Tip Clearance Flow Visualization of a Turbine Blade Cascade With Active and Passive Flow Control

2008 ◽  
Author(s):  
Daniel K. Van Ness ◽  
Thomas C. Corke ◽  
Scott C. Morris
Keyword(s):  
Flow Control ◽  
Flow Visualization ◽  
Total Pressure ◽  
Plasma Actuator ◽  
Tip Clearance ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Blade Cascade ◽  
Clearance Flow ◽  
Blade Tip

The secondary flow in the tip clearance region of a stationary linear low pressure turbine blade cascade was studied using two types of surface flow visualization and documented using wake pressure measurements in order to identify the potential means and impact of flow control to reduce losses associated with the tip clearance flow. An evaporating fluid mixture was used for flow visualization on the casing surface of the tip clearance. An oil ink-dot tracing method was used on the blade tip. These measurements illustrate the important features of the near-casing flow physics, including the size and chordwise extent of the blade tip separation bubble, separation lines on the casing, the flow direction on the blade tip and casing, the size and exit trajectory of the tip leakage and passage vortices, as well as the total pressure loss and secondary velocity vectors downstream of the blade. The flow was visualized in this way for a plain, flat tip, a tip mounted plasma actuator, and a partial suction side squealer tip. Both flow control devices were observed to affect the flow in the clearance. The plasma actuator was shown to improve the total pressure loss in the tip leakage vortex by as much as 9% from the loss over the plain tip blade. The tests were performed over a Reynolds numbers range between 5.3 × 104 and 1.04 × 105 at a fixed tip clearance of 2% of axial chord.

Plasma Actuator Blade Tip Clearance Flow Control in a Linear Turbine Cascade

2012 ◽  
Vol 28 (3) ◽  
pp. 504-516 ◽  
Author(s):  
Daniel K. Van Ness ◽  
Thomas C. Corke ◽  
Scott C. Morris
Keyword(s):  
Flow Control ◽  
Plasma Actuator ◽  
Tip Clearance ◽  
Turbine Cascade ◽  
Tip Clearance Flow ◽  
Clearance Flow ◽  
Blade Tip ◽  
Blade Tip Clearance

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%.

Experimental Investigation of Tip Clearance Flow in a Transonic Compressor With and Without Plasma Actuators

2014 ◽  
Vol 137 (4) ◽  
Author(s):  
S. Saddoughi ◽  
G. Bennett ◽  
M. Boespflug ◽  
S. L. Puterbaugh ◽  
A. R. Wadia
Keyword(s):  
Flow Control ◽  
High Speed ◽  
Plasma Actuator ◽  
Tip Clearance ◽  
Plasma Actuators ◽  
Tip Clearance Flow ◽  
Transonic Compressor ◽  
Low Aspect Ratio ◽  
Clearance Flow ◽  
Design Speed

Blade tip losses represent a major performance penalty in low aspect ratio transonic compressors. This paper reports on the experimental evaluation of the impact of tip clearance with and without plasma actuator flow control on performance of an U.S. Air Force-designed low aspect ratio, high radius ratio single-stage transonic compressor rig. The detailed stage performance measurements without flow control at three clearance levels, classified as small, medium, and large, are presented. At design-speed, increasing the clearance from small to medium resulted in a stage peak efficiency drop of almost six points with another four point drop in efficiency with the large clearance (LC). Comparison of the speed lines at high-speed show significantly lower pressure rise with increasing tip clearance, the compressor losing 8% stall margin (SM) with medium clearance (MC) and an additional 1% with the LC. Comparison of the stage exit radial profiles of total pressure and adiabatic efficiency at both part-speed and design-speed and with throttling are presented. Tip clearance flow-control was investigated using dielectric barrier discharge (DBD) type plasma actuators. The plasma actuators were placed on the casing wall upstream of the rotor leading edge and the compressor mapped from part-speed to high-speed at three clearances with both axial and skewed configurations at six different frequency levels. The plasma actuators did not impact steady state performance. A maximum SM improvement of 4% was recorded in this test series. The LC configuration benefited the most with the plasma actuators. Increased voltage provided more SM improvement. Plasma actuator power requirements were almost halved going from continuous operation to pulsed plasma. Most of the improvement with the plasma actuators is attributed to the reduction in unsteadiness of the tip clearance vortex near-stall resulting in additional reduction in flow prior to stall.

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 Simulation of Tip Clearance Flow Control in Axial Turbine Rotor: Part 1—Active Flow Control Injection From Turbine Blade Tip

2008 ◽  
Author(s):  
Wei Li ◽  
Wei-Yang Qiao ◽  
Kai-Fu Xu ◽  
Hua-Ling Luo
Keyword(s):  
Flow Control ◽  
Turbine Blade ◽  
Stokes Equations ◽  
Tip Clearance ◽  
Tip Leakage Flow ◽  
Injection Hole ◽  
Tip Clearance Flow ◽  
Clearance Flow ◽  
Flow Part ◽  
Blade Tip

Reducing loss and increasing efficiency are always pursued in the designing of the turbine, and flow control is an efficient solution to minimize the tip clearance loss. Recently it aroused much attention in the field of the turbine tip clearance flow. Part-1 of this paper aims to numerically investigate the effect of active turbine clearance flow control by injection from a turbine blade tip on the tip clearance flow. Part-2 of this paper focus on the passive turbine tip clearance flow control. A density-correction based, 3D Reynolds-averaged Navier-Stokes equations CFD code with Reynolds Stress Model, which was proved to be validated, was adopted. The variable specific heat was considered. The effects of injection on the tip clearance flow were simulated in two tip clearance heights, and each height corresponds to five injection hole locations and five injection mass flow rates. Accordingly, the mechanisms of active injection control were put in evidence; the effects of the injection on the turbine efficiency which includes the effect of the jet and the tip clearance flow were highlighted; and the tip clearance flow structure was analyzed topologically. If the tip leakage flow corresponding to the injection location is subsonic, this injection can increase the efficiency, such as the first and the second jet. The combined jet could increase the efficiency by 0.35% for the case of loose tip clearance and by 0.3% for the case of tight tip clearance. The number of saddle points was equal to that of nodes near the injection hole, which could satisfy the singularity point total number law.

scholarly journals An improved model for tip clearance loss in transonic axial compressors

2017 ◽  
Vol 232 (4) ◽  
pp. 295-314
Author(s):  
Shubo Ye ◽  
Qingjun Zhao ◽  
Weiwei Cui ◽  
Guang Xi ◽  
Jianzhong Xu
Keyword(s):  
Flow Control ◽  
Computational Study ◽  
Control Volume ◽  
Pressure Rise ◽  
Tip Clearance ◽  
Incoming Flow ◽  
Flow Angle ◽  
Tip Clearance Flow ◽  
Clearance Flow ◽  
Blade Tip

An improved compressible model for estimating tip clearance loss in transonic compressors is presented with the emphasis on the effects of blade tip loading distribution and double leakage flow. Tip clearance flow is treated as three parts along the chord and the progressive relations from upstream to downstream part is revealed to be responsible for the formation of tip clearance flow. Control volume method is applied to simplify the mixing process and calculate the mixed-out loss for the three parts, separately. Computational study shows that mass flow of the incoming flow entering the control volume is consistent with that passing through an equivalent area of about half of tip leakage vortex region. The new model reveals that the second part of tip clearance flow has a larger mixed-out loss capacity than the two other parts. This difference is attributed to two factors: larger injection flow angle and more enrolled incoming flow, and both factors tend to increase the mixed-out loss. The success of the model implies that blade design or flow control strategies turning the tip clearance/main flow interface’s arrival onto blade tip pressure side downstream and the shock’s impingement point onto blade tip suction side upstream may be beneficial in desensitizing compressor performance to tip clearance size, without trading off pressure rise.

Numerical Simulation of a Transonic Centrifugal Compressor Blades Tip Clearance Flow of Vehicle Turbocharger

2008 ◽  
Author(s):  
Gongda Guo ◽  
Yangjun Zhang ◽  
Jianzhong Xu ◽  
Xinqian Zheng ◽  
Weilin Zhuge
Keyword(s):  
Shock Waves ◽  
Centrifugal Compressor ◽  
Tip Clearance ◽  
Tip Leakage Flow ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Transonic Centrifugal Compressor ◽  
Clearance Flow ◽  
Blade Tip ◽  
Blade Tip Clearance

Flow induced by blade tip clearance is important for centrifugal compressor, especially for the high charging ratio transonic centrifugal compressor of the vehicle. Based on three-dimensional CFD method, the evolution and mechanism of tip clearance flow for the high charging ratio transonic centrifugal compressor are investigated. It is verified that shock waves have important effect on blade tip clearance flow. The original position and strength of leakage vortices depend on the position and intensity of shock waves. The tip leakage vortex (TLV) evolution is influenced by the evolution of passage vortex (PV), corner vortex (CV) and separated vortex (SV). Shock wave, adverse pressure gradient and casing boundary layer accelerate the leakage vortices breakdown. Leakage vortex loss is the most important factor of impeller loss. The research on the blades tip leakage flow of transonic centrifugal compressor for vehicle lays a foundation for transonic centrifugal compressor flow control.

Measurements of the Tip Clearance Flow for a High-Reynolds-Number Axial-Flow Rotor

1995 ◽  
Vol 117 (4) ◽  
pp. 522-532 ◽  
Author(s):  
W. C. Zierke ◽  
K. J. Farrell ◽  
W. A. Straka
Keyword(s):  
Reynolds Number ◽  
Flow Visualization ◽  
Vortex Core ◽  
Rotor Blade ◽  
High Reynolds Number ◽  
Tip Clearance ◽  
Tip Leakage Vortex ◽  
Tip Leakage ◽  
Blade Tip ◽  
High Reynolds

A high-Reynolds-number pump (HIREP) facility has been used to acquire flow measurements in the rotor blade tip clearance region, with blade chord Reynolds numbers of 3,900,000 and 5,500,000. The initial experiment involved rotor blades with varying tip clearances, while a second experiment involved a more detailed investigation of a rotor blade row with a single tip clearance. The flow visualization on the blade surface and within the flow field indicate the existence of a trailing-edge separation vortex, a vortex that migrates radially upward along the trailing edge and then turns in the circumferential direction near the casing, moving in the opposite direction of blade rotation. Flow visualization also helps in establishing the trajectory of the tip leakage vortex core and shows the unsteadiness of the vortex. Detailed measurements show the effects of tip clearance size and downstream distance on the structure of the rotor tip leakage vortex. The character of the velocity profile along the vortex core changes from a jetlike profile to a wakelike profile as the tip clearance becomes smaller. Also, for small clearances, the presence and proximity of the casing endwall affects the roll-up, shape, dissipation, and unsteadiness of the tip leakage vortex. Measurements also show how much circulation is retained by the blade tip and how much is shed into the vortex, a vortex associated with high losses.

Method for Non-Dimensional Tip Leakage Flow Characterization in Radial Turbines

2018 ◽  
Author(s):  
José Ramón Serrano ◽  
Roberto Navarro ◽  
Luis Miguel García-Cuevas ◽  
Lukas Benjamin Inhestern
Keyword(s):  
Suction Side ◽  
Tip Clearance ◽  
Navier Stokes ◽  
The Novel ◽  
Tip Leakage Flow ◽  
Navier Stokes Equation ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Wide Range ◽  
Clearance Flow

Tip leakage loss characterization and modeling plays an important role in small size radial turbine research. The momentum of the flow passing through the tip gap is highly related with the tip leakage losses. The ratio of fluid momentum driven by the pressure gradient between suction side and pressure side and the fluid momentum caused by the shroud friction has been widely used to analyze and to compare different sized tip clearances. However, the commonly used number for building this momentum ratio lacks some variables, as the blade tip geometry data and the viscosity of the used fluid. To allow the comparison between different sized turbocharger turbine tip gaps, work has been put into finding a consistent characterization of radial tip clearance flow. Therefore, a non-dimensional number has been derived from the Navier Stokes Equation. This number can be calculated like the original ratio over the chord length. Using the results of wide range CFD data, the novel tip leakage number has been compared with the traditional and widely used ratio. Furthermore, the novel tip leakage number can be separated into three different non-dimensional factors. First, a factor dependent on the radial dimensions of the tip gap has been found. Second, a factor defined by the viscosity, the blade loading, and the tip width has been identified. Finally, a factor that defines the coupling between both flow phenomena. These factors can further be used to filter the tip gap flow, obtained by CFD, with the influence of friction driven and pressure driven momentum flow.

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