scholarly journals On the Effects of Tip Clearance and Operating Condition on the Flow Structures Within an Axial Turbomachine Rotor Passage

2019 ◽  
Vol 141 (11) ◽  
Author(s):  
Yuanchao Li ◽  
Huang Chen ◽  
David Tan ◽  
Joseph Katz
Keyword(s):  
Particle Image ◽  
Suction Side ◽  
Tip Clearance ◽  
Flow Structures ◽  
Narrow Gap ◽  
Piv Measurements ◽  
Tip Leakage ◽  
Image Velocimetry ◽  
Stereo Particle Image Velocimetry ◽  
Turbomachine Rotor

Abstract Effects of tip clearance size and flowrate on the flow around the tip of an axial turbomachine rotor are studied experimentally. Visualizations and stereo-particle image velocimetry (PIV) measurements in a refractive index-matched facility compare the performance, leakage velocity, and the trajectory, growth rate, and strength of the tip leakage vortex (TLV) for gaps of 0.49% and 2.3% of the blade chord, and two flowrates. Enlarging the tip clearance delays the TLV breakup in the aft part of the rotor passage at high flowrates but causes earlier breakup under pre-stall conditions. It also reduces the entrainment of endwall boundary layer vorticity from the separation point where the leakage and passage flows meet. Reducing the flowrate or tip gap shifts the location of the TLV detachment from the blade suction side (SS) upstream to points where the leakage velocity is 70–80% of the tip speed. Once detached, the growth rates of the total shed circulation are similar for all cases, i.e., varying the gap or flowrate mostly shifts the detachment point. The TLV migration away from the SS decreases with an increasing gap but not with the flowrate. Two mechanisms dominate this migration: initially, the leakage jet pushes the TLV away from the blade at 50% of the leakage velocity. Further downstream, the TLV is driven by its image on the other side of the endwall. Differences in migration rate are caused by the smaller distance between the TLV and its image for the narrow gap, and the increase in initial TLV strength with decreasing flowrate and gap.

scholarly journals Stereo PIV measurements of oscillatory plasma forcing in the cross-plane of a channel flow

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Marc T. Hehner ◽  
Lars H. Von Deyn ◽  
Jacopo Serpieri ◽  
Saskia Pasch ◽  
Timo Reinheimer ◽  
...  
Keyword(s):  
Channel Flow ◽  
Particle Image ◽  
Dynamic Range ◽  
Turbulent Channel Flow ◽  
Plasma Actuator ◽  
Piv Measurements ◽  
Stochastic Fluctuations ◽  
Image Velocimetry ◽  
Field Dynamic ◽  
Stereo Particle Image Velocimetry

The present work describes an experimental investigation that applies stereo particle image velocimetry in a cross-plane of a turbulent channel flow that is additionally perturbed by spanwise oscillatory body forces, induced by a plasma actuator and designed to mimic the effect of spanwise wall oscillations. The experiment is aimed at retrieving the forcing-correlated scales and the turbulent flow stochastic fluctuations for the measured cross-plane. The first are macroscopic scales and require a larger investigation domain while the latter benefit of a higher resolution. Furthermore, the extended flow-field dynamic range posed a challenge on the experiment design, finally leading to an optimal tradeoff. The results of the unactuated flow compare well to the direct numerical simulations of Hoyas and Jimenez ́ (2008), while the actuated case demonstrates strong near-wall momentum addition and spanwise modulation of the streamwise flow component.

scholarly journals An Experimental Study of Stall Suppression and Associated Changes to the Flow Structures in the Tip Region of an Axial Low Speed Fan Rotor by Axial Casing Grooves

2017 ◽  
Vol 139 (12) ◽  
Author(s):  
Huang Chen ◽  
Yuanchao Li ◽  
Subhra Shankha Koley ◽  
Nick Doeller ◽  
Joseph Katz
Keyword(s):  
Large Scale ◽  
Leading Edge ◽  
Rotating Stall ◽  
Flow Structures ◽  
Flow Angle ◽  
Blade Loading ◽  
Low Speed ◽  
Tip Leakage ◽  
Image Velocimetry ◽  
Stereo Particle Image Velocimetry

The effects of axial casing grooves (ACGs) on the performance and flow structures in the tip region of an axial low speed fan rotor are studied experimentally in the JHU refractive index-matched liquid facility. The four-per-passage semicircular grooves are skewed by 45 deg, overlapping partially with the blade leading edge (LE) and extending upstream. They reduce the stall flow rate by 40% compared to the same machine with a smooth endwall. Stereo-particle image velocimetry (SPIV) measurements show that the inflow into the downstream side of the grooves and the outflow from their upstream side vary periodically, peaking when the inlet is aligned with the blade pressure side (PS). This periodic suction has three effects: first, substantial fractions of the leakage flow and the tip leakage vortex (TLV) are entrained into the groove, causing a reduction in TLV strength starting from midchord. Second, the grooves prevent the formation of large-scale backflow vortices (BFVs), which are associated with the TLV, propagate from one blade passage to the next, and play a key role in the onset of rotating stall in the untreated fan. Third, the flow exiting from the grooves causes periodic variations of the relative flow angle around the blade LE, presumably affecting the blade loading. The distributions of turbulent kinetic energy (TKE) provide statistical evidence that in contrast to the untreated casing, very little turbulence originating from the TLV and BFV of one blade propagates across the tip gap to the next passage.

PIV Measurements in the Condenser Region of a Gas-Loaded Thermosyphon

2008 ◽  
Author(s):  
Martin Cleary ◽  
Ronan Grimes ◽  
Marc Hodes ◽  
Mark T. North
Keyword(s):  
Vapor Phase ◽  
Particle Image ◽  
Flow Structures ◽  
Evaporator Temperature ◽  
Piv Measurements ◽  
3 Dimensional ◽  
Quantitative Measurements ◽  
Passive Devices ◽  
Image Velocimetry ◽  
Heat Loads

Thermosyphons are passive devices used to transfer heat via a liquid-vapor phase change cycle. By adding a secondary non-condensable gas (NCG) to the vapor phase of the thermosyphon it is possible to provide some control over the evaporator temperature as heat load and or ambient temperature vary. The objective of this paper is to perform measurements on the vapor phase in the condenser region of a gas-loaded thermosyphon using particle image velocimetry (PIV). An optically-accessible water/air thermosyphon with a 34.5 mm diameter was designed, constructed and characterized for a range of fill ratios, heat loads, coolant temperatures and masses of NCG. Smoke particles, added with the NCG, were used to seed the flow. The flow field in the condenser was found to be unsteady except with low masses of NCG. It was found that there was no discernable vapor/NCG front present. A large amount of mixing of the vapor and NCG and recirculation of the NCG was observed. Due to the complex 3-dimensional non-axisymmetric nature of the flow it is very difficult to obtain useful quantitative measurements, however, PIV was found to be a very useful tool in visualizing the flow providing an insight in to the flow structures in the condenser.

Flow Characteristics of Pressure-Driven Water in Serpentine Micro-Channels

2006 ◽  
Author(s):  
Renqiang Xiong ◽  
J. N. Chung
Keyword(s):  
Particle Image Velocimetry ◽  
Particle Image ◽  
Flow Characteristics ◽  
Flow Structures ◽  
Micro Channel ◽  
Pressure Drops ◽  
Micro Particle Image Velocimetry ◽  
Image Velocimetry ◽  
Micro Channels ◽  
Shape And Size

Flow structures and pressure drops were investigated in rectangular serpentine micro-channels with miter bends which had hydraulic diameters of 0.209mm, 0.395mm and 0.549mm respectively. To evaluate the bend effect, the additional pressure drop due to the miter bend must be obtained. Three groups of micro-channels were fabricated to remove the inlet and outlet losses. A validated micro-particle image velocimetry (μPIV) system was used to achieve the flow structure in a serpentine micro-channel with hydraulic diameter of 0.173mm. The experimental results show the vortices around the outer and inner walls of the bend do not form when Re<100. Those vortices appear and continue to develop with the Re number when Re> 100-300, and the shape and size of the vortices almost remain constant when Re>1000. The bend loss coefficient Kb was observed to be related with the Re number when Re<100, with the Re number and channel size when Re>100. It almost keeps constant and changes in the range of ± 10% When Re is larger than some value in 1300-1500. And a size effect on Kb was also observed.

An experimental and numerical study of the resonant flow between a hull and a wall

2021 ◽  
Vol 930 ◽  
Author(s):  
I.A. Milne ◽  
O. Kimmoun ◽  
J.M.R. Graham ◽  
B. Molin
Keyword(s):  
Vortex Shedding ◽  
Particle Image ◽  
Numerical Study ◽  
Numerical Models ◽  
Vertical Wall ◽  
Liquefied Natural Gas ◽  
Narrow Gap ◽  
Image Velocimetry ◽  
High Degree ◽  
Wave Induced

The wave-induced resonant flow in a narrow gap between a stationary hull and a vertical wall is studied experimentally and numerically. Vortex shedding from the sharp bilge edge of the hull gives rise to a quadratically damped free surface response in the gap, where the damping coefficient is approximately independent of wave steepness and frequency. Particle image velocimetry and direct numerical simulations were used to characterise the shedding dynamics and explore the influence of discretisation in the measurements and computations. Secondary separation was identified as a particular feature which occurred at the hull bilge in these gap flows. This can result in the generation of a system with multiple vortical regions and asymmetries between the inflow and outflow. The shedding dynamics was found to exhibit a high degree of invariance to the amplitude in the gap and the spanwise position of the barge. The new measurements and the evaluation of numerical models of varying fidelity can assist in informing offshore operations such as the side by side offloading from floating liquefied natural gas facilities.

Numerical Simulation of Tip Clearance Control in Axial Turbine Rotor: Part 2—Passive Control of Five Different Tip Platforms

2008 ◽  
Author(s):  
Wei Li ◽  
Wei-Yang Qiao ◽  
Kai-Fu Xu ◽  
Hua-Ling Luo
Keyword(s):  
Flow Control ◽  
Passive Control ◽  
Suction Side ◽  
Turbine Rotor ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Clearance Flow

The tip leakage flow has significant effects on turbine in loss production, aerodynamic efficiency, etc. Then it’s important to minimize these effects for a better performance by adopting corresponding flow control. The active turbine tip clearance flow control with injection from the tip platform is given in Part-1 of this paper. This paper is Part-2 of the two-part papers focusing on the effect of five different passive turbine tip clearance flow control methods on the tip clearance flow physics, which consists of a partial suction side squealer tip (Partial SS Squealer), a double squealer tip (Double Side Squealer), a pressure side tip shelf with inclined squealer tip on a double squealer tip (Improved PS Squealer), a tip platform extension edge in pressure side (PS Extension) and in suction side (SS Extension) respectively. Combined with the turbine rotor and the numerical method mentioned in Part 1, the effects of passive turbine tip clearance flow controls on the tip clearance flow were sequentially simulated. The detailed tip clearance flow fields with different squealer rims were described with the streamline and the velocity vector in various planes parallel to the tip platform or normal to the tip leakage vortex core. Accordingly, the mechanisms of five passive controls were put in evidence; the effects of the passive controls on the turbine efficiency and the tip clearance flow field were highlighted. The results show that the secondary flow loss near the outer casing including the tip leakage flow and the casing boundary layer can be reduced in all the five passive control methods. Comparing the active control with the passive control, the effect brought by the active injection control on the tip leakage flow is evident. The turbine rotor efficiency could be increased via the rational passive turbine tip clearance flow control. The Improved PS Squealer had the best effect on turbine rotor efficiency, and it increased by 0.215%.

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