Validation of the Non-Linear Harmonic Approach for Quasi-Unsteady Simulations in Turbomachinery

2009 ◽  
Author(s):  
Michael Hembera ◽  
Andreas Loos ◽  
Andreas Ku¨hrmann ◽  
Florian C. T. Danner ◽  
Hans-Peter Kau ◽  
...  
Keyword(s):  
Main Idea ◽  
Simulation Method ◽  
Computational Time ◽  
Fourier Decomposition ◽  
Axial Compressors ◽  
Sliding Mesh ◽  
Multi Stage ◽  
Unsteady Simulation ◽  
Dependent Flow ◽  
Flow Variables

Unsteady simulations, which are necessary to resolve the time-dependent flow between stationary and rotating parts in axial compressors, require an appropriate rotor-stator interface. For this interface, usually the so called domain-scaling or sliding mesh approach is used. This method requires the pitch of the simulated blades to be equal, to allow the usage of periodic boundary conditions and to cut down the number of represented blade passages in order to save computational time. This is based on the assumption that the flow is identical inside all blade passages. When it comes to the simulation of modern multi-stage compressors, it becomes almost impossible to conduct unsteady simulations with this approach, as blade numbers of different rows usually don’t have common multiples. In order to overcome that problem, a new method called the nonlinear harmonic approach has been introduced. The main idea of the method is, that the different calculated flow variables are divided into a time-averaged part and another part based on a Fourier decomposition, which represents the oscillating influence of the perturbations caused by the adjacent rows. Superimposing these two parts leads to a quasi-unsteady solution. For this simulation method, the pitches of the different blade rows don’t have to be changed, so that it also becomes possible to simulate multistage machines with discretizing only one passage per blade row. For this paper, a full-annulus unsteady simulation with about 40 million gridpoints was performed and the results are compared to a NLH simulation with only 1 simulated blade passage per row with 1.38 million gridpoints. Additionally, a NLH simulation with a much finer mesh with 7 million gridpoints is also included.

Steady compressible flow in collapsible tubes: application to forced expiration

1989 ◽  
Vol 203 ◽  
pp. 401-418 ◽  
Author(s):  
David Elad ◽  
Roger D. Kamm ◽  
Ascher H. Shapiro
Keyword(s):  
External Pressure ◽  
Forced Expiration ◽  
Simple Description ◽  
System Parameters ◽  
Collapsible Tubes ◽  
Influence Coefficients ◽  
Cross Section Area ◽  
Wall Stiffness ◽  
Dependent Flow ◽  
Flow Variables

Steady, one-dimensional flow of a compressible fluid through a collapsible tube is analysed. A general model is employed, incorporating axial variations in the parameters of the conducting system, such as the tube unstressed cross-section area and wall stiffness, the external pressure and energy exchange with the environment. The flow variables are described in differential form as functions of the conduit system parameters. A coupled set of equations for the dependent flow variables is summarized in a table of influence coefficients, which provides a clear and simple description of the effects produced by the system parameters. Examples of the effects of fluid compressibility in the respiratory system are presented for forced expiration manoeuvres. The effects are found to be generally small, but are most accentuated when breathing heavy gases and when the airways are pathologically stiffened.

scholarly journals Investigation of the Optimum Clocking Position in a Two-Stage Axial Turbine

2005 ◽  
Vol 2005 (3) ◽  
pp. 202-210 ◽  
Author(s):  
Dieter Bohn ◽  
Sabine Ausmeier ◽  
Jing Ren
Keyword(s):  
Flow Field ◽  
Unsteady Flow ◽  
Preliminary Design ◽  
Two Stage ◽  
Axial Turbine ◽  
Sliding Mesh ◽  
Field Distributions ◽  
Unsteady Simulation

A frozen rotor approach in a steady calculation and a sliding mesh approach in an unsteady simulation are performed in a stator clocking investigation. The clocking is executed on the second stator in a two-stage axial turbine over several circumferential positions. Flow field distributions as well as the estimated performances from two approaches are compared with each other. The optimum clocking positions are predicted based on the estimated efficiency from the two approaches. The consistence of the optimum clocking positions is discussed in the paper. The availability and the limit of the frozen rotor approach in predicting the optimum clocking position is analyzed. It is concluded that the frozen rotor approach is available to search the optimum clocking position in the preliminary design period, although it misses some features of the unsteady flow field in the multistage turbines.

The Measurement and Interpretation of Flow within Rotating Stall Cells in Axial Compressors

1978 ◽  
Vol 20 (2) ◽  
pp. 101-114 ◽  
Author(s):  
I. J. Day ◽  
N.A. Cumpsty
Keyword(s):  
Flow Direction ◽  
Axial Flow ◽  
Tangential Direction ◽  
Rotating Stall ◽  
Design Flow ◽  
Flow Measurements ◽  
Axial Compressors ◽  
Multi Stage ◽  
Wide Range ◽  
Flow Compressor

Detailed flow measurements obtained by a new measuring technique are presented for the flow in a stalled axial-flow compressor. Results were obtained from a wide range of compressor builds, including multi-stage and single-stage configurations of various design flow rates and degrees of reaction. Instantaneous recordings of absolute velocity, flow direction and total and static pressures have been included for both full-span and part-span stall. With the aid of these results, it has been shown that the conventional model of the flow in a stall cell is erroneous. An alternative model is proposed, based on the observation that the fluid must cross from one side of the cell to the other in order to preserve continuity in the tangential direction. An investigation of the experimental results also reveals the finer details of the flow in the cell and shows how these details are related to the design flow rate of the compressor. The influence of these cell details on the power absorbed by a stalled compressor are investigated, and consideration is given to the complex pressure patterns encountered in the compressor.

Research of service selection algorithm for net-centric simulation task community

2014 ◽  
Vol 05 (03) ◽  
pp. 1450006
Author(s):  
Liyang Sun ◽  
Jianning Lin ◽  
Zhenqi Ju ◽  
Shaojie Mao ◽  
Zhong Liu ◽  
...  
Keyword(s):  
Large Scale ◽  
Traditional Approach ◽  
Main Idea ◽  
Service Selection ◽  
Simulation Method ◽  
Global Constraints ◽  
Variation Method ◽  
Local Optimum ◽  
Selection Algorithm ◽  
Simulation Task

Being a new-generation C4ISR system simulation method, the construction approach of net-centric simulation (NCS) is developing toward net-centric from the traditional approach of platform-centric. NCS is mainly completed by the construction of the simulation task community (STC), the key to which being the dynamic integration of the various services spread in the network in order to form a new STC that meets the requirements of different users. In this study, a simulation task community service selection algorithm (STCSSA) is proposed. The main idea of this algorithm is to transform the construction of STC to the searching of optimal multi-objectives services with QoS global constraints. This paper first introduces the QoS model of STC and evaluates the service composition process, then presents the detailed operating process of STCSSA and design of the dynamic inertia weight strategy of the algorithm, and also proposes an optional variation method. Comparative tests were performed on STCSSA with other particle swarm optimization algorithms. It was validated from the perspective of performance that the proposed algorithm has advantages in improving the rate of convergence and avoiding local optimum, and from the perspective of practical application STCSSA also demonstrated feasibility in the construction of large-scale NCS task community.

Investigations on Impulse Blade Cascades with Medium Deflection

1978 ◽  
Vol 100 (3) ◽  
pp. 432-438
Author(s):  
K. Bammert ◽  
B. Ahmadi
Keyword(s):  
Wind Tunnel ◽  
Axial Compressor ◽  
Two Dimensional ◽  
Axial Compressors ◽  
High Reaction ◽  
Multi Stage ◽  
Tandem Cascades

The transformation of energy in the stages of high-reaction axial compressors can be considerably increased if the rotor blading consists of tandem cascades. This also involves aerodynamically higher loading of the stator cascades deflecting the flow. The behavior of the base, mean, and tip sections impulse cascades of the stator of a multi-stage axial compressor designed on this basis was examined in a two-dimensional cascade wind tunnel. The results of these investigations are reported and discussed.

A Criterion for Axial Compressor Hub-Corner Stall

2006 ◽  
Author(s):  
V. M. Lei ◽  
Z. S. Spakovszky ◽  
E. M. Greitzer
Keyword(s):  
Flow Control ◽  
Substantial Reduction ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Diffusion Parameter ◽  
Design Parameters ◽  
Diffusion Limit ◽  
Specific Flow ◽  
Multi Stage ◽  
Flow Variables

This paper presents a new criterion for estimating the size and strength of three-dimensional hub-corner stall in rotors and shrouded stators of multi-stage axial compressors. A simple, first-of-a-kind description for the formation of hub-corner stall is derived, consisting of (i) a stall indicator, which quantifies the extent of the reversed flow via the local blade loading and thus indicates whether corner stall occurs, and (ii) a diffusion parameter which defines the diffusion limit. The stall indicator can be cast in terms of a Zweifel loading coefficient. The diffusion parameter is based on preliminary design type flow variables and geometry. Computational simulations and single and multi-stage compressor data are used to show the applicability of the criterion over a range of blade design parameters. The criterion also enables determination of specific flow control actions needed to mitigate hub-corner stall. To illustrate the latter a flow control blade, designed using the ideas developed, is seen to achieve a substantial reduction in the flow non-uniformity associated with hub-corner stall.

On the Interpretation of Casing Measurements in Axial Compressors

2008 ◽  
Author(s):  
Joshua D. Cameron ◽  
Scott C. Morris ◽  
Sean T. Barrows ◽  
Jen-Ping Chen
Keyword(s):  
Experimental Studies ◽  
Rotating Stall ◽  
Basic Flow ◽  
Tip Clearance ◽  
Stall Inception ◽  
Tip Clearance Flow ◽  
Axial Compressors ◽  
Clearance Flow ◽  
Flow Variables ◽  
Insight Into

Experimental studies of stall inception in axial compressors typically involve the measurement of basic flow variables (often pressure or velocity) with low spatial resolution. These measurements are used to make inferences about the fluid dynamics of stall. This experimental paradigm has been used by many investigators to great effect over the last several decades. However, several limitations remain which restrict the utility of these types of measurements for developing further insight into stall inception physics. Primary among these limitations is the impracticality of making measurements within the rotating blade passages. This is especially troublesome in light of recent computational studies which indicate that the generation of short length-scale rotating disturbances is related to the rotor tip clearance flow. This study utilized the results of a recent full annulus rotating stall simulation to investigate the relationships between the casing pressure field and less observable flow quantities which are believed to be causally related to the generation of rotating disturbances. The CFD results are assumed to represent the true flow physics within the compressor. To the extent that this approximation is true, these results can be used to interpret the meaning of experimental measurements of basic flow variables. These observations not only provide new insight into the interpretation of the large catalog of experimental stall measurements found in the literature, they also give directives for future measurements and numerical simulations.

scholarly journals A Study of a Competitive Reinforcement Learning Approach for Joint Spatial Division and Multiplexing in Massive MIMO

2021 ◽  
Vol 19 (1) ◽  
pp. 83-93
Author(s):  
Tanyaluk Deeka ◽  
Boriboon Deeka ◽  
Surajate On-rit
Keyword(s):  
Massive Mimo ◽  
Energy Use ◽  
Multiple Input Multiple Output ◽  
Main Idea ◽  
Base Station ◽  
Machine Learning Algorithms ◽  
System Throughput ◽  
Computational Time ◽  
User Grouping ◽  
Input Multiple Output

Massive Multiple-Input Multiple-Output (MIMO) is widely considered a pivotal communication technology for future generations of wireless networks. Massive MIMO uses a large number of antennas at the base station, which offers better effectiveness in spectral and energy use. However, a Frequency Division Duplex (FDD) system is challenging in reciprocity since it is difficult to estimate channels and requires feeding back channel state information. Joint Spatial Division and Multiplexing (JSDM) is a simplified FDD technique to provide massive MIMO gains. The main idea of JSDM is related to grouping users with approximately similar channel covariance. Many machine learning algorithms have been applied to conduct user grouping. In this paper, to improve the user grouping, we employ Reinforcement Guided Competitive Learning (RGCL) to the user grouping and then compare it with clustering techniques, including K-means, and sequential K-means to achieve the appropriate user grouping. The experimental results show that the RGCL technique represents better performance in computational time and system throughput than the other two above mentioned techniques, since RGCL can avoid being trapping in local minima.

Study of Tip Flows in High Hub-to-Tip Ratio Axial Compressors at Low Speed With Varying Tip Gaps, Inflow Conditions and Tip Shapes

2010 ◽  
Author(s):  
Bhaskar Roy ◽  
A. M. Pradeep ◽  
A. Suzith ◽  
Dinesh Bhatia ◽  
Aditya Mulmule
Keyword(s):  
Axial Compressor ◽  
Tip Vortex ◽  
Low Flow ◽  
Tip Leakage Flow ◽  
Design Point ◽  
Axial Compressors ◽  
Tip Leakage ◽  
Compressor Rotor ◽  
Multi Stage ◽  
Performance Deterioration

The present study involves simulation of a single compressor rotor with a high hub-to-tip ratio blade. The study includes the effect of variation of tip gap, of tip shapes and of inlet axial velocity profiles, with inflows simulated similar to that of a typical rear stage environment of a multi-stage axial compressor. Numerical studies were carried out on a baseline rotor blade (without sweep or dihedral) and then on blades with sweep and dihedral applied at the tip region of the rotor. Simulation of these part-span sweep and dihedral shapes are done to study their effects on blade tip leakage flow. Results show that sweep and dihedral, in some cases, produce favorable tip flows, improving blade aerodynamics. Positive dihedral caused weakening of tip leakage vortex at design point as well as at peak pressure point. Negative dihedral may help postpone stall at the high pressure, low flow operation. Backward sweep weakened tip vortex at the design point. Contrary to some of the studies reported earlier forward sweep, when applied at the tip region, showed performance deterioration over the most of the operating range of the high hub-to-tip rotor.

Towards a Faster Image Segmentation Using the K-means Algorithm on Grayscale Histogram

2016 ◽  
Vol 8 (2) ◽  
pp. 57-69 ◽  
Author(s):  
Lamine Benrais ◽  
Nadia Baha
Keyword(s):  
Image Segmentation ◽  
Equilibrium State ◽  
Clustering Algorithm ◽  
Main Idea ◽  
Computation Time ◽  
Computational Time ◽  
Original Image ◽  
Grayscale Images

The K-means is a popular clustering algorithm known for its simplicity and efficiency. However the elapsed computation time is one of its main weaknesses. In this paper, the authors use the K-means algorithm to segment grayscale images. Their aim is to reduce the computation time elapsed in the K-means algorithm by using a grayscale histogram without loss of accuracy in calculating the clusters centers. The main idea consists of calculating the histogram of the original image, applying the K-means on the histogram until the equilibrium state is reached, and computing the clusters centers then the authors use the clusters centers to run the K-means for a single iteration. Tests of accuracy and computational time are presented to show the advantages and inconveniences of the proposed method.

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