# Aerodynamic Analyses of Airfoils Using Machine Learning as an Alternative to RANS Simulation
###### Abstract  
The accurate prediction of aerodynamic properties is an essential requirement for the design of applications that involve fluid flows, especially in the aerospace industry. The aerodynamic characteristics of fluid flows around a wing or an airfoil are usually forecasted using the numerical solution of the Reynolds-averaged Navier-Stokes equation. However, very heavy computational expenses and lengthy progression intervals are associated with this method. Advancements in computational power and efficiency throughout the present era have considerably reduced these costs; however, for many practical applications, performing numerical simulations is still a very computationally expensive and time-consuming task. The application of machine learning techniques has seen a sharp rise in various fields over recent years, including fluid dynamics, and they have proved their worth. In the present study, a famous machine learning model that is known as the back-propagation neural network was implemented for the prediction of the aerodynamic coefficients of airfoils. The most important aerodynamic properties of the coefficient of lift and the coefficient of drag were predicted by providing the model with the name, flow Reynolds number, Mach number and the angle of attack of the airfoils with respect to the incoming flows as input parameters. The dataset for the current study was obtained by performing CFD simulations using the RANS-based Spalart-Allmaras turbulence model on four different NACA series airfoils under varying aerodynamic conditions. The data that were obtained from the CFD simulations were divided into two subsets: 70% were used as training data and the remaining 30% were used as validation and testing data. The BPNN showed promising results for the prediction of the aerodynamic coefficients of airfoils under different conditions. An RMSE value of \(3.57\times 10^{-7}\) was achieved for the best performance validation case with 28 epochs when there were 10 neurons in the hidden layer. The regression plot also depicted a close to perfect fit between the predicted and actual values for the regression curves. a 2022 2022 2022 2022 2022 20222  
this approach. The advancements in computational power and efficiency over the course of the present era have considerably reduced these costs; however, for many practical applications, performing numerical simulations is still a very computationally expensive and time-consuming task. The application of machine learning techniques has seen a sharp increase in various fields over recent years and they have proved their worth. Various academics and researchers have worked on the possibility of the application of deep learning techniques for the prediction of the aerodynamic characteristics of fluid flows around airfoils. Lately, both classification algorithms and regression models that have built upon machine learning methods and their application in fluid mechanics problems have become a much more relevant topic for investigation by researchers and academics. A brief literature overview of some of these studies is presented below. [PERSON] et al. [1] suggested the use of an amalgamation of a deep convolutional neural network (CNN) with a deep multilayer perceptron (MLP) for the prediction of flow fields around airfoils with incompressible laminar steady-state patterns. They achieved results in two steps, in which the airfoil geometry parameters were initially extracted using CNN and were subsequently fed into the MLP model network, along with the flow Reynolds number and angle of attack of the airfoils, to obtain the required flow parameters. They were able to produce a prediction accuracy of up to 99% for training and testing cases. [PERSON] et al. [2] proposed an encoder-decoder CNN approach for the prediction of pressure fields around an airfoil.