Overview
Experimental Investigation of Pressure Analysis on NACA 2418 Airfoil Across Varying Angles of Attack. The Cooper Union needed to develop a method for analyzing airfoil data for numerous related projects across the mechanical engineering department.
I designed, manufactured, and testing an airfoil rig to measure pressures on a NACA 2418 airfoil. This rig continues to be used by students today (2024) for preliminary data for engineering principles, aerodynamics, and capstone classes.
Overview
Experimental Investigation of Pressure Analysis on NACA 2418 Airfoil Across Varying Angles of Attack. The Cooper Union needed to develop a method for analyzing airfoil data for numerous related projects across the mechanical engineering department.
I designed, manufactured, and testing an airfoil rig to measure pressures on a NACA 2418 airfoil. This rig continues to be used by students today (2024) for preliminary data for engineering principles, aerodynamics, and capstone classes.
Overview
Experimental Investigation of Pressure Analysis on NACA 2418 Airfoil Across Varying Angles of Attack. The Cooper Union needed to develop a method for analyzing airfoil data for numerous related projects across the mechanical engineering department.
I designed, manufactured, and testing an airfoil rig to measure pressures on a NACA 2418 airfoil. This rig continues to be used by students today (2024) for preliminary data for engineering principles, aerodynamics, and capstone classes.
Motivations
This project aimed to experimentally determine the pressure distributions over the NACA 2418 which is a low-camber airfoil.
A test airfoil was designed to have six pressure taps on the top surface that are collinear with six pressure taps on the bottom surface. Measurements were taken in the AEROLAB Educational Wind Tunnel set to 40 miles per hour with the airfoil angled at 0°-12°. A custom manometer setup was manufactured to measure the pressure at three points on the airfoil.
Increasing the angle of attack resulted in increased pressure differentials between the top and bottom surfaces. The lift force was determined from the observed pressure differentials. Increasing the angle of attack increased the pressure differentials and the lift force.
Motivations
This project aimed to experimentally determine the pressure distributions over the NACA 2418 which is a low-camber airfoil.
A test airfoil was designed to have six pressure taps on the top surface that are collinear with six pressure taps on the bottom surface. Measurements were taken in the AEROLAB Educational Wind Tunnel set to 40 miles per hour with the airfoil angled at 0°-12°. A custom manometer setup was manufactured to measure the pressure at three points on the airfoil.
Increasing the angle of attack resulted in increased pressure differentials between the top and bottom surfaces. The lift force was determined from the observed pressure differentials. Increasing the angle of attack increased the pressure differentials and the lift force.
Principles
The shape of an airfoil lends itself to aerodynamic favorability because it uses the pressure differential across its surfaces to generate lift. Lift is the force of the pressure differential that acts on the surface area of the airfoil.
The lift of an airfoil is defined as the sum of the products of the pressure and the surface area in the normal direction across a closed surface (Anderson, 2017).
For thin airfoils such as the NACA2418, a small angle approximation can be made for angle of attacks 0° to 12°. For small angle angles of attack, lift is directly proportional to angle of attack (Anderson, 2017). As the air flows across the airfoil, it sticks to the surface due to skin friction and creates a boundary layer. Varying the angle of attack changes the boundary layer region and flow separation may be observed. Once the flow of the air is detached from the upper surface of the airfoil, the pressure differential no longer exists resulting in a stall velocity. An airfoil at stall velocity (which is also at the critical angle of attack) no longer experiences lift.
Manufacturing
The final design of the airfoil was produced using 3D printed PLA. The NACA2418 airfoil was traced in Solidworks. Three sets of two pressure taps were made on the top and bottom surfaces of the airfoil. The pressure taps are cut from the airfoil such that the pressure taps on the top and bottom surfaces are collinear and normal to the surfaces as noted in Figure 4. The pressure taps are highlighted in blue.
Manufacturing
The final design of the airfoil was produced using 3D printed PLA. The NACA2418 airfoil was traced in Solidworks. Three sets of two pressure taps were made on the top and bottom surfaces of the airfoil. The pressure taps are cut from the airfoil such that the pressure taps on the top and bottom surfaces are collinear and normal to the surfaces as noted in Figure 4. The pressure taps are highlighted in blue.
To measure airflow, hypodermic needles were inserted into the channel exits on the airfoil, transferring air into the manometer tubing (see picture below). These needles, along with the tubing, were securely attached to the leading and trailing edge channels using superglue, ensuring an airtight seal. The PVC tubing connected to the airfoil and hypodermic needles allows water inside the tubing to move in response to air pressure changes on the airfoil. The manometer, constructed from PVC tubes filled with water and arranged in a U-shape, provides accurate pressure readings.
Manometer Rig
A water manometer is used with the airfoil to measure air pressure from the pressure taps. PVC tubing from the airfoil is vertically fixed and wrapped around an acrylic board in a U-shape. Additionally, a gauge pressure PVC tube, configured similarly, measures wind tunnel pressure. The acrylic board features laser-cut markings for precise fluid displacement measurements.
Manometer Rig
A water manometer is used with the airfoil to measure air pressure from the pressure taps. PVC tubing from the airfoil is vertically fixed and wrapped around an acrylic board in a U-shape. Additionally, a gauge pressure PVC tube, configured similarly, measures wind tunnel pressure. The acrylic board features laser-cut markings for precise fluid displacement measurements.
To ensure accurate measurements, PVC tubes were kept vertical, recording the height difference of the water as data. The constant tubing diameter and U-shape design resulted in a height change twice the manometer readings. Water in the manometer measured airfoil pressure. The airfoil was positioned in the wind tunnel with the acrylic rod fixed to the left wall and tubing exiting through the right wall.
Data Collected
Increased Angle of Attack and Lift
Increasing the angle of attack of the NACA2418 airfoil resulted in higher pressure differentials and, consequently, increased lift. The maximum lift force of 5.479 N was observed at the leading edge (position A) with a 12° angle of attack. The leading edge experienced the greatest lift likely because it encountered the airflow first, avoiding disturbances that could affect positions further down the chord line. Minor disturbances and skin friction effects, possibly due to pressure tap holes and surface imperfections, likely affected readings toward the center and trailing edge.
The trailing edge pressure taps showed minimal height changes, indicating less pressure and lift, possibly due to faulty pressure taps or flow separation at higher angles of attack.
Applications and Future Experiments
These findings are valuable in the aerospace industry for optimizing the angle of attack during cruise flight to maintain steady altitude with minimal pilot input. Repeated experiments on airfoil pressures can aid in designing future airfoils for maximum lift or developing adjustable tabs for precise lift control.
Repeating the experiment with more pressure taps at various positions across the airfoil could provide higher resolution pressure data. This experiment was limited to 12 pressure taps, and adding more, especially towards the trailing edge, could reveal flow separation details at higher wind speeds.
