Drag Coefficient Research Articles

Effect of Submerged Vegetation Density on Flow Hydrodynamics, Bulk Drag Coefficient, and Bed Friction

Effect of Submerged Vegetation Density on Flow Hydrodynamics, Bulk Drag Coefficient, and Bed Friction

Numerical research on two typical flow structures and aerodynamic drag characteristics of blunt-nosed trains

Purpose This study aims to provide new insights into aerodynamic drag reduction for increasingly faster blunt-nosed trains, such as urban and freight trains. Specifically, this work investigates two distinctly different wake structures and associated aerodynamic drag of blunt-nosed trains. Design/methodology/approach Three typical cases of blunt-nosed trains with 1-, 2- and 3-m nose lengths are selected. The time-averaged and unsteady flow structures around the trains are analyzed using the improved delayed detached eddy simulation model and proper orthogonal decomposition method. Findings The simulation results indicate that for 2- and 3-m nose lengths, the flow separates at first and then reattaches to the slanted surface of the tail, with a pair of longitudinal vortices dominating the wake. In contrast, for the 1-m nose length case, the wake structure is characterized by complete separation, attributed to the larger curvature of the slanted tail surface. Consequently, the total time-averaged drag coefficient is reduced by 27.2% and 19.2% for the 1-m nose length case compared to the 2- and 3-m cases, respectively. Moreover, the predominant unsteady structures with Strouhal numbers St = 0.30 and St = 0.28 are detected in the near-wake of the 2- and 3-m nose length cases, respectively. These structures result from periodic vortex shedding at the lower slanted tail surface. In contrast, for the 1-m nose length case, the predominant unsteady structure with St = 0.19 is induced by the nearly periodic expansion and contraction of the upper bubbles. Originality/value Two distinctly different wake structures in blunt-nosed trains are identified. Unlike high-speed trains with longer, streamlined noses, for blunt-nosed trains, shorter nose lengths result in lower aerodynamic drag. Insights for reducing energy consumption in blunt-nosed trains are provided.

On the Relation between Overwater Friction Velocity and the Wind Speed During Tropical Cyclones

In the realm of marine meteorology, physical oceanography, and coastal and ocean engineering, the wind-stress across the air-sea interface plays a dominant role. However, under tropical cyclone conditions, there is no consensus for the formulation of the drag coefficient, <em>C</em><sub>d</sub>, in the literature. Based on the wind-gust method and the measurements from data buoy 42001 during Hurricane Lili, it is demonstrated that, <em>U</em><sub>*</sub> = 0.073<em>U</em><sub>10</sub> - 0.44, which is valid up to wind speed 47 m s<sup>-1</sup> and wind gust to 66 m s<sup>-1</sup>, here <em>U</em><sub>*</sub> is the friction velocity and <em>U</em><sub>10</sub> is the wind speed at 10-m height. This formula is also supported by the atmospheric vorticity method. Applications for this proposed formula to estimate the variation of the wind speed with height and to determine the wind-stress storm surge or saltwater flooding during the most recent Hurricane Helene in 2024 are successful. In addition, it is found that <em>C</em><sub>d</sub> = (1.29<em>Ln</em>(<em>H</em><sub>s</sub>) + 0.27)/1000, which may be used to explain the behavior of the variation of <em>C</em><sub>d</sub> with the significant wave height, <em>H</em><sub>s</sub>. In order to further substantiate the proposed formula, more datasets during other tropical cyclones are incorporated for the validation.

Exploring the Design of Low Cd BEV by Comparing the Characteristic Parameters and Curves of the Li Auto Mega and ZEEKR 009

As the Battery Electric Vehicle (BEV) market expands, consumer expectations for BEV performance are rising rapidly, with range anxiety becoming a major concern. Merely increasing battery size isnt a long-term solution. Instead, optimizing key design parameters to enhance aerodynamic efficiency is crucial. This paper examines the evolution of Multi-Purpose Vehicles (MPVs) by comparing the traditional MPV designs with newer, low drag models. in terms of appearance parameters and explore the future development of MPVs appearance. Specifically, the Li Auto Mega and ZEEKR 009 are analyzed, highlighting the stark differences in their designs. The study finds that the more aggressive and innovative design elements of the Mega effectively reduce the drag coefficient (Cd), offering valuable insights for future MPV designs

Numerical analysis of aerodynamic performance characteristics of NACA 2412 and NACA 4412 at Re = 4000000

This paper conducts a numerical analysis of the two-dimensional aerodynamic characteristics of the NACA 2412 and NACA 4412 aerofoils at a Reynolds number of Re = 4106. Employing the fluid simulation software Ansys Fluent, which is based on the finite volume method, for numerical analysis. Both the geometric model and mesh of the aerofoil are established by using Fluent Meshing, and the simulation calculation is performed based on the pressure solver. Based on the Navier-Stokes equations, the SST k- turbulence model and coupled algorithm are employed for the simulation processing. The paper systematically compares the aerodynamic characteristics of NACA 2412 and NACA 4412, including the pressure and velocity distributions, as well as the variations in the lift coefficient, drag coefficient, and lift-to-drag ratio concerning the angle of attack. The results indicate that at Re = 4106, the peak value of the lift-to-drag ratio of the NACA 2412 aerofoil is attained under the 8 condition, for the NACA 4412 aerofoil, the lift-to-drag ratio reaches its peak value at a 6 angle of attack. Additionally, the stall angles of both types of aerofoils under the studied operating conditions are 16.

Effect of Reynolds number and angle of attack on aerodynamic performance of NACA2412

Numerous studies have been carried out on various flow control techniques aimed at enhancing the aerodynamic performance of different aerofoil designs. This research examines the aerodynamic properties of the NACA2412 aerofoil across different Reynolds numbers and angles of attack through numerical simulations. A structured mesh along with a 'C'-type computational domain was utilized, and CFD analyses were performed in Fluent to evaluate the lift coefficient (CL) and drag coefficient (CD) for Reynolds numbers between 20,000 and 100,000, as well as angles of attack from 0 to 20. The findings reveal that an increase in Reynolds number results in a higher CL; however, CD also rises significantly at elevated Reynolds numbers. Furthermore, as the angle of attack increases, CL reaches its maximum at 15 before experiencing a sharp decrease, while CD shows a steep increase indicative of stall conditions. This study offers valuable insights for optimizing aerofoil design and enhancing aerodynamic performance.

The influence of trailing edge flaps on the aerodynamic characteristics of S1223 aerofoil

The S1223 aerofoil is a low Reynolds number high lift aerofoil. Analysing the aerodynamic characteristics of this aerofoil can provide a theoretical basis for enhancing flight efficiency in the design of small unmanned aerial vehicles. This study employed the k--SST turbulence model in the fluid simulation software (ANSYS Fluent) to conduct two-dimensional numerical aerodynamic simulations on the original aerofoil and its modified versions, which included flaps (deflected 10 at 70% chord length) and slotted flaps (deflected 10 at 70% chord length with a slot width of 1.5% of the chord). The aerofoil's aerodynamic performance was confirmed by comparing lift and drag coefficients at different angles of attack under Reynolds number 5.0105, as well as by analysing the pressure and velocity gradients in the flow field. The results indicate that both the lower flap and the slotted flap can greatly enhance the lift-to-drag ratio. In contrast, slotted flaps delay boundary layer separation, providing greater lift at high angles of attack while reducing the impact on drag.

Comparison of aerodynamic characteristics of NACA 2415 and NACA 4415 Aerofoils

This study compared the two-dimensional aerodynamic characteristics of NACA 2415 and NACA 4415 at different angles of attack. In this study, the Reynolds number is 2.3e6, under which the velocity of the air is 33 m/s. The mesh of C-type is established based on ANSYS Meshing; to simplify the calculation, the chord length is set to 1 m. The fluid simulation is done by ANSYS Fluent, and the simulation calculation is performed based on the pressure solver. The N-S equation is used as the governing equation. Velocity inlet and pressure outlet are set as the boundary condition, and the k-omega SST viscous model is chosen for the simulation processing. This study compares the aerodynamics of NACA 2415 and NACA 4415 at different angles of attack, including the pressure and velocity distribution, lift and drag coefficient, and lift-drag ratio. The results of this research would help optimize wing design and develop new aerofoil and testing.

Impact of driving characteristic parameters and vehicle type on fuel consumption and emissions performance over real driving cycles.

With the growing need for sustainable transportation solutions, understanding the relationship between driving characteristic parameters, vehicle type, and their impact on emissions and fuel consumption over real driving scenarios is becoming increasingly important. In this paper, four conventional vehicles and one hybrid vehicle with different technologies were compared in four distinct routes in Tehran city. Nineteen real driving cycles were generated using widely employed K-means and PCA algorithms. The vehicles were simulated on MATLAB/Simulink according to their specifications. Twelve driving characteristic parameters, fuel consumption, CO, NOx, HC, and CO2 of vehicles with different powertrains, engines, and body styles were calculated over real and standard driving cycles. Notable findings show that driving characteristic parameters exhibit distinct influences on fuel consumption and emissions, depending on the specific driving conditions and vehicle type. Additionally, the hybrid vehicle achieved 39% and 26% fuel savings compared to gasoline and dual fuel vehicles, respectively. However, it emitted significantly higher levels of CO and HC. In contrast, the turbocharged vehicle increased CO and HC emissions compared to the naturally aspirated vehicle, but consumed less fuel (approximately 6%) and emitted lower amounts of CO2 (approximately 19%). In real driving cycles, the sedan vehicle generally exhibited slightly lower values compared to petrol SUV due to lower weight and drag coefficient.

Cooperative Eco-Driving for an All-Electric and Mixed Two-Vehicle Platoon Based on Pontryagin's Minimum Principle

Abstract Cooperative eco-driving (Co-ED) is a promising technology for improving vehicle efficiency through appropriate coordination. Additionally, platooning can significantly improve the vehicle's energy efficiency by reducing aerodynamic resistance. The optimal trajectory of the Co-ED vehicles in a platoon will be challenging to derive due to the high nonlinearity of the aerodynamic drag coefficient. Furthermore, although the electrification of vehicles has made rapid progress, the traffic on the road will still tend to be a mix of conventional vehicles (CVs) and electric vehicles (EVs) for a long time. It is critical to take the energy consumption characteristics of different vehicle types into account for a mixed platoon during Co-ED. This paper considers the platooning effects and heterogeneity of leading vehicles in two-vehicle platoons and utilizes Pontryagin's Minimum Principle (PMP) to derive the optimal speed trajectories for both homogeneous (all-electric) platoon and heterogeneous platoons (with different fuel types of vehicle). Simulation results from the proposed PMP-based Co-ED strategy show that the platooning effect has a noticeable impact on the Co-ED driving behaviors (particularly the inter-vehicle space and the transient performance). Simulation results also demonstrated that the same following EV will result in less energy consumption by 4.8% in an EV-led platoon under urban/suburban scenario and approximately same energy consumption under interstate scenario compared in a CV-led platoon.

Based on AVL-CRUISE Hybrid and Electric Vehicle Simulation and FTP-72 Circle Power Consumption Factor Analysis

With the rapid advancement of technology and the growing scarcity of energy resources, finding effective ways to reduce power consumption has become increasingly crucial. Hybrid and electric vehicles play a vital role in this endeavor, warranting deeper exploration and focus. In this study, I utilized AVL-Cruise software, a powerful tool for simulation and data modeling, to conduct comprehensive simulations of hybrid and electric vehicle performance, with a specific focus on analyzing the FTP72 cycle.The simulation results are highly encouraging. The vehicle achieved a maximum speed of 164 km/h, an acceleration rate of 3 m/s, a 0 to 100 km/h acceleration time of 9 seconds, and a maximum climbing slope of approximately 74%. These figures not only demonstrate that hybrid and electric vehicles can meet performance expectations but also highlight their capability to deliver on key metrics. Furthermore, the total energy consumption was recorded at 4200 kJ, underscoring the efficiency of these vehicles.In addition to the simulation outcomes, I delved into various factors that influence vehicle performance, including vehicle mass, drag coefficient, and motor power.Using MATLAB, I conducted a detailed analysis of the relationships between these factors and energy consumption, incorporating residual analysis and deriving a mathematical equation to describe these interactions.Through this extensive data analysis and model fitting, we gain a deeper understanding of hybrid and electric vehicle dynamics. This research not only contributes to the field but also has the potential to drive further development, broadening the focus and scope of hybrid and electric vehicle technology

An experimental and numerical investigation on aerodynamic characteristics for different airfoil sections for external flow

This research presents the development of a subsonic wind tunnel designed for streamlined airflow, featuring a squared cross-sectional area along its length. The primary focus is on measuring drag and lift on external flow across two different airfoil models. Utilizing a variable-speed centrifugal blower motor in the absence of converging and diverging sections ensures streamlined airflow in the test section. Two airfoil models, NACA-0012 and NACA-2414, fabricated from galvanized iron thin gauge sheet metal, undergo analysis through wind tunnel experiments and numerical simulation. Within the wind tunnel, strain gauge load cells are incorporated to accurately measure drag and lift across the airfoils. Comparative assessments of drag and lift coefficients are conducted at four varying angles of attack (-6.3 degrees to 12.6 degrees) for each airfoil. Results from both wind tunnel experiments and numerical simulations demonstrate precision, closely aligning with literature.

Drag, lift, and torque on a near-wall oblate spheroid in linear shear flow

This study performs particle resolved simulations (PRSs) to investigate the behavior of linear shear flow over a near-wall oblate spheroidal particle. Simulations are conducted for particles with aspect ratios (λ) of 1.5, 2, and 4, covering Reynolds numbers (Re) ranging from 1 to 200 and particle inclination angles (θ) from 0° to 180°. The resulting drag, lift, and torque coefficients exhibit unique patterns of variation with respect to θ, showing significant differences compared to particles in unbounded uniform flow. These variations are elucidated by examining the flow field surrounding the particle, alongside the distribution of pressure and skin-friction coefficients on its surface. Based on these findings, correlations for the drag, lift, and torque coefficients are proposed, demonstrating strong agreement with the PRS results across different aspect ratios and Reynolds numbers, thereby providing accurate predictive models for near-wall oblate spheroidal particles in linear shear flow.

Data driven analysis of particulate systems for development of reliable model to determine drag coefficient of non-spherical particles

Data driven analysis of particulate systems for development of reliable model to determine drag coefficient of non-spherical particles

PASSIVE FLOW CONTROL AROUND A NACA4415 AIRFOIL BY MEANS OF VORTEX GENERATORS

The present paper intends to improve the aerodynamic performance of a NACA4415 airfoil using low-profile vortex generators. Numerical flow analysis yielded the values of the lift and drag coefficients for impacts ranging from incidence 0° to 24°. The steady Reynolds averaged Navier Stokes equations have been solved with the ANSYS CFX 2019 R2 calculation tool utilizing the shear stress transport turbulence model at a Reynolds number Re = 2.13 × 10<sup>5</sup>. The approach of tetra-mixed meshing was employed. The impact of several parameters (height, span-wise distance, installation angle β, skew angle φ) have been investigated. Experimental data has been used to validate the results. According to the numerical outcomes, the skewed angle vortex generators (Φ = 20°) placed upstream of the separation zone with a short spanwise distance are beneficial for delaying the stall angle from α = 20° (clean airfoil) to α = 24° and enhance the lift coefficient by 39%. However, the overall optimal lift-to-drag ratio was achieved when φ = 0°.

Geometrical parameters effect on aerodynamic performance of infinite tubercle leading edge wings

ABSTRACT Micro aerial vehicles (MAVs) encounter aerodynamic challenges due to their small size and low flying speed, often experiencing stall at low angles of attack. This study aims to investigate the effects of sectional airfoil geometries, including thickness, maximum thickness location, and camber, on the aerodynamic performance of fixed-wing MAVs inspired by the passive control method observed in Humpback whales. The investigation employs 3D, unsteady, viscous, and turbulent simulations using the detached eddy simulation turbulence model to understand the physical phenomena. Results reveal that increasing the thickness of the infinite wing by approximately 9.5% results in a decrease of lift and drag coefficients by 19.8% and 12%, respectively. Furthermore, shifting the maximum thickness location from 18%c to 36%c enhances the lift-to-drag ratio (L/D) by nearly 16%. However, an increase in camber leads to a rise in drag coefficient. In conclusion, this research sheds light on the aerodynamic effects of sectional airfoil geometries on fixed-wing MAVs, particularly in pre-stall conditions. Understanding these effects contributes to the development of strategies for improving MAV maneuverability and aerodynamic performance.

Enhancing aerodynamic efficiency: shape modification of airfoils

Small wind turbines (SWTs) are essential for harnessing renewable energy, particularly in developing regions where energy demands are significant. They provide a sustainable solution to meet the critical energy needs of these areas. However, the low Reynolds number (Re) airflow characteristics can pose challenges, making optimising airfoil shapes essential for enhancing aerodynamic performance and energy capture. This study offers a thorough analysis of six different airfoil profiles within a Re range of 50k to 500k. Modifications to the thickness-to-camber ratio (t/c) were strategically targeted to improve aerodynamic efficiency and structural viability. Using QBLADE software, we evaluated these design alterations to optimise the lift coefficient ( C L ), drag coefficient ( C D ), stall angle of attack ( α stall ) and lift-to-drag coefficient ratio (L/D). The analysis revealed significant improvements in the maximum power coefficient ( C p . max ), with the modified BW-3 airfoil achieving a C p . max of 0.441 at a Re of 500k – a remarkable 40.5% increase over baseline values. This consistent enhancement across various Re emphasises the essential impact of aerodynamic design in enhancing energy capture and reinforcing the feasibility of SWT applications across diverse operating conditions, along with material savings that lead to lighter wind turbine (WT) blades.

Numerical Study of Thermal and Resistance Characteristics in the Vortex-Enhanced Tube

Heat transfer enhancement is always pursued in the industry to achieve high-performance and low-energy-consumption heat exchange devices and systems. For decades, various types of heat transfer-enhancing tubes with differing geometries and wall configurations have been developed. In this paper, the heat transfer and pressure drop characteristics of air inside an innovative heat transfer tube with regular wall dimples, namely a vortex-enhanced tube, which has a great application prospect in the gas–gas heat exchanger, are numerically studied with an experimentally validated model. The effects of the depth, axial pitch, and radial rotation angle of the dimple in the tube wall on the convective heat transfer coefficient and friction drag coefficient are comprehensively analyzed. Based on the Performance Evaluation Criteria (PEC) of the tubes, the optimal parameters of the vortex-enhanced tube are obtained. When Re ranges from 10,000 to 40,000, the comprehensive evaluation factor of the vortex-enhanced tube is 1.29 times higher than the smooth tube. Dimple pacing, dimple depth, and dimple helical angle of the optimal tube type are 8 mm, 6 mm, and 83°, respectively.

Aerofoil optimization using SLSQP and validation using numerical and analytical methods

Aircraft design optimization is one among the research enriched topic in the aerospace industry, with enhancing aircraft performance, safety, and efficiency numerous being the prime focus areas. The work done demonstrates the application of the Sequential Least Squares Programming (SLSQP) technique over a symmetrical aerofoil “NACA 0012” to improve its aerodynamic performance. The optimized aerofoil is validated using Design and Analysis Tools for Composite Aircraft (DATCOM) and Computational Fluid Dynamics (CFD) methods. The study focuses on optimizing the performance of a symmetric aerofoil, where drag minimization is crucial, subject to list constraints, such as in the design of fuel-efficient aircraft. The results reveal, the optimized aerofoil has a significant reduction in drag coefficient of closer to 11 % between 8° and 10° compared to the initial design. The validation using DATCOM and CFD methods confirms the accuracy and usefulness of the optimization results. Validation error values are found to be negligible when compared to the optimization data, coming in at 5.7% and 6.5% for DATCOM and CFD, respectively. The paper highlights that the SLSQP technique is efficient and reliable optimization method for designing high-performance aerofoils.

UAV Icing: Aerodynamic Degradation Caused by Intercycle and Runback Ice Shapes on an RG-15 Airfoil

Electrothermal de-icing systems are a popular approach to protect unmanned aerial vehicles (UAVs) from the performance degradation caused by in-cloud icing. However, their power and energy requirements must be minimized to make these systems viable for small and medium-sized fixed-wing UAVs. Thermal de-icing systems allow intercycle ice accretions and can result in runback icing. Intercycle and runback ice increase the aircraft’s drag, requiring more engine thrust and energy. This study investigates the aerodynamic influence of intercycle and runback ice on a typical UAV wing. Lift and drag coefficients from a wind tunnel campaign and Ansys FENSAP-ICE simulations are compared. Intercycle ice shapes result in a drag increase of approx. 50% for a realistic cruise angle of attack. While dispersed runback ice increases the drag by 30% compared to the clean wing, a spanwise ice ridge can increase the drag by more than 170%. The results highlight that runback ice can significantly influence the drag coefficient. Therefore, it is important to design the de-icing system and its operation sequence to minimize runback ice. Understanding the need to minimize runback ice helps in designing viable de-icing systems for UAVs.