Influence of Rotation on Dynamic Stall

2013 ◽  
Vol 58 (3) ◽  
pp. 1-9 ◽  
Author(s):  
A. D. Gardner ◽  
K. Richter
Keyword(s):  
Three Dimensional ◽  
Time History ◽  
Turbulence Models ◽  
Dynamic Stall ◽  
Test Case ◽  
Test Cases ◽  
Pitching Moment ◽  
Pitching Motion ◽  
Rotating Blade ◽  
Wind Tunnel Data

A computational investigation of the effect of rotation on two-dimensional (2D) deep dynamic stall has been undertaken, showing that the effect of rotation is to reduce the severity of the pitching moment peak and cause earlier reattachment of the flow. A generic single blade rotor geometry was investigated, which had a pitching oscillation around the quarter-chord axis while in hover, causing angle-driven dynamic stall. The results at the midpoint of the blade have the same Mach number (0.31), Reynolds number (1.15 × 106), and pitching motion (α = 13° ± 7°) as a dynamic stall test case for which significant experimental wind tunnel data and 2D computations exist. The rotating blade is compared with 2D computations and computations using the same blade without rotation at Mach 0.31 and with the same pitching motion. All test cases involve geometries propagating into undisturbed flow with no downwash. The three-dimensional (3D) grid computed without rotation had lower lift at the reference section than for a 2D computation with the same geometric angle of attack time history, and the lift overshoot classically observed for Spalart–Allmaras turbulence models during 2D dynamic stall was significantly reduced in the 3D case. Rotation reduced the strength of the dynamic stall vortex, which reduced the accompanying pitching moment peak by 25%.

Experimental Investigation of Dynamic Stall Performance for the EDI-M109 and EDI-M112 Airfoils

2013 ◽  
Vol 58 (1) ◽  
pp. 1-13 ◽  
Author(s):  
A. D. Gardner ◽  
K. Richter ◽  
H. Mai ◽  
A. R. M. Altmikus ◽  
A. Klein ◽  
...  
Keyword(s):  
Experimental Investigation ◽  
Dynamic Performance ◽  
Dynamic Stall ◽  
Test Cases ◽  
Pitching Moment ◽  
Pitching Motion ◽  
Maximum Angle ◽  
Low Amplitude ◽  
Similar Dynamic ◽  
Transonic Wind Tunnel

An experimental investigation of the dynamic performance of two new rotor blade airfoils was undertaken in a transonic wind tunnel. The EDI-M109 and EDI-M112 airfoils were tested at 0.3 ≤ M≤ 0.5 for pitching motions with amplitude 0.5° ≤ α± ≤8° and frequencies 3.3 Hz ≤ f ≤ 45 Hz. The results show the dynamic stall performance of both new airfoils, and the effect of frequency, amplitude, and higher order pitching motion on these results is described. The pitching moment peak size was found to have an approximately linear correlation to the normalized mean angular velocity, and thus test cases with the same maximum angle of attack and oscillation frequency had similar dynamic stall qualities. The correlation between low aerodynamic damping for high-frequency, low-amplitude pitching motion, and poor dynamic stall performance is shown to be low. The pitching moment peak of the EDI-M112 airfoil is shown to be smaller for M = 0.3 and 0.4, and peak for the EDI-M109 airfoil is lower at M = 0.5. The dynamic performance of the airfoils is compared to the OA209.

scholarly journals Numerical Investigations of Unsteady Flow in a Centrifugal Pump with a Vaned Diffuser

2013 ◽  
Vol 2013 ◽  
pp. 1-14 ◽  
Author(s):  
Olivier Petit ◽  
Håkan Nilsson
Keyword(s):  
Centrifugal Pump ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Centrifugal Impeller ◽  
Test Case ◽  
Vaned Diffuser ◽  
Pump Test ◽  
Steady Simulation ◽  
Turbulent Models ◽  
Cfd Analyses

Computational fluid dynamics (CFD) analyses were made to study the unsteady three-dimensional turbulence in the ERCOFTAC centrifugal pump test case. The simulations were carried out using the OpenFOAM Open Source CFD software. The test case consists of an unshrouded centrifugal impeller with seven blades and a radial vaned diffuser with 12 vanes. A large number of measurements are available in the radial gap between the impeller and the diffuse, making this case ideal for validating numerical methods. Results of steady and unsteady calculations of the flow in the pump are compared with the experimental ones, and four different turbulent models are analyzed. The steady simulation uses the frozen rotor concept, while the unsteady simulation uses a fully resolved sliding grid approach. The comparisons show that the unsteady numerical results accurately predict the unsteadiness of the flow, demonstrating the validity and applicability of that methodology for unsteady incompressible turbomachinery flow computations. The steady approach is less accurate, with an unphysical advection of the impeller wakes, but accurate enough for a crude approximation. The different turbulence models predict the flow at the same level of accuracy, with slightly different results.

scholarly journals Numerical Investigation of Boundary Layers in Wet Steam Nozzles

2016 ◽  
Author(s):  
Jörg Starzmann ◽  
Fiona R. Hughes ◽  
Alexander J. White ◽  
Marius Grübel ◽  
Damian M. Vogt
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Three Dimensional ◽  
Side Wall ◽  
Turbulence Models ◽  
Test Case ◽  
Wet Steam ◽  
Compression Waves ◽  
Wall Boundary Layer ◽  
Two Dimensional Flow

Condensing nozzle flows have been used extensively to validate wet steam models. Many test cases are available in the literature and in the past a range of numerical studies have dealt with this challenging task. It is usually assumed that the nozzles provide a one- or two-dimensional flow with a fully turbulent boundary layer. The present paper reviews these assumptions and investigates numerically the influence of boundary layers on dry and wet steam nozzle expansions. For the narrow nozzle of Moses and Stein it is shown that the pressure distribution is significantly affected by the additional blockage due to the side wall boundary layer. Comparison of laminar and turbulent flow predictions for this nozzles suggests that laminar-turbulent transition only occurs after the throat. Other examples are the Binnie nozzle and the Moore nozzles for which it is known that sudden changes in wall curvature produce expansion and compression waves that interact with the boundary layers. The differences between two- and three-dimensional calculations for these cases and the influence of laminar and turbulent boundary layers are discussed. The present results reveal that boundary layer effects can have a considerable impact on the mean nozzle flow and thus on the validation process of condensation models. In order to verify the accuracy of turbulence modelling a test case that is not widely known internationally is included within the present study. This experimental work is remarkable because it includes boundary layer data as well as the usual pressure measurements along the nozzle centreline. Predicted and measured boundary layer profiles are compared and the effect of different turbulence models is discussed. Most of the numerical results are obtained with the in-house wet steam RANS-solver, Steamblock, but for the purpose of comparison the commercial program ANSYS CFX is also used, providing a wider range of standard RANS-based turbulence models.

Using the DLR-F6 Aircraft Model for the Evaluation of the Academic CFD Code “Galatea”

2014 ◽  
Author(s):  
Georgios N. Lygidakis ◽  
Ioannis K. Nikolos
Keyword(s):  
Large Fraction ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Fluid Flows ◽  
Wind Tunnels ◽  
Navier Stokes ◽  
Test Case ◽  
Tetrahedral Elements ◽  
Computational Performance ◽  
Volume Method

Nowadays, the research in the aerospace scientific field relies strongly on CFD (Computational Fluid Dynamics) algorithms, avoiding (initially at least) a large fraction of the extremely time and money consuming experiments in wind tunnels. In this paper such a recently developed academic CFD code, named Galatea, is presented in brief and validated against a benchmark test case. The prediction of compressible fluid flows is succeeded by the relaxation of the Reynolds Averaged Navier-Stokes (RANS) equations, along with appropriate turbulence models (k-ε, k-ω and SST), employed on three-dimensional unstructured hybrid grids, composed of prismatic, pyramidical and tetrahedral elements. For the discretization of the computational field a node-centered finite-volume method is implemented, while for improved computational performance Galatea incorporates an agglomeration multigrid methodology and a suitable parallelization strategy. The proposed algorithm is evaluated against the Wing-Body (WB) and the Wing-Body-Nacelles-Pylons (WBNP) DLR-F6 aircraft configurations, demonstrating its capability for a good performance in terms of accuracy and geometric flexibility.

Suite for Smooth Particle Hydrodynamic Code Relevant to Spherical Plasma Liner Formation and Implosion

2019 ◽  
Vol 5 (4) ◽  
Author(s):  
Kevin Schillo ◽  
Jason Cassibry ◽  
Mitchell Rodriguez ◽  
Seth Thompson
Keyword(s):  
Three Dimensional ◽  
Smooth Particle Hydrodynamic ◽  
Momentum Conservation ◽  
Plasma Jets ◽  
Test Case ◽  
Test Cases ◽  
Stage Of Development ◽  
Plasma Liner ◽  
L2 Norm ◽  
Hydrodynamic Code

Three-dimensional (3D) modeling of magneto-inertial fusion (MIF) is at a nascent stage of development. A suite of test cases relevant to plasma liner formation and implosion is presented to present the community with some exact solutions for verification of hydrocodes pertaining to MIF confinement concepts. MIF is of particular interest to fusion research, as it may lead to the development of smaller and more economical reactor designs for power and propulsion. The authors present simulated test cases using a new smoothed particle hydrodynamic (SPH) code called SPFMax. These test cases consist of a total of six problems with analytical solutions that incorporate the physics of radiation cooling, heat transfer, oblique-shock capturing, angular-momentum conservation, and viscosity effects. These physics are pertinent to plasma liner formation and implosion by merging of a spherical array of plasma jets as a candidate standoff driver for MIF. An L2 norm analysis was conducted for each test case. Each test case was found to converge to the analytical solution with increasing resolution, and the convergence rate was on the order of what has been reported by other SPH studies.

scholarly journals Performance Investigation of a Turbocharger Compressor

2012 ◽  
Author(s):  
A. L. de Wet ◽  
T. W. von Backström ◽  
S. J. van der Spuy
Keyword(s):  
Pressure Ratio ◽  
Three Dimensional ◽  
Rotating Stall ◽  
Test Case ◽  
Test Cases ◽  
Vaned Diffuser ◽  
One Dimensional ◽  
Verification Process ◽  
The One ◽  
Modelling Methods

The compressor section of a diesel locomotive turbocharger was re-designed to increase its maximum total-to-total pressure ratio and efficiency. Tests conducted on the prototype compressor showed possible rotating stall in the diffuser section before the designed higher pressure ratio could be achieved. It was decided to simulate the prototype compressor’s operation by using one-dimensional theory [1], followed by a three-dimensional CFD analysis of the compressor. This publication focuses on implementation of the impeller, vaneless annular passage and vaned diffuser one-dimensional theories. A verification process was followed to show the accuracy of the one- and three-dimensional modelling methods using two well-known centrifugal compressor test cases found in the literature [2–5]. Comparing the test case modelling results to available experimental results indicated sufficient accuracy to investigate the prototype compressor’s impeller and diffuser. Conclusions drawn on the prototype compressor’s performance using the one- and three-dimensional modelling methods led to a recommendation to redesign the impeller and diffuser of the prototype compressor.

Simulation and Validation of Mach Number Effects on Secondary Flow in a Transonic Turbine Cascade Using a Multigrid, k–ε Solver

1998 ◽  
Vol 120 (2) ◽  
pp. 285-297 ◽  
Author(s):  
M. Koiro ◽  
B. Lakshminarayana
Keyword(s):  
Secondary Flow ◽  
Incompressible Flows ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Test Case ◽  
Turbine Cascade ◽  
Efficient Manner ◽  
Wall Boundary Layer ◽  
Transonic Turbine ◽  
Mach Numbers

An existing three-dimensional Navier–Stokes flow solver with an explicit Runge–Kutta algorithm and a low-Reynolds-number k–ε turbulence model has been modified in order to simulate turbomachinery flows in a more efficient manner. The solver has been made to converge more rapidly through use of the multigrid technique. Stability problems associated with the use of multigrid in conjunction with two-equation turbulence models are addressed and techniques to alleviate instability are investigated. Validation for the new code was performed with a transonic turbine cascade tested by Perdichizzi. In the fully three-dimensional turbulent cascade, real convergence (i.e., CPU time) was improved nearly two times the original code. Robustness was enhanced with the full multigrid initialization procedure. The same test case was then used to perform a series of simulations that investigated the effect of different exit Mach numbers on secondary flow features. This permitted an in-depth study into the mechanisms of secondary flow formation and secondary losses at high Mach numbers. In this cascade, it was found that secondary losses and secondary flow deviation, which are fairly constant in incompressible flows with similar geometries, underwent a large reduction in the compressible flow range. The structure of the trailing edge shock system and the reduced end wall boundary layer at supersonic exit conditions were shown to be very significant in reducing the amount of secondary flow and losses.

scholarly journals Simulation and Validation of Mach Number Effects on Secondary Flow in a Transonic Turbine Using a Multigrid, k-ε Solver

1996 ◽  
Author(s):  
M. Koiro ◽  
B. Lakshminarayana
Keyword(s):  
Secondary Flow ◽  
Incompressible Flows ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Test Case ◽  
Efficient Manner ◽  
Transonic Turbine ◽  
Mach Numbers ◽  
High Mach

An existing three dimensional Navier-Stokes flow solver with an explicit Runge-Kutta algorithm and a low Reynolds number k-ε turbulence model has been modified in order to simulate turbomachinery flows in a more efficient manner. The solver has been made to converge more rapidly through use of the mutligrid technique. Stability problems associated with use of multigrid in conjunction with two equation turbulence models are addressed and techniques to alleviate instability are investigated. Validation for the new code was performed with a transonic turbine cascade tested by Perdichizzi. In the fully three dimensional turbulent cascade, real convergence (i.e. CPU time) was improved nearly two times the original code. Robustness was enhanced with the full multigrid initialization procedure. The same test case was then used to perform a series of simulations that investigated the effect of different exit Mach numbers on secondary flow features. This permitted an in depth study into the mechanisms of secondary flow formation and secondary losses at high Mach numbers. In this cascade, it was found that secondary losses and secondary flow deviation, which are fairly constant in incompressible flows with similar geometries, underwent a large reduction in the compressible flow range. The structure of the trailing edge shock system and the reduced endwall boundary layer at supersonic exit conditions were shown to be very significant in reducing the amount of secondary flow and losses.

scholarly journals Techniques for Turbulence Tripping of Boundary Layers in RANS Simulations

2021 ◽  
Author(s):  
Narges Tabatabaei ◽  
Ricardo Vinuesa ◽  
Ramis Örlü ◽  
Philipp Schlatter
Keyword(s):  
Boundary Layer ◽  
Passive Control ◽  
Target Location ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Transition Process ◽  
Navier Stokes ◽  
Test Cases ◽  
And Performance

AbstractThe exact placement of the laminar–turbulent transition has a significant effect on relevant characteristics of the boundary layer and aerodynamics, such as drag, heat transfer and flow separation on e.g. wings and turbine blades. Tripping, which fixes the transition position, has been a valuable aid to wind-tunnel testing during the past 70 years, because it makes the transition independent of the local condition of the free-stream. Tripping helps to obey flow similarity for scaled models and serves as a passive control mechanism. Fundamental fluid-mechanics studies and many engineering developments are based on tripped cases. Therefore, it is essential for computational fluid dynamics (CFD) simulations to replicate the same forced transition, in spite of the advanced improvements in transition modelling. In the last decade, both direct numerical simulation (DNS) and large-eddy simulations (LES) include tripping methods in an effort to avoid the need for modeling the complex mechanisms associated with the natural transition process, which we would like to bring over to Reynolds-averaged Navier–Stokes (RANS) turbulence models. This paper investigates the implementation and performance of such a technique in RANS and specifically in the $$k-\omega$$ k - ω SST model. This study assesses RANS tripping with three alternatives: First, a recent approach of turbulence generation, denoted as turbulence-injection method (kI), is evaluated and investigated through different test cases; second, a predefined transition point is used in a traditional transition model (denoted as IM method); and third a novel formulation combining the two previous methods is proposed, denoted $$\gamma -k$$ γ - k I. The model is compared with DNS, LES and experimental data in a variety of test cases ranging from a turbulent boundary layer on a flat plate to the three-dimensional (3D) flow over a wing section. The desired tripping is achieved at the target location and the simulation results compare very well with the reference results. With the application of the novel model, the challenging transition region can be excluded from a simulation, and consequently more reliable results can be provided.

A Numerical Investigation of the Influence of the Blade–Vortex Interaction on the Dynamic Stall Onset

2021 ◽  
Author(s):  
Camille Castells ◽  
François Richez ◽  
Michel Costes
Keyword(s):  
High Speed ◽  
Three Dimensional ◽  
Dynamic Stall ◽  
Test Case ◽  
Vortex Interaction ◽  
Fluid Structure ◽  
Speed Test ◽  
Vortex Model ◽  
Flow Parameters ◽  
Blade Vortex Interaction

Recently, fluid–structure coupling simulations of helicopter rotors in high-thrust forward flight suggested that dynamic stall might be triggered by the blade–vortex interaction. However, no clear evidence of a correlation between dynamic stall and blade–vortex interaction has yet been given. We propose in this paper a simplified two-dimensional numerical model that can be used to indicate the role that the blade–vortex interaction plays in dynamic stall onset for different flight conditions. In this model, the rotor blade element is considered in pitching oscillation motion with a nonuniform translation, and a simplified vortex model can be introduced or not in the simulation to highlight the effect of blade–vortex interaction. All flow parameters of this simplified model are deduced from data provided by previous three-dimensional high-fidelity fluid–structure simulations. The method is used for validation and analysis of three flight conditions. The results show that, for the two cases with moderate advance ratio, the dynamic stall event is only triggered when a blade–vortex interaction occurs in the stall region. For the high-speed test case, the dynamic stall event seems to be only triggered by the very high angle of attack due to the motion of the blade.

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