scholarly journals The onset of compressibility effects for aerofoils in ground effect

2007 ◽  
Vol 111 (1126) ◽  
pp. 797-806 ◽  
Author(s):  
G. Doig ◽  
T. J. Barber ◽  
E. Leonardi ◽  
A. J. Neely
Keyword(s):  
Mach Number ◽  
High Speed ◽  
Subsonic Flow ◽  
Flow Characteristics ◽  
Ground Effect ◽  
Aerodynamic Performance ◽  
Computational Studies ◽  
Pressure Gradients ◽  
Cfd Simulations ◽  
Compressibility Effects

Abstract The influence of flow compressibility on a highly-cambered inverted aerofoil in ground effect is presented, based on two-dimensional computational studies. This type of problem has relevance to open-wheel racing cars, where local regions of high-speed subsonic flow form under favourable pressure gradients, even though the maximum freestream Mach number is typically considerably less than Mach 0·3. An important consideration for CFD users in this field is addressed in this paper: the freestream Mach number at which flow compressibility significantly affects aerodynamic performance. More broadly, for aerodynamicists, the consequences of this are also considered. Comparisons between incompressible and compressible CFD simulations are used to identify important changes to the flow characteristics caused by density changes, highlighting the inappropriateness of incompressible simulations of ground effect flows for freestream Mach numbers as low as 0·15.

scholarly journals Flow compressibility effects around an open-wheel racing car

2014 ◽  
Vol 118 (1210) ◽  
pp. 1409-1431 ◽  
Author(s):  
J. Keogh ◽  
G. Doig ◽  
S. Diasinos
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Numerical Investigation ◽  
Ground Effect ◽  
Aerodynamic Performance ◽  
Additional Consideration ◽  
Cfd Simulations ◽  
Computational Expense ◽  
Mach Numbers ◽  
Compressibility Effects

AbstractA numerical investigation has been conducted into the influence of flow compressibility effects around an open-wheeled racing car. A geometry was created to comply with 2012 F1 regulations. Incompressible and compressible CFD simulations were compared – firstly with models which maintained Reynolds number as Mach number increased, and secondly allowing Mach number and Reynolds number to increase together as they would on track. Results demonstrated significant changes to predicted aerodynamic performance even below Mach 0·15. While the full car coefficients differed by a few percent, individual components (particularly the rear wheels and the floor/diffuser area) showed discrepancies of over 10% at higher Mach numbers when compressible and incompressible predictions were compared. Components in close ground proximity were most affected due to the ground effect. The additional computational expense required for the more physically-realistic compressible simulations would therefore be an additional consideration when seeking to obtain maximum accuracy even at low freestream Mach numbers.

Numerical investigation of the aerodynamic characteristics of a train subjected to different ground conditions

2018 ◽  
Vol 232 (10) ◽  
pp. 2371-2384 ◽  
Author(s):  
Ji-qiang Niu ◽  
Xi-feng Liang ◽  
Dan Zhou ◽  
Yue-ming Wang
Keyword(s):  
Wind Tunnel ◽  
Boundary Layers ◽  
High Speed ◽  
Rapid Development ◽  
Ground Effect ◽  
Aerodynamic Performance ◽  
Detached Eddy Simulation ◽  
Scaled Model ◽  
Ground Conditions ◽  
Ground Condition

Due to the rapid development of high-speed railways and the increasing speed of trains, the aerodynamic phenomenon caused by moving trains could be affected. Therefore, the scaled model test has been widely used to simulate the aerodynamic performance of the stationary train in wind tunnel. However, it is difficult to disregard the influence of the ground effect on the aerodynamic performance of trains. In this study, the delayed detached eddy simulation based on the shear stress transport κ–ω turbulence model is used to investigate the aerodynamic performance of trains on three ground conditions (stationary floor + stationary ballast, stationary ground + stationary ballast, and stationary ballast). The numerical method used in this paper is verified by a wind tunnel test. The way the three ground conditions influence the flow field around the train is also analyzed. The results show that the ground condition affects the thickness of the ballast boundary layers without a train, thickness of the train boundary layers, train drag, distribution of pressure and velocity along the train, and the size of the wake region; however, the ground condition had a little effect on the flow structures around the train tail. These findings can help in designing the wind tunnel experiment.

Impact of Nonuniform Leading Edge Coatings on the Aerodynamic Performance of Compressor Airfoils

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Michael E. Elmstrom ◽  
Knox T. Millsaps ◽  
Garth V. Hobson ◽  
Jeffrey S. Patterson
Keyword(s):  
Mach Number ◽  
Computational Fluid Dynamic ◽  
Total Pressure ◽  
Fluid Dynamic ◽  
Leading Edge ◽  
Aerodynamic Performance ◽  
Transition To Turbulence ◽  
Navier Stokes ◽  
Pressure Gradients ◽  
Small Separation

A computational fluid dynamic (CFD) investigation is presented that provides predictions of the aerodynamic impact of uniform and nonuniform coatings applied to the leading edge of a compressor airfoil in a cascade. Using a NACA 65(12)10 airfoil, coating profiles of varying leading edge nonuniformity were added. A nonuniform coating is obtained when a liquid coating is applied to a surface with high curvature, such as an airfoil leading edge. The CFD code used, RVCQ3D, is a Reynolds averaged Navier–Stokes solver, with a k-omega turbulence model. The code predicted that these changes in leading edge shape can lead to alternating pressure gradients in the first few percent of chord that create small separation bubbles and possibly early transition to turbulence. The change in total pressure loss and trailing edge deviation are presented as a function of a coating nonuniformity parameter. Results are presented over a range of negative and positive incidences and inlet Mach numbers from 0.6 to 0.8. A map is provided that shows the allowable degree of coating nonuniformity as a function of incidence and inlet Mach number.

scholarly journals SHOCKWAVE STUDY ON THE WINGS NACA 0012, NACA 64 - 206, AND NASA SC (2) - 0706 WITH Λ = 15O AT 0.85 MACH NUMBER

2021 ◽  
Vol 2 (1) ◽  
pp. 025-032
Author(s):  
Dewi Puspitasari ◽  
Kasyful Warist Kiat
Keyword(s):  
Mach Number ◽  
High Speed ◽  
Cfd Simulation ◽  
Lower Surface ◽  
Aerodynamic Performance ◽  
Ansys Fluent ◽  
Aircraft Wings ◽  
Contour Plots ◽  
The Difference ◽  
Naca 0012

Airfoil is used as a basic form on aircraft wings. Airfoil on the wing of the aircraft is used to produce lift that will lift the fuselage into the air. Lifting force results from the difference in pressure between the upper surface and the lower surface of an aircraft wings. In high speed flights shockwave will occur at certain parts of the wing which will adversely affect the aerodynamic performance of the wing. Wing aerodynamic performance at high speeds can be improved in various ways, one of which is by giving a angle to the wing span called a swept angle. This study will use 3D CFD simulation methods using Ansys Fluent. The airfoil used are NACA 0012, NACA 64-206, and NASA SC (2) -0706 with a chord length of 1 m, AR = 5, and λ = 1 with backward swept angle Λ = 15 °. Free stream flow is air flowing with Mach Number = 0,85 at sea level and steady conditions. Based on the simulation results, shock occurs on the upper and lower surfaces for NACA 0012 with Cl = 0 due to symmetric airfoil, whereas shock occurs only on the upper surface for NACA 64-206 and NASA SC (2) - 0706 with a Cl / Cd value of 18.55 ( NACA 64-206) and 20.78 (NASA SC (2) - 0706). This simulation also provides a visual representation of Mach Number contour plots in the middle stretch (Midspan) of the wing and Cl and Cd data.

Experimental and Computational Studies on Flow Characteristics of Single Expansion Nozzle

2021 ◽  
Author(s):  
Dakshina Murthy Inturi ◽  
Lovaraju Pinnam ◽  
Ramachandra Raju Vegesna
Keyword(s):  
Mach Number ◽  
Flow Field ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Oblique Shock ◽  
Solid Boundary ◽  
Computational Studies ◽  
Nozzle Pressure Ratio ◽  
Nozzle Pressure ◽  
Flow Field Characteristics

Abstract The present investigation aims to study the flow field characteristics of a single expansion nozzle (SEN). The flow field characteristics of conventional convergent-divergent (C-D) nozzle are also investigated for comparison. The experimental and computational studies were carried out for nozzle pressure ratios of 1.45, 1.55, 1.75, 2, 3, 4 and 5. The studies reveal that, for the single expansion nozzle the oblique shock moves towards the solid boundary with the increase of nozzle pressure ratio, which makes the flow to accelerate continuously in the majority of the divergent portion. The single expansion nozzle delivers the flow with higher Mach number than the C-D nozzle at the exit of the nozzle.

Development of Large Intermittent Wind Tunnels

1955 ◽  
Vol 59 (532) ◽  
pp. 259-278 ◽  
Author(s):  
J. Lukasiewicz
Keyword(s):  
Mach Number ◽  
Wind Tunnel ◽  
Mass Flow ◽  
High Speed ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Wind Tunnels ◽  
Number Range ◽  
Pressure Storage ◽  
Vacuum Storage

SummaryTwo types of intermittent wind tunnel drives, the pressure storage drive(with atmospheric exhaust) and the vacuum storage drive (with atmospheric inlet), are examined and found to match well the tunnel pressure ratio-mass flow characteristics over a wide Mach number range (0 to 4). The design of components of intermittent wind tunnel installations, their operation and instrumentation are then considered in some detail. In order to increase the output of intermittent wind tunnels to a level comparable to that of continuously running tunnels, it is proposed to drive the models during each tunnel run through a range of incidence. This technique is at present under development in the National Aeronautical Establishment's High Speed Aerodynamics Laboratory and results so far obtained are discussed. Two tunnels are considered as examples of large intermittent installations: a 4 ft. square pressure-driven tunnel and a 6 ft. square vacuum-driven tunnel. The former is found to be a more compact and economical installation. Relative merits of continuous and intermittent installations are discussed.

Aerodynamic Performance of Novel Lightweight Turbine Blade

2016 ◽  
Author(s):  
Yoji Okita ◽  
Kozo Nita ◽  
Seiji Kubo
Keyword(s):  
Mach Number ◽  
Turbine Blade ◽  
Weight Reduction ◽  
Pressure Loss ◽  
High Speed ◽  
Aerodynamic Performance ◽  
Pressure Side ◽  
Design Point ◽  
Aerodynamic Loss ◽  
Cooling Passage

The primary contribution of this research is to clarify the aerodynamic performance of a novel lightweight turbine blade with internal cooling passage and external film cooling, which is invented aiming at drastic weight reduction of a cooled blade. With a considerably thinner airfoil, a significant separation region is formed along the pressure side, and therefore aerodynamic performance with such a flow field should be investigated. First, the lightweight cooled airfoil is designed. In the design process, a conventional thick airfoil is first defined as a baseline. With the baseline airfoil, only the mid and rear part of pressure side profile is redesigned to thin the airfoil without any change in the suction side geometry. The airfoil geometry is optimized so as not to bring significant aerodynamic loss increase. In this numerical optimization, the airfoil shape is gradually changed and evaluated step by step. In every step, an adjoint variable method is used to seek better airfoil shape, and then the generated new shape is evaluated with full RANS calculation. This iteration is repeated until any further recognizable weight reduction cannot be obtained without sensitive pressure loss increase and/or the airfoil shape reaches some geometrical constraints. The resultant optimized airfoil is approximately 20% lighter than the baseline hollow airfoil without any noticeable change in aerodynamic loss in the numerical solution. Next, the optimized airfoil is tested in a high speed linear cascade rig to verify its aerodynamic performance. The baseline airfoil is also tested for comparison. The rig is composed of six airfoil passages. The compressed air is supplied to the cascade and discharges to the atmospheric exhaust chamber. The air is also heated up to about 540 K upstream of the cascade. The cascade exit Mach number at the design point is 1.25, while in the experiment other several off-design conditions are also tested to check if there is any Mach number sensitivity. At the design point, the optimized lightweight airfoil shows less total pressure loss compared to the baseline airfoil. Also, at any other off-design Mach number conditions tested, the magnitude of the pressure loss is less with the lightweight airfoil. These results verify that the proposed airfoil does not only bring a considerable weight advantage but also compares favorably with the conventional airfoil in aerodynamic performance.

Impact of Non-Uniform Leading Edge Coatings on the Aerodynamic Performance of Compressor Airfoils

2005 ◽  
Author(s):  
Michael E. Elmstrom ◽  
Knox T. Millsaps ◽  
Garth V. Hobson ◽  
Jeffrey S. Patterson
Keyword(s):  
Mach Number ◽  
Total Pressure ◽  
Fluid Dynamic ◽  
Leading Edge ◽  
Aerodynamic Performance ◽  
Transition To Turbulence ◽  
Navier Stokes ◽  
Pressure Gradients ◽  
Uniform Coating ◽  
Small Separation

A computational fluid dynamic (CFD) investigation is presented that provides predictions of the aerodynamic impact of uniform and non-uniform coatings applied to the leading edge of a compressor airfoil in a cascade. Using a NACA 65(12)10 airfoil, coating profiles of varying leading edge non-uniformity were added. A non-uniform coating is obtained when a liquid coating is applied to a surface with high curvature, such as an airfoil leading edge. The CFD code used, RVCQ3D, is a Reynolds Averaged, Navier-Stokes (RANS) solver, with a k-omega turbulence model. The code predicted that these changes in leading edge shape can lead to alternating pressure gradients in the first few percent of chord that create small separation bubbles and possibly early transition to turbulence. The change in total pressure loss and trailing edge deviation are presented as a function of a coating non-uniformity parameter. Results are presented over a range of negative and positive incidences and inlet Mach numbers from 0.6 to 0.8. A map is provided that shows the allowable degree of coating non-uniformity as a function of incidence and inlet Mach number.

Compressibility effects on the structural evolution of transitional high-speed planar wakes

2016 ◽  
Vol 796 ◽  
pp. 5-39 ◽  
Author(s):  
Jean-Pierre Hickey ◽  
Fazle Hussain ◽  
Xiaohua Wu
Keyword(s):  
Mach Number ◽  
Linear Stability ◽  
High Speed ◽  
Three Dimensional ◽  
Structural Evolution ◽  
Base Flow ◽  
Length Scale ◽  
Two Dimensional ◽  
Linear Mode ◽  
Compressibility Effects

The compressibility effects on the structural evolution of the transitional high-speed planar wake are studied. The relative Mach number ($Ma_{r}$) of the laminar base flow modifies two fundamental features of planar wake transition: (i) the characteristic length scale defined by the most unstable linear mode; and (ii) the domain of influence of the structures within the staggered two-dimensional vortex array. Linear stability results reveal a reduced growth (approximately 30 % reduction up to $Ma_{r}=2.0$) and a quasilinear increase of the wavelength of the most unstable, two-dimensional instability mode (approximately 20 % longer over the same $Ma_{r}$ range) with increasing $Ma$. The primary wavelength defines the length scale imposed on the emerging transitional structures; naturally, a longer wavelength results in rollers with a greater streamwise separation and hence also larger circulation. A reduction of the growth rate and an increase of the principal wavelength results in a greater ellipticity of the emerging rollers. Compressibility effects also modify the domain of influence of the transitional structures through an increased cross-wake and inhibited streamwise communication as characteristic paths between rollers are deflected due to local $Ma$ gradients. The reduced streamwise domain of influence impedes roller pairing and, for a sufficiently large relative $Ma$, pairing is completely suppressed. Thus, we observe an increased two-dimensionality with increasing Mach number: directly contrasting the increasing three-dimensional effects in high-speed mixing layers. Temporally evolving direct numerical simulations conducted at $Ma=0.8$ and 2.0, for Reynolds numbers up to 3000, support the physical insight gained from linear stability and vortex dynamics studies.

scholarly journals A Compressible Turbulence Model for Pressure—Strain

Fluids ◽  
2022 ◽  
Vol 7 (1) ◽  
pp. 34
Author(s):  
Hechmi Khlifi ◽  
Adnen Bourehla
Keyword(s):  
Mach Number ◽  
Shear Flow ◽  
Turbulent Flows ◽  
High Speed ◽  
Turbulence Models ◽  
Mixing Layers ◽  
Compressible Turbulence ◽  
Homogeneous Shear ◽  
Homogeneous Shear Flow ◽  
Compressibility Effects

This work focuses on the performance and validation of compressible turbulence models for the pressure-strain correlation. Considering the Launder Reece and Rodi (LRR) incompressible model for the pressure-strain correlation, Adumitroaie et al., Huang et al., and Marzougui et al., used different modeling approaches to develop turbulence models, taking into account compressibility effects for this term. Two numerical coefficients are dependent on the turbulent Mach number, and all of the remaining coefficients conserve the same values as in the original LRR model. The models do not correctly predict the compressible turbulence at a high-speed shear flow. So, the revision of these models is the major aim of this study. In the present work, the compressible model for the pressure-strain correlation developed by Khlifi−Lili, involving the turbulent Mach number, the gradient, and the convective Mach numbers, is used to modify the linear mean shear strain and the slow terms of the previous models. The models are tested in two compressible turbulent flows: homogeneous shear flow and the newly developed plane mixing layers. The predicted results of the proposed modifications of the Adumitroaie et al., Huang et al., and Marzougui et al., models and of its universal versions are compared with direct numerical simulation (DNS) and experiment data. The results show that the important parameters of compressibility in homogeneous shear flow and in the mixing layers are well predicted by the proposal models.

Sign in / Sign up

Export Citation Format

Share Document