Aerodynamic Characteristics of Radar Antenna in Stationary and Azimuthal Rotational Motion

To study the effects of aerodynamic loads on the aerodynamic characteristics of stationary and azimuthally rotating antennas, wind tunnel force tests are conducted using solid and porous plate antennas. The variation of aerodynamic coefficient with azimuth angle is obtained when the antenna is stationary and azimuthal rotation, and the results are compared with those from numerical simulations. The variation in the aerodynamic coefficients with respect to the azimuth angle is found to be sinusoidal for both the solid and porous plate antennas rotating in azimuth. Compared with the antenna stationary, quantitative analysis indicates that the rotational motion increases the maximum value and root mean square of the aerodynamic coefficient. For solid plate antenna, |Cx|_max, |Cmy|_max, and |Cmz|_max increase by 41.6%, 15.0%, and 47.3%, respectively; Cx_rms, Cmy_rms, and Cmz_rms increase by 19.0%, 20.0%, and 19.1%, respectively. For porous plate antenna, |Cx|_max, |Cmy|_max, and |Cmz|_max increase by 30.6%, 71.4%, and 40.9%, respectively; Cx_rms, Cmy_rms, and Cmz_rms increase by 22.9%, 50%, and 20%, respectively. The wind tunnel tests verify the feasibility of using numerical simulations to obtain the flow field results. By analyzing the surface pressure coefficient and vortex core track distribution, the effects of azimuthal rotation on the aerodynamic characteristics of the antenna are further clarified.

Programa de Cómputo para Estimar el Rendimiento de una Hélice Empleando una Corrección por Número de Mach a la Teoría Combinada

En este trabajo se propone una corrección empírica por número de Mach a la teoría combinada para hélices y se describe el programa de cómputo desarrollado para determinar el comportamiento de la misma. El programa requiere como datos de entrada la geometría de la hélice y los coeficientes aerodinámicos en función del número de Mach de los perfiles de la pala de la hélice. Éste calcula los coeficientes aerodinámicos y las velocidades inducidas de cada elemento de pala empleando la teoría combinada, corrige los coeficientes aerodinámicos por efecto de compresibilidad y calcula la eficiencia, así como los coeficientes de tracción y de potencia de la hélice para diferentes velocidades de avance y, finalmente, los presenta en forma gráfica. Se observa que los resultados obtenidos con la teoría combinada corregida por número de Mach fueron satisfactorios ya que se aproximan más a los resultados experimentales que la teoría combinada simple. This work proposes an empirical correction by Mach number to the BEM (Blade-Element Momentum) Theory for propellers and describes the software developed to determine the behavior of it. The input for the software is the geometry of the propeller and the aerodynamic coefficient in function of the Mach number for the airfoils used for the propeller chosen. The software calculates the aerodynamic coefficients and the induced velocities at each station of the blade of the propeller using the BEM theory, then corrects these coefficients by the effect of compressibility and calculates the efficiency, the traction and power coefficients for a range of forward velocities, and finally presents a graph with the results obtained. We can observe that the results obtain are satisfactory comparing with the experimental results and obtaining lower difference error by this method than with the simple BEM theory.

Validation of Aero-Load Estimator for Convair 880 Aircraft Flight Simulator Benchmark with Electro-Hydrostatic Actuators

Simulating an aircraft model using of high fidelity models of subsystems for its primary and secondary flight control actuators requires measuring or estimating aero-load data acting on flight control surfaces. One solution would be to incorporate the data recorded from flight tests, which is a time-consuming and costly process. This paper proposes another solution based on the validation of an aero-loads estimator or on the hinge moments predictor for fully electrical aircraft simulator benchmark. This estimator is based on an aerodynamic coefficient calculation methodology, inspired by Roskam’s method that uses the geometrical data of the wing and control surfaces airfoils. The hinge moment values are found from two-dimensional lookup tables where the deflections of the control surfaces, aircraft altitude, and aircraft angles of attack are the input vectors of the tables; and the resulting hinge moment coefficients are the output vectors. The resulting hinge moment coefficients of the Convair 880 primary flight control surfaces are compared to those of its recorded flight test data; the results from the new software solution were found to be very accurate. Hinge moment lookup tables are integrated in the Convair 880 high fidelity flight simulation benchmark using mathematical models of energy-efficient Electro-Hydrostatic Actuators (EHA). Autopilot controls are designed for the roll, pitch, attitude and yaw damper motions using Proportional Integral (PI) controller scheduled for different flight conditions. Several different aircraft simulation scenarios are evaluated to demonstrate the efficacy and accuracy of the predicted hinge moment results.

Computerized dynamic fluid simulation (CFD) for measuring the influence of the cab deflector on the aerodynamics of trucks

This paper refers to how the cab deflector of trucks can influence the aerodynamic coefficient. The first part of the paper includes some generalities taken from previous studies, regarding the types of solutions to improve aerodynamics for trucks. The second part of the paper is a more practical one and has two main chapters: modeling and simulation of modeled parts. In this sense, a truck and 3 cabin deflectors were schematically modeled in Catia v5. After assembly in the Catia v5 program, the impact of the cabin deflector was analyzed. Thus, a computerized dynamic fluid simulation (CFD) was performed using the specific module in Ansys. The simulation included the CFD analysis of the four possible variants: truck without deflector, truck + deflector 1, truck + deflector 2, truck + deflector 3. All mentioned variants were analyzed at 3 different speeds: 50 km / h, 70 km / h and 90 km /. This analysis revealed information on the efficiency of each deflector, the value of the pressure as well as the most affected areas, the value of the turbulent kinetic energy, the value of the drag force and the aerodynamic coefficient.

Prediction of Moment Using a Modified Discrete Vortex Method in Ground Effect

The aerodynamics around a wing is modified when it comes near the ground. This is generally referred to as ground effect. In this work, a discrete vortex method based model which can predict two-dimensional (2D) ground effect from its free flight data is proposed. The required data in free flight could be generated either from high fidelity CFD solver or experiments. In this method, strength of the vortex distribution as obtained from discrete vortex based method is modified using a constrained optimisation procedure to match the free flight aerodynamic data. This vortex distribution is further modified due the presence of the ground. The efficacy of present model is demonstrated for predicting the moment of multi element airfoils in ground effect. The predicted aerodynamic coefficient in ground effect compares well with high fidelity CFD data.

On the application of surrogate regression models for aerodynamic coefficient prediction

Computational fluid dynamics (CFD) simulations are nowadays been intensively used in aeronautical industries to analyse the aerodynamic performance of different aircraft configurations within a design process. These simulations allow to reduce time and cost compared to wind tunnel experiments or flight tests. However, for complex configurations, CFD simulations may still take several hours using high-performance computers to deliver results. For this reason, surrogate models are currently starting to be considered as a substitute of the CFD tool with a reasonable prediction. This paper presents a review on surrogate regression models for aerodynamic coefficient prediction, in particular for the prediction of lift and drag coefficients. To compare the behaviour of the regression models, three different aeronautical configurations have been used, a NACA0012 airfoil, a RAE2822 airfoil and 3D DPW wing. These databases are also freely provided to the scientific community to allow other researchers to make further comparison with other methods.