure 6: 2D Geometry of the CFJ NACA 4412 Airfoil putting the values of d, we can determine the injection velocity.

Figure 8 :Figure 9 :
Figure 8: Validation of the baseline NACA 4412 model comparing CL vs. AOA curve

Figure 10 :
Figure 10: Comparison of CD vs AOA in Baseline airfoil and CFJ incorporated airfoil

Figure 11 :
Figure 11: Comparison of CL vs AOA in Baseline airfoil and CFJ incorporated airfoil

Figure 13 :
Figure 13: Velocity contour of CFJ airfoil5.4Comparison of CL vs. CD between Baseline Airfoil and CFJ AirfoilThe values of CL/CD from both the baseline airfoil and the CFJ incorporated airfoil are plotted against AOA on the same graph and shown below.

Figure 14 :
Figure 14: Comparison of CL/CD vs AOA in Baseline airfoil and CFJ incorporated airfoil

Table 1 :
Simulation of Baseline naca 4412 at a 13-degree angle of attack in various mesh size

Table 2 :
Simulation of cfj naca 4412 at a 13-degree angle of attack in various mesh size