Strain Response and Aerodynamic Damping of a Swirl Distortion Generator Using Computational Fluid Dynamics

2021 ◽  
Author(s):  
Andrew Hayden ◽  
Alexandrina Untaroiu
Keyword(s):  
Fuel Efficiency ◽  
Operating Conditions ◽  
Computational Method ◽  
Mode Shapes ◽  
Flow Distortion ◽  
Element Analysis ◽  
Aerodynamic Damping ◽  
Aerodynamic Pressure ◽  
Modal Response ◽  
Operating Points

Abstract Boundary layer ingestion (BLI) concepts have become a prominent topic in research and development due to their increase in fuel efficiency for aircraft. Virginia Tech has developed the StreamVane™, a secondary flow distortion generator, which can be used to efficiently test BLI and its aeromechanical effects on turbomachinery. To ensure the safety of this system, the complex vanes within StreamVanes must be further analyzed structurally and aerodynamically. In this paper, the induced strain of two common vane shapes at three different operating conditions is computationally determined. Along with these predictions, the aerodynamic damping of the vanes is calculated to predict flutter conditions at the same three operating points. To achieve this, steady CFD calculations are done to acquire the aerodynamic pressure loading on the vanes. Finite element analysis (FEA) is performed to obtain the strain and modal response of the StreamVane structure. The mode shapes and steady CFD are used to initialize an unsteady CFD analysis which acquires the aerodynamic damping results of the vanes. The testcase used for this evaluation was specifically designed to overstep the structural limits of a StreamVane, and the results provide an efficient computational method to observe flutter conditions of stationary systems.

Strain Response and Aerodynamic Damping of a Swirl Distortion Generator Using Computational Fluid Dynamics

2020 ◽  
Author(s):  
Andrew Hayden ◽  
Alexandrina Untaroiu
Keyword(s):  
Fuel Efficiency ◽  
Operating Conditions ◽  
Computational Method ◽  
Mode Shapes ◽  
Flow Distortion ◽  
Element Analysis ◽  
Aerodynamic Damping ◽  
Aerodynamic Pressure ◽  
Modal Response ◽  
Operating Points

Abstract Boundary layer ingestion (BLI) concepts have become a prominent topic in research and development due to their increase in fuel efficiency for aircraft. Virginia Tech has developed the StreamVane™, a secondary flow distortion generator, which can be used to efficiently test BLI and its aeromechanical effects on turbomachinery. To ensure the safety of this system, the complex vanes within StreamVanes must be further analyzed structurally and aerodynamically. In this paper, the induced strain of two common vane shapes at three different operating conditions is computationally determined. Along with these observations, the aerodynamic damping of these vanes are calculated to predict flutter conditions at the same three operating points. Steady CFD calculations are done to acquire the aerodynamic pressure loading on the vanes. Finite element analysis (FEA) is performed to obtain the strain and modal response of the StreamVane structure. The mode shapes and steady CFD are used to initialize an unsteady CFD analysis which determines the aerodynamic damping of the vanes. The testcase used for this evaluation was specifically designed to overstep the structural limits of a StreamVane, and the results provide an efficient computational method to observe flutter conditions of stationary systems.

Dynamic Properties of a Heliostat Structure Determined by Numerical and Experimental Modal Analysis

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
J. Felipe Vásquez-Arango ◽  
Reiner Buck ◽  
Robert Pitz-Paal
Keyword(s):  
Modal Analysis ◽  
Vortex Shedding ◽  
Natural Frequencies ◽  
Dynamic Properties ◽  
Simple Approach ◽  
Operating Conditions ◽  
Mode Shapes ◽  
Fe Model ◽  
Damping Coefficients ◽  
Operating Points

An experimental and numerical modal analysis was performed on an 8 m2 T-shaped heliostat structure at different elevation angles. The experimental results were used to validate a finite element (FE) model by comparing natural frequencies and mode shapes. The agreement between experiments and simulations is good in all operating points investigated. In addition, damping coefficients were determined experimentally for each mode, in order to provide all necessary information for the development of a dynamic model. Furthermore, potentially critical operating conditions caused by vortex shedding were identified using a simple approach.

scholarly journals Computation of Aerodynamic Damping for Flutter Analysis of a Transonic Fan

2011 ◽  
Author(s):  
Parthasarathy Vasanthakumar
Keyword(s):  
Phase Angle ◽  
Stokes Equations ◽  
Mode Shapes ◽  
Navier Stokes ◽  
Aerodynamic Load ◽  
Exchange Method ◽  
Flow Solver ◽  
Aerodynamic Damping ◽  
Transonic Fan ◽  
Operating Points

This paper describes the computational analysis of aerodynamic damping for prediction of flutter characteristics of a transonic fan stage that consists of a highly loaded rotor along with a tandem stator. Three dimensional, linearized Navier-Stokes flow solver TRACE is used to numerically analyse the flutter stability of the fan. The linear flow solver enables the modeling of a single blade passage to simulate the desired inter-blade phase angle. The unsteady aerodynamic load on a vibrating blade is obtained by solving the unsteady Navier-Stokes equations on a dynamically deforming grid and the energy exchange method is used to calculate the aerodynamic damping. The calculation of aerodynamic damping for the prediction of flutter characteristics of the fan rotor is carried out with and without considering the influence of the disk. The blade mode shapes from finite element modal analysis are obtained accordingly and the flutter calculations are carried out for three blade vibration modes at the design speed and at part speeds for all possible inter-blade phase angles. Two operating points, one on the working line and the other near stall are investigated at every rotational speed. Different aspects that affect the aerodynamic damping behaviour like part speed operation, variation in unsteady blade surface pressure fluctuation between operating points on the working line and at near stall and the corresponding variation in aerodynamic work, inter-blade phase angle etc., are described. This analysis primarily focuses on the variations in aerodynamic damping of the fan with and without the influence of the disk. In addition, influence and effect of shock wave on the aerodynamic damping is also discussed.

A Linearized Theory on Ground-Based Vibration Response of Rotating Asymmetric Flexible Structures

2006 ◽  
Vol 128 (3) ◽  
pp. 375-384 ◽  
Author(s):  
I. Y. Shen ◽  
Hyunchul Kim
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Equation Of Motion ◽  
Vibration Response ◽  
Mode Shapes ◽  
Element Analysis ◽  
Secondary Resonances ◽  
Modal Response ◽  
Resonance Frequencies ◽  
Unified Algorithm

This paper is to develop a unified algorithm to predict vibration of spinning asymmetric rotors with arbitrary geometry and complexity. Specifically, the algorithm is to predict vibration response of spinning rotors from a ground-based observer. As a first approximation, the effects of housings and bearings are not included in this analysis. The unified algorithm consists of three steps. The first step is to conduct a finite element analysis on the corresponding stationary rotor to extract natural frequencies and mode shapes. The second step is to represent the vibration of the spinning rotor in terms of the mode shapes and their modal response in a coordinate system that is rotating with the spinning rotor. The equation of motion governing the modal response is derived through use of the Lagrange equation. To construct the equation of motion, explicitly, the results from the finite element analysis will be used to calculate the gyroscopic matrix, centrifugal stiffening (or softening) matrix, and generalized modal excitation vector. The third step is to solve the equation of motion to obtain the modal response, which, in turn, will lead to physical response of the rotor for a rotor-based observer or for a ground-based observer through a coordinate transformation. Results of the algorithm indicate that Campbell diagrams of spinning asymmetric rotors will not only have traditional forward and backward primary resonances as in axisymmetric rotors, but also have secondary resonances caused by higher harmonics resulting from the mode shapes. Finally, the algorithm is validated through a calibrated experiment using rotating disks with evenly spaced radial slots. Qualitatively, all measured vibration spectra show significant forward and backward primary resonances as well as secondary resonances as predicted in the theoretical analysis. Quantitatively, measured primary and secondary resonance frequencies agree extremely well with those predicted from the algorithm with mostly <3.5% difference.

Investigation on the Failures Experienced in Deaerators and Solution Recommendation

2010 ◽  
Author(s):  
Aun Ming Lim ◽  
Simon Yuen
Keyword(s):  
Finite Element ◽  
Natural Frequency ◽  
Thermal Stresses ◽  
Operating Conditions ◽  
Mode Shapes ◽  
Flow Induced Vibration ◽  
Element Analysis ◽  
Root Cause ◽  
Bottom Side ◽  
Refinery Plant

The internals in the deaerators of a refinery plant were reported to have experienced a series of failures since their installation in 1985. These failures included development of cracks in the floor plates, damage of supports and breakage of fillet welds. Two possible root causes were initially identified; thermal stresses due to transient conditions and flow induced vibration. The former cause was classified as unlikely since the deaerators were always operating on steady-state conditions. No cyclic operating conditions were imposed on these deaerators. Vibrations however posed as the most likely root cause for the series of failures. The refinery plant inspectors reported that vibrations on the deaerators, although have not been measured, could be physically felt. These vibrations appear to be continuous and increase linearly with load. A finite element analysis was performed to determine the natural frequency of the deaerators. Mode shapes predicted from this calculation show that vibrations could have caused the failures of the internals. Furthermore, the lowest natural frequency of the deaerators appeared to fall within the actual vibration frequency on site (∼20 Hz). Although not confirmed, it is highly suspected that the vibration was excited by the flow (low pressure steam). Several repair options were explored to overcome this problem. These options were concentrated in increasing the stiffness of the steam inlet pipe and the deaerator floor. Finite element assessments demonstrated that the current flexible deaerator floor was the reason for the low natural frequency. An option of introducing reinforcement strips to the bottom side of the floor was identified as the best option to increase the natural frequency of the deaerator and this is expected to overcome the vibration problem. Only one vessel was assessed but the results apply to the other vessels since they are similar in design.

Dynamic analysis of loads and stresses in connecting rods

2006 ◽  
Vol 220 (5) ◽  
pp. 615-624 ◽  
Author(s):  
P. S. Shenoy ◽  
A Fatemi
Keyword(s):  
Stress State ◽  
Combustion Engine ◽  
Fuel Efficiency ◽  
Complex Loading ◽  
High Volume ◽  
Operating Conditions ◽  
Engine Fuel ◽  
Connecting Rod ◽  
Element Analysis ◽  
Bending Stresses

Automobile internal combustion engine connecting rod is a high volume production component subjected to complex loading. Proper optimization of this component, which is critical to the engine fuel efficiency and more vigorously pursued by the automotive industry in recent years, necessitates a detailed understanding of the applied loads and resulting stresses under in-service conditions. In this study, detailed load analysis under service loading conditions was performed for a typical connecting rod, followed by quasi-dynamic finite element analysis (FEA) to capture stress variations over a cycle of operation. On the basis of the resulting stress-time histories, variation of stress ratio, presence of mean and bending stresses, and multi-axiality of stress states in various locations of the connecting rod under service operating conditions were investigated. It was found that even though connecting rods are typically tested and analyzed under axial loading and stress state, bending stresses are significant and a multiaxial stress state exists at the critical regions of connecting rod. A comparison is also made between stresses obtained using static FEA which is commonly performed and stresses using quasi-dynamic FEA. It is shown that considerable differences in obtained stresses exist between the two sets of analyses.

Aeroelastic Stability of Axial Compressor Blades Under Different Operating Conditions

2020 ◽  
Author(s):  
Mingchang Fang ◽  
Yanrong Wang
Keyword(s):  
Axial Compressor ◽  
Operating Conditions ◽  
Tip Clearance ◽  
Aeroelastic Stability ◽  
Compressor Blades ◽  
Aerodynamic Damping ◽  
Reduced Frequency ◽  
Modal Component ◽  
Stall Flutter ◽  
Operating Points

Abstract Flutter is one of the important issues in turbomachinery analysis. There are four common types of flutter, including sub/transonic stall flutter, choke flutter, supersonic stall flutter, and supersonic non-stall flutter. Flutter may occur under many different operating conditions. Therefore, it is important to study the aeroelastic stability of blades when the compressor operates under different conditions. Based on the energy method proposed by Carta [1], this paper studied the aeroelastic stability of the second-stage rotor blade of an axial compressor under different operating conditions. It is found that the aerodynamic damping of the blade under the near-stall operating point of the compressor is negative. Three typical operating points are selected to study the differences in flutter mechanism between different operating conditions. The 90% span section is selected as the reference section to analyze the variation of the aerodynamic work at different operating points. The influence of reduced frequency, modal component, and tip clearance on aerodynamic damping are analyzed under three operating points.

Vibration Analysis of Rotating Asymmetric Structures

2005 ◽  
Author(s):  
I. Y. Shen ◽  
Hyunchul Kim
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Lagrange Equation ◽  
Equation Of Motion ◽  
Mode Shapes ◽  
Element Analysis ◽  
Asymmetric Structures ◽  
Modal Response ◽  
Physical Response ◽  
Unified Algorithm

This paper is to develop a unified algorithm to analyze vibration of spinning asymmetric rotors with arbitrary geometry and complexity. As a first approximation, the effects of housings and bearings are not included in this analysis. The unified algorithm consists of three steps. The first step is to conduct a finite element analysis on the corresponding stationary rotor to extract natural frequencies and mode shapes. The second step is to represent the vibration of the spinning rotor in terms of the mode shapes and their modal response in a coordinate system that is rotating with the spinning rotor. Through use of the Lagrange equation, one can derive the modal equation of motion. To construct the equation of motion explicitly, the results from the finite element analysis will be used to calculate the gyroscopic matrix, centrifugal stiffening (or softening) matrix, and generalized modal excitation vector. The third step is to solve the equation of motion to obtain the modal response, which, in turn, will lead to physical response of the rotor for a rotor-based observer or for a ground-based observer through a coordinate transformation. Finally, application of the algorithm to rotationally periodic rotors indicates that Campbell diagrams of the rotors will not only have traditional forward and backward branches as in axisymmetric rotors, but also have secondary resonances caused by higher harmonics resulting from the mode shapes. Calibrated experiments were conducted on an air bearing spindles carrying slotted circular disks to verify the theoretical predictions in the ground-based coordinates.

Forced Response of a Large Civil Fan Assembly

2008 ◽  
Author(s):  
J. S. Green
Keyword(s):  
Ground Plane ◽  
Time History ◽  
Forced Response ◽  
Operating Conditions ◽  
Response Analysis ◽  
Analysis Tool ◽  
Flow Distortion ◽  
Modal Response ◽  
Engine Order ◽  
Compressor Inlet

Forced response analysis has become commonplace for predicting the vibration amplitude of turbomachinery blading. These analyses are usually limited because they rely on predicting a well defined source of flow distortion, such as blade wakes and shocks etc. However, the sources of excitation of civil fans are not well defined and yet are able to produce high levels of force. The objective of the work described in this paper is to investigate the forced response of a large civil fan assembly using CFD. An unsteady, time accurate, 3D CFD model of the complete low pressure compression system has been used to calculate the modal response of a large civil fan. The mesh consists of the ground plane, intake, fan, OGV, bypass duct and compressor inlet stator, with every aerofoil passage modelled. The analysis tool allows calculation of a time history of modal response for a range of modes simultaneously to provide a description of the overall vibration behaviour. The results of the analyses have been used to investigate the modal contributions to the off-resonant first engine order response at a range of operating conditions to assess the contribution of various geometric features. The response is shown to compare well with measured strain gauge data for both ground and altitude conditions. The response of the majority of resonances was found to be heavily influenced by the presence of the ground plane, which is consistent with the available experimental data.

Experimental and CFD Based Determination of Flutter Limits in Supersonic Space Turbines

2008 ◽  
Author(s):  
Pieter J. Groth ◽  
Hans E. Ma˚rtensson ◽  
Niklas Edin
Keyword(s):  
Operating Conditions ◽  
Total System ◽  
Nodal Diameter ◽  
Aerodynamic Damping ◽  
Velocity Flow ◽  
Flutter Boundary ◽  
Predicted Values ◽  
Operating Points ◽  
Amplitude Growth

Turbines operating at high pressure in high velocity flow are susceptible to flutter. As reduced frequencies become sufficiently low, negative aerodynamic damping will be found in some modes. Ensuring that the total system damping is positive over the entire turbine operating envelope for all modes is of utmost importance in any design since flutter in a turbine often causes blade failures. This is in contrast to the normal engineering approach, which is to require a positive aerodynamic damping. A unique test campaign with a 1.5 stage supersonic space turbine has been performed. The turbine was operated at simulated running conditions over a large operating envelope in order to map out flutter limits. During the test, flutter was intentionally triggered at seven different operating conditions. Unique data have been obtained during the test that supports validation of design tools and enables better understanding of flutter in this type of turbine. Based on the data the flutter boundary for the turbine could be established. Using CFD tools flutter was predicted at all operating points where the flutter limit was crossed. Both in predictions and as evidenced in test the 2 nodal diameter backward traveling mode was the most unstable. In addition to this predicted values of aerodynamic damping at flutter agreed well with damping estimated from measured amplitude growth.

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