Unsteady Force Measurement for a Beam Using Small Piezoelectric End Sensors

2014 ◽  
Author(s):  
Margalit Z. Goldschmidt ◽  
Michael L. Jonson ◽  
George A. Lesieutre
Keyword(s):  
Lift Force ◽  
Experimental Validation ◽  
Pressure Field ◽  
Force Measurement ◽  
Propeller Blade ◽  
Unsteady Forces ◽  
Unsteady Force ◽  
Beam Surface ◽  
Propeller Blades ◽  
Unsteady Lift

A new method to measure the total unsteady lift force across a propeller blade is presented in this paper. Unsteady forces across propeller blades are generated from the interaction of the blade boundary with a rotating pressure field associated with the propeller. The oscillating nature of the unsteady forces, particularly at higher harmonics, suggests that the unsteady lift fluctuations nearly cancel out over the blade span, and that it is possible to find the total unsteady force across the propeller from parameters at the root and tip. These parameters were determined from an approximation provided by the Method of the Stationary Phase. A newly designed apparatus for the measurement of total unsteady force across a propeller blade based on this theory is described in detail. For future experimental validation of the newly designed sensors, a propeller blade is modeled as a uniform beam, and a known unsteady force is generated across the beam surface.

Unsteady Forces of Rotor Blades in Full and Partial Admission Turbines

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Narmin Baagherzadeh Hushmandi ◽  
Jens E. Fridh ◽  
Torsten H. Fransson
Keyword(s):  
Pressure Field ◽  
Dynamic Pressure ◽  
Turbine Blades ◽  
Leading Edge ◽  
Rotational Frequency ◽  
Rotor Blades ◽  
Computational Domain ◽  
Unsteady Forces ◽  
Partial Admission ◽  
Unsteady Force

A numerical and experimental study of partial admission in a low reaction two-stage axial air test turbine is performed in this paper. In order to model one part load configuration, corresponding to zero flow in one of the admission arcs, the inlet was blocked at one segmental arc, at the leading edge of the first stage guide vanes. Due to the unsymmetrical geometry, the full annulus of the turbine was modeled numerically. The computational domain contained the shroud and disk cavities. The full admission turbine configuration was also modeled for reference comparisons. Computed unsteady forces of the first stage rotor blades showed cyclic change both in magnitude and direction while moving around the circumference. Unsteady forces of first stage rotor blades were plotted in the frequency domain using Fourier analysis. The largest amplitudes caused by partial admission were at first and second multiples of rotational frequency due to the existence of single blockage and change in the force direction. Unsteady forces of rotating blades in a partial admission turbine could cause unexpected failures in operation; therefore, knowledge about the frequency content of the unsteady force vector and the related amplitudes is vital to the design process of partial admission turbine blades. The pressure plots showed that the nonuniformity in the static pressure field decreases considerably downstream of the second stage’s stator row, while the nonuniformity in the dynamic pressure field is still large. The numerical results between the first stage’s stator and rotor rows showed that the leakage flow leaves the blade path down into the disk cavity in the admitted sector and re-enters downstream of the blocked channel. This process compensates for the sudden pressure drop downstream of the blockage but reduces the momentum of the main flow.

PRESSURE DISTRIBUTION DUE TO STERN TAB DEFLECTION AT MODEL SCALE

2021 ◽  
Vol 157 (A1) ◽  
Author(s):  
T Arnold ◽  
J Lavroff ◽  
M R Davis
Keyword(s):  
Pressure Distribution ◽  
High Speed ◽  
Lift Force ◽  
Force Measurement ◽  
Maximum Pressure ◽  
Model Scale ◽  
Measure Model ◽  
Overall Resistance ◽  
Hydraulics Laboratory ◽  
The University

Trim tabs form an important part of motion control systems on high-speed watercraft. By altering the pitch angle, significant improvements in propulsion efficiency can be achieved by reducing overall resistance. For a ship in heavy seas, trim tabs can also be used to reduce structural loads by changing the vessel orientation in response to encountered waves. In this study, trials have been conducted in the University of Tasmania hydraulics laboratory using a closed- circuit water tunnel to measure model scale trim tab forces. The model scale system replicates the stern tabs on the full- scale INCAT Tasmania 112 m high-speed wave-piercer catamaran. The model was designed for total lift force measurement and pressure tappings allowed for pressures to be measured at fixed locations on the underside of the hull and tab. This investigation examines the pressures at various flow velocities and tab deflection angles for the case of horizontal vessel trim. A simplified two-dimensional CFD model of the hull and tab has also been analysed using ANSYS CFX software. The results of model tests and CFD indicate that the maximum pressure occurs in the vicinity of the tab hinge and that the pressure distribution is long-tailed in the direction forward of the hinge. This accounts for the location of the resultant lift force, which is found to act forward of the tab hinge.

scholarly journals On Structural Optimization of the Propeller Blade

2018 ◽  
Vol 7 (4.36) ◽  
pp. 1203
Author(s):  
Mikhail Aleshin ◽  
Aleksandr Smirnov ◽  
Margarita Murzina ◽  
Yuri Boldyrev
Keyword(s):  
Composite Material ◽  
Structural Optimization ◽  
Computational Time ◽  
Geometrical Parameters ◽  
Propeller Blade ◽  
Aerodynamic Loads ◽  
Change Mechanism ◽  
Blade Shape ◽  
Optimization Parameters ◽  
Propeller Blades

The results of the structural optimization of propeller blades are presented taking into account its composite structure and pitch change mechanism of the propeller and using FSI (Fluid-Structure Interaction) approaches.  The optimality criterion of the problem is the propeller thrust with optimization parameters being the characteristics of the internal structure of the propeller blade made from a composite. Together with the optimization of the blade shape, the problem is considered which concerns the reduction of the deformations caused by loads occurring during the operation of the propeller, since significant deformations of the blades lead to decreased thrust.Thus, the following optimization problem can be formulated: to find the optimal configuration of the composite material and its micro-geometrical parameters along the height of the blade to minimize deformations and increase the thrust of the propeller.  At the same time, the optimization parameters are limited by the weight of the propeller and the strength characteristics.The technique presented in the paper allows us to obtain the reliable values of thrust and reduce the estimated computational time.  The influence of the structure of the composite material on the mechanical properties of the blades is shown; the values of deformation of the blades under the action of centrifugal and aerodynamic loads are given. 

Nonlinear Reduced-Order Models for Aerodynamic Lift of Oscillating Airfoils

2016 ◽  
Author(s):  
Muhammad Saif Ullah Khalid ◽  
Imran Akhtar
Keyword(s):  
Numerical Simulations ◽  
Strouhal Number ◽  
Lift Force ◽  
Multiple Scales ◽  
Primary Resonance ◽  
Nonlinear Damping ◽  
Van Der Pol Oscillator ◽  
Reduced Order ◽  
Naca 0012 ◽  
Unsteady Lift

For the present study, setting Strouhal Number as the control parameter, we perform numerical simulations for the flow over oscillating NACA-0012 airfoil at Reynolds Number 103. Temporal profiles of the unsteady lift, and their respective spectra clearly indicate the solution to be a period-1 attractor for low Strouhal numbers. This study reveals that aerodynamic forces produced by the oscillating airfoils are independent of the initial kinematic conditions that proves existence of the limit cycle. Frequencies present in the oscillating lift force are composed of the fundamental harmonics, and its odd harmonics. Using these numerical simulations, we observe the shedding frequencies nearly equal to the excitation frequencies in all the cases. Hence, considering it as a primary resonance case, we model the unsteady lift force through a modified van der Pol oscillator. Using the method of multiple scales and spectral analysis of the steady-state CFD solutions, we estimate the frequencies and the damping terms in the reduced-order model. We prove the applicability of this model to all the planar motions of airfoil; heaving, pitching and flapping. With the increasing Strouhal number, the nonlinear damping terms for all types of motion approach similar magnitudes. Another important aspect in one of the currently-proposed model is capturing the time-averaged value of the aero-dynamic lift force.

scholarly journals Unsteady forces on spheres during free-surface water entry

2012 ◽  
Vol 704 ◽  
pp. 173-210 ◽  
Author(s):  
Tadd T. Truscott ◽  
Brenden P. Epps ◽  
Alexandra H. Techet
Keyword(s):  
Free Surface ◽  
Surface Water ◽  
High Speed ◽  
Accurate Determination ◽  
Water Entry ◽  
High Speed Imaging ◽  
Air Cavity ◽  
Unsteady Forces ◽  
Unsteady Force ◽  
Low Mass

AbstractWe present a study of the forces during free-surface water entry of spheres of varying masses, diameters, and surface treatments. Previous studies have shown that the formation of a subsurface air cavity by a falling sphere is conditional upon impact speed and surface treatment. This study focuses on the forces experienced by the sphere in both cavity-forming and non-cavity-forming cases. Unsteady force estimates require accurate determination of the deceleration for both high and low mass ratios, especially as inertial and hydrodynamic effects approach equality. Using high-speed imaging, high-speed particle image velocimetry, and numerical simulation, we examine the nature of the forces in each case. The effect of mass ratio is shown, where a lighter sphere undergoes larger decelerations and more dramatic trajectory changes. In the non-cavity-forming cases, the forces are modulated by the growth and shedding of a strong, ring-like vortex structure. In the cavity-forming cases, little vorticity is shed by the sphere, and the forces are modulated by the unsteady pressure required for the opening and closing of the air cavity. A data-driven boundary-element-type method is developed to accurately describe the unsteady forces using cavity shape data from experiments.

Experimental and numerical studies on the flow-induced vibration of propeller blades under nonuniform inflow

2016 ◽  
Vol 231 (2) ◽  
pp. 481-495
Author(s):  
Jin Tian ◽  
Paul Croaker ◽  
Jiasheng Li ◽  
Hongxing Hua
Keyword(s):  
Wire Mesh ◽  
Strain Gauges ◽  
Strain Response ◽  
Flow Induced Vibration ◽  
Numerical Work ◽  
Unsteady Forces ◽  
Eddy Simulation ◽  
Numerical Studies ◽  
Screen Plane ◽  
Propeller Blades

This article presents the experimental and numerical studies on the flow-induced vibration of propeller blades under periodic inflows. A total of two 7-bladed highly skewed model propellers of identical geometries but different elastic characteristics were operated in four-cycle and six-cycle inflows to study the blade vibratory strain response. A total of two kinds of wire mesh wake screens located 400 mm upstream of the propeller plane were used to generate four-cycle and six-cycle inflows. A laser Doppler velocimetry system located 100 mm downstream of the wake screen plane was used to measure the axial velocity distributions produced by the wake screens. Strain gauges were bonded onto the propeller blades in different positions. Data from strain gauges quantified vibratory strain amplitudes and excitation frequencies induced by the wake screens. The propellers were accelerated through the flexible propeller’s fundamental frequency to investigate the effect of resonance on vibratory strain response. The numerical work was conducted using large eddy simulation and moving mesh technique to predict the unsteady forces acting on the propeller blade when operating in a nonuniform inflow.

Comments on the Low-Aspect-Ratio Unsteady Propeller Force Theory of N. A. Brown

1984 ◽  
Vol 28 (04) ◽  
pp. 238-239
Author(s):  
Steven P. Schneider ◽  
Gregory A. Biaisdell ◽  
David M. Nelson
Keyword(s):  
Aspect Ratio ◽  
Power Series ◽  
Legendre Polynomials ◽  
Approximate Formula ◽  
Propeller Blade ◽  
Low Aspect Ratio ◽  
Unsteady Force

A paper written by N. A. Brown [1], (3) develops an approximate formula for the prediction of the unsteady force on a propeller blade in terms of a theory based on a representation of the inflow field by a power series. This formula is then intuitively changed to one based on a representation of the inflow field in terms of Legendre polynomials. We here use the orthogonality of Legendre polynomials to demonstrate that this intuitive step is incorrect. Our further work is then discussed. The notation of the original paper is used.

On Structural Optimization of The Propeller Blade

2018 ◽  
Vol 7 (4.36) ◽  
pp. 1203
Author(s):  
Mikhail Aleshin ◽  
Aleksandr Smirnov ◽  
Margarita Murzina ◽  
Yuri Boldyrev
Keyword(s):  
Composite Material ◽  
Structural Optimization ◽  
Computational Time ◽  
Geometrical Parameters ◽  
Propeller Blade ◽  
Aerodynamic Loads ◽  
Change Mechanism ◽  
Blade Shape ◽  
Optimization Parameters ◽  
Propeller Blades

The results of the structural optimization of propeller blades are presented taking into account its composite structure and pitch change mechanism of the propeller and using FSI (Fluid-Structure Interaction) approaches.  The optimality criterion of the problem is the propeller thrust with optimization parameters being the characteristics of the internal structure of the propeller blade made from a composite. Together with the optimization of the blade shape, the problem is considered which concerns the reduction of the deformations caused by loads occurring during the operation of the propeller, since significant deformations of the blades lead to decreased thrust.Thus, the following optimization problem can be formulated: to find the optimal configuration of the composite material and its micro-geometrical parameters along the height of the blade to minimize deformations and increase the thrust of the propeller.  At the same time, the optimization parameters are limited by the weight of the propeller and the strength characteristics.The technique presented in the paper allows us to obtain the reliable values of thrust and reduce the estimated computational time.  The influence of the structure of the composite material on the mechanical properties of the blades is shown; the values of deformation of the blades under the action of centrifugal and aerodynamic loads are given.   

scholarly journals Preliminary Determination of Propeller Aerodynamic Characteristics for Small Aeroplanes

10.14311/558 ◽  
2004 ◽  
Vol 44 (2) ◽  
Author(s):  
S. Slavík
Keyword(s):  
Aerodynamic Characteristics ◽  
Propeller Blade ◽  
Analytical Functions ◽  
Advance Ratio ◽  
Propeller Blades ◽  
Lift And Drag ◽  
S Model ◽  
Integral Decomposition ◽  
Preliminary Determination

This paper deals with preliminary determination of propeller thrust and power coefficients depending on the advance ratio by means of some representative geometric parameters of the blade at a specific radius: propeller blade chord and blade angle setting at 70 % of the top radius, airfoil thickness at the radius near the tip and the position of the maximum blade width. A rough estimation of the non-linear influence of propeller blades number is included.The published method is based on Lock`s model of the characteristic section and the Bull-Bennett lift and drag propeller blade curves. Lock`s integral decomposition factors and the loss factor were modified by the evolution of the experimental propeller characteristics. The numerical-obtained factors were smoothed and expressed in the form of analytical functions depending on the geometric propeller blade parameters and the advance ratio.

On the Prediction of Unsteady Forces on Gas Turbine Blades: Part 2—Analysis of the Results

1992 ◽  
Vol 114 (1) ◽  
pp. 123-131 ◽  
Author(s):  
T. Korakianitis
Keyword(s):  
Potential Flow ◽  
Turbine Blades ◽  
Interaction Mechanism ◽  
Rotor Blades ◽  
Unsteady Forces ◽  
Flow Angle ◽  
Gas Turbine Blades ◽  
Flow Interaction ◽  
Unsteady Force ◽  
Outlet Flow

This article investigates the generation of unsteady forces on turbine blades due to potential-flow interaction and viscous-wake interaction from upstream blade rows. A computer program is used to calculate the unsteady forces on the rotor blades. Results for typical stator-to-rotor-pitch ratios and stator outlet-flow angles show that the first spatial harmonic of the unsteady force may decrease for higher stator-to-rotor-pitch ratios, while the higher spatial harmonics increase. This (apparently counterintuitive) trend for the first harmonic, and other blade row interaction issues, are explained by considering the mechanisms by which the viscous wakes and the potential-flow interaction affect the flow field. The interaction mechanism is shown to vary with the stator-to-rotor-pitch ratio and with the outlet flow angle of the stator. It is also shown that varying the axial gap between rotor and stator can minimize the magnitude of the unsteady part of the forces generated by the combined effects of the two interactions.

Sign in / Sign up

Export Citation Format

Share Document