scholarly journals Numerical analysis of high-lift configurations with oscillating flaps

2021 ◽  
Author(s):  
Johannes Ruhland ◽  
Christian Breitsamter
Keyword(s):  
Reynolds Number ◽  
Flow Separation ◽  
Separated Flow ◽  
Navier Stokes ◽  
Rotational Axis ◽  
High Lift ◽  
Hinge Point ◽  
Reduced Frequency ◽  
Flap Deflection ◽  
The Impact

AbstractThis study presents two-dimensional aerodynamic investigations of various high-lift configuration settings concerning the deflection angles of droop nose, spoiler and flap in the context of enhancing the high-lift performance by dynamic flap movement. The investigations highlight the impact of a periodically oscillating trailing edge flap on lift, drag and flow separation of the high-lift configuration by numerical simulations. The computations are conducted with regard to the variation of the parameters reduced frequency and the position of the rotational axis. The numerical flow simulations are conducted on a block-structured grid using Reynolds Averaged Navier Stokes simulations employing the shear stress transport $$k-\omega $$ k - ω turbulence model. The feature Dynamic Mesh Motion implements the motion of the oscillating flap. Regarding low-speed wind tunnel testing for a Reynolds number of $$0.5 \times 10^{6}$$ 0.5 × 10 6 the flap movement around a dropped hinge point, which is located outside the flap, offers benefits with regard to additional lift and delayed flow separation at the flap compared to a flap movement around a hinge point, which is located at 15 % of the flap chord length. Flow separation can be suppressed beyond the maximum static flap deflection angle. By means of an oscillating flap around the dropped hinge point, it is possible to reattach a separated flow at the flap and to keep it attached further on. For a Reynolds number of $$20 \times 10^6$$ 20 × 10 6 , reflecting full scale flight conditions, additional lift is generated for both rotational axis positions.

Computational Fluid Dynamic Applications for Jet Propulsion System Integration

1991 ◽  
Vol 113 (1) ◽  
pp. 40-50 ◽  
Author(s):  
R. H. Tindell
Keyword(s):  
System Integration ◽  
Fluid Dynamic ◽  
Low Cost ◽  
Separated Flow ◽  
Propulsion System ◽  
Navier Stokes ◽  
Aerospace Vehicles ◽  
Design Engineers ◽  
Flow Phenomena ◽  
The Impact

The impact of computational fluid dynamics (CFD) methods on the development of advanced aerospace vehicles is growing stronger year by year. Design engineers are now becoming familiar with CFD tools and are developing productive methods and techniques for their applications. This paper presents and discusses applications of CFD methods used at Grumman to design and predict the performance of propulsion system elements such as inlets and nozzles. The paper demonstrates techniques for applying various CFD codes and shows several interesting and unique results. A novel application of a supersonic Euler analysis of an inlet approach flow field, to clarify a wind tunnel-to-flight data conflict, is presented. In another example, calculations and measurements of low-speed inlet performance at angle of attack are compared. This is highlighted by employing a simplistic and low-cost computational model. More complex inlet flow phenomena at high angles of attack, calculated using an approach that combines a panel method with a Navier-Stokes (N-S) code, is also reviewed. The inlet fluid mechanics picture is rounded out by describing an N-S calculation and a comparison with test data of an offset diffuser having massively separated flow on one wall. Finally, the propulsion integration picture is completed by a discussion of the results of nozzle-afterbody calculations, using both a complete aircraft simulation in a N-S code, and a more economical calculation using an equivalent body of revolution technique.

scholarly journals Propulsion Performance of the Full-Active Flapping Foil in Time-Varying Freestream

2020 ◽  
Vol 10 (18) ◽  
pp. 6226
Author(s):  
Zhanfeng Qi ◽  
Lishuang Jia ◽  
Yufeng Qin ◽  
Jian Shi ◽  
Jingsheng Zhai
Keyword(s):  
Flow Velocity ◽  
Steady Flow ◽  
Navier Stokes ◽  
Time Varying ◽  
Flapping Foil ◽  
Propulsion Performance ◽  
Reduced Frequency ◽  
Motion Parameters ◽  
Volume Method ◽  
The Impact

A numerical investigation of the propulsion performance and hydrodynamic characters of the full-active flapping foil under time-varying freestream is conducted. The finite volume method is used to calculate the unsteady Reynolds averaged Navier–Stokes by commercial Computational Fluid Dynamics (CFD) software Fluent. A mesh of two-dimensional (2D) NACA0012 foil with the Reynolds number Re = 42,000 is used in all simulations. We first investigate the propulsion performance of the flapping foil in the parameter space of reduced frequency and pitching amplitude at a uniform flow velocity. We define the time-varying freestream as a superposition of steady flow and sinusoidal pulsating flow. Then, we study the influence of time-varying flow velocity on the propulsion performance of flapping foil and note that the influence of the time-varying flow is time dependent. For one period, we find that the oscillating amplitude and the oscillating frequency coefficient of the time-varying flow have a significant influence on the propulsion performance of the flapping foil. The influence of the time-varying flow is related to the motion parameters (reduced frequency and pitching amplitude) of the flapping foil. The larger the motion parameters, the more significant the impact of propulsion performance of the flapping foil. For multiple periods, we note that the time-varying freestream has little effect on the propulsion performance of the full-active flapping foil at different pitching amplitudes and reduced frequency. In summary, we conclude that the time-varying incoming flow has little effect on the flapping propulsion performance for multiple periods. We can simplify the time-varying flow to a steady flow field to a certain extent for numerical simulation.

Influence of Liquid Properties on Energy Conversion During Crown Evolution Following Drop Impact Upon Films

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Yujia Zhang ◽  
Peiqing Liu ◽  
Qiulin Qu ◽  
Fanglin Liu ◽  
Ramesh K. Agarwal
Keyword(s):  
Reynolds Number ◽  
Energy Conversion ◽  
Weber Number ◽  
Stokes Equations ◽  
Drop Impact ◽  
Navier Stokes ◽  
Impact Process ◽  
Vof Model ◽  
The Moment ◽  
The Impact

Abstract The energy conversion is proposed to analyze the effects of liquid properties on the formation of an ejecta sheet, prompt splashing, and crown evolution. The incompressible laminar Navier–Stokes equations coupled with the volume-of-fluid (VOF) model are solved numerically in an axisymmetric frame to simulate the impact process. Based on the energy conversion curves and liquid–gas interface shapes, the Weber number is shown to be the main dimensionless quantity controlling the impact process, especially with regard to crown evolution. However, the Reynolds number does have some influence on the drop impact process, especially during the stage of ejecta sheet formation and prompt splashing. By studying energy conversion during the impact process, the crown evolution is shown to be accelerated significantly with decreasing Weber number, but is hardly affected by the Reynolds number. A linear relation is found between the time to the moment of crown stabilization (when the crown height reaches its maximum value) and the square root of the Weber number. The relationship between the Weber number and the energy distribution at the moment of crown stabilization is also studied.

A CFD Study of Low Reynolds Number Flow in High Lift Cascades

2010 ◽  
Author(s):  
Roberto Pacciani ◽  
Michele Marconcini ◽  
Andrea Arnone ◽  
Francesco Bertini
Keyword(s):  
Reynolds Number ◽  
Separation Bubble ◽  
Structural Characteristics ◽  
Low Reynolds Number ◽  
Separated Flow ◽  
Flow Region ◽  
Suction Side ◽  
Transitional Region ◽  
High Lift ◽  
Low Reynolds

A study of the separated flow in high-lift, low-Reynolds-number cascade, has been carried out using a novel three-equation, transition-sensitive, turbulence model. It is based on the coupling of an additional transport equation for the so-called laminar kinetic energy with the Wilcox k-ω model. Such an approach takes into account the increase of the non-turbulent fluctuations in the pre-transitional and transitional region. Two high-lift cascades (T106C and T108), recently tested at the von Ka´rma´n Institute in the framework of the European project TATMo (Turbulence and Transition Modelling for Special Turbomachinery Applications), were analyzed. The two cascades have different loading distributions and suction side diffusion rates, and therefore also different separation bubble characteristics and loss levels. The analyzed Reynolds number values span the whole range typically encountered in aeroengines low-pressure turbines operations. Several expansion ratios for steady inflow conditions characterized by different freestream turbulence intensities were considered. A detailed comparison between measurements and computations, including bubble structural characteristics, will be presented and discussed. Results with the proposed model show its ability to predict the evolution of the separated flow region, including bubble bursting phenomena, in high-lift cascades operating in LP-turbine conditions.

Active Flow Control of Separated Turbulent Flow Over a Hump Using RANS, DES, and LES

2008 ◽  
Author(s):  
Subhadeep Gan ◽  
Urmila Ghia ◽  
Karman Ghia
Keyword(s):  
Reynolds Number ◽  
Flow Control ◽  
Flow Separation ◽  
Turbulence Modeling ◽  
Active Flow Control ◽  
Separated Flow ◽  
Experimental Results ◽  
Complex Flow ◽  
Active Flow ◽  
Turbulent Separated Flow

Most practical flows in engineering applications are turbulent, and exhibit separation. Losses due to separation are undesirable because they generally have adverse effects on performance and efficiency. Therefore, control of turbulent separated flows has been a topic of significant interest as it can reduce separation losses. It is of utmost importance to understand the complex flow dynamics that leads to flow separation and come up with methods of flow control. In the past, passive flow-control was mostly implemented that does not require any additional energy source to reduce separation losses but it leads to increasing viscous losses at higher Reynolds number. More recent work has been focused primarily on active flow-control techniques that can be turned on and off depending on the requirement of flow-control. The present work is focused on implementing flow control using steady suction in the region of flow separation. The present work is Case 3 of the 2004 CFD Validation on Synthetic Jets and Turbulent Separation Control Workshop, http://cfdval2004.larc.nasa.gov/case3.html, conducted by NASA for the flow over a wall-mounted hump. The flow over a hump is an example of a turbulent separated flow. This flow is characterized by a simple geometry, but, nevertheless, is rich in many complex flow phenomena such as shear layer instability, separation, reattachment, and vortex interactions. The baseline case has been successfully simulated by Gan et al., 2007. The flow is simulated at a Reynolds number of 371,600, based on the hump chord length, C, and Mach number of 0.04. The flow control is being achieved via a slot at approximately 65% C by using steady suction. Solutions are presented for the three-dimensional RANS SST, steady and unsteady, turbulence model and DES and LES turbulence modeling approaches. Multiple turbulence modeling approaches help to ascertain what techniques are most appropriate for capturing the physics of this complex separated flow. Second-order accurate time derivatives are used for all implicit unsteady simulation cases. Mean-velocity contours and turbulent kinetic energy contours are examined at different streamwise locations. Detailed comparisons are made of mean and turbulence statistics such as the pressure coefficient, skinfriction coefficient, and Reynolds stress profiles, with experimental results. The location of the reattachment behind the hump is compared with experimental results. The successful control of this turbulent separated flow causes a reduction in the reattachment length, compared with the uncontrolled case. The effects of steady suction on flow separation and reattachment are discussed.

scholarly journals Swirl boundary layer and flow separation at the inlet of a rotating pipe

2016 ◽  
Vol 811 ◽  
pp. 350-371 ◽  
Author(s):  
F.-J. Cloos ◽  
D. Stapp ◽  
P. F. Pelz
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Flow Separation ◽  
Momentum Equation ◽  
Layer Growth ◽  
Boundary Layer Theory ◽  
Critical Flow ◽  
Flow Number ◽  
The Impact ◽  
Momentum Boundary Layer

When a fluid enters a rotating circular pipe, an angular momentum or swirl boundary layer appears at the wall and interacts with the axial momentum boundary layer. In the centre of the pipe, the fluid is free of swirl and is accelerated due to boundary layer growth. Below a critical flow number, defined as the ratio of average axial velocity to circumferential velocity of the pipe, there is flow separation, known in the turbomachinery context as part load recirculation. To describe this phenomenon analytically, we extended boundary layer theory to a swirl boundary layer interacting with the axial momentum boundary layer. The solution of the resulting generalized von Kármán momentum equation takes into account the influence of the Reynolds number and flow number. We show the impact of swirl on the axial boundary layer and conduct experiments in which we vary Reynolds number, flow number and surface roughness to validate the analytical results. The extended boundary layer theory predicts a critical flow number which is analytically derived and validated. Below this critical flow number, separation is expected.

Numerical and Experimental Investigation of Low Reynolds Number Effects on Laminar Flow Separation and Transition in a Cascade of Compressor Blades

2000 ◽  
Author(s):  
Shunji Enomoto ◽  
C. Hah ◽  
G. V. Hobson
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Flow Separation ◽  
Low Reynolds Number ◽  
Numerical Procedure ◽  
Compressor Blade ◽  
Navier Stokes ◽  
Flow Transition ◽  
Reynolds Number Effects ◽  
Low Reynolds

The results of an experimental and numerical comparison of the effects of low Reynolds number on flow separation and transition in a controlled-diffusion compressor cascade are presented. The flow separation and subsequent flow transition are associated with low Reynolds number effects in the compressor blade rows. Current steady-state Reynolds-averaged Navier-Stokes codes with available turbulence and transition models do not calculate the current flow phenomena properly. An unsteady three-dimensional Navier-Stokes calculation that applies a third-order accurate upwind method has been performed and the numerical results are compared to the measurements in detail. The results from the current numerical procedure agree very well with the measurements in terms of laminar flow separation, reattachment, and subsequent flow transition at low Reynolds numbers. The present study indicates that flow separation and flow transition inside compressor blade rows at low Reynolds number are phenomena dominated by relatively larger eddies near the wall and can be simulated with the current type of unsteady numerical procedure.

scholarly journals The Suction Control Characteristics of Flow Separation on NACA 23012

2020 ◽  
Vol 2 (1) ◽  
pp. 1-15
Author(s):  
Moses Oluwatosin Julius ◽  
Saheed Adewale Adio ◽  
Adam Olatunji Muritala ◽  
Oluwasanmi Alonge
Keyword(s):  
Flow Separation ◽  
Aerodynamic Characteristics ◽  
Control Technique ◽  
Navier Stokes ◽  
Suction Control ◽  
Lift Enhancement ◽  
Stall Angle ◽  
The Impact ◽  
Drag Ratio ◽  
Lift To Drag Ratio

The enormous loss of momentum leads to stall and adversely affects the aerodynamic performance of aeroplane wings which may lead to a disaster, more importantly, risking the safety of the aeroplane by putting lives of passengers on it in danger. Therefore, this paper focuses on the enhancement of aerodynamic characteristics of NACA 23012 through the mitigation of flow separation and delay of the stall at higher angles of attack by using suction for Reynolds number (Re) = 3.4 x 106 . Considering the different suction features such as suction width, suction position, and suction coefficient, the separation delay capability of a suction control is studied. Also, the lift to drag ratio and the impact of energy consumption variation during the control technique are used for estimating the control effects. The Reynolds Average Navier-Stokes (RANS) equations are employed together with the Menter’s shear stress turbulent model. The result of this study revealed that the jet position just behind the separation point at 0.2 % of the chord length shows an outstanding control outcome on the separation and stall, thereby increasing the lift. The lift to drag ration increased proportionately when the suction jet coefficient was increased. At suction coefficient Cq = 0.00225, a 92.1% drag reduction and 72.7% lift enhancement is observed. Hence, the stall angle is moved beyond 21.5o from an initial angle of 16° and the more energy was saved at a high angle of attack.

Effect of Gurney Flaps on an Elliptical Airfoil

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Lance W. Traub
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Separated Flow ◽  
Pitching Moment ◽  
Airfoil Surface ◽  
Low Speed ◽  
Gurney Flaps ◽  
Lift Curve ◽  
The Impact ◽  
Low Speed Wind Tunnel

A low-speed wind tunnel investigation is presented characterizing the impact of Gurney flaps on an elliptical airfoil. The chordwise attachment location and height of the flaps were varied, as was the Reynolds number. The results showed strong nonlinearities in the lift curve which were present for all tested geometries. Flap effectiveness was seen to diminish as the flap was moved closer to the trailing edge stemming from flap submersion in separated flow. For the tested cases, the measured lift coefficients showed a weak Re dependency. The upper airfoil surface was shown to carry approximately 80% of the total lift load. The top surface caused a pitching moment reversal associated with nonlinearity in the lift curve.

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