Experimental and Computational Investigation of the Tip Clearance Flow for an Axial Ventilation Fan

2003 ◽  
Author(s):  
Xiaocheng Zhu ◽  
Wanlai Lin ◽  
Zhaohui Du
Keyword(s):  
Numerical Simulation ◽  
Experimental Measurement ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip ◽  
Ventilation Fan

The tip leakage flow in an axial ventilation fan with various tip clearances is investigated by experimental measurement and numerical simulation. The characteristic of a ventilation fan is an extreme low-pressure difference, a large tip clearance with a low rotating speed. A three dimensional PDA (Particle Dynamics Analysis) system is used for the measurement of the velocity field in the tip clearance region. The flow field is surveyed across the whole passage at fifteen axial locations (from 100% axial chord in front of the leading edge to 100% axial chord behind the trailing edge), mainly focusing on areas close to the blade tip (from 90% of the blade span to the casing wall). Both experimental measurement and numerical simulation indicate that the leakage flow originating from the tip clearance along the chord rolls up into a three-dimensional spiral structure to form a leakage flow vortex. A low axial velocity zone shows up in the tip region, which leads to blockage of the main flow. There are under-turning zones near and in the blade tip region, and an overturning zone in a lower span region with a critical span-wise position of about 94%. A reverse flow appears at the suction side near the trailing edge. As the tip clearance increases, the tip leakage flow and the reverse flow become stronger and fully developed. In addition, the position of the first appearance of the tip leakage vortex moves further downstream in a direction parallel to the mid chord line.

Experimental and Numerical Investigation of the Flow Field in the Tip Region of an Axial Ventilation Fan

2004 ◽  
Vol 127 (2) ◽  
pp. 299-307 ◽  
Author(s):  
Xiaocheng Zhu ◽  
Wanlai Lin ◽  
Zhaohui Du
Keyword(s):  
Numerical Simulation ◽  
Experimental Measurement ◽  
Reverse Flow ◽  
Main Flow ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Direction Parallel ◽  
Tip Leakage ◽  
Ventilation Fan

The tip leakage flow in an axial ventilation fan with various tip clearances is investigated by experimental measurement and numerical simulation. For a low-rotating-speed ventilation fan with a large tip clearance, both experimental measurement and numerical simulation indicate that the leakage flow originating from the tip clearance along the chord rolls up into a three-dimensional spiral structure to form a leakage flow vortex. The mixing interaction between the tip leakage flow and the main flow produces a low axial velocity region in the tip region, which leads to blockage of the main flow. As the tip clearance increases, the tip leakage flow and the reverse flow become stronger and fully developed. In addition, the position of the first appearance of the tip leakage vortex moves further downstream in a direction parallel to the mid chord line.

Three-Dimensional Navier-Stokes Analysis of Turbine Rotor and Tip-Leakage Flowfield

1997 ◽  
Author(s):  
J. Luo ◽  
B. Lakshminarayana
Keyword(s):  
Three Dimensional ◽  
Turbine Rotor ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Navier Stokes ◽  
Leakage Flow ◽  
Mean Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

The 3-D viscous flowfield in the rotor passage of a single-stage turbine, including the tip-leakage flow, is computed using a Navier-Stokes procedure. A grid-generation code has been developed to obtain embedded H grids inside the rotor tip gap. The blade tip geometry is accurately modeled without any “pinching”. Chien’s low-Reynolds-number k-ε model is employed for turbulence closure. Both the mean-flow and turbulence transport equations are integrated in time using a four-stage Runge-Kutta scheme. The computational results for the entire turbine rotor flow, particularly the tip-leakage flow and the secondary flows, are interpreted and compared with available data. The predictions for major features of the flowfield are found to be in good agreement with the data. Complicated interactions between the tip-clearance flows and the secondary flows are examined in detail. The effects of endwall rotation on the development and interaction of secondary and tip-leakage vortices are also analyzed.

Effect of Turbine Blade Tip Cooling Configuration on Tip Leakage Flow and Heat Transfer

2020 ◽  
Vol 142 (2) ◽  
Author(s):  
Sergen Sakaoglu ◽  
Harika S. Kahveci
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Gas Turbines ◽  
Thermal Response ◽  
Thermal Conditions ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

Abstract The pressure difference between suction and pressure sides of a turbine blade leads to tip leakage flow, which adversely affects the first-stage high-pressure (HP) turbine blade tip aerodynamics. In modern gas turbines, HP turbine blade tips are exposed to extreme thermal conditions requiring cooling. If the coolant jet directed into the blade tip gap cannot counter the leakage flow, it will simply add up to the pressure losses due to leakage. Therefore, the compromise between the aerodynamic loss and the gain in tip-cooling effectiveness must be optimized. In this paper, the effect of tip-cooling configuration on the turbine blade tip is investigated numerically from both aerodynamics and thermal aspects to determine the optimum configuration. Computations are performed using the tip cross section of GE-E3 HP turbine first-stage blade for squealer and flat tips, where the number, location, and diameter of holes are varied. The study presents a discussion on the overall loss coefficient, total pressure loss across the tip clearance, and variation in heat transfer on the blade tip. Increasing the coolant mass flow rate using more holes or by increasing the hole diameter results in a decrease in the area-averaged Nusselt number on the tip floor. Both aerodynamic and thermal response of squealer tips to the implementation of cooling holes is superior to their flat counterparts. Among the studied configurations, the squealer tip with a larger number of cooling holes located toward the pressure side is highlighted to have the best cooling performance.

Effects of Tip Clearance on Unsteady Flow Characteristics in an Axial Turbine Stage

2009 ◽  
Author(s):  
Hao Sun ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Rotor Blade ◽  
Suction Side ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Turbine Stage ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

The clearance between the rotor blade tip and casing wall in turbomachinery passages induces leakage flow loss and thus degrades aerodynamic performance of the machine. The flow field in turbomachinery is significantly influenced by the rotor blade tip clearance size. To investigate the effects of tip clearance size on the rotor-stator interaction, the turbine stage profile from Matsunuma’s experimental tests was adopted, and the unsteady flow fields with two tip clearance sizes of 0.67% and 2.00% of blade span was numerical simulated based on Harmonic method using NUMECA software. By comparing with the domain scaling method, the accuracy of the harmonic method was verified. The interaction mechanism between the stator wake and the leakage flow was investigated. It is found that the recirculation induced by the stator wake is separated by a significant “interaction line” from the flow field close to the suction side in the clearance region. The trend of the pressure fluctuation is contrary on both sides of the line. When the stator wakes pass by the suction side, the pressure field fluctuates and the intensity of the tip leakage flow varies. With the clearance size increasing, the “interaction line” is more far away from the suction side and the intensity of tip leakage flow also fluctuates more strongly.

Numerical investigations on tip leakage flow characteristics and vortex trajectory prediction model in centrifugal compressor

2016 ◽  
Vol 230 (8) ◽  
pp. 757-772 ◽  
Author(s):  
Huijing Zhao ◽  
Zhiheng Wang ◽  
Shubo Ye ◽  
Guang Xi
Keyword(s):  
Prediction Model ◽  
Flow Instability ◽  
Leading Edge ◽  
Tip Clearance ◽  
Centrifugal Impeller ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Blade Tip

To better understand the characteristics of tip leakage flow and interpret the correlation between flow instability and tip leakage flow, the flow in the tip region of a centrifugal impeller is investigated by using the Reynolds averaged Navier–Stokes solver technique. With the decrease of mass flow rate, both the tip leakage vortex trajectory and the mainflow/tip leakage flow interface are shifted towards upstream. The mainflow/tip leakage flow interface finally reaches the leading edge of main blade at the near-stall condition. A prediction model is proposed to track the tip leakage vortex trajectory. The blade loading at blade tip and the averaged streamwise velocity of main flow within tip clearance height are adopted to determine the tip leakage vortex trajectory in the proposed model. The coefficient k in Chen’s model is found to be not a constant. Actually, it is correlated with h/b (the ratio of blade tip clearance height to blade tip thickness), because h/b will significantly influence the flow structure across the tip clearance. The effectiveness of the proposed prediction model is further demonstrated by tracking the tip leakage vortex trajectories in another three centrifugal impellers characterized with different h/b (s).

A Genetic Algorithm Based Multi-Objective Optimization of Squealer Tip Geometry in Axial Flow Turbines: A Constant Tip Gap Approach

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
H. Maral ◽  
C. B. Şenel ◽  
K. Deveci ◽  
E. Alpman ◽  
L. Kavurmacıoğlu ◽  
...  
Keyword(s):  
Genetic Algorithm ◽  
Tip Clearance ◽  
Design Parameters ◽  
Leakage Flow ◽  
Optimization Approach ◽  
Multi Objective Optimization ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Multi Objective ◽  
Blade Tip

Abstract Tip clearance is a crucial aspect of turbomachines in terms of aerodynamic and thermal performance. A gap between the blade tip surface and the stationary casing must be maintained to allow the relative motion of the blade. The leakage flow through the tip gap measurably reduces turbine performance and causes high thermal loads near the blade tip region. Several studies focused on the tip leakage flow to clarify the flow-physics in the past. The “squealer” design is one of the most common designs to reduce the adverse effects of tip leakage flow. In this paper, a genetic-algorithm-based optimization approach was applied to the conventional squealer tip design to enhance aerothermal performance. A multi-objective optimization method integrated with a meta-model was utilized to determine the optimum squealer geometry. Squealer height and width represent the design parameters which are aimed to be optimized. The objective functions for the genetic-algorithm-based optimization are the total pressure loss coefficient and Nusselt number calculated over the blade tip surface. The initial database is then enlarged iteratively using a coarse-to-fine approach to improve the prediction capability of the meta-models used. The procedure ends once the prediction errors are smaller than a prescribed level. This study indicates that squealer height and width have complex effects on the aerothermal performance, and optimization study allows to determine the optimum squealer dimensions.

Effect of Turbine Blade Tip Cooling Configuration on Tip Leakage Flow and Heat Transfer

2019 ◽  
Author(s):  
Sergen Sakaoglu ◽  
Harika S. Kahveci
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Gas Turbines ◽  
Thermal Response ◽  
Thermal Conditions ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage ◽  
Blade Tip

Abstract The pressure difference between suction and pressure sides of a turbine blade leads to the so-called phenomenon, the tip leakage flow, which most adversely affects the first-stage high-pressure (HP) turbine blade tip aerodynamics. In modern gas turbines, HP turbine blade tips are also exposed to extreme thermal conditions requiring the use of tip cooling. If the coolant jet directed into the blade tip gap cannot counter the leakage flow, it will simply add up to the pressure losses due to this leakage flow. Therefore, it is necessary to handle the design of tip cooling in such a way that the compromise between the aerodynamic loss and the gain in the tip cooling effectiveness is optimized. In this paper, the effect of tip cooling configuration on the turbine blade tip is investigated numerically both from the aerodynamics and thermal aspects in order to determine the optimum tip cooling configuration. The studies are carried out using the tip cross-section of General Electric E3 (Energy Efficient Engine) HP turbine first-stage blade for two different tip geometries, squealer tip and flat tip, where the number, location, and diameter of the cooling holes are varied. The study presents a discussion on the overall loss coefficient, the total pressure loss across the tip clearance, and the variation of heat transfer on the blade tip. The aerodynamic and heat transfer results are compared with the experimental data from literature. It is observed that increasing the coolant mass flow rate by using more holes or by increasing the hole diameter results in a decrease in the area-averaged Nusselt number on the tip floor, as expected. The findings show that both aerodynamic and thermal response of the squealer tips to the implementation of cooling holes is superior to their flat counterparts. Among the studied configurations, the squealer tip with larger number of cooling holes located towards the pressure side is highlighted as the configuration having the best cooling performance.

Numerical Investigation of Tip Clearance Flow in an Axial Compressor Cascade

2014 ◽  
Vol 599-601 ◽  
pp. 368-371
Author(s):  
Zhi Hui Xu ◽  
He Bin Lv ◽  
Ru Bin Zhao
Keyword(s):  
Computational Simulation ◽  
Suction Side ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Compressor Cascade ◽  
Tip Leakage Flow ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Clearance Flow ◽  
Blade Tip

Using blade tip winglet to control the tip leakage flow has been concerned in the field of turbomachinery. Computational simulation was conducted to investigate the phenomenological features of tip clearance flow. The simulation results show that suction-side winglet can reduce leakage flow intensity. The tip winglet can also decrease tip leakage mass flow and weaken tip leakage flow mixing with the mainstream and therefore reduce the total pressure loss at the blade tip.

Numerical Analysis of Transonic Compressor With Various Tip Clearance Gap

2016 ◽  
Author(s):  
Yasunori Sakuma ◽  
Toshinori Watanabe ◽  
Takehiro Himeno
Keyword(s):  
Tip Clearance ◽  
Leakage Flow ◽  
Numerical Instability ◽  
Tip Leakage Flow ◽  
Trailing Edge ◽  
Stall Margin ◽  
Tip Leakage ◽  
Transonic Compressor ◽  
Blade Tip ◽  
Edge Separation

Computational analysis has been conducted on the NASA Rotor 37 transonic compressor with various tip clearance gap heights. Using steady rotor-only analysis, the change in overall performance, basic flow characteristics, and near-casing phenomena have been carefully observed. The results have clarified that the peak efficiency of the compressor decreases almost linearly with the increase in gap height. Meanwhile, the stall margin was prone to deterioration in cases of significantly small or significantly large clearance gaps. The peak stall margin was attained when the gap was set to 75% of the original height. Focusing on the flow structures, the tip leakage flow and tip leakage vortex seemed to be dominant loss sources in the case of a large tip clearance gap. On the other hand, trailing edge separation at the blade tip was the major loss source in case of a small tip clearance gap. The difference in the near-casing flow structure also determined the onset process of numerical instability. In case of a large tip clearance gap, the advance of the interface between the main flow and tip leakage flow seemed to cause an accumulation of blockage in the region near the casing, possibly triggering the tip-initiated stall. In the case of a small tip clearance gap, interaction among the wall separation, blade tip trailing edge separation, and shockwave /boundary layer interaction was significant. These phenomena appeared to play a major role in the onset of numerical instability in the blade tip region.

Active Tip Clearance Flow Control for an Axial-Flow Turbine Rotor Using Ring-Type Plasma Actuators

2014 ◽  
Author(s):  
Takayuki Matsunuma ◽  
Takehiko Segawa
Keyword(s):  
Flat Plate ◽  
Turbine Rotor ◽  
Plasma Actuator ◽  
Tip Clearance ◽  
Plasma Actuators ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Ring Type ◽  
Tip Leakage ◽  
Blade Tip

Tip leakage flow through the small gap between the blade tip and the casing wall in turbomachinery reduces the aerodynamic performance of the blade. New ring-type dielectric barrier discharge (DBD) plasma actuators have been developed to facilitate active control of the tip leakage flow of a turbine rotor. In the present study, the ring-type plasma actuators consisted of metallic wires coated with insulation material, mounted in an insulator embedded in the tip casing wall. For the fundamental experiments using a flat plate and a single airfoil with tip clearance, particle image velocimetry (PIV) was used to obtain two-dimensional velocity field measurements near the plate and blade tip regions. From flat plate experiments in a static flow field, it was confirmed that the operation of the plasma actuator generates an upward flow at the corner between the blade tip and the casing wall, and this forms a perpendicular obstacle to the tip leakage flow. In flat plate experiments on tip leakage flow in a wind tunnel, the forcibly-induced tip leakage flow was successfully dissipated by means of the plasma actuator flow control. In single airfoil experiments, the tip leakage flow was also reduced by the plasma actuator. In annular turbine rotor experiments, the plasma emission at the blade tip and its motion with blade rotation were determined. Single-element hot-wire anemometry was used to measure the turbulence intensity distributions at the turbine rotor exit. The amplitude of input voltage for the plasma actuator was varied from ±3.0 to ±6.0 kV. The high turbulence intensity region created by the tip leakage flow was reduced with an increase in the input voltage of the plasma actuator.

Sign in / Sign up

Export Citation Format

Share Document