Lift Coefficient Cl Research Articles

Review of effects the rear spoiler aerodynamic analysis on ground vehicle performance

Recently reduce in fuel consumption and concern regarding the ground vehicle safety, automotive engineers are faced with the immediate task of introducing more efficient aerodynamic performance vehicles. Hence, the rear spoiler attached on the ground vehicle was presented. Rear spoiler is a device commonly found on road vehicle for improving their aerodynamic performance. Review on the research effects of the rear spoiler aerodynamic analysis on ground vehicle performance is reported in this paper. This review intends to enhance the stability and safety by attaching the rear spoiler on ground vehicle. The review mainly focus on aerodynamic analysis and control of the rear spoiler for different types ground vehicle in term of improving vehicle performance. Researches carried out by a number of researchers with regard to analyze and control the rear spoiler of ground vehicle and their effect on ground vehicle performance. Aerodynamic analysis i.e. computational fluid dynamics(CFD), design optimization, drag coefficient (Cd ) and lift coefficient (Cl ) and control methods i.e. passive control and active control had been reviewed. Meanwhile, progressive research on the rear spoiler aerodynamic analysis was observed due to its flexibility for wide range of application in the different type vehicles.

Effect of windshields on the aerodynamic performance of a four-box bridge deck

A new type of bridge deck section consisting of four-box decks, two side decks for vehicular traffic lanes and two middle decks for railway traffic, has been experimentally investigated for determining its aerodynamic properties. The eight flutter derivatives were determined by the Iterative Least Squares (ILS) method for this new type of four-box deck model, with two windshields of 30 mm and 50 mm height respectively. Wind tunnel experiments were performed for angles of attack α=±6°, ±4°, ±2° and 0° and Re numbers of 4.85x105 to 6.06x105 and it was found that the four-box deck with the 50 mm windshields had a better aerodynamic performance. Also, the results showed that the installation of the windshields reduced the values of the lift coefficient CL for the negative angles attack in the range of -6° to 0°, but the drag coefficient CD increased in the positive angle of attack range. However, galloping instability was not encountered for the tested reduced wind speeds, of up to 9.8. The aerodynamic force coefficients and the flutter derivatives for the four-box deck model were consistent with the results reported for the Messina triple-box bridge deck, but were different from those reported for the twin-box bridge decks.

Determination of Aerodynamic Characteristics of NACA 0012 Using ANSYS for High Subsonic Flow

Aerodynamic characteristics play a very important role in determining the forces acting on the aerofoil sections and thereby are very important for airplane performance. Determination of these characteristics can be done in two ways - experimental and simulation. The data obtained from experiments and simulation complement each other in the current era. The presented work deals with the determination of aerodynamic characteristics such as lift coefficient (Cl) and drag coefficient (Cd) of a NACA 0012 aerofoil at high subsonic speed for inviscid flow condition by performing numerical simulation using commercial software ANSYS.

PR-DNS on the momentum and heat transfer of a rotating ellipsoidal particle in a fluid

Particle resolved direct numerical simulations (PR-DNS) are conducted to study the forced convection process of a cold flow passing over a rotating hot ellipsoidal particle. The numerical model is firstly verified against previously published data on both stationary and rotating particles. Then, one hundred case studies are carried out by changing five particle aspect ratios, five Reynolds numbers and four particle spin numbers, respectively. The effects of particle rotation on drag coefficient (Cd), lift coefficient (Cl), moment coefficient (Cm) and average Nusselt number (Nu) are investigated in detail. The changing trends of Cd, Cl, Cm and Nu with the particle incident angle in different cases are comprehensively analysed and compared. Numerical results of a rotating non-spherical particle show quite interesting and different phenomena compared with the stationary case. It is indicated that the particle rotation must be considered when evaluating the momentum and heat transfer between non-spherical particles and fluids. The findings provide important evidence to properly evaluate the role of particle rotation in the macro-scale modelling of multiphase flows.

On the influence of blade thickness-to-chord ratio on dynamic stall phenomenon in H-type Darrieus wind rotors

The present work examines the influence of blade thickness-to-chord ratio (t/c) on dynamic stall phenomenon in an H-type Darrieus wind rotor. A 2D incompressible numerical study is conducted on a single-bladed rotor at a tip speed ratio (TSR) of 2 with a motivation to understand the intricate flow physics around the blade by employing a transitional shear stress transport (TSST) model. Five different t/c ratios (9%, 12%, 15%, 18% and 21%) have been studied for symmetrical NACA airfoils. It is found that in case of thinner airfoils (t/c = 9% and 12%), the formation of the dynamic stall vortex (DSV) is preceded by the formation and bursting of leading edge (LE) laminar separation bubble (LSB) leading to a more abrupt LE type stall. For t/c = 15%, a mixed type stall is observed with LSBs distributed over the airfoil resulting in two coherent vortex structures that subsequently merge to form the DSV. A trailing edge (TE) type stall was observed in case of thicker airfoils (t/c = 18% and 21%). The largest peak in the lift and drag coefficients (Cl, Cd) values of 1.87 and 1.27, respectively are obtained with the thinnest airfoil. However, the largest peak in the moment coefficient (Cm) value is achieved with t/c = 12%. Further, due to the DSV separation at the lift stall point, a further increase of 6.3%, 7.1%, 1.5%, 8.94% and 11.8% in Cd values is observed for increasing order of t/c. Overall, the study sheds light on the capability of TSST model in capturing the dynamic stall phenomenon efficiently.

Experiment and modeling of lift force acting on single high Reynolds number bubbles rising in linear shear flow

The lift force acting on single bubbles rising in a downward linear shear flow is measured experimentally. The flow is generated by a 90° sharply bent rectangular water channel, with uniformly distributed vanes installed directly after the corner, and the linear velocity profile is validated by particle image velocimetry. In the flow, single contaminated bubbles with a volume equivalent diameter d ranging from 2 mm to 20 mm are tested, corresponding to a Reynolds number Re based on d and relative velocity of the bubble in the quasi-steady state from 440 to 7200. The experimental results of the lift coefficient CL at d < 8 mm (Re < 2100) are consistent with both the data and correlation in the literature. In the case of d > 8 mm, the results of CL exhibit similar tendencies and magnitudes to those of Li et al. (2016a). Based on the ideal modeling of the vortex detachment, the wake-induced contribution of CL is estimated. Good agreement is achieved between the newly derived model and experimental results.

Numerical study on flow around partially buried two-dimensional ribs at high Reynolds numbers

Numerical simulations of flow around wall-mounted two-dimensional (2D) ribs with a rectangular cross-section that represent a simplified model of partially buried cubic artificial reefs on the seabed with different normalized heights of the structure (H/D) subjected to a boundary layer flow at different Reynolds numbers (Re) with different normalized thicknesses of the boundary layer (δ/D), are carried out in the present study. Here D is the characteristic length of the flow and is set as the width of the rectangular cross-section in the present study. The hydrodynamic quantities of the flow on the partially buried ribs are studied by using 2D Reynolds-averaged Navier-Stokes (RANS) equations with the k–ω shear-stress transport (SST) turbulence model. By comparing the simulation results with the published experimental measurements, it can be concluded that the RANS model with the k–ω SST turbulence model can provide satisfactory numerical results. Moreover, parametric studies have been carried out to investigate the effects of Re, δ/D and H/D on the hydrodynamic quantities, i.e. the drag coefficient Cd, the lift coefficient Cl, and the recirculation length xR/D of the wake behind the structure and the results are discussed systematically. The results indicate that the hydrodynamic quantities Cd, Cl and xR/D decrease with the decreasing H/D.

Research on Underbody Flattening of a Passenger Vehicle towards Aerodynamics Optimization

A CFD method for the full-scale external flow of a passenger vehicle is established. Based on the comparison between the simulation and wind tunnel test results, the reliability to use this model and method for the aerodynamic drag coefficient (Cd) and lift coefficient (Cl) prediction of the vehicle is verified. The trend of Cd and Cl for five models with different underbody flattening degree shows the significance of underbody flattening on the aerodynamic performance, with nearly 18% on the drag and over 30% on the lift coefficient optimization

Experimental study of yaw angle effect on the aerodynamic characteristics of a road vehicle fitted with a rear spoiler

This study investigates the yaw angle effect on the aerodynamic performance of a hatchback model fitted with a roof spoiler. Although the aerodynamic performance of road vehicles is highly dependent on its yaw angle, it has rarely been considered in studies pertaining to roof spoiler applications. Two common types of spoilers are studied, namely, strip and wing types. The hatchback model is based on the Ahmed body at 35° slant angle. The yaw angle affects the aerodynamic performance of the hatchback model negatively regardless of the presence of a spoiler. However, the impact is more pronounced with the absence of a spoiler, particularly at higher yaw angles. Most importantly, the use of a spoiler prevents the bi-stability behaviour of flow which occurred in the model without the spoiler. Furthermore, the strip spoiler reduces both the drag and lift coefficients (Cd and Cl), whereas the wing type results in a greater reduction in Cl while penalising Cd. The results of the surface pressures indicate that the changes in the flow around the rear slanted body are the main factors affecting the aerodynamic performance of the hatchback model using the spoiler.

CFD Analysis of Supersonic flow performance around a scramjet engines

This paper talks about the optimal design outline and examination of a NASA X-43. The X-43 was an unmanned test hypersonic air vehicle with numerous arranged scale varieties intended to test different parts of hypersonic. Investigation is shown in relentless state 3D computational liquid components (CFD) at Mach 4.5 to Mach 9.0. In this method for examination, Lift, Drag, Lift Coefficient (Cl) and Drag Coefficient (Cd) are measured and taken a gander at isolated Mach numbers, Pressure structures and speed shapes are plotted and the Turbulence zone is foreseen from streamline sees examination were analysed in CFD. NASA and other groups are actively searching for ways to dramatically reduce the cost of lifting objects into earth orbit, currently estimated at approximately $20,000 per kilogram. One of the most promising prospects is the concept of an air breathing engine capable of propelling an aircraft in the hypersonic (Mach 5+) range. A supersonic combustion ramjet or scramjet, theoretically has the capability of reaching orbital velocities. The payload and economy benefits of such an engine become readily apparent when one considers the weight of a typical rocket-based space launch vehicle (like the Space Shuttle) is two thirds oxidizer.

A Computational Aerodynamic Study of Tandem Rotating Wheels in Contact with the Ground

Wheels have significant impact on noise and drag of road vehicles, which may influence their fuel consumption, emission and comfort. A number of studies have analyzed flow and aerodynamics of isolated wheel in contact with the ground, but limited attention has been given to interaction between wheels. The present study aims to compare the aerodynamics and flow structure between single and tandem wheels. To that end, flow around single and tandem wheels are simulated using a turbulence Scaled Adaptive Unsteady Reynolds Average Navier Stokes (URANS) model. Wheel geometry was based on the actual wheel used in the experiments of Fackrell and Harvey. Flow around single and tandem wheels were examined and compared, along with their respective drag and lift coefficients. Results for single wheel in contact with the ground show good agreement with previous experiments. In the tandem wheel case, the rear wheel exhibits lower drag coefficient (CD = 0.37) and more downforce (lift coefficient CL = -0.14) compared to the front wheel. The present investigation may help to illustrate impact of wheel interaction on their aerodynamics.

Experimental Investigation of the Aerodynamics and Flowfield of a NACA 0015 Airfoil Over a Wavy Ground

The aerodynamic properties and flowfield of a NACA 0015 airfoil over a wavy ground were investigated experimentally via surface pressure and particle image velocimetry (PIV) measurements. Flat-surface results were also obtained to be served as a comparison. For the wavy ground, there exhibited a cyclic variation in the sectional lift coefficient Cl over an entire wavelength. The maximum Cl observed at the wave peak (produced by the wavy ground-induced RAM pressure) and minimum Cl occurred at the wave valley (resulting from the unusual suction pressure developed on the airfoil's lower surface due to the converging-diverging flow passage developed underneath it) reduced with increasing ground distance. By contrast, the pitching-moment coefficient showed an opposite trend to the variation in Cl and had an almost all-negative value. Meanwhile, two peak values in the drag coefficient over each wavelength were observed. The wavy ground effect-produced gains in the mean Cl and lift-to-drag ratio were at the expense of longitudinal stability. Additional measurements considering different wavelengths and amplitudes are needed to further quantify the impact of wavy ground on wing-in-ground effect (WIG) airfoils and wings.

Freely vibrating circular cylinder in the vicinity of fully developed scour holes at low Reynolds numbers

In this work, a numerical study is conducted on the flow past an elastically mounted circular cylinder with two degrees of freedom (2-DoF) placed in the vicinity of a fully developed scour hole in both two-dimension (2D) and three-dimension (3D). This paper focuses to study how different fully developed scour profiles affect the hydrodynamic quantities of vortex-induced vibrations (VIV) of an elastically mounted circular cylinder in proximity and the flow fields. To begin with, we systematically conduct the 2D simulations at Reynolds number of Re=200 in the laminar flow regime and characterize the cylinder amplitudes, the hydrodynamic force coefficients and phase differences. For the 2D study, two representative fully developed scour hole profiles with Shields parameters of θ*=0.098 and 0.048 are considered and the case of a plane wall (i.e. θ*=∞) is taken into account as a reference for comparison. In the 3D simulations at Re=300, which is at the beginning of the subcritical flow regime, with θ*=0.098, the cylinder response characteristics and the 3D flow fields are investigated. It is shown that the upper boundary of the lock-in regime at θ*=0.048 is much smaller than those of θ*=0.098 and ∞, and the vortex shedding is ceased for Ur ≥ 5.3 at θ*=0.048. It is also found that the equilibrium scour profile affects the mean force coefficients to a large extent: the mean lift coefficient CL¯ for θ*=∞ is larger than those of θ*=0.098 and 0.048 in the pre-lock-in and post-lock-in regimes; and the mean drag coefficient CD¯ for θ*=∞ is larger than those of θ*=0.098 and 0.048 in all regimes.

Experimental Investigation of Spoiler Deployment on Wing Stall

Upper surface wing flaps, known as spoiler, are typically used to reduce lift and increase drag at touchdown; however spoilers have been shown to increase lift and reduce drag at near-stall conditions. The purpose of this experiment was to determine the spoilers’ impact on lift, drag, moment, and aerodynamic efficiency of a NACA 2412 airfoil at angles of attack (α) from −8 ° to 32 °. The experiment was conducted in the Ryerson Low-Speed Wind Tunnel (closed-circuit, 1 m × 1 m test section) at Re=783761, Ma=0.136. The lift coefficient (Cl), drag coefficient (Cd), moment coefficient about the quarter-chord () were captured with a changing spoiler deflection angle (δ) and spoiler length (b in percent chord). It was found that deflecting the spoiler resulted in an increase maximum lift of up to 2.497%. It was found that deflecting the spoiler by 8° was optimal for the b=10 cases. Any larger deflection reduced the lift gain, and a deflection of 25° caused the maximum lift to be 2.786% less than the clean configuration. In the b=15 case, δ=15° was optimal (1.760% maximum lift coefficient increase). The b=10 cases increased maximum lift coefficient between 0.35% and 2.10% higher than the b=15 cases. The source of the lift gain at high angles of attack is apparent in an analysis of the airfoil pressure distribution. The spoiler increased the suction peak on the airfoil surface upstream of the spoiler, and increased the pressure downstream. However the suction increase upstream is larger than the pressure increase downstream, resulting in a net increase in lift. The spoiler increased the stall angle 37.658% to 87.658% higher than the clean configuration. Stall angle increased with both δ and with an increased spoiler length. The spoiler airfoil produced less drag than the clean configuration at high angles of attack. The combination of the increased lift, and reduced drag resulted in an increase in aerodynamic efficiency at high angle of attack.

Numerical Investigations on Aerodynamic Forces of Deformable Foils in Hovering Motions

The aerodynamic effects of wing deformation for hover flight are numerically investigated by a two-dimensional finite-volume (FV) Arbitrary Langrangian Eulerian (ALE) Navier-Stokes solver. Two deformation models are employed to study these effects in this paper, which are a full deformation model and a partial deformation one. Attentions are paid to the generation and development of leading edge vortex (LEV) and trailing edge vortex (TEV) which may illustrate the differences of lift force generation mechanisms from those of rigid wings. Moreover, lift coefficient Cl, drag coefficient Cd, and figure of merit, as well as energy consumption in hovering motion for different deformation foil models, are also studied. The results show that the deformed amplitude, 0.1*chord, among the cases simulated is an optimized camber amplitude for full deformation. The results obtained from the partial deformation foil model show that both Cl and Cd decrease with the increase of camber amplitude. It is found that the effect of deformation in the partial deformation model does not enhance lift force due to unfavorable camber. But TEV is significantly changed by the local AOA due to the deformation of the foil. Introduction.

Numerical Simulation of Dynamic Stall Characteristics for Wind Turbine under Yawed Condition

When a horizontal axis wind turbine rotor works under yawed condition, a cyclic variation of Angle of Attack (AOA) at blades will causes dynamic stall phenomenon and accordingly increases the fatigue load. In order to relate the yawed condition with dynamic stall characteristic, a 3D and time-accurate Computational Fluid Dynamics (CFD) is used for the simulations of flow-field and dynamic stall characteristic on the National Renewable Energy Laboratory (NREL) Phase VI wind turbine rotor at yaw 30 degrees. The local AOA and airfoil aerodynamics, i.e., lift coefficient Cl and drag coefficient Cd, are computed based on CFD results. The results show that the horizontal component of yawed inflow and unsteady flow around sections of blade will delay the formation of separation vortex and also the occurrence of stall. The dynamic load accompanied with dynamic stall phenomenon is significantly increased on blade, and the hysteresis characteristic of airfoil lift and drag is more remarkable at the inboard blade sections. The derived results are helpful to develop more reliable aerodynamic models for wind turbine design codes, and also can provide theoretical guidance for the optimal design of a wind turbine.

Improving the aerodynamic performance of a cycloidal rotor through active compliant morphing

ABSTRACTCycloidal rotors are a novel form of propulsion system that can be adapted to various forms of transport such as air and marine vehicles, with a geometrical design differing significantly from the conventional screw propeller. Research on cycloidal rotor design began in the early 1930s and has developed throughout the years to the point where such devices now operate as propulsion systems for various aerospace applications such as micro air vehicles, unmanned air vehicles and compound helicopters. The majority of research conducted on the cycloidal rotor’s aerodynamic performance have not assessed mitigating the dynamic stall effect, which can have a negative impact on the rotor performance when the blades operate in the rotor retreating side. A solution has been proposed to mitigate the dynamic stall effect through employment of active, compliant leading-edge morphing. A review of the current state of the art in this area is presented. A two-dimensional, implicit unsteady numerical analysis was conducted using the commercial computational fluid dynamics software package STAR CCM+, on a two-bladed cycloidal rotor. An overset mesh technique, otherwise known as a chimera mesh, was used to apply complex transient motions to the simulations. Active, compliant leading-edge morphing is applied to an oscillating NACA 0015 aerofoil to attempt to mitigate the dynamic stall whilst maintaining the positive dynamic lift coefficient (Cl) contributions. It was verified that by applying a pulsed input leading-edge rotational morphing schedule, the leading-edge vortex does not fully form and the large flow separation is prevented. Further work in this investigation will focus on coupling the active, leading-edge motion to the cycloidal rotor model with the aim to maximise aerodynamic performance.

Lift crisis of a spinning table tennis ball

The aerodynamic properties of a spinning table tennis ball were investigated using flight experiments. Using high-speed video cameras, the trajectory and rotation of an official ball (Nittaku 3-Star Premium), which was launched by a three rotor machine, were recorded. The drag and lift coefficients (CD and CL) were determined by analysing the video images. The measurements covered the speed and rotation range of typical table tennis shots in the form of the Reynolds number (Re) and dimensionless spin rate (SP), i.e. 3.0 × 104 < Re < 9.0 × 104 and 0 < SP < 1.0, and CD and CL were obtained as functions of Re and SP. We determined that the lift coefficient CL is not a monotonically increasing function of SP. A deep valley of CL was found around SP = 0.5, and the lift force exerted on a spinning ball almost vanished at Re = 9.0 × 104 and 0.48 < SP < 0.5. These results qualitatively agree with the results from recent wind tunnel tests, but quantitative differences owing to the unsteady nature of the flight experiments remain. This anomaly in the lift coefficient should be called the ‘lift crisis’.

Dimensionally and Physically Proper Lift, Drag, and Thrust-Related Numbers as Figures of Merit: Normalized Lift, Drag, and Thrust, ηL, ηD, and ηT

AbstractTextbooks state that the lift, drag, and thrust coefficients CL, CD, and CT, are numbers that must be dimensionally proper (i.e., dimensionless) for their use in comparing different data se...

Automotive shape optimization using the radial basis function model based on a parametric surface grid

By optimizing the aerodynamic shape parameters, the aerodynamic performance of the vehicle becomes better as the aerodynamic drag decreases. The driving stability also becomes better as the aerodynamic lift decreases. This research presents aerodynamic shape optimization which employs the multi-variable parametric model and the iterative optimal approach to reduce the aerodynamic drag and the aerodynamic lift. For aerodynamic studies with computational fluid dynamics simulations, a parametric surface grid model was used to morph and enhance the mesh quality by linear deformation of the exterior surfaces. This method employed the radial basis function model, and integrated optimization with multi-software provides excellent morphing ability and reasonable optimal designs. In this paper, the process of aerodynamic optimization for a vehicle body is divided into two phases. The first phase is two-dimensional body optimization aimed at a global search, and the second phase aims at a local approximation by running three-dimensional body optimization. The iterative optimal approach can optimize efficiently the aerodynamic characteristics with a reduction in the aerodynamic drag of 13.23% and a marked improvement in the aerodynamic lift. Sensitivity analysis of the design parameters demonstrated that the hood angle is the major factor in the aerodynamic drag coefficient CD. For the aerodynamic lift coefficient CL, the trunk lid angle is the major factor. In addition, the angle of the windshield and the angle of the side window have small influences on CL. The results obtained are accurate reference values for application in automotive engineering.