Numerical simulation of shock wave/tip leakage vortex interaction for a transonic axial fan rotor

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Yan Xue ◽  
Ning Ge
Keyword(s):  
Shock Wave ◽  
Vortex Breakdown ◽  
Flow Region ◽  
Operating Conditions ◽  
Tip Vortex ◽  
Flow Structures ◽  
Axial Fan ◽  
Complex Flow ◽  
Vortex Stability ◽  
Theoretical Criterion

Abstract This paper presents the steady numerical investigation on SW/TLV interaction with SST turbulence model at two characteristic operating conditions for a transonic fan rotor, NASA Rotor 67. The main purpose of the present work is to reveal the main flow structures and properties during the SW/TLV interaction, and a theoretical criterion for vortex stability is engineeringly utilized to determine such shock wave-induced vortex stability. The validations for all numerical schemes have been conducted by comparing the RANS solutions with detailed experimental data before the analyses of flow phenomenon and mechanism. The simulation results indicate that numerical methods used in NUAA-Turbo 2.0 solver, independently developed by our team, enable to accurately capture the complex flow structures including shock wave and vortex systems within the blade passages, especially in the tip region. Similar to wing-tip vortex created by vortex generator, the TLV has the same wake-type characteristics. The flow pattern generated by such interaction is characterized by the bulged-forward shock front followed by a subsonic flow region and a slight expansion of vortex core. No apparent vortex breakdown was examined by both intuitive visualization of three-dimensional vortex structure and a theoretical criterion.

scholarly journals Engineering Application of an Identification Method to Shock-Induced Vortex Stability in the Transonic Axial Fan Rotor

2021 ◽  
Vol 2021 ◽  
pp. 1-24
Author(s):  
Yan Xue ◽  
Ning Ge
Keyword(s):  
Vortex Breakdown ◽  
Flow Analysis ◽  
Engineering Application ◽  
Tip Vortex ◽  
Axial Fan ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Vortex Stability ◽  
Vortex Model ◽  
Identification Method

In the present paper, the steady RANS (Reynolds-Averaged Navier-Stokes) simulations based on our independently developed CFD (Computational Fluid Dynamics) solver NUAA-Turbo 2.0, are carried out to investigate the shock wave/tip leakage vortex (SW/TLV) interaction in two representative transonic axial fan rotors, NASA Rotor 67 and NASA Rotor 37. The intent of this study is mainly to verify if an identification method derived from relevant theories is suitable for shock-induced vortex stability in the real engineering environment. As the additional findings, a universal tip vortex model is established and the characteristics of vortex breakdown or not are also summarized under different load levels. To ensure the prediction accuracy of all numerical methods selected in this research, detailed comparisons are made between computational and experimental results before flow analysis. The excellent agreement between the both indicates that the current code is capable of capturing the dominant secondary flow structures and aerodynamic phenomenon, especially the vortex system in tip region and SW/TLV interaction. It is found that three vortical structures such as tip leakage vortex (TLV), shock-induced vortex (SIV), tip separation vortex (TSV) in addition the tip leakage vortex-induced vortex (TLV-IV, which only occurs when the TLV strength increases to a certain extent) frequently exist near the blade tip and then abstracted as a tip vortex model. A stable TLV after passing through the passage shock is commonly characterized by tight rolling-up, slow deceleration and slight expansion. Conversely, the vortex behaves in a breakdown state. The final verification results show that the above two vortex states can be satisfactorily detected by the theoretical discriminant introduced in this work.

Topological Flow Structures of Annular Swirling Jets

2001 ◽  
Vol 17 (3) ◽  
pp. 131-138
Author(s):  
Feng Chin Tsai ◽  
Rong Fung Huang
Keyword(s):  
Vortex Breakdown ◽  
Swirling Flow ◽  
Single Bubble ◽  
Flow Structures ◽  
Complex Flow ◽  
Swirl Number ◽  
Recirculation Bubble ◽  
Annular Jet ◽  
Ring Mode ◽  
Dual Ring

AbstractThe effects of blockage and swirl on the macro flow structures of the annular jet past a circular disc are experimentally studied through the time-averaged streamline patterns. In the blockage-effect regime, the flows present multiple modes, single bubble, dual rings, vortex breakdown, and triple rings, in different regimes of blockage ratio and swirl number. The topological models of the flow structures are proposed and discussed according to the measured flow fields to manifest the complex flow structures. The single bubble is a closed recirculation bubble with a stagnation point on the central axis. The dual-ring flow is an open-top recirculsation zone, in which a pair of counter-rotating vortex rings exists in the near wake. The fluids in the dual rings are expelled downstream through a central jet-like swirling flow. A vortex breakdown may occur in the central jet-like swirling flow if the exit swirl number exceeds critical values. When the vortex breakdown interacts with the dual rings, a complex triple-ring flow structure forms. Axial distributions of the local swirl number are presented and discussed. The local swirl number increases with the increase of the exit swirl number and attains the maximum in the dual-ring mode. At large exit swirl numbers where the vortex breakdown occurs, the local swirl number decreases drastically to a low value.

Effects of Sand Ingestion Through an Axial Fan With Blade Staggering

2008 ◽  
Author(s):  
Adel Ghenaiet
Keyword(s):  
High Speed ◽  
Air Flow ◽  
Operating Conditions ◽  
Sand Particle ◽  
Computational Domain ◽  
Axial Fan ◽  
Complex Flow ◽  
Particle Trajectories ◽  
Flow Rates ◽  
The Impact

This paper presents the numerical results of sand particle trajectories and erosion patterns in a single stage axial fan used in industrial air ventilation, and the subsequent deterioration of the blade geometry. Attention is focused in particular on the effects of rotor blade staggering and the operating flow rates. By adopting the Lagrangian formulation to study the dynamics of particulate air-flow, the flow-field within the blade passage is solved separately. Particle trajectories computation is based on a stochastic tracking algorithm, which includes eddy-lifetime concept for turbulence, and accounts for the complex flow patterns near walls, random particle rebound factors, in addition to particle size, shape and fragmentation. The equations of motion are solved in a stepwise manner, whereas, particle tracking in different cells of the computational domain is based on the finite element method. The computation of the particle trajectories yields the impact locations along the blade surfaces, where the corresponding erosion patterns are calculated by using experimental correlations. The results of the numerical simulations carried out at low and high concentrations of MIL-E5007E sand particles, for different fan blade staggering and mass flow rates, revealed that the main impacted areas are found along the blade leading edge, over a strip of the blade suction side and a large area of the pressure side, in addition to the tip and casing, but with rare impacts on the hub. The rates of erosion in this axial fan are found to depend strongly on the air flow condition and the blade staggering. In all operating conditions of this axial fan, the rates of erosion are lower in comparison to high speed fans and compressors. Erosion analysis could be used in aerodynamic and mechanical design procedures to produce turbomachinery blading that would be less susceptible to erosion.

Efficient Passage-Spectral Method For Unsteady Flows Under Stall Conditions

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
David Romera ◽  
Roque Corral
Keyword(s):  
Spectral Method ◽  
Large Scale ◽  
Vortex Breakdown ◽  
Computational Cost ◽  
Three Dimensional ◽  
Unsteady Flows ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Complex Flow ◽  
Stall Inception

Abstract This paper presents an efficient method of approximating unsteady flows using a block-wise discrete spatial Fourier series for the modeling of three-dimensional non-axisymmetric flows without making any hypothesis about its temporal periodicity. The method aims at capturing the long-wavelength flow patterns that are present in many unsteady problems of industrial interest, such as compressor stability, with a drastic reduction in computational resources. The method is intended to be used to compute flows exhibiting large-scale instabilities and where the fundamental frequency of the problem is not known beforehand. The approach discretizes the domain using a finite number of blocks or passages, where the flow variables at the supposedly periodic boundaries are continuously updated using the spatial Fourier coefficients of a uniformly spaced set of reduced-passage domains. The NASA rotor 67 under the effect of distorted inflow conditions has been used as verification case to demonstrate the effectiveness and viability of the method. The comparison between the passage-spectral method and the full-annulus solution shows that sound solutions can be obtained with a low number of harmonics. The new method has also been applied to investigate the rotating stall inception of the NASA rotor 67 for distorted inlet flows near stall operating conditions. The method is shown to accurately reproduce the full-annulus solution with a few spatial harmonics, capturing the characteristic features of the complex flow induced by the tip leakage vortex breakdown. The computational cost in this application has been reduced by a factor of between three and seven. This number heavily depends on the ratio between the number of retained harmonics to the number of blades.

Efficient Passage-Spectral Method for Unsteady Flows Under Stall Conditions

2019 ◽  
Author(s):  
David Romera ◽  
Roque Corral
Keyword(s):  
Fourier Series ◽  
Large Scale ◽  
Vortex Breakdown ◽  
Computational Cost ◽  
Three Dimensional ◽  
Unsteady Flows ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Complex Flow ◽  
Stall Inception

Abstract This paper presents an efficient method of approximating unsteady flows using a blockwise discrete spatial Fourier series for the modeling of three-dimensional non-axisymmetric flows without making any hypothesis about its temporal periodicity. The method aims at capturing the long wavelength flow patterns which are present in many unsteady problems of industrial interest, such as compressor stability, with a drastic reduction in computational resources. The method is intended to be used to compute flows exhibiting large-scale instabilities and where the fundamental frequency of the problem is not known beforehand. The approach discretizes the domain using a finite number of blocks or passages, where the flow variables at the supposedly periodic boundaries are continuously updated using the spatial Fourier coefficients of a uniformly spaced set of reduced-passage domains. The NASA rotor 67 under stall conditions has been used as verification validation case to demonstrate the effectiveness and viability of the proposed modeling strategy. The comparison between the solutions obtained with the discrete Fourier series and the full-annulus solution shows that accurate solutions can be obtained with a low number of harmonics. The new method has been applied to investigate the rotating stall inception of the NASA rotor 67 for clean and distorted inlet flow near stall operating conditions. The method is shown to accurately reproduce the full-annulus solution with a few spatial harmonics, capturing the characteristic features of the complex flow induced by the tip leakage vortex breakdown. The computational cost in this application has been reduced by a factor of between three and seven, although this number heavily depends on the ratio between the number of retained harmonics and the number of blades.

The asymptotic study of dissipation and breakdown of a wing-tip vortex

1994 ◽  
Vol 274 ◽  
pp. 293-337 ◽  
Author(s):  
V. N. Trigub ◽  
A. B. Blokhin ◽  
I. N. Simakin
Keyword(s):  
Bifurcation Point ◽  
Numerical Solutions ◽  
Vortex Breakdown ◽  
Asymptotic Methods ◽  
Nodal Point ◽  
Flow Region ◽  
Tip Vortex ◽  
Reversed Flow ◽  
Wing Tip Vortex ◽  
Wing Tip

The steady axisymmetrical wing-tip vortex is studied in this paper by means of asymptotic methods within the limit of high Reynolds numbers. The smooth regrouping of the vortex under the action of viscous forces is described by a quasicylindrical approximation. The solutions of the quasi-cylindrical approximation are thoroughly analysed numerically and it is shown that a saddle-point bifurcation appears at certain critical values of circulation. At these values the solution may be continued in two ways: as a supercritical branch which approaches the Batchelor limit far downstream; and a subcritical one, which passes the second, nodal-point bifurcation. The parabolic quasi-cylindrical equations past this point allow the downstream disturbances to propagate upstream, like for example, boundary-layer equations in the regime of strong hypersonic interaction. The flow past the second bifurcation point was studied numerically and it was shown that solutions of the quasicylindrical approximation with large reversed-flow regions exist. An asymptotic expansion of such solutions far downstream was constructed, and it turned out that the reversed-flow region expands exponentially. This process is halted by elliptical effects in the external flow. An asymptotic theory of large reversed-flow regions is suggested including viscosity and elliptical effects. Numerical solutions for unbounded vortex breakdown parabolically expanding far downstream are presented. Then the general asymptotic problem statement which describes the flow near the bifurcation points is used to study the asymptotic solutions near the first bifurcation point. The problem is investigated numerically and two kinds of solution, which may be treated as transcritical jumps and marginal vortex breakdown, are found and discussed.

Unsteady Modelling of the Tip Clearance Flow in an Inlet Vaned, Low-Speed Axial Fan: Deterministic Interactions of Stator Wakes and Tip Vortex Structures

2009 ◽  
Author(s):  
Jesu´s Manuel Ferna´ndez Oro ◽  
Katia Mari´a Argu¨elles Di´az ◽  
Carlos Santolaria Morros ◽  
Mo´nica Galdo Vega
Keyword(s):  
Three Dimensional ◽  
Vortex Structures ◽  
Operating Conditions ◽  
Tip Vortex ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Axial Fan ◽  
Low Speed ◽  
Tip Leakage ◽  
The Impact

In last years, numerical modelling has reached a significant level of maturity in the analysis of axial turbomachinery flows. Full-unsteady, three-dimensional computations have been demonstrated as a powerful tool to characterize viscous phenomena on blade row interactions and blade passage structures. In particular, major effects have been focused on the study of deterministic fluctuations in order to quantify the impact of periodic unsteadiness on the time-averaged flow. An additional complexity concerns to the influence of the tip vortex structures on the deterministic patterns. Hence, some researchers have advanced experimental evidences on the contribution of tip leakage flow to the time-resolved distributions. Tip vortex, shedding energy at a wide range of scales, has been shown to be significant in the description of the spanwise momentum transfer and the appearance of mixing losses. Recently, the authors have investigated the impact of the tip vortex on the passage flow structures of a jet fan with symmetric blades. This work revealed valuable information about tip vortex transport in low-speed axial turbomachinery and demonstrated the ability of commercial codes to simulate three-dimensional, vortical structures with high accuracy. The present paper takes advantage of the same numerical methodology to highlight the influence of the deterministic correlations that describe the stator-rotor interaction on the tip vortex in a single-stage axial fan. Up to now, few works addressing deterministic contributions over the tip leakage flow are available in the literature, so more investigation is needed to understand the complexity of these physical mechanisms. Our contribution to the topic is based on a 3D, unsteady numerical simulation of the flow within a reduced periodic domain of the full-annulus axial stage, composed by only 3-vane and 2-blade passages. This simplification allows an enhancement of the grid density when massive parallel computations are employed. Also, comparison with experimental data measured using hot-wire anemometry is provided to validate the numerical model. The results show how the non-uniformities of the stator wake-core structure in the relative frame of reference are conditioning the tip leakage flow, addressing the influence of the operating conditions or the interrow spacing. The final objective is to provide levels of instabilities in the tip vortex derived from deterministic non-uniformities associated to vane-to-vane flow patterns, applicable in further modelling of deterministic stresses.

scholarly journals Flow Field Investigation in the Exit Region of a Radial Inflow Turbine Using LDV

1994 ◽  
Author(s):  
D. Muthuvel Murugan ◽  
Widen Tabakoff ◽  
Awatef Hamed
Keyword(s):  
Flow Field ◽  
Field Investigation ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Complex Flow ◽  
Tip Clearance Flow ◽  
Exit Region ◽  
Flow Investigation ◽  
Clearance Flow ◽  
Radial Inflow Turbine

Detailed flow investigation in the downstream region of a radial inflow turbine has been performed using a three component Laser Doppler Velocimetry. The flow velocities are measured in the exit region of the turbine at off-design operating conditions. The results are presented as contour and vector plots of mean velocities, flow angles and turbulent stresses. The measured parameters are correlated to the rotor blade rotation to observe any periodic nature of the flow. The measurements reveal a complex flow pattern near the tip region at the rotor exit due to the interaction of the tip clearance flow. The degree of swirl of the flow near the tip region at the rotor exit is observed to be high due to the gross under turning of the flow near the tip region. The effect of the rotor on the exit flow field is observed in the proximity of the rotor exit.

Self-Excited Oscillation of Transonic Flow Around an Airfoil in Two-Dimensional Channel

1989 ◽  
Author(s):  
Kazuomi Yamamoto ◽  
Yoshimichi Tanida
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Transonic Flow ◽  
Stokes Equations ◽  
Flow Region ◽  
Boundary Layer Separation ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Layer Separation ◽  
Excited Oscillation

A self-excited oscillation of transonic flow in a simplified cascade model was investigated experimentally, theoretically and numerically. The measurements of the shock wave and wake motions, and unsteady static pressure field predict a closed loop mechanism, in which the pressure disturbance, that is generated by the oscillation of boundary layer separation, propagates upstream in the main flow and forces the shock wave to oscillate, and then the shock oscillation disturbs the boundary layer separation again. A one-dimensional analysis confirms that the self-excited oscillation occurs in the proposed mechanism. Finally, a numerical simulation of the Navier-Stokes equations reveals the unsteady flow structure of the reversed flow region around the trailing edge, which induces the large flow separation to bring about the anti-phase oscillation.

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