A Transient Computational Fluid Dynamics, Phase Modulated, Multifrequency Approach for Impeller Rotordynamic Forces

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Farzam Mortazavi ◽  
Alan Palazzolo
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Flow Condition ◽  
American Petroleum Institute ◽  
Rotating Stall ◽  
Path Model ◽  
Flow Coefficient ◽  
Specific Speed ◽  
Rotordynamic Forces ◽  
Force Data

Modern high performance turbomachines frequently operate in supercritical condition above their first critical speed, rendering these machines prone to rotordynamic instability. The American Petroleum Institute (API) standards require advanced simulation models for level II stability analysis of impellers. Such data are then incorporated into rotor-bearing vibration response models. Despite recent advancements in high fidelity, general modeling (i.e., three-dimensional viscous transient nonaxisymmetric model) of closed impeller rotordynamic forces, no such general model is available for open impellers, especially the centrifugal type. This paper extends the transient computational fluid dynamics (CFD) model previously used for closed impellers to open impellers. The recent model uses a phase modulated, multifrequency approach for enhanced computational efficiency and robustness. Results are validated against literature experiments at design and off-flow condition. The model is further applied to a spectrum of specific speeds to extract the dimensionless rotordynamic forces for each class of impellers at design and off-flow conditions. Such dimensionless force data can be used to estimate the rotordynamic forces of impellers with similar specific speed. Depending on specific speed and the relative flow coefficient, many of these impellers are found to be excited by forward or backward whirl. Strong interaction with rotating stall typically appears in the force data at off-flow condition. Simulations of the isolated leakage path model (ILPM) for equivalent closed impellers reveal similar bumps and dips associated with highly swirling inflow which naturally occurs at part flow condition.

Multi-Objective Optimization of a High Specific Speed Centrifugal Volute Pump Using Three-Dimensional Inverse Design Coupled With Computational Fluid Dynamics Simulations

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Luying Zhang ◽  
Gabriel Davila ◽  
Mehrdad Zangeneh
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Design Method ◽  
Three Dimensional ◽  
Inverse Design ◽  
Computational Time ◽  
Specific Speed ◽  
Meridional Shape ◽  
Inverse Design Method ◽  
Blade Geometry

Abstract This paper presents three different multiobjective optimization strategies for a high specific speed centrifugal volute pump design. The objectives of the optimization consist of maximizing the efficiency and minimizing the cavitation while maintaining the Euler head. The first two optimization strategies use a three-dimensional (3D) inverse design method to parametrize the blade geometry. Both meridional shape and 3D blade geometry are changed during the optimization. In the first approach, design of experiment (DOE) method is used and the pump efficiency is obtained from computational fluid dynamics (CFD) simulations, while cavitation is evaluated by using minimum pressure on blade surface predicted by 3D inverse design method. The design matrix is then used to create a surrogate model where optimization is run to find the best tradeoff between cavitation and efficiency. This optimized geometry is manufactured and tested and is found to be 3.9% more efficient than the baseline with reduced cavitation at high flow. In the second approach, only the 3D inverse design method output is used to compute the efficiency and cavitation parameters and this leads to considerable reduction to the computational time. The resulting optimized geometry is found to be similar to the computationally more expensive solution based on 3D CFD results. In order to compare the inverse design based optimization to the conventional optimization, an equivalent optimization is carried out by parametrizing the blade angle and meridional shape.

Three-Dimensional Computational Fluid Dynamics Prediction of Turbocharger Centrifugal Compression System Instabilities

2019 ◽  
Vol 141 (8) ◽  
Author(s):  
Rick Dehner ◽  
Ahmet Selamet
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Flow Rate ◽  
Pressure Fluctuations ◽  
Three Dimensional ◽  
Rotating Stall ◽  
Flow Reversal ◽  
Constant Speed ◽  
Local Flow ◽  
Stall Cells

The present work combines experimental measurements and unsteady, three-dimensional computational fluid dynamics predictions to gain further insight into the complex flow-field within an automotive turbocharger centrifugal compressor. Flow separation from the suction surface of the main impeller blades first occurs in the mid-flow range, resulting in local flow reversal near the periphery, with the severity increasing with decreasing flow rate. This flow reversal improves leading-edge incidence over the remainder of the annulus, due to (a) reduction of cross-sectional area of forward flow, which increases the axial velocity, and (b) prewhirl in the direction of impeller rotation, as a portion of the tangential velocity of the reversed flow is maintained when it mixes with the core flow and transitions to the forward direction. As the compressor operating point enters the region where the slope of the constant speed compressor characteristic (pressure ratio versus mass flow rate) becomes positive, rotating stall cells appear near the shroud side diffuser wall. The angular propagation speed of the diffuser rotating stall cells is approximately 20% of the shaft speed, generating pressure fluctuations near 20% and 50% of the shaft frequency, which were also experimentally observed. For the present compressor and rotational speed, flow losses associated with diffuser rotating stall are likely the key contributor to increasing the slope of the constant speed compressor performance curve to a positive value, promoting the conditions required for surge instabilities. The present mild surge predictions agree well with the measurements, reproducing the amplitude and period of compressor outlet pressure fluctuations.

Analysis and Simulation of Inner Flow Condition of a Novel Rotary on/off Valve

2012 ◽  
Vol 220-223 ◽  
pp. 1698-1702
Author(s):  
Jian Chen ◽  
Zhu Ming Su ◽  
Qi Zhou ◽  
Jian Ping Shu
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Flow Condition ◽  
High Speed ◽  
Ansys Fluent ◽  
Revolution Speed ◽  
Pressure Profiles ◽  
Open Case ◽  
Computational Fluid Dynamics Cfd ◽  
Cfd Method

A novel hydraulic rotary high speed on/off valve is investigated. The function of the outlet turbine and the effect on revolution speed of valve spool are analyzed. The inner fluid flow condition under full open case of the on/off valve is simulated using computational fluid dynamics(CFD) method based on Ansys/Fluent and velocity and pressure profiles of fluid inside valve are obtained. Suggestions on optimizing the geometry of valve to decrease transition losses are given.

scholarly journals Computational fluid dynamics simulations of blade damage effect on the performance of a transonic axial compressor near stall

2014 ◽  
Vol 229 (12) ◽  
pp. 2242-2260 ◽  
Author(s):  
Yan-Ling Li ◽  
Abdulnaser I Sayma
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Axial Compressor ◽  
Rotating Stall ◽  
Damage Effect ◽  
Computational Fluid Dynamics Simulations ◽  
Compressor Performance ◽  
Transonic Axial Compressor ◽  
Dynamics Simulations ◽  
Rotor Assembly

Gas turbine axial compressor blades may encounter damage during service for various reasons such as damage by debris from casing or foreign objects impacting the blades, typically near the rotor’s tip. This may lead to deterioration of performance and reduction in the surge margin. The damage breaks the cyclic symmetry of the rotor assembly; thus, computational fluid dynamics simulations have to be performed using full annulus compressor assembly. Moreover, downstream boundary conditions are unknown during rotating stall or surge, and simulations become difficult. This paper presents unsteady computational fluid dynamics analyses of compressor performance with tip curl damage. Computations were performed near the stall boundary. The primary objectives are to understand the effect of the damage on the flow behaviour and compressor stability. Computations for the undamaged rotor assembly were also performed as a reference case. A transonic axial compressor rotor was used for the time-accurate numerical unsteady flow simulations, with a variable area nozzle downstream simulating an experimental throttle. Computations were performed at 60% of the rotor design speed. Two different degrees of damage for one blade and multiple damaged blades were investigated. Rotating stall characteristics differ including the number of stall cells, propagation speed and rotating stall cell characteristics. Contrary to expectations, damaged blades with typical degrees of damage do not show noticeable effects on the global compressor performance near stall.

Rotating Stall Induced in Vaneless Diffusers of Very Low Specific Speed Centrifugal Blowers

1985 ◽  
Vol 107 (2) ◽  
pp. 514-519 ◽  
Author(s):  
Y. Kinoshita ◽  
Y. Senoo
Keyword(s):  
Flow Analysis ◽  
Rotating Stall ◽  
Experimental Results ◽  
Flow Coefficient ◽  
Critical Flow ◽  
Flow Rates ◽  
Small Flow ◽  
Low Specific Speed ◽  
Specific Speed ◽  
Vaneless Diffusers

The limit of rotating stall was experimentally determined for three very small specific speed centrifugal blowers. The impellers were specially designed for stall-free at very small flow rates, so that the cause of rotating stall could be attributed to the vaneless diffusers. Experimental results demonstrated that the blowers did not stall until the flow coefficient was reduced to very small values, which had never been reported in the literature. The critical flow coefficient for rotating stall agreed very well with the prediction based on a flow analysis and a criterion for rotating stall in vaneless diffusers developed by the authors.

Effects of Impeller Squealer Tip on Centrifugal Compressor Performance

2016 ◽  
Author(s):  
Riccardo Da Soghe ◽  
Cosimo Bianchini ◽  
Lorenzo Toni ◽  
Dante Tommaso Rubino
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Flow ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Performance Improvements ◽  
Positive Effects ◽  
Computational Fluid Dynamics Cfd ◽  
Compressor Performance ◽  
Load Conditions

This paper summarizes the main results sorted out from a Design of Experiment (DoE) based on a validated Computational Fluid Dynamics (CFD). Several tip recessed geometries applied to an unshrouded impeller were considered in conjunction with two tip clearance levels. The computations show that recessed tip geometries have positive effects when considering high flow coefficient values while in part-load conditions the gain is reduced. Starting from the results obtained when studying tip cavities, a single rim tip squealer geometry was then analysed: the proposed geometry leads to performance improvements for all the tested conditions considered in this work.

Effects of Impeller Squealer Tip on Centrifugal Compressor Performance

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Riccardo Da Soghe ◽  
Cosimo Bianchini ◽  
Dante Tommaso Rubino ◽  
Lorenzo Toni
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
High Flow ◽  
Tip Clearance ◽  
Flow Coefficient ◽  
Performance Improvements ◽  
Positive Effects ◽  
Computational Fluid Dynamics Cfd ◽  
Compressor Performance ◽  
Load Conditions

This paper summarizes the main results sorted out from a design of experiment (DoE) based on a validated computational fluid dynamics (CFD). Several tip recessed geometries applied to an unshrouded impeller were considered in conjunction with two tip clearance levels. The computations show that recessed tip geometries have positive effects when considering high-flow coefficient values, while in part-load conditions the gain is reduced. Starting from the results obtained when studying tip cavities, a single rim tip squealer geometry was then analyzed: the proposed geometry leads to performance improvements for all the tested conditions considered in this work.

Automatic computational fluid dynamics-based procedure for the optimization of a centrifugal impeller

2005 ◽  
Vol 219 (7) ◽  
pp. 549-557 ◽  
Author(s):  
F Martelli ◽  
S Pazzi ◽  
V Michelassi
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
New Technologies ◽  
Geometric Constraints ◽  
Flow Coefficient ◽  
Low Flow ◽  
Centrifugal Impeller ◽  
Geometrical Parameters ◽  
Design Point ◽  
Blade Thickness

A typical centrifugal impeller characterized by a low flow coefficient and cylindrical blades is redesigned by means of an intelligent automatic search program. The procedure consists of a feasible sequential quadratic programming algorithm (Fletcher, R. Practical Methods of optimization, 2000 (Wiley)) coupled to a lazy learning (LL) interpolator 1 to speed-up the process. The program is able to handle geometric constraints to reduce the computational effort devoted to the analysis of non-physical configurations. The objective function evaluator is an in-house developed structured computational fluid dynamics (CFD) code. The LL approx-imator is called each time the stored database can provide a sufficiently accurate performance estimate for a given geometry, thus reducing the effective CFD computations. The impeller is represented by 25 geometric parameters describing the vane in the meridional and s-0 planes, the blade thickness, and the leading edge shape. The optimization is carried out on the impeller design point maximizing the polytropic efficiency with nearly constant flow coefficient and polytropic head. The optimization is accomplished by maintaining unaltered those geometrical parameters which have to be kept fixed in order to make the impeller fit the original stage. The optimization, carried out on a cluster of 16 PCs, is self-learning and leads to a geometry presenting an increased design point efficiency. The program is completely general and can be applied to any component which can be described by a finite number of geometrical parameters and computed by any numerical instrument to provide performance indices. The work presented in this paper was done under the METHOD EC funded project for the implementation of new technologies for optimization of centrifugal compressors.

scholarly journals A simple method for high-precision evaluation of valve flow coefficient by computational fluid dynamics simulation

2017 ◽  
Vol 9 (7) ◽  
pp. 168781401771370 ◽  
Author(s):  
Xiao-Ming Zhou ◽  
Zhi-Kun Wang ◽  
Yi-Fang Zhang
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Pressure Drop ◽  
Adaptation Strategy ◽  
Flow Coefficient ◽  
Dynamics Simulation ◽  
Accurate Estimation ◽  
Simple Method ◽  
Pressure Losses ◽  
The Difference

Flow coefficient is an important performance index associated with the energy efficiency of a valve, and an effective method to evaluate valve flow coefficient is necessary for valve industry. However, theoretical estimation often results in poor accuracy, while experimental measurements involve significant costs in time and equipment. In this article, a computational fluid dynamics method is proposed to achieve simple and accurate evaluation of valve flow coefficient. For each valve, a computational fluid dynamics model is established containing a valve section, an upstream section, and a downstream section. A grid-adaptation strategy is then applied to improve the accuracy of simulation. To calculate flow coefficient, the most important issue is to determine the net pressure loss induced by valve (Δ Pv). Herein, the overall pressure drop (Δ Po) is obtained first, and the pipe-induced pressure drop (Δ Pp) is estimated by linear fitting. Then, Δ Pv is calculated as the difference between Δ Po and Δ Pp. To ensure accurate estimation of the pressure losses, a length of 26 times of pipe diameter is preferred for the upstream section. The experiments demonstrated that the presented method can accurately predict flow coefficient for various types of valves and thus has great potential to be widely used in the valve industry.

Vortex Pump as Turbine—A Type Turbine for Energy Generation or Recovery Based on Computational Fluid Dynamics Prediction

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Wenguang Li
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Flow Structure ◽  
Conversion Factor ◽  
Pressure Profile ◽  
Reverse Direction ◽  
Centrifugal Pumps ◽  
Cavitation Performance ◽  
Vortex Pump ◽  
Specific Speed

An experimental vortex pump with a specific speed of 76 is investigated to get its performance and flow structure under noncavitation and cavitation conditions when the pump operates as turbine in the reverse direction by using computational fluid dynamics (CFD) method. A method is proposed to extract hydraulic, volumetric, and mechanical efficiencies for the first time. It is shown that a vortex pump can operate as turbine but it is subject to poor cavitation performance. The performance conversion factors of flow rate and head are 2.33 and 2.74 which are much larger than existing centrifugal pumps as turbine with the same specific speed. The conversion factor of efficiency is 0.98, which agrees with the conversion factor of efficiency for a centrifugal pump as turbine. There are a rope cavity and a vortex flow in the same rotational direction of the impeller. It is shown that flow structure is complex in the impeller in pump and turbine modes, particularly on the blade-to-blade surface, while static pressure profile in the volute and impeller as well as the space between the casing and the impeller is simple. The flow in the space between the impeller and the casing cannot be regarded as a forced vortex in both modes. The cavitation performance improvement and rope cavity control may be key issues in the future.

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