Optimisation and analysis of efficiency for contra-rotating propellers for high-altitude airships

2019 ◽  
Vol 123 (1263) ◽  
pp. 706-726
Author(s):  
J. Tang ◽  
X. Wang ◽  
D. Duan ◽  
W. Xie
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
High Altitude ◽  
Reference Frames ◽  
Lift Coefficient ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Optimization Approach ◽  
Axial Distance ◽  
The Individual

ABSTRACTAn improved variational optimization approach is established to optimize and analyse the propulsion efficiency of the high-altitude contra-rotating propellers for high-altitude airships based on the Vortex Lattice Lifting Line Method. The optimum radial circulation distribution, chord and pitch distribution are optimized under the maximum lift-to-drag ratio of aerofoils. To consider the effects of the actual Reynolds number and the Mach number of each aerofoil section, aerodynamics such as lift coefficient, drag coefficient and lift-to-ratio are obtained by interpolating a CFD database, which is established by numerical simulations under different Reynolds number, Mach number and angles-of-attack. The improved method is verified by validation cases on a high-altitude CRP using the three-dimensional steady Reynolds-averaged Navier-Stokes solver and moving reference frames technique. The optimization results of thrust, torque and efficiency for both the individual front/rear propeller and CRP are shown to agree reasonably well with the CFD results. Using the improved approach, the influence of blade numbers, diameter, rotation speeds, axial distance and torque ratio on the optimum efficiency of CRPs is illustrated in detail by conducting parametric studies.

Numerical Simulation on Aerodynamics of Ramjet Projectiles

2011 ◽  
Vol 201-203 ◽  
pp. 89-92 ◽  
Author(s):  
Jia Xian Zhang ◽  
Yan Na Wang ◽  
Rui Min Liu
Keyword(s):  
Numerical Simulation ◽  
Mach Number ◽  
Lift Coefficient ◽  
Three Dimensional ◽  
Numerical Algorithms ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Pressure Center ◽  
Complex Wave ◽  
Center Increase

Three-dimensional Reynolds-averaged Navier-Stokes simulations have been performed to explore the aerodynamic characteristics of ramjet projectiles. The turbulence model used is the RNG k-ε model. The numerical algorithms termed total variational diminishing (TVD) was adopted. The complex wave structures of ramjet projectiles with different architecture at different inflow Mach number were achieved by numerical simulation. The influence of inflow Mach number on aerodynamic characteristics and pressure center of ramjet projectiles were analyzed. Results show that lift coefficient and pressure center increase with the argument of inflow Mach number. Ramjet projectiles with different architecture have different drag coefficient trend.

Validation of Numerical Analysis to Estimate Airfoil Aerodynamic Characteristics at Low Reynolds Number Region

2015 ◽  
Author(s):  
Donghwi Lee ◽  
Taku Nonomura ◽  
Akira Oyama ◽  
Kozo Fujii
Keyword(s):  
Reynolds Number ◽  
Numerical Method ◽  
Low Reynolds Number ◽  
Lift Coefficient ◽  
Three Dimensional ◽  
Aerodynamic Characteristics ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Eddy Simulation ◽  
Low Reynolds

In this study, two-dimensional laminar simulation (2-D Lam), two-dimensional Reynolds Averaged Navier-Stokes simulation with the Spalart-Allmaras turbulence model (2-D RANS(SA)), and implicit three-dimensional large-eddy simulation (3-D LES) are performed for NACA0012, NACA0006, and Ishii airfoils at Rec = 3.0 × 104. The relation between a predictability of airfoil aerodynamic characteristics and a dependence of airfoil geometry shape of each numerical method is evaluated at the low Reynolds number. Although little discrepancy is observed for the lift coefficient predictability, significant differences are presented in terms of the separation and reattachment points predictability depending on the numerical methods. The 2-D Lam simulation can predict the lift coefficients as well as the separation and reattachment points qualitatively as similar to the 3-D LES results except for the high angle of attack which is accompanied by the massive separation. The 2-D RANS(SA), the weak nonlinearity and stall phenomena for the lift coefficients are observed. A good predictability of the separation point are shown, however, it cannot be estimated the reattachment points due to the trend to predict widely for the separation region. The predictabilities of each numerical method appear regardless of the airfoil shapes.

Dynamic Stall Simulation of Flow Over NACA0012 Airfoil at 1 Million Reynolds Number

2015 ◽  
Author(s):  
Venkata Ravishankar Kasibhotla ◽  
Danesh Tafti
Keyword(s):  
Reynolds Number ◽  
Flow Field ◽  
Lift Coefficient ◽  
Three Dimensional ◽  
Dynamic Stall ◽  
Sharp Drop ◽  
Airfoil Surface ◽  
Naca0012 Airfoil ◽  
Reduced Frequency ◽  
Edge Vortex

The paper is concerned with the prediction and analysis of dynamic stall of flow past a pitching NACA0012 airfoil at 1 million Reynolds number based on the chord length of the airfoil and at reduced frequency of 0.25 in a three dimensional flow field. The turbulence in the flow field is resolved using large eddy simulations with the dynamic Smagorinsky model at the sub grid scale. The development of dynamic stall vortex, shedding and reattachment as predicted by the present study are discussed in detail. This study has shown that the downstroke phase of the pitching motion is strongly three dimensional and is highly complex, whereas the flow is practically two dimensional during the upstroke. The lift coefficient agrees well with the measurements during the upstroke. However, there are differences during the downstroke. The computed lift coefficient undergoes a sharp drop during the start of the downstroke as the convected leading edge vortex moves away from the airfoil surface. This is followed by a recovery of the lift coefficient with the formation of a secondary trailing edge vortex. While these dynamics are clearly reflected in the predicted lift coefficient, the experimental evolution of lift during the downstroke maintains a fairly smooth and monotonic decrease in the lift coefficient with no lift recovery. The simulations also show that the reattachment process of the stalled airfoil is completed before the start of the upstroke in the subsequent cycle due to the high reduced frequency of the pitching cycle.

A CFD-Based Parametric Study on Modification of Discrete Sister Holes Location for the Film Cooling Flow

2014 ◽  
Author(s):  
Siavash Khajehhasani ◽  
Bassam Jubran
Keyword(s):  
Film Cooling ◽  
Numerical Study ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Base Case ◽  
Spanwise Direction ◽  
Cooling Performance ◽  
Cooling Flow ◽  
Lift Off ◽  
The Individual

A numerical study on the effects of sister holes locations on film cooling performance is presented. This includes the change of the location of the individual discrete sister holes in the streamwise and spanwise directions, where each one of these directions includes 9 different locations, The simulations are performed using three-dimensional Reynolds-Averaged Navier Stokes analysis with the realizable k–ε model combined with the standard wall function. The variation of the sister holes in the streamwise direction provides similar film cooling performance as the base case for both blowing ratios of 0.5 and 1. On the other hand, the spanwise variation of the sister holes’ location has a more prominent effect on the effectiveness. In some cases, as a result of the anti-vortices generated from the sister holes and the repositioning of the sister holes in the spanwise direction, the jet lift-off effect notably decreases and more volume of coolant is distributed in the spanwise direction.

scholarly journals Computed Eccentricity Effects on Turbine Rim Seals at Engine Conditions With a Mainstream

1994 ◽  
Author(s):  
Zhou Guo ◽  
David L. Rhode ◽  
Fred M. Davis
Keyword(s):  
Reynolds Number ◽  
Temperature Rise ◽  
Three Dimensional ◽  
Computer Code ◽  
Interaction Effects ◽  
Navier Stokes ◽  
Radial Clearance ◽  
Turbine Wheel ◽  
Blade Root

A previously verified axisymmetric Navier-Stokes computer code was extended for three-dimensional computation of eccentric rim seals of almost any configuration. All compressibility and thermal/momentum interaction effects are completely, included, and the temperature, pressure and Reynolds number of the mainstream, coolant stream and turbine wheel are fixed at actual engine conditions. Regardless of the seal eccentricity, both ingress and egress are found between θ = −30° and 100°. which encompasses the location of maximum radial clearance at θ = 0°. All other θ locations within the rim seal show only egress, as does the concentric basecase for all circumferential locations. Further, the maximum ingress occurs near θ = 30° for all eccentricities. This is found to produce a blade root/retainer temperature rise from the concentric case of 390 percent at 50 percent eccentricity and a 77 percent rise at 7.5 percent eccentricity. In addition, the nature of an increased eccentricity causing a decreased seal effectiveness is examined, along with the corresponding increase of cavity-averaged temperature.

scholarly journals Nonlinear amplification in hydrodynamic turbulence

2021 ◽  
Vol 930 ◽  
Author(s):  
Kartik P. Iyer ◽  
Katepalli R. Sreenivasan ◽  
P.K. Yeung
Keyword(s):  
Reynolds Number ◽  
Isotropic Turbulence ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Developed Turbulence ◽  
Advection Term ◽  
Nonlinear Amplification

Using direct numerical simulations performed on periodic cubes of various sizes, the largest being $8192^3$ , we examine the nonlinear advection term in the Navier–Stokes equations generating fully developed turbulence. We find significant dissipation even in flow regions where nonlinearity is locally absent. With increasing Reynolds number, the Navier–Stokes dynamics amplifies the nonlinearity in a global sense. This nonlinear amplification with increasing Reynolds number renders the vortex stretching mechanism more intermittent, with the global suppression of nonlinearity, reported previously, restricted to low Reynolds numbers. In regions where vortex stretching is absent, the angle and the ratio between the convective vorticity and solenoidal advection in three-dimensional isotropic turbulence are statistically similar to those in the two-dimensional case, despite the fundamental differences between them.

scholarly journals A Review of Passive Micromixers with a Comparative Analysis

Micromachines ◽  
2020 ◽  
Vol 11 (5) ◽  
pp. 455 ◽  
Author(s):  
Wasim Raza ◽  
Shakhawat Hossain ◽  
Kwang-Yong Kim
Keyword(s):  
Reynolds Number ◽  
Comparative Analysis ◽  
Three Dimensional ◽  
Navier Stokes ◽  
Number Range ◽  
Pressure Drops ◽  
Convection Diffusion ◽  
Wide Range ◽  
Quantitative Analyses ◽  
Mixing Costs

A wide range of existing passive micromixers are reviewed, and quantitative analyses of ten typical passive micromixers were performed to compare their mixing indices, pressure drops, and mixing costs under the same axial length and flow conditions across a wide Reynolds number range of 0.01–120. The tested micromixers were selected from five types of micromixer designs. The analyses of flow and mixing were performed using continuity, Navier-Stokes and convection-diffusion equations. The results of the comparative analysis were presented for three different Reynolds number ranges: low-Re (Re ≤ 1), intermediate-Re (1 < Re ≤ 40), and high-Re (Re > 40) ranges, where the mixing mechanisms are different. The results show a two-dimensional micromixer of Tesla structure is recommended in the intermediate- and high-Re ranges, while two three-dimensional micromixers with two layers are recommended in the low-Re range due to their excellent mixing performance.

Numerical Three-Dimensional Pressure Patterns in a Recess of a Turbulent and Compressible Hybrid Journal Bearing

2003 ◽  
Vol 125 (2) ◽  
pp. 301-308 ◽  
Author(s):  
Mathieu Helene ◽  
Mihai Arghir ◽  
Jean Frene
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Journal Bearing ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Wire Mesh ◽  
Primary Concern ◽  
Reference Parameters ◽  
Exit Mach Number

The present work investigates the flow in the feeding recess of a hybrid journal bearing. Numerical integration of the complete Navier-Stokes equations was performed with an appropriate turbulence model. Of primary concern is the pressure field on the rotating journal surface that is commonly known as the recess pressure pattern. The goal of the work is to determine the influences of fluid compressibility, operating conditions and recess geometry. Reference parameters selected for this study comprise feeding Reynolds number Rea of 2.105, sliding Reynolds number Rec of 5.103 and recess depth over film thickness ratio e/H of 2.2. Compressibility was considered first. Three values of the axial exit Mach number were selected for computation, namely 0.2, 0.45, and 0.7. As no significant variation was found, the Mach number was fixed at 0.45 in subsequent studies concerning other parameters:     Feeding Reynolds number, Rea       2.104,2.105,4.105     Recess depth, e/H           0, 2.2, 8     Feedhole axis inclination        90°, 135°, 165°     Feedhole location (Figs. 1(a) and 13)   centered, downstream offset. As each parameter is varied, wire mesh plot of pressure and its sectional profiles are examined and effects of varying various parameters are discussed in reference to flow processes as they may affect the support characteristics of the hybrid journal bearing.

The Three-Dimensional Turbulent Boundary Layer on an Infinite Yawed Wing

1971 ◽  
Vol 22 (4) ◽  
pp. 346-362 ◽  
Author(s):  
J. F. Nash ◽  
R. R. Tseng
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Turbulent Boundary Layer ◽  
Lift Coefficient ◽  
Three Dimensional ◽  
Numerical Representation ◽  
Two Dimensional ◽  
Incompressible Turbulent Boundary Layer ◽  
Displacement Thickness ◽  
Attachment Line

SummaryThis paper presents the results of some calculations of the incompressible turbulent boundary layer on an infinite yawed wing. A discussion is made of the effects of increasing lift coefficient, and increasing Reynolds number, on the displacement thickness, and on the magnitude and direction of the skin friction. The effects of the state of the boundary layer (laminar or turbulent) along the attachment line are also considered.A study is made to determine whether the behaviour of the boundary layer can adequately be predicted by a two-dimensional calculation. It is concluded that there is no simple way to do this (as is provided, in the laminar case, by the principle of independence). However, with some modification, a two-dimensional calculation can be made to give an acceptable numerical representation of the chordwise components of the flow.

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