scholarly journals Flow and Fast Fourier Transform Analyses for Tip Clearance Effect in an Operating Kaplan Turbine

Energies ◽  
2019 ◽  
Vol 12 (2) ◽  
pp. 264 ◽  
Author(s):  
Hyoung-Ho Kim ◽  
Md Rakibuzzaman ◽  
Kyungwuk Kim ◽  
Sang-Ho Suh
Keyword(s):  
Fourier Transform ◽  
Fast Fourier Transform ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Tip Clearance Flow ◽  
Kaplan Turbine ◽  
Turbine Performance ◽  
Wide Range ◽  
Clearance Flow ◽  
Fft Analysis

The Kaplan turbine is an axial propeller-type turbine that can simultaneously control guide vanes and runner blades, thus allowing its application in a wide range of operations. Here, turbine tip clearance plays a crucial role in turbine design and operation as high tip clearance flow can lead to a change in the flow pattern, resulting in a loss of efficiency and finally the breakdown of hydro turbines. This research investigates tip clearance flow characteristics and undertakes a transient fast Fourier transform (FFT) analysis of a Kaplan turbine. In this study, the computational fluid dynamics method was used to investigate the Kaplan turbine performance with tip clearance gaps at different operating conditions. Numerical performance was verified with experimental results. In particular, a parametric study was carried out including the different geometrical parameters such as tip clearance between stationary and rotating chambers. In addition, an FFT analysis was performed by monitoring dynamic pressure fluctuation on the rotor. Here, increases in tip clearance were shown to occur with decreases in efficiency owing to unsteady flow. With this study’s focus on analyzing the flow of the tip clearance and its effect on turbine performance as well as hydraulic efficiency, it aims to improve the understanding on the flow field in a Kaplan turbine.

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.

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.

Experimental Investigations on Mixed Flow Impeller and Vane Diffuser Under Various Operating Conditions

2012 ◽  
Author(s):  
D. Ramesh Rajakumar ◽  
S. Ramamurthy ◽  
M. Govardhan
Keyword(s):  
Pressure Ratio ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Experimental Investigations ◽  
Compressor Stage ◽  
Mixed Flow ◽  
Tip Clearance Flow ◽  
Clearance Flow ◽  
Flow Compressor ◽  
Vane Diffuser

Experimental Investigations are carried out to study the effect of tip clearance flow in a mixed flow compressor stage. Two configurations, namely; constant and variable clearance gaps between impeller and stationary shroud are considered. For the purpose of the present investigations, a mixed flow compressor stage is designed and fabricated. The flow investigations were carried out in a closed circuit compressor rig. Detailed steady and unsteady measurements were carried out for three clearance gaps, namely; 0.5 mm, 0.75 mm, 0.9 mm. From the experimental investigations it is shown that constant tip clearance configurations show better performance in terms of pressure ratio and efficiency compared to variable clearance configurations. For a given configuration the pressure ratio and efficiency of the stage decrease with increase in the tip gap without indicating any optimum value. Tip clearance flow has considerable effect on the flow through the diffuser and the unsteady flow gets amplified and carried away into the vane diffuser.

scholarly journals Experimental and Computational Investigation of the Tip Clearance Flow in a Transonic Axial Compressor Rotor

1996 ◽  
Vol 118 (2) ◽  
pp. 218-229 ◽  
Author(s):  
K. L. Suder ◽  
M. L. Celestina
Keyword(s):  
Axial Compressor ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Vortex Interaction ◽  
Peak Efficiency ◽  
Tip Clearance Flow ◽  
Compressor Rotor ◽  
Clearance Flow ◽  
Transonic Axial Compressor ◽  
Design Speed

Experimental and computational techniques are used to investigate tip clearance flows in a transonic axial compressor rotor at design and part-speed conditions. Laser anemometer data acquired in the endwall region are presented for operating conditions near peak efficiency and near stall at 100 percent design speed and at near peak efficiency at 60 percent design speed. The role of the passage shock/leakage vortex interaction in generating endwall blockage is discussed. As a result of the shock/vortex interaction at design speed, the radial influence of the tip clearance flow extends to 20 times the physical tip clearance height. At part speed, in the absence of the shock, the radial extent is only five times the tip clearance height. Both measurements and analysis indicate that under part-speed operating conditions a second vortex, which does not originate from the tip leakage flow, forms in the end-wall region within the blade passage and exits the passage near midpitch. Mixing of the leakage vortex with the primary flow downstream of the rotor at both design and part-speed conditions is also discussed.

Experimental Study on Different Tip Clearance of Low-Speed Axial Fan

2021 ◽  
Author(s):  
Ming Zhang ◽  
Jia Li ◽  
Xu Dong ◽  
Dakun Sun ◽  
Xiaofeng Sun
Keyword(s):  
Experimental Studies ◽  
Pressure Rise ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Signal Spectrum ◽  
Tip Clearance Flow ◽  
Low Speed ◽  
Clearance Flow ◽  
Casing Pressure

Abstract Tip clearance flow is not only the source of undesirable noise but also a potential indicator for critical operating conditions with rotating stall or surge. It can induce blade vibration, which would cause premature blade failure when the vibration is strong enough. The paper presents experimental studies on the effects of tip clearance on the stall inception process in a low-speed high-load single stage fan with different tip clearance. From the point of view of flow range, it has been proved by computations that there is an optimal gap value, and an explanation is given according to different stall mechanisms of large and small tip clearance. However, the experiment of no tip clearance is not easy to achieve. In this experiment, a wearable soft wall casing was used to achieve “zero clearance”, and an explicit conclusion was obtained. The pressure rise and efficiency are improved at small tip clearance. Instantaneous Casing Pressure Field Measurement was carried out: instantaneous casing pressure fields were measured by 9 high response pressure transducers mounted on the casing wall. At the near stall point with large tip clearance, a narrow band increase of the amplitudes in the frequency spectrum at roughly half of the blade passing frequency can be observed according to the spectrum of static pressure at points on the endwall near the leading-edge and above the rotor. This phenomenon was explained from two aspects: tip clearance flow structure and pressure signal spectrum.

3-D Digital PIV Measurements of the Tip Clearance Flow in an Axial Compressor

2002 ◽  
Author(s):  
Mark P. Wernet ◽  
Dale Van Zante ◽  
Tony J. Strazisar ◽  
W. Trevor John ◽  
P. Susan Prahst
Keyword(s):  
Three Dimensional ◽  
Axial Compressor ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Tip Clearance Flow ◽  
Compressor Rotor ◽  
Image Velocimetry ◽  
Clearance Flow ◽  
Compressor Performance ◽  
Tip Clearance Vortex

The accurate characterization and simulation of rotor tip clearance flows has received much attention in recent years due to their impact on compressor-performance and stability. At NASA Glenn the first known three dimensional Digital Particle Image Velocimetry (DPIV) measurements of the tip region of a low speed compressor rotor have been acquired to characterize the behavior of the rotor tip clearance flow. The measurements were acquired phase-locked to the rotor position so that changes in the tip clearance vortex position relative to the rotor blade can be seen. The DPIV technique allows the magnitude and relative contributions of both the asynchronous motions of a coherent structure and the temporal unsteadiness to be evaluated. Comparison of measurements taken at the peak efficiency and at near stall operating conditions characterizes the mean position of the clearance vortex and the changes in the unsteady behavior of the vortex with blade loading. Comparisons of the 3-D DPIV measurements at the compressor design point to a 3D steady N-S solution are also done to assess the fidelity of steady, single-passage simulations to model an unsteady flow field.

Simulation of Tip-Clearance Effects in a Transonic Compressor

2015 ◽  
Author(s):  
Marcus Lejon ◽  
Niklas Andersson ◽  
Lars-Erik Eriksson ◽  
Lars Ellbrant
Keyword(s):  
Total Pressure ◽  
Tip Clearance ◽  
Computational Time ◽  
Tip Clearance Flow ◽  
Transonic Compressor ◽  
Modeling Approaches ◽  
Wide Range ◽  
Sst Model ◽  
Clearance Flow ◽  
Compressor Performance

Tip clearance flow can have a large impact on compressor performance and is therefore important to consider in compressor design. A wide range of computational approaches can be used for modeling tip clearance flow. The different modeling strategies reflect compromises between accuracy and computational time. The present study investigates a large tip gap configuration (1.65% of the rotor tip chord) of the highly loaded transonic 1.5 stage compressor Hulda. The aim of the study is to evaluate different modeling approaches and find a method that can predict the effects of a large tip clearance on compressor performance. The modeling approaches investigated are the SAS-SST model in CFX and the k-ε turbulence model using a wall function and Chien’s low-Reynolds model in the in-house CFD solver VolSol++. Results obtained using the chosen solvers and turbulence models are compared with experimental data, and all approaches are shown to predict the overall performance trends. However, the turbulence kinetic energy in the tip clearance flow and the trajectory of the vortex are shown to vary depending on the method. The SAS-SST model predicts the performance well in terms of total pressure ratio, polytropic efficiency as well as radial distribution of total pressure downstream the rotor. Based on the results from the study, SAS-SST is concluded to be a good candidate for detailed studies of transonic compressors with large tip gaps.

Similarity Analysis of Compressor Tip Clearance Flow Structure

1991 ◽  
Vol 113 (2) ◽  
pp. 260-269 ◽  
Author(s):  
G. T. Chen ◽  
E. M. Greitzer ◽  
C. S. Tan ◽  
F. E. Marble
Keyword(s):  
Velocity Field ◽  
Three Dimensional ◽  
Normal Pressure ◽  
Tip Clearance ◽  
Pressure Gradients ◽  
Tip Clearance Flow ◽  
Wide Range ◽  
Dominant Feature ◽  
Clearance Flow ◽  
Similarity Scaling

A new approach is presented for analyzing compressor tip clearance flow. The basic idea is that the clearance velocity field can be (approximately) decomposed into independent throughflow and crossflow, since chordwise pressure gradients are much smaller than normal pressure gradients in the clearance region. As in the slender body approximation in external aerodynamics, this description implies that the three-dimensional, steady, clearance flow can be viewed as a two-dimensional, unsteady flow. Using this approach, a similarity scaling for the crossflow in the clearance region is developed and a generalized description of the clearance vortex is derived. Calculations based on the similarity scaling agree well with a wide range of experimental data in regard to flow features such as crossflow velocity field, static pressure field, and tip clearance vortex trajectory. The scaling rules also provide a useful way of exploring the parametric dependence of the vortex trajectory and strength for a given blade row. The emphasis of the approach is on the vortical structure associated with the tip clearance because this appears to be a dominant feature of the endwall flow; it is also shown that this emphasis gives considerable physical insight into overall features seen in the data.

scholarly journals Experimental and Computational Investigation of the Tip Clearance Flow in a Transonic Axial Compressor Rotor

1994 ◽  
Author(s):  
Kenneth L. Suder ◽  
Mark L. Celestina
Keyword(s):  
Axial Compressor ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Vortex Interaction ◽  
Peak Efficiency ◽  
Tip Clearance Flow ◽  
Compressor Rotor ◽  
Clearance Flow ◽  
Transonic Axial Compressor ◽  
Design Speed

Experimental and computational techniques are used to investigate tip clearance flows in a transonic axial compressor rotor at design and part speed conditions. Laser anemometer data acquired in the endwall region are presented for operating conditions near peak efficiency and near stall at 100% design speed and at near peak efficiency at 60% design speed. The role of the passage shock / leakage vortex interaction in generating endwall blockage is discussed. As a result of the shock / vortex interaction at design speed, the radial influence of the tip clearance flow extends to 20 times the physical tip clearance height. At part speed, in the absence of the shock, the radial extent is only 5 times the tip clearance height. Both measurements and analysis indicate that under part-speed operating conditions a second vortex, which does not originate from the tip leakage flow, forms in the endwall region within the blade passage and exits the passage near midpitch. Mixing of the leakage vortex with the primary flow downstream of the rotor at both design and part speed conditions is also discussed.

Experimental Off-Design Investigation of Unsteady Secondary Flow Phenomena in a Three-Stage Axial Compressor at 68% Nominal Speed

2004 ◽  
Author(s):  
Andreas Bohne ◽  
Reinhard Niehuis
Keyword(s):  
Dynamic Pressure ◽  
Axial Compressor ◽  
Operating Conditions ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Tip Clearance Flow ◽  
Pressure Transducers ◽  
Surge Margin ◽  
Clearance Flow ◽  
Flow Phenomena

This paper deals with unsteady measurements in a highspeed three-stage axial compressor with inlet guide vanes (IGV) and controlled diffusion airfoils (CDA) at off-design conditions. The compressor under consideration exhibits design features of real industrial compressors. The main emphasis is put on the experimental investigation of two operating points at 68% nominal speed where a significant mismatching of the stages occurs. The first operating point is the last stable one near the surge margin whereas the second one represents choke. Probe traverses with a high resolution both in space and time show the significant potential upstream influence of the rotor blades. This effect and the disturbances caused by the convected wakes do strongly influence the unsteady boundary layer behaviour of the stator blades which are detected by glue-on hot-film sensors at different spanwise positions. Dynamic pressure transducers on the casing show that the structure of the rotor tip clearance flow strongly depends on the operating conditions of the compressor. Conclusions can be drawn concerning the consideration of the discussed unsteady effects within the design process of multistage axial compressors with respect to the presented results.

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