Analysis of tip-leakage flow in an axial fan at varying tip-gap sizes and operating conditions

2019 ◽  
Vol 183 ◽  
pp. 107-129 ◽  
Author(s):  
Seyed Mohsen Alavi Moghadam ◽  
Matthias Meinke ◽  
Wolfgang Schröder
Keyword(s):  
Operating Conditions ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Axial Fan ◽  
Tip Leakage

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.

A Study on the Mechanism of Tip Leakage Flow Unsteadiness in an Isolated Compressor Rotor

2006 ◽  
Author(s):  
Hongwu Zhang ◽  
Xiangyang Deng ◽  
Feng Lin ◽  
Jingyi Chen ◽  
Weiguang Huang
Keyword(s):  
Pressure Difference ◽  
Operating Conditions ◽  
Static Balance ◽  
Leakage Flow ◽  
Flow Mechanism ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Aerodynamic Loading ◽  
Compressor Rotor ◽  
Through Flow

A numerical study of unsteady tip leakage flow in an isolated axial compressor rotor is presented, aiming at clarifying the originating flow mechanism of this unsteady phenomenon. First, CFD simulations utilizing a three-dimensional, time-accurate, Reynolds-averaged Navier-Stokes solver demonstrates that the tip leakage flow pattern, which manifests itself as an interacting cross- and through-flow in the tip region, can become periodically oscillatory in a range of operating conditions. A flow mechanism is then clarified to explain this unsteady flow phenomenon at its onset that this periodic flow oscillation is a result of dynamic balance, as opposed to static balance, between two counter-acting driving “forces”. One such “force” is the aerodynamic loading of the blades, i.e. the pressure difference across the pressure and suction sides of the compressor blades created by the main through flow. Its counter-acting “force” is the unloading of the blades, i.e. the reduction of the pressure difference caused by the tip leakage cross flow that originates from the pressure side, rushes into the suction side through the tip clearance. At operating conditions in which both “forces” are strong and in the same order, their static balance will be broken. While a larger blade loading creates a stronger tip leakage flow, the tip leakage flow tends to diminish itself because its accompanying effect is to unload the blade. Since the weaker tip leakage flow cannot overcome the ability of the main through flow to recover the original aerodynamic loading for the blade, the whole process restarts and periodically oscillatory tip leakage flow forms. Furthermore, a dimensionless analysis shows that the onset of the observed unsteadiness is conditioned by the tip leakage flow, which can or cannot reach the neighboring blade before mixing with the main flow.

Tip leakage flow and aeroacoustics analysis of a low-speed axial fan

2020 ◽  
Vol 98 ◽  
pp. 105700 ◽  
Author(s):  
Bo Luo ◽  
Wuli Chu ◽  
Haoguang Zhang
Keyword(s):  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Axial Fan ◽  
Low Speed ◽  
Tip Leakage

Improving Vibration Response of Radial Turbine in Variable Geometry Turbochargers With CFD Analysis

2021 ◽  
Author(s):  
Bipin Gupta ◽  
Toyotaka Yoshida ◽  
Shinji Ogawa ◽  
Yosuke Danmoto ◽  
Takashi Yoshimoto
Keyword(s):  
Safety Factor ◽  
Surface Pressure ◽  
Leading Edge ◽  
Operating Conditions ◽  
Wake Flow ◽  
Leakage Flow ◽  
Variable Geometry ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Nozzle Vane

Abstract Recent advancements in internal combustion engine for efficient fuel combustion, such as application of miller cycle, where the closing of engine intake valve is purposely delayed to provide more cooling of air-fuel mixture during compression stroke for better engine efficiency, has led to a requirement for turbochargers to function at a wider operating range and higher compression ratio. One of the methods which have been largely accepted is the use of variable geometry turbochargers. As compared to diesel engine, operating conditions for gasoline engine require the turbine to operate at higher exhaust temperature, which increases the risk of damaging the rotor. This paper discusses a detailed flow analysis of the effect of tip leakage and nozzle vane wake flow on surface pressure distribution of the turbine rotor, especially at the severe condition when vane trailing edge and rotor leading edge are in proximity. It was observed in steady and unsteady CFD simulations that the origination and propagation of tip leakage flow can be varied depending on the blade loading at the rotor leading edge, and the major interaction of nozzle wake can be switched from pressure surface to suction surface as rotor blade crossed a nozzle vane, which can drastically affect the alternating aerodynamic stresses. The sensitivity to this phenomenon has been evaluated by calculating the safety factor. The authors modified the rotor design to weaken the effect of tip leakage flow in order to suppress variations in rotor surface pressure as it crosses the nozzle vane. It significantly reduced the alternating stress and increased the safety factor at vibration mode 2 from 0.3 to 9.3 and mode 3 from 0.6 to 3.2 respectively.

Effect of Turbine Inlet Temperature on Blade Tip Leakage Flow and Heat Transfer

2009 ◽  
Author(s):  
Sung In Kim ◽  
Md Hamidur Rahman ◽  
Ibrahim Hassan
Keyword(s):  
Heat Transfer ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Turbine Inlet Temperature ◽  
Maximum Heat ◽  
Tip Leakage ◽  
Turbine Inlet ◽  
Blade Tip

One of the most critical gas turbine engine components, rotor blade tip and casing, are exposed to high thermal load. It becomes a significant design challenge to protect the turbine materials from this severe situation. As a result of geometric complexity and experimental limitations, Computational Fluid Dynamics (CFD) tools have been used to predict blade tip leakage flow aerodynamics and heat transfer at typical engine operating conditions. In this paper, the effect of turbine inlet temperature on the tip leakage flow structure and heat transfer has been studied numerically. Uniform low (LTIT: 444 K) and high (HTIT: 800 K) turbine inlet temperature have been considered. The results showed the higher turbine inlet temperature yields the higher velocity and temperature variations in the leakage flow aerodynamics and heat transfer. For a given turbine geometry and on-design operating conditions, the turbine power output can be increased by 1.48 times, when the turbine inlet temperature increases 1.80 times. Whereas the averaged heat fluxes on the casing and the blade tip become 2.71 and 2.82 times larger, respectively. Therefore, about 2.8 times larger cooling capacity is required to keep the same turbine material temperature. Furthermore, the maximum heat flux on the blade tip of high turbine inlet temperature case reaches up to 3.348 times larger than that of LTIT case. The effect of the interaction of stator and rotor on heat transfer features is also explored using unsteady simulations.

Numerical and experimental investigation of stepped tip gap effects on a subsonic axial-flow compressor rotor

2005 ◽  
Vol 219 (8) ◽  
pp. 605-615 ◽  
Author(s):  
X Lu ◽  
J Zhu ◽  
W Chu
Keyword(s):  
Flow Field ◽  
Axial Compressor ◽  
Numerical Procedure ◽  
Operating Conditions ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Compressor Rotor ◽  
Small Clearance ◽  
Clearance Level

This article investigates the flow field at the tip region of compressor rotor. In particular, the effect of stepped tip gaps on the performance and flow field of axial compressor was reviewed using experimental and computational methods. An axial compressor rotor with no inlet guide vanes was tested under subsonic conditions. A parametric study of clearance levels and step profiles was performed using eight different casing geometries. This study was aimed at comparing compressor performance in specified configurations. The experimental results showed that the inclusion of stepped tip gaps with the small clearance level gave increased pressure ratio, efficiency, and stall margin throughout the mass flow range at both speeds. However, when using medium and large clearance levels, the benefits of stepped tip gaps were not noticed for all rotor operating conditions when compared with the baseline case. Steady-state Navier-Stokes analyses were performed for cases involving small clearance level and stepped tip gap geometries. They highlighted the mechanisms associated with performance improvement. The numerical procedure correctly predicted the overall effects of stepped tip gaps. Detailed numerical simulation results showed that the interaction between the stepped groove flow and the blade passage flow could entrain the blockage produced by upstream tip leakage flow into the tip gap of adjacent blades of the compressor rotor. It is through this process that stepped tip gaps can help in dissipating blockage that was caused by upstream tip leakage flow. Thus, the path and extent of the blockage in the tip region are altered to increase the passage through-flow area, and so, the rotor performance can be improved.

The Effects of Stepped Tip Gap on Performance and Flowfield of a Subsonic Axial-Flow Compressor Rotor

2005 ◽  
Author(s):  
Xingen Lu ◽  
Junqiang Zhu ◽  
Wuli Chu ◽  
Rugen Wang
Keyword(s):  
Axial Flow ◽  
Operating Conditions ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Axial Flow Compressor ◽  
Compressor Rotor ◽  
Small Clearance ◽  
Clearance Level ◽  
Flow Compressor

This paper investigates the flow field at the tip region of compressor rotor. In particular, the effect of stepped tip gaps on the performance and flowfield of an axial-flow compressor rotor was reviewed using both experimental and computational methods. An axial compressor rotor with no inlet guide vanes was tested under subsonic condition. A parametric study of clearance levels and step profiles was performed using eight different casing geometries. This study was aimed at comparing compressor performance in specified configurations. The experimental results showed that the inclusion of stepped tip gaps with the small clearance level gave increased pressure ratio, efficiency, and stall margin throughout the mass flow range at both speeds. However, when using medium and large clearance level, the benefits of stepped tip gaps were not noticed for all rotor operating conditions if compared with the baseline case. Steady-state Navier-Stokes analyses were performed for cases involving small clearance level and stepped tip gap geometries. They highlighted the mechanisms associated with performance improvement. The numerical procedure correctly predicted the overall effects of stepped tip gaps. Detailed numerical simulation results showed that the interaction between the stepped groove flow and blade passage flow could entrain the blockage produced by upstream tip leakage flow into the tip gap of adjacent blades of the compressor rotor. It is through this process that stepped tip gaps can help dissipating blockage that was caused by upstream tip leakage flow. Thus the path and extent of the blockage in the tip region is altered to increase the passage throughflow area and so, the rotor performance can be improved.

Tip Leakage in Small Radial Turbines: Optimum Tip-Gap and Efficiency Loss Correlations

2010 ◽  
Author(s):  
Jasper Kammeyer ◽  
Christoph Natkaniec ◽  
Joerg R. Seume
Keyword(s):  
Internal Combustion Engines ◽  
Operating Conditions ◽  
Test Facility ◽  
Leakage Flow ◽  
Combustion Engines ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Turbine Efficiency ◽  
Flow Mechanisms ◽  
Radial Turbines

The tip-leakage flow mechanisms in turbocharger turbines used for downsized internal combustion engines and the associated losses are investigated over a range of operating conditions. Experiments are performed on a small, 35 mm diameter turbocharger turbine with varying tip-gap heights in a turbocharger test facility and numerical simulations are presented for extending the parameter range to sizes not covered experimentally. The sensitivity of turbine efficiency to tip-gap is evaluated and correlations for the estimation of tip-leakage related loss of efficiency are developed. An optimum applicable tip-gap size for radial turbines is suggested. The results show that the magnitude of the tip-leakage losses, e.g. in downsizing turbocharger turbines, provides a high potential for their improvement.

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