An Investigation of Confined Vortex Flow Phenomena

1972 ◽  
Vol 94 (3) ◽  
pp. 689-696 ◽  
Author(s):  
Clyde C. K. Kwok ◽  
Ngo Dinh Thinh ◽  
Sui Lin
Keyword(s):  
Apparent Viscosity ◽  
Tangential Velocity ◽  
Vortex Chamber ◽  
Experimental Investigations ◽  
Fluid Viscosity ◽  
Analytical Technique ◽  
Runge Kutta Method ◽  
Analytical Results ◽  
Flow Phenomena ◽  
Viscosity Factor

The swirling, incompressible flow within a short vortex chamber of aspect ratio 1/9, defined by the ratio of chamber height to chamber diameter, has been investigated analytically. The theoretical analysis consists of the adaptation of Wormley’s analytical technique and the extension of the method to include the apparent viscosity factor. The Runge-Kutta method is used to solve numerically the set of differential equations. The analytical results are compared with those of the experimental investigations conducted by Savino and Keshock. The analytical results prove that the values of apparent viscosity seriously affect the velocity profiles within the vortex chamber. The results also show that the apparent viscosity varies from 7000μ at the vortex chamber periphery to 4500μ at the orifice exit plane, where μ is the operating fluid viscosity. An empirical expression for the apparent viscosity is found in the form μa = K1νδn + K2, where n, K1, and K2 are constants and νδ is the tangential velocity. The constants n, K1, and K2 are found to be −1/3, 0.01, and 0.0005, respectively, for this investigation.

Effects of Flow Distortions as They Occur in S-Duct Inlets on the Performance and Stability of a Jet Engine

2015 ◽  
Author(s):  
Rudolf. P. M. Rademakers ◽  
Stefan Bindl ◽  
Reinhard Niehuis
Keyword(s):  
Mesh Size ◽  
Experimental Investigations ◽  
Test Bed ◽  
Flow Distortion ◽  
Jet Engine ◽  
Jet Propulsion ◽  
Inlet Distortion ◽  
Flow Phenomena ◽  
The Impact ◽  
Duct Design

One of the research areas at the Institute of Jet Propulsion focuses on the design and optimization of s-shaped engine inlet configurations. The distortion being evoked within such inlet ducts should be limited to ensure an optimal performance, stability, and durability of the engine’s compression system. Computational Fluid Dynamics (CFD) play a major role in the design process of bent engine inlet ducts. The flow within such ducts can be computed, distortion patterns can be visualized, and related distortion coefficients are easily calculated. The impact of a distortion on flow phenomena within the compressor system can, however, only be computed with major computational efforts and thus the quality of an s-duct design in development is usually assessed by analyzing the evoked distortion with suitable distortion coefficients without a true knowledge of the duct’s influence on the downstream propulsion system. The influence of inlet distortion on both the performance and stability of the Larzac 04 jet engine was parameterized during experimental investigations at the engine test bed of the Institute of Jet Propulsion. Both pressure and swirl distortion patterns as they typically occur in s-duct inlet configurations were reproduced with distortion generators. Pressure distortion patterns were generated using seven types of distortion screens. The intensity of the distortion varies with the mesh size of the screen whereas the extension of the distortion is defined by the dimensions of the screen in radial and circumferential direction. A typical counter rotating twin-swirl was generated with a deltawing installed upstream of the compressor system. First, the development of flow distortion was analyzed for several engine operating points (EOPs). A linear relation between the total pressure loss in the engine inlet and the EOPs was found. Secondly, the flow within the compressor system with an inlet distortion was analyzed and unsteady flow phenomena were detected for severe inlet distortions. Finally, the effect of both pressure and swirl distortion on the performance and stability of the test vehicle was parameterized. A loss in engine performance with increasing inlet distortion is observable. The limiting inlet distortion with respect to engine stability was found and moreover it was shown that pressure distortion has a stronger influence on the stability of the compressor system compared to a counter rotating twin-swirl distortion. The presented parameterization is essential for the s-duct design, which is under development for an experimental set-up with the Larzac 04 jet engine.

Efficiency Improvement and Noise Reduction Through Stator-Stator Clocking Effect of a Two-Stage Turbine

2005 ◽  
Author(s):  
Jaroslaw R. Blaszczak
Keyword(s):  
Acoustic Noise ◽  
Experimental Investigations ◽  
Two Stage ◽  
Machine Vibration ◽  
Low Pressure Turbine ◽  
Measurement Results ◽  
Stator Vane ◽  
Flow Phenomena ◽  
Inlet Conditions ◽  
Good Agreement

The objective of the presented test program was to further experimentally investigate vane-indexing effect influence on the performance, noise and vibration of two-stage low-pressure turbine. Keeping the inlet conditions strictly constant during the tests, two turbine stages were experimentally investigated. Herein, some flow measurement results and the external characteristics for different circumferential positions of the stator vanes are described. Comparisons were made with numerical simulation and they showed good agreement. Experimental data and numerical simulations of stator vane surface pressures are presented to determine how the flow phenomena were affected by indexing of the airfoils for two cases: for nominal rotational speed and for off-design turbine conditions. In addition, correlation to acoustic noise and machine vibration level is presented. They have been found to be clocking dependent. The experimental investigations have been carried out on a two-stage turbine research facility at the Institute of Turbomachinery of the Technical University of Lodz, Poland.

Experimental Investigation of the Diffuser Vane Clearance Effect in a Centrifugal Compressor Stage With Adjustable Diffuser Geometry—Part I: Compressor Performance Analysis

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Stefan Ubben ◽  
Reinhard Niehuis
Keyword(s):  
Centrifugal Compressor ◽  
Negative Impact ◽  
Pressure Ratio ◽  
Industrial Applications ◽  
Experimental Investigations ◽  
Flow Measurements ◽  
Flow Phenomena ◽  
Compressor Performance ◽  
Compressor Map ◽  
The Impact

Adjustable diffuser vanes offer an attractive design option for centrifugal compressors applied in industrial applications. However, the knowledge about the impact on compressor performance of a diffuser vane clearance between vane and diffuser wall is still not satisfying. This two-part paper summarizes results of experimental investigations performed with an industrial-like centrifugal compressor. Particular attention was directed toward the influence of the diffuser clearance on the operating behavior of the entire stage, the pressure recovery in the diffuser, and on the diffuser flow by a systematic variation of the parameters diffuser clearance height, diffuser vane angle, radial gap between impeller exit and diffuser inlet, and rotor speed. Compressor map measurements provide a summary of the operating behavior related to diffuser geometry and impeller speed, whereas detailed flow measurements with temperature and pressure probes allow a breakdown of the losses between impeller and diffuser and contribute to a better understanding of relevant flow phenomena. The results presented in Part I show that an one-sided diffuser clearance does not necessarily has a negative impact on the operation and loss behavior of the centrifugal compressor, but instead may contribute to an increased pressure ratio and improved efficiency as long as the diffuser passage is broad enough with respect to the clearance height. The flow phenomena responsible for this detected performance behavior are exposed in Part II, where the results of detailed measurements with pressure probes at diffuser exit and particle image velocimetry (PIV) measurements conducted inside the diffuser channel are discussed. The experimental results are published as an open computational fluid dynamics (CFD) testcase “Radiver 2.”

scholarly journals Impinging jets – a short review on strategies for heat transfer enhancement

2018 ◽  
Vol 32 ◽  
pp. 01013
Author(s):  
Ilinca Nastase ◽  
Florin Bode
Keyword(s):  
Heat Transfer ◽  
Large Scale ◽  
Short Review ◽  
Great Difficulty ◽  
Impinging Jets ◽  
Industrial Applications ◽  
Experimental Investigations ◽  
Small Scale ◽  
Strong Shear ◽  
Flow Phenomena

In industrial applications, heat and mass transfer can be considerably increased using impinging jets. A large number of flow phenomena will be generated by the impinging flow, such as: large scale structures, large curvature involving strong shear and normal stresses, stagnation in the wall boundary layers, heat transfer with the impinged wall, small scale turbulent mixing. All these phenomena are highly unsteady and even if nowadays a substantial number of studies in the literature are dedicated, the impinging jets are still not fully understood due to the highly unsteady nature and more over due to great difficulty of performing detailed numerical and experimental investigations.

Experimental Investigations of Tip Clearance Flow and its Influence on Secondary Flows in a 1-1/2 Stage Axial Turbine

2000 ◽  
Author(s):  
B. Stephan ◽  
H. E. Gallus ◽  
R. Niehuis
Keyword(s):  
Flow Field ◽  
Flow Behavior ◽  
Secondary Flows ◽  
Tip Clearance ◽  
Radial Clearance ◽  
Experimental Investigations ◽  
Axial Turbine ◽  
Tip Clearance Flow ◽  
Clearance Flow ◽  
Flow Phenomena

A multistage turbomachine has inherently unsteady flow fields due to the relative motion between rotor and stator airfoils, which lead to viscous and inviscid interactions between the blade rows. Additionally, the radial clearance between casing and rotor strongly influences the 3D flow field and the loss generation in turbomachines. The objective of the presented study is to investigate the effects of tip clearance on secondary flow phenomena and, in consequence, on the performance of a 1-1/2 stage axial turbine. The low aspect ratio of the blades and their prismatic design leads to a high degree of secondary flows and three-dimensionality. Extended measurements of the flow field behind each blade row with pneumatic and hotwire probes have been conducted for three different tip clearances. Experimental results reveal significant change of flow behavior and turbine performance with increasing tip clearance.

Measurement and Analysis of an Efficient Turbine Rotor Pump Work Reduction System Incorporating Pre-Swirl Nozzles and a Free Vortex Pressure Augmentation Chamber

2004 ◽  
Author(s):  
V. Laurello ◽  
M. Yuri ◽  
K. Fujii ◽  
K. Ishizaka ◽  
T. Nakamura ◽  
...  
Keyword(s):  
Relative Velocity ◽  
Static Pressure ◽  
Tangential Velocity ◽  
Pressure Rise ◽  
Turbine Rotor ◽  
Vortex Chamber ◽  
Free Vortex ◽  
Pressure Losses ◽  
Cooling Air ◽  
Velocity Pressure

Measurements and analysis of an efficient turbine rotor pump work reduction system is presented. The system features; a “low” radius pre-swirl nozzle comprised of cascade vanes with a radial orientation, equal radius seals downstream of the nozzle, “jumper” tubes across the nozzle, and a free vortex chamber. A scaled experimental rig was utilized to measure and compare with predictions the following; rotor pump work, average tangential velocity exiting the nozzle, tangential velocity variation in the axial and radial direction, free vortex chamber static pressure rise, effect of relative velocity pressure losses, and effect of “pollution” by seal flow. The effort focused on measuring pump work reduction and the efficiency of the pressure augmentation system. In contrast to aero-engines where the main objective of pre-swirl is to reduce cooling air temperature to the blades, the main objective for this industrial gas turbine is to reduce pump work and increase output. An external pre-cooler is utilized to achieve the large cooling air temperature reduction required to maintain disk material limits. The analytical results and rig test data are presented and compared. The results substantiated the following: the level of reduced rotor pump work due to pre-swirl, the static pressure rise in the free vortex chamber, the effect of eliminating “pollution”, and relative velocity pressure losses. CFD analytical results are compared with the rig data.

scholarly journals Rheological Behavior of Carbon Nanotubes as an Additive on Lithium Grease

2013 ◽  
Vol 2013 ◽  
pp. 1-4 ◽  
Author(s):  
Alaa Mohamed ◽  
Aly Ahmed Khattab ◽  
Tarek Abdel Sadek Osman ◽  
Mostafa Zaki
Keyword(s):  
Carbon Nanotubes ◽  
Shear Stress ◽  
Electron Microscope ◽  
Apparent Viscosity ◽  
Experimental Investigations ◽  
Lithium Grease ◽  
Transmission Electron ◽  
Viscosity Increase ◽  
Homogeneous Network ◽  
Long Fibers

The rheological behaviors of carbon nanotubes (CNTs) as an additive on lithium grease at different concentrations were examined under various settings of shear rate, shear stress, and apparent viscosity. The results indicated that the optimum content of the CNTs was 2%. These experimental investigations were evaluated with a Brookfield Programmable Rheometer DV-III ULTRA. The results indicated that the shear, stress and apparent viscosity increase with the increase of CNTs concentration. The microstructure of CNTs and lithium grease was examined by high resolution transmission electron microscope (HRTEM) and scanning electron microscope (SEM). The results indicated that the microscopic structure of the lithium grease presents a more regular and homogeneous network structure, with long fibers, which confirms the rheological stability.

scholarly journals Direct Numerical Simulation of Fluid Flow in a 5x5 Square Rod Bundle Using Nek5000

2020 ◽  
Author(s):  
Adam Kraus ◽  
Elia Merzari ◽  
Thomas Norddine ◽  
Oana Marin ◽  
Sofiane Benhamadouche
Keyword(s):  
Spectral Element ◽  
Navier Stokes ◽  
Experimental Investigations ◽  
Reynolds Stresses ◽  
Complex Flow ◽  
Local Conditions ◽  
Rod Bundle ◽  
Flow Phenomena ◽  
Resolution Analysis ◽  
Water Reactors

Abstract Rod bundle flows are commonplace in nuclear engineering, and are present in light water reactors (LWRs) as well as other more advanced concepts. Inhomogeneities in the bundle cross section can lead to complex flow phenomena, including varying local conditions of turbulence. Despite the decades of numerical and experimental investigations regarding this topic, and the importance of elucidating the physics of the flow field, to date there are few publicly available direct numerical simulations (DNS) of the flow in multiple-pin rod bundles. Thus a multiple-pin DNS study can provide significant value toward reaching a deeper understanding of the flow physics, as well as a reference simulation for development of various reduced-resolution analysis techniques. To this end, DNS of the flow in a square 5 × 5 rod bundle at Reynolds number of 19,000 has been performed using the highly-parallel spectral element code Nek5000. The geometrical dimensions were representative of typical LWR fuel designs. The DNS was designed using microscales estimated from an advanced Reynolds-Averaged Navier-Stokes (RANS) model. Characteristics of the velocity field, Reynolds stresses, and anisotropy are presented in detail for various regions of the bundle. The turbulent kinetic energy budget is also presented and discussed.

Unsteady 3D-Numerical Investigation of the Influence of the Blading Design on the Stator-Rotor Interaction in a 2-Stage Turbine

2005 ◽  
Author(s):  
Dieter E. Bohn ◽  
Jing Ren ◽  
Christian Tu¨mmers ◽  
Michael Sell
Keyword(s):  
Gas Turbines ◽  
Flow Characteristics ◽  
Computer Code ◽  
Experimental Investigations ◽  
Blade Design ◽  
Test Rig ◽  
3D Flow ◽  
Two Stage ◽  
Flow Phenomena ◽  
Flow Through

An important goal in the development of turbine bladings is improving their efficiency to achieve an optimized usage of energy resources. This requires a detailed insight into the complex 3D-flow phenomena in multi-stage turbines. In order to investigate the flow characteristics of modern highly loaded turbine profiles, a test rig with a two-stage axial turbine has been set up at the Institute of Steam and Gas Turbines, Aachen University. The test rig is especially designed to investigate different blading designs. In order to analyze the influence of the blade design on the unsteady blade row interaction, the 3D flow through the two-stage turbine is simulated numerically, using an unsteady Navier-Stokes computer code. The investigations include a comparison of two bladings with different design criteria. The reference blading is a commonly used cylindrical designed blading. This blade design will be compared with a bow-blading, which is designed to minimize the secondary flow phenomena near the endwall in order to achieve a balanced mass flow through nearly the whole passage height. The investigations will focus on the different loss behavior of the two bladings. Unsteady profile pressure distributions and radial efficiencies of the two blade designs will be discussed in detail. The flow conditions are taken from experimental investigations performed at the Institute of Steam and Gas Turbines. On the basis of the experiments a validation of the code will be performed by comparing the numerical results to the corresponding experimental data at the inlet and the outlet of the blading.

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