Research Paper (Natural-laminar-flow (NLF) airfoil and wing design)

Running head: NATURAL LAMINAR AIRFLOW AIRFOIL 1

NATURAL LAMINAR AIRFLOW AIRFOIL 2

Natural Laminar Airflow and Wing Design

Student’s Name: Ahmed Emam

Institution: ERAU

Course: ASCI 509

Instructor’s Name: Dr. Tony Farina

Date: 11/21/2020

Natural Laminar Airflow Airfoil and Wing Design

Introduction Comment by Dhaval Patel: APA format recommends naming the introduction section as Abstract. Within Abstract include the overview of the paper, body, and conclusion drawn for readers to expect

The natural laminar airflow airfoil is amongst the most recent innovations in the aviation industry. This airfoil design was motivated by the observations made and the ideas generated from the earlier designs. Some of the properties that were included in this design resembled the earlier versions, such as the coefficient of lift range, which was maintained as that of the turbulent flow airfoil. This design was considered effective since it was the solution to the lack of tolerances and surface smoothness in the wings that existed before. The design of these wings was not easy and mainly tried to provide the problems associated with the earlier designs (Sommers & Horstmann, 2017). These challenges included the loss of the laminar flow due to the leading-edge contamination, which happened at some point and therefore resulted in the reduction of the lift coefficient, and this had a dangerous effect since it affected the landing and the take-off processes. At some point, the use of these airfoils led to trim-drag penalties, which was due to nose-down pitching moments. However, the recent innovations have addressed all these issues, and therefore they are reliable, and they are not affected by the challenges that existed in the earlier versions of these airfoils. Comment by Dhaval Patel: Were there other design alternatives studied in the research paper? It would be beneficial to include trade study or analysis of alternative design listed in the research paper to provide context why laminar airflow is optimum design choice

Airfoil Design Objectives

The airfoil design technique is a method that is used in the design of airfoil. In this design process, there are several issues and constraints that should be taken into consideration in order to ensure the design is reliable and efficient. Most of the requirements that should be addressed in the design of the airfoils are the solution to the problems that were experienced in the earlier designs (Holmes et al., 2017). The current design mainly aims at producing an airfoil design which has a lift range similar to that of the NACA 23015 but having lower drag characteristics which are similar to those of NACA 63-215 airfoil. The low profile is desired within the range of CI = 0.1 at R = 9 X 106 (the cruise condition)to CI = 0.6 at R = 4 X 10" (the climb condition). The stick forces and the control forces should also be considered, and they should not be excessive. The main focus of the recent design was to produce a wing that has enhanced natural laminar flow characteristics, as well as one that depicts the understanding of the aerodynamic and geometric features that can lead to the optimization of the wing toward NLF enhancement. Comment by Dhaval Patel: For reader visualization, it would be good to have image of the airfoil mentioned here

Airfoil Design Techniques

The recent natural laminar flow airfoil wing was designed using the EpplerAirfoil Design and Analysis Code. In the recent model design, there were several approaches that were considered, and they relate to the previously used principle. The methodology used to design the wing was based on numerical optimization. The whole design process can be divided into two main components, which are the optimizer and the analyzer. The optimizer controls the scan of the design space, and the analyzer evaluates the performance of a configuration on the optimizer request (Sommers & Horstmann, 2017). This methodology is effective, but it requires numerous computations to come up with numerous optimizer iterations to ensure that all the variables are taken into consideration. The design requirements, constraints, and objectives are defined to ensure that the design fits and addresses all the requirements. The design is evaluated in terms of fitness using 3-D Euler aerodynamic analysis, a 3-D boundary layer computation, and a boundary layer stability analysis. Various tools and chains have been considered effective in the design of the natural laminar airflow airfoil. Comment by Dhaval Patel: For the methodology, can you describe assumptions, constraints and requirements (functional and performance) for the wing design? Comment by Dhaval Patel: For thorough research, can you elaborate on whether there are other tools or techniques used to evaluate performance of the design? Possibly setting up a DOE?

This process flow describes the chains and tools used in the optimization process of the natural laminar airflow airfoil design process. This loop is generated by linking the optimizer, having a mesh generator and an evaluation module, and they exchange information only with each other. The optimizer communicates with the mesh generator through the design variables, and the configuration geometry produced is passed to the evaluation model to be evaluated and returns the values of the constraints and the objectives to the optimizer (Gano & Renaud, 2017). The aerodynamic performance determines the function that gives the fitness of the design in terms of the inviscid drag, transition, and laminar separation location as well as the lift and the pitching moments coefficients. The design also considers the constraints used, and they can be in the form of geometrical nature, which includes the maximum. Other constraints that are well addressed in the design include the lift force, and this can be achieved by considering the variation of a free parameter such as the incidence angle. Comment by Dhaval Patel: I see constraints here, good. Mention assumption, and how the wing design would be validated and verified against requirements

Technique for 3-D Computation and Computation of Stability.

While designing the wing, it is important to consider several essential factors when estimating the laminar-to-turbulent transition on the wing's surface. The designer is supposed to obtain an acceptable compromise that will differentiate between speed and accuracy. It is important to establish the difference between the two since there will be a number of computations to be performed. This approach will use the 3D Euler inviscid method to conduct the boundary layer analysis.

Flowchart of transition prediction on wing by Holmes et al., 2017

Boundary-Layer Stability Analysis

Several tools have been used in order to analyze the stability of the boundary-layer. These tools work based on the local linear stability theory together with the eN method. These tools are considered to be faster and efficient, however, they require many calculations in order to identify the transition location, and the process is very time-consuming and therefore requires much time to execute the process (Holmes et al., 2017). These methods also require the convergence method to give more reliable predictions, which cannot be performed automatically. This method gives results based on the idea to represent the growth rate of unstable disturbances as a function of the boundary layer parameters. This method has the capability of computing the rates of the crossflow waves which are experienced on the wings. Comment by Dhaval Patel: Elaborate on the tools used to conduct 3D analysis. There are tools like Ansys Fluent, Abaqus, can those be used here?

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The representation of local angle on the wing by Prock et al., 2016

The above images show the wing's given point, which gives the local angle between the external streamline and the external streamline (Prock et al., 2016). These coordinates are given as the x, y, and the z-axis. In this coordinate system y is the normal axis to the wall, the x-axis gives the local angle between the external streamline and the chosen direction, and y gives the normal to the wall. The main purpose of developing the database method is in order to get the growth rate while using only one frequency and using the projected Reynolds constant and the two parameters which are: Comment by Dhaval Patel: Good job explaining the graph coherently

Ui = U 2DyiP = yi (dU2D/dy) y = yi Comment by Dhaval Patel: Good use of putting equation in the paper. Recommend using Math equation option in word if you get to it.

From the above formula, yi denotes the distance of the inflection point from the wall. It is also assumed that all the quantities in the equation are dimensionless according to Ue;2D and 1;2D. When considering the two parameters Ui; P, the physical mean boundary-layer Uy, it is expected that at a constant frequency, then the growth rate which is depicted by 2D of the projected profile is fully dependent on the Reynolds number, and two half parabolas exhibit the relationship. These two parabolas are mainly characterized by R0, Rm, R1, and m for, and the results obtained work well, and they have a 10% difference compared to the exact stability results. However, the expression mentioned above does not work efficiently when the frequency is zero.

Choice of Critical N Factor

In this wing's design, it is important to choose a critical factor to be used at transition. However, there is a lot of research done to obtain the best calibrations and the correlations that can be used effectively to give the transition through the eN method in the transonic flows. However, it is evident that no similar data exists, which can be used for the supersonic flows (Prock et al., 2016). Therefore, to investigate the laminar flow on the wing, the N factor should be considered plausible and approximate and should not be considered a precise threshold. Since the ability of the wing to be compressed is minimal because it has a damping factor, then the disturbances on the boundary-layer are stabilized, and the effect is minimized. The most suitable critical factor to consider is 15 since it effectively monitors the transition location on the wing throughout the design process.

The development of the natural laminar airflow airfoil is based on the distribution from which the airfoil is determined. The main factor to consider in the airfoil design is that different parts can be designed separately and then combined with working together or with performing different operations under different conditions (Prock et al., 2016). The velocity gradient over a given segment of the airfoil can be used to attain the desired boundary-development, which enables the laminar flow. This design can be made to adapt to the flow by designing the upper part to sustain laminar flow at the upper corner, and the lower part can as well be manipulated for the lower corner of the laminar bucket, and this will lead to the design of the desired envelope. Comment by Dhaval Patel: Can you look up a graph showing how the distribution is impacted by natural laminar flow?

Theoretical boundary-layer diagram representation by Cebeci, 2015

Advantages

The natural laminar airflow airfoil design has several advantages and has a major impact on the aviation industry. The first aircraft designed to use the airflow airfoils was the North American P-51 Mustang. This wing mostly contributed to the lift of the aircraft, and for an airplane to obtain lift, there are several forces that act on it. Therefore, the airfoil design enables the air to travel over the wing faster than the air that is traveling below it. This, in turn, creates lesser pressure above the airfoil, and therefore, the greater pressure on the lower part of the wing pushes the airplane upwards (Cebeci, 2015). The lift can as well result due to the Coanda effect, which creates differences in the air pressure, and this effect explains why the trailing edge of the airfoil should be sharper as compared to the leading edge and it should also be aimed diagonally downward if it has to be responsible for the creation of lift. Hence, both surfaces provide lift by deflecting the air both downwards and upwards, and the air deflected sticks downwards on the surface of the airfoil. Therefore, the effect of the natural lamina airflow provides the lift more easily without any difficulties and therefore makes the production of the lift to be easier. Comment by Dhaval Patel: What would cause disturbance to the laminar flow? Excellent explanation on the conada effect and how lift is generated, wondering to keep the flow laminar over the wing, are there design consideration accounted to maintain that flow? Does the North American P-51 have that capability?

There are two main types of airfoils, and they have a significant effect on the airplane's movement. The laminar airfoils are advantageous since they make the plane move faster due to the laminar airfoil thickness. The leading edge on the laminar airfoil is also very thin compared to the conventional airfoil, and the leading edge is also more pointed, and its upper surfaces and the lower surfaces are close to being symmetrical (Cebeci, 2015). The increased speed is as well attributed to the 50% chord, which is in the thickest part of the laminar airfoil, and the conventional airfoil is slower since the thickest part is at 25% chord.

Reinventing the wing by Baptiste (2017)

The laminar flow airfoil is also very advantageous since it reduces the drag experienced on the wings and therefore reduces the energy required to go through the air (Wlezien et al., 2015). These wings also experience uniform pressure on the surface due to the wing's camber from the leading edge to the tailing end. The lesser energy required to overcome the drag enables the plane to consume minimal fuel, making it cost-effective. The laminar flow can minimize the drag by up to 10% for an airbus and reduce the fuel consumption by 5% on a range of 1480km. Comment by Dhaval Patel: How cost-effective, can you provide reference to where the number was derived in case missed.

This design of the laminar airfoil gives high levels of surface smoothness on the airplane, making it easier to obtain the tolerances. Therefore, this is advantageous since it enables the airplane to achieve significant levels of performance and therefore, it is reliable.

Disadvantages

The laminar airfoils are, however, disadvantageous since they have high sensitivity levels to bugs and dirt that may be on the surface. These bugs have much impact on the plane's movement since they can alter the smooth flow of the plane and therefore lead to the formation of turbulent flows and, in turn, increase the drag between the plane and the air (Joshi & Tidwell, 2017). The laminar airfoils can as well function well but later on exhibit abrupt changes in the performance, especially when the laminar flow breaks. Therefore, in order to avoid this, most designers opt to have turbulent boundary layers and therefore forgo the efficiency for the sake of having predictable performance characteristics. Comment by Dhaval Patel: Can you provide graphical representation of Cl vs Cd for laminar flow and turbulent flow with a choice of aircraft to visualize the disadvantage

The laminar airfoils' design is also challenging since it is impossible to design a large-scale size of a wing that is smooth enough to attain a laminar airflow and produce a strong wing that is strong enough to sustain the desired effect in the operations of the airline. This process of designing the wings also requires very high levels of accuracy in designing and the assembly process (Joshi & Tidwell, 2017). This is because very small faults such as gaps, edge slats as well as the fasteners may affect the laminar flow and even break the flow. This might reduce the wings' efficiency and increase the drag on the airfoil, leading to an increase in fuel consumption. Comment by Dhaval Patel: Very true. Flush hardware is surely drag reducing elements

The main aim of designing the airfoil using this design was to ensure that the air flows smoothly on the wing's surface. The curvature that was considered as the best is where the leading edge was relatively thin, and the thickness increased progressively (Squire & Young, 2016). The airfoil had a similar curvature both on the upper side and on the lower side. The main aim of this design was to ensure that the adhesion of the boundary layers is maintained. However, if the design had some inclusions on the surface, then the laminar flow would turn into a turbulent flow, affecting the airplane, especially at high speeds. It is therefore important to ensure that the surface roughness of the airfoil is well checked in order to ensure its failure. Comment by Dhaval Patel: Is there a point where flow turns in to turbulent for specific material roughness. The airfoil model with the roughness located at the trailing edge shows minimum drag and maximum lift up to the stall angle compared to the other cases of different roughness locations. Reference https://journals.sagepub.com/doi/10.1260/0309524043028136

While using the laminar airfoils, it is also essential to consider several factors, which increases the cost of maintenance. The laminar flow is only maintained by ensuring that there is a favorable pressure gradient. The laminar airfoils are mainly designed to accommodate adverse pressure gradients on their aft ends, and the favorable pressure gradients vary between 30% to 70% of the chord (Joshi & Tidwell, 2017). Therefore, it is important to ensure that the pressure gradient is established to ensure that the laminar flow is not broken and transited to turbulent flow.

Impact of The Design to The Industry Comment by Dhaval Patel: Editorial Error – move the title to new page

The design of the laminar airfoil has led to a positive impact on the aviation industry. This airfoil has remarkable capabilities, and the laminar flow can easily be controlled in order to ensure that there is no transition to turbulent flow. The boundary-layer is distributed effectively in order to suppress the laminar-turbulent transition. The distributed suction reduces the thickness of the boundary layer and creates a much fuller velocity profile within this layer, thus giving the effect of a favorable pressure gradient (Abbott& Von, 2016). This is an effect that enables the layer to become more stable, and therefore it can withstand the disturbances that might occur in the form of waves. The distributed suction as well as much impact on the Reynolds number as it increases it to a significant amount.

The development of the laminar airfoil has also led to a significant impact in the industry in terms of fuel consumption. This design has enabled the airplanes to consume a lesser amount of fuel compared to the amount that would have been consumed when using the conventional airfoils. Comment by Dhaval Patel: Can you comment on challenges in manufacturing natural laminar flow wings?

Advancements That Could Be Done on the Current Airfoil

Several modifications have been made in order to advance the model and to make it more effective. At the leading edge of the laminar airfoil, there are Krueger flaps, which increase the lift of the plane and protect the leading edge from the impact of the insects when landing or when taking off (Moran, 2016). The advancements have also been experienced in the form of the manufacturing techniques used to produce these airfoils. The laser drilling technique is a useful technique that uses electron beam technology and enables the leading edges to be made smoothly and, therefore, increases the airfoil's efficiency. The laser method uses perforated skins, which makes it easier for the distribution of suction, and this as well increases the efficiency of the airfoil. Comment by Dhaval Patel: Are there other techniques used to reduce drag and maintain laminar flow. What would leading edge airfoil radius?

There is more advancement that is being done on this airfoil where hybrid laminar airfoils are being considered. However, the hybrid Laminar airfoils can only be suitable for the swept-back wing since it cannot maintain laminar flow over these wings using the laminar flow obtained naturally alone. However, there is room for more advancement in the aviation industry. The morphing technology can be considered effective in order to ensure the drag on the laminar airfoil is completely eliminated (Joshi & Tidwell, 2017). This technology will enable the airfoil to change its shape in order to be able to function effectively during conditions such as during take-off and when landing, and this will enable it also to have maximum performance and be highly efficient. However, this modification will only be achieved by deforming the foil to ensure it conforms to all the configurations made to make it suit the given conditions. The laminar airfoils tend to depict reduced drags on the surface as compared to the conventional airfoils; however, they have the highest levels of drag at the angles of attack outside the laminar bucket. Comment by Dhaval Patel: If you can find, data comparing the airfoils would be great. Great job listing the advancement.

Diagram of drag reduction by Joshi & Tidwell, 2017

However, the process of deforming the airfoil is long and time-consuming, but it increases the efficiency of the airfoil with a very big range (Joshi & Tidwell, 2017). The process of deforming will first be done by rotating the leading-edge. The airfoil will be rotated considering the center of rotation as (xr, yr), and the rotational angle will be considered as ծ and the leading-edge point 0; 0 will then be transferred to x0; y0. The deformed leading edge and the baseline airfoil will be connected at (x, xc). If the airfoil has a twin-spar structure, the front spar will be primarily located around xc=c 0:25. The shape of the deformed leading-edge part of the airfoil will be transformed using camber line camber and thickness distributions that are vertical to the camber line. The camber line camber and the half-thickness t will be expressed using the following equations

Ycamber(Z)/c =Y=A +BZ +CZ2 +DZ3 + EZ4 Comment by Dhaval Patel: Great work explaining the equation in detail.

Conceptual design of leading-edge deformation by Joshi & Tidwell, 2017

Conclusion

Therefore, it is evident that the laminar airflow airfoil wing is suitable compared to the conventional airfoils. The laminar airfoils allow for smooth and uninterrupted airflow and thus reduce the drag that is experienced on the surface of the wing. The laminar airfoil and minimizes the energy that the airplane requires to go through the air; therefore, this reduces the amount of fuel consumed by 30%. The design of the laminar airfoil also considers specific techniques that are considered adequate. The laminar airfoil also has several shortcomings since very small defects on the surface can transmit the laminar flow to a turbulent flow and, therefore, affect the airplane's performance. There are also some modifications that can be done to increase the airfoil's ability to reduce the drag effectively. These modifications can be in the form of Krueger flaps or using morphing technology. Therefore, the laminar airfoils are more advantageous, and they have a positive impact on the aviation industry. Comment by Dhaval Patel: Good job backing up the hypothesis with concrete evidence. Comment by Dhaval Patel: Since the laminar flow are sensitive to tiny obstruction against the flow, are the natural laminar flow feasible for high rate production aircrafts? What would be ideal environment for this wing design use case?

References Comment by Dhaval Patel: Confirm if research paper are obtained from online source, include website where it was retrieved.

Abbott, I. H., and Von Doenhoff, A. E. (2017). Theory of Wing Sections Including a Summary of Airfoil data

Cebeci, T., (2015). Modeling and Computation of Boundary-Layer Flows

Gano, S. E., and Renaud, J. E. (2017). Optimized Unmanned Aerial Vehicle with Wing Morphing for Extended Range and Endurance.

Holmes, B, J Obara, C. J., and Yip, L. P. (2017). Natural Laminar Flow Experiments on Modern Airplane Surfaces.

Joshi, S., & Tidwell, Z. (2017). Comparison of Morphing Wing Strategies Based Upon Aircraft Performance Impacts.

Moran, J. (2016). An Introduction to Theoretical and Computational Aerodynamics.

Prock, C., Weisshaar, A., & Crossley, W. (2016). Morphing Airfoil Shape Change Optimization with Minimum Actuator Energy as an Objective.

Somers, D. M., and Horstmann, K. H. (2017). Design of a Medium Speed, Natural-Laminar-Flow Airfoil for Commuter Aircraft Applications.

Squire, B., &Young, D. (2016). The Calculation of the Profile Drag of Aero foils. Aeronautical Research Council. Comment by Dhaval Patel: If there are date in format of month, include the date the article was written or published. Look up the APA reference criteria for exact format

Wlezien, R. W., Horner, G. C., McGowan, A. R., Padula, S. L., Scott, M. A., Silcox, R. J., & Simpson, O. (2015). The Aircraft Morphing Program.