Strain Gauge Balance Research Articles

Different calibration methods for a three-component strain gauge balance to measure aerodynamic forces on airfoils

Wind tunnel testing of small-scale models using aerodynamic balances is a widely used and valuable methodology, particularly in pivotal sectors as wind energy and aerospace industry. Previous works introduced a novel concept of scalable, external, three-component strain gauge balance, which was further validated showing a remarkable agreement against existing experimental data. However, potential applications involving complex airfoil flow environments, or the examination of passive flow control devices are highly demanding in terms of precision, accuracy and uncertainty. This research presents a complete dataset from extensive measurements and explores different calibration methods to address these challenges. Special effort was placed on providing a detailed description of the methodology to ensure reproducibility, and the distinct requirements of each calibration method have been meticulously considered in a comprehensive comparison. The results lead to significant conclusions, indicating that exact solution linear calibration methods are adequate for some applications when suitable calibration loads are used. Nevertheless, for more advanced applications, third-order least-squares models offer the most accurate results and are thus recommended. Finally, this work identifies potential areas for further research, such as exploring double-sided calibration models and assessing the influence of model mounting on the balance behavior, which could contribute to advances in the field.

Non-stationary load measurement using six-component strain-gauge balances

A novel method using six-component strain-gauge balances has been proposed to solve an important mechanics problem in aircraft model wind tunnel testing – measuring the non-stationary force and moment vectors. A physical model is at the method’s core: the sensitive elements of each balance component are replaced by damped springs. This model measures arbitrary non-stationary loads over the entire frequency range of the balance, including the natural frequency. The problem is solved for the general case of a non-inertial balance coordinate system. The standard deviation of the proposed method for measuring non-stationary loads did not exceed 2.8%. The proposed method solves a second problem – measuring object mass and the positions of its centre of mass and moments of inertia with respect to three mutually perpendicular axes. The method is experimentally verified. An estimation of the frequency range of the strain-gauge balance for measuring non-stationary loads was made using the developed method.

Novel method for measuring non-stationary pitch and roll angles with a pendulous accelerometer in the presence of vibrations

We developed a novel universal method to solve an important mechanics problem arising during wind tunnel tests of aircraft models: the measurement of non-stationary pitch and roll angles of aircraft models and strain-gauge balances using a pendulous accelerometer. The method is based on a physical model in which the accelerometer pendulum is replaced by a proof mass and its hinge is replaced by a spring with damping. This model makes it possible to measure non-stationary pitch and roll angles in a wide range of vibration frequencies, including the accelerometer’s eigenfrequency. We propose a method for determining the accelerometer’s natural frequency in the absence of damping (resonance frequency) as well as the ratio of the damping coefficient to the pendulum’s mass. We also conducted experimental studies in which an acceleration similar in form to the Heaviside function was applied to the accelerometer; the results verify the proposed method.

Effect of Adjacent Blade Oscillation on the Forces on A Blade of a Compressor Cascade

The current trend of aircraft engines is one towards attaining high isentropic efficiency while minimizing its weight. This leads to a state where the blades are highly loaded and consequently susceptible to vibrations. High cycle fatigue caused as a result of such self-excited flutter or forced vibration due to defects in the air stream are detrimental to the engine. An understanding of the onset of instabilities is essential to predict their occurrences to avoid a catastrophic failure during operation or costly redesign during the development phase. The critical parameters in turbomachine aeroelasticity are the reduced frequency and the interblade phase angle. The damping of the system is known to be a function of the phase difference between the blade forces and the blade motion. In the present study, a linear cascade of five blades is considered to understand the effect of harmonically varying boundary conditions. The second and fourth blades of the cascade are subjected to torsional oscillation by an external mechanism. The third blade, considered as the reference, is stationary and instrumented. The unsteady pressure along the reference blade surface is measured simultaneously with the loads acting on the blade. The unsteady pressures are measured using a multi-sensor pressure scanner by multiplexing and the loads are measured using a five-channel strain gage balance. The blade displacement is determined from the integrated accelerometer signal mounted on an oscillating blade. The experiments are conducted at a low-subsonic speed and multiple oscillation frequencies. The cascade is set at zero incidence and four stagger angles. The effect of inter-blade phase angle is included as the oscillation of the walls adjacent to the reference blade. The phase difference between the harmonic motion of the neighboring walls and the pressure and load signals on the reference blade is related to the damping characteristics of the reference blade. The variation in damping is studied for the range of blade motion phase difference angles and reduced frequencies. The effect of the phase difference between the oscillating blades is seen to strongly affect the damping characteristics of the reference airfoil.

Force measurement using strain-gauge balance in shock tunnel based on deep learning

When a force test is conducted in a shock tunnel, vibration of the Force Measurement System (FMS) is excited under the strong flow impact, and it cannot be attenuated rapidly within the extremely short test duration of milliseconds order. The output signal of the force balance is coupled with the aerodynamic force and the inertial vibration. This interference can result in inaccurate force measurements, which can negatively impact the accuracy of the test results. To eliminate inertial vibration interference from the output signal, proposed here is a dynamic calibration modeling method for an FMS based on deep learning. The signal is processed using an intelligent Recurrent Neural Network (RNN) model in the time domain and an intelligent Convolutional Neural Network (CNN) model in the frequency domain. Results processed with the intelligent models show that the inertial vibration characteristics of the FMS can be identified efficiently and its main frequency is about 380 Hz. After processed by the intelligent models, the inertial vibration is mostly eliminated from the output signal. Also, the data processing results are subjected to error analysis. The relative error of each component is about 1%, which verifies that the modeling method based on deep learning has considerable engineering application value in data processing for pulse-type strain-gauge balances. Overall, the proposed dynamic calibration modeling method has the potential to improve the accuracy and reliability of force measurements in shock tunnel tests, which could have significant implications for the field of aerospace engineering.

Wire-driven parallel robot suspension system for SDM in a low-speed wind tunnel

A wire-driven parallel robot with eight wires (WDPR-8) acting as the suspension system for an aircraft model in a low-speed wind tunnel is introduced in this paper. A kinematics model for WDPR-8 is established here. A theoretical basis is also provided, through which movement control of the model is achieved by changing the wire length. A model motion control subsystem, a monocular vision measurement subsystem for the model position, and a data acquisition subsystem were also developed for WDPR-8. A prototype of WDPR-8 was built and mounted in a low-speed wind tunnel with an open test section. A six-component strain-gauge balance was installed inside the test model to acquire aerodynamic parameters. The aerodynamic coefficients of the static test show reasonable agreement with reference results. The difference between the test result of WDPR-8 and the results from reference is smaller in the positive angle of attack than the negative angle of attack, and the total difference between WDPR-8 and other facilities is under 10%. Pitch dynamic tests with different amplitudes and frequencies were used to verify the aerodynamic hysteresis phenomena. The research indicates it is successful that the solution of measuring aerodynamic parameters with strain-gauge balance set into the standard dynamic model suspended by WDPR. It demonstrates that WDPR-8 is effective and feasible as a model suspension system in a low-speed wind tunnel. Furthermore, test results without interference correction in accordance with the reference data proves that the interference of Wire-Driven support system to flow field during wind tunnel tests is negligible. Finally, WDPR suspension system introduced in this paper will remarkably improve the efficiency and accuracy in wind tunnel test.

Features of laying underwater pipeline crossings

Introduction. To date, pipeline transport is an important, highly efficient and promising method of transporting water, gas, oil, etc. It is often necessary to overcome water barriers in the course of laying pipelines. At the design stage, many engineering problems can be solved by analyzing the velocity distribution and evaluating hydraulic resistances. The value of hydraulic resistances depends on the position of the pipeline crossing relative to the incoming flow.
 
 Materials and methods. Experimental studies of models of pipeline crossings in a wind tunnel were conducted to determine the values of coefficients of hydrodynamic resistance and the lifting force.
 
 Results. During the experiments, components of the flow force, acting on the pipeline crossing, were measured using the strain gauge balance at different Reynolds numbers applied to find values of coefficients of hydrodynamic resistance and the lifting force for a pipeline lying on a screen at different angles to the incoming flow. 1/2 and 1/3 of the pipeline diameter was buried in the riverbed and safeguarded by flexible concrete mats.
 
 Conclusions. The lowest values of coefficients of hydrodynamic resistance and the lifting force were obtained for a pipeline with 1/2 of the pipeline diameter buried in the riverbed and laid perpendicularly to the flow direction. Concrete mats are the optimal loading for non-buried pipelines.

Aerodynamic Performance of VAWT Airfoils: Comparison between Wind Tunnel Testing Using a New Three-Component Strain Gauge Balance and CFD Modelling

Vertical axis wind turbines are an emerging and in-development wind energy technology which are characterized by their complicated aerodynamics. Detached flow conditions, which are typically developed at operational tip speed ratios, demand a rigorous characterization of the airfoils for an accurate prediction of the turbine performance. In this work, a custom-built, three-component external strain gauge balance, specifically developed for airfoil testing, is validated. The physical reasons responsible for discrepancies with reference data are also analyzed. Two- and three-dimensional flat plates, as well as the DU06-W-200 airfoil, are tested in a wind tunnel. Lift and drag coefficients and pitching moments are obtained for a wide angular range at Re = 200,000. The results are compared with data from the bibliography and CFD simulations, performed with the recently developed GEKO (generalized k-omega) turbulence model, achieving remarkable agreement. Instantaneous forces are also analyzed with both experimental and CFD techniques, providing interesting results of the unsteady fluid dynamics. Finally, critical factors affecting the measurements are identified and enhancements are proposed for future works. In summary, a thorough evaluation of this new balance design is provided, showing its valuable potential for VAWT applications.

Verification of the Method for Assessing Systematic Errors of the Bench for Calibrating Six-Component Strain-Gauge Balances

Verification of the Method for Assessing Systematic Errors of the Bench for Calibrating Six-Component Strain-Gauge Balances

General Problems of Metrology and Measurement Technique Static Component of Temperature Error in the Strain-Gauge Balance: Determination of the Temperature Sensitivity Coefficient

General Problems of Metrology and Measurement Technique Static Component of Temperature Error in the Strain-Gauge Balance: Determination of the Temperature Sensitivity Coefficient

Flight Measurement System for Airship Propeller Based on Tube-type Strain Gauge Balance

Flight Measurement System for Airship Propeller Based on Tube-type Strain Gauge Balance

Heat transfer and skin-friction in channel with flow behind a cylinder

The paper presents the results of an experimental study of the parameters of the boundary layer, distribution of static pressure, heat transfer and friction coefficients of smooth surface located in the wake behind the cylinder in the channel. Cylinders of various diameters were placed in a slotted channel with a height of 30 mm on its axis. In all experiments, the flow velocity at the inlet was 50 m/s. The cylinder was made unheated. The friction coefficients of the smooth model were determined both from the velocity profile in the boundary layer and by direct weighing of the model on a one-component strain-gage balance. The local values of the heat transfer coefficients were determined by transient heat-transfer method using a thermal imager. The values of the heat transfer and friction coefficients in the wake behind the cylinder, referred to the values on the smooth wall in the undisturbed flow, varied in the range 1.15–1.65 and 1.3–1.75, respectively. The value of the Reynolds analogy factor for all cylinder diameters turned out to be less than unity.

Lift and Drag Performance Based on Varying Flapping Wing Camber at Low Reynolds Number of Micro Air Vehicles (MAVs)


 
 
 Flapping-Wing Micro Air Vehicles (FW-MAVs) are small hand-held flying vehicles that can maneuver in constrained space owing to their lightweight, low aspect ratio and the ability to fly in a low Reynolds number environment. In this study, the aerodynamic characteristics such as time-averaged lift (CL avg) and time-averaged drag (CD avg) of camber wings with different five wind tunnel test models with 6, 9, 12, and 15 per cent camber were developed and the results were compared with a flat wing to assess the effects of camber wing on the aerodynamic performance for flapping flight applications. The experiments were performed in an open chamber with non-return airflow with a test section of (0.3 x 0.3) m and capable of speeds from 0.5 to 30 m/s. The (CL avg) and (CD avg) as functions of the angle of attack at 100, associated with flapping frequency at 9 Hz and low Re = 3600 of the flapping motions concerning the incoming flows are measured by using a strain gauge balance and KYOWA PCD- 300A sensor interface data acquisition system. It is found that camber would bring significant aerodynamic benefits in a higher lift in comparison to the flat wing and increase with increasing camber instead of drag shows contrary a decreasing of performance with increase drag when the camber raised.
 
 

Design optimization of strain gauge mounting cross section length of strain gauge balance component for wind tunnel application

The main purpose of this study is to optimize strain gauge mounting cross section length of strain gage (gauge) balance component to measure forces and moments experienced by test models. This is done by using three dimensional models of balance component using version NX 10.0 unigraphics software and the results are analysed using high- fidelity finite element modelling altair hyperworks software version13.0 and optistruct solver. It may be noted that a maximum diameter of 25 mm and 200 mm length is permitted for strain gauge balance component design. The material used for calculation of the balance component is maraging C-250 steel with maximum yield stress of 1655 N/mm2. It is very important that designer is supposed to choose the strain gauge mounting cross section length by considering the limits of the design. Distance between front and aft loading location is specifically 100 mm. The present work involves design of cross sectional length for wind tunnel integral strain gauge balance component with minimum factor of safety of 2.5, maximum deflection of 1.2 mm and maximum stress 662 N/mm2 which is permitted.

Design and Structural Analysis of Three Component Strain Gauge Balance

Design and Structural Analysis of Three Component Strain Gauge Balance

Effects of spin rate on the surface pressure distribution of a rotating model

A new experimental technique has been developed to measure the pressure distribution over the surface of a rotating model in a wind tunnel for various spin rates, free-stream Mach numbers, and angles of attack. In this method, all of the measuring instruments are placed inside the rotating model which eliminated previous operational limitations and technical problems associated with attempts to measure the Magnus effect. The validity and reliability of the measured data was verified by comparing the integrated surface pressure values and aerodynamic forces, with those directly measured from an internal strain gauge balance. From the acquired surface pressure data distribution of both local and total Magnus force on the model as well as the interpretation of the boundary layer and flow separation effects on the rotating model could be determined. The Magnus force distribution shows that the local Magnus force increases along the length of the model and the maximum local Magnus force occurs at the end of the projectile. The acquired experimental data were further compared with the numerical simulations and satisfactory results were achieved. This new experimental technique can be easily applied to a variety of model configurations testing at different Mach numbers, spin rates, angles of attack, etc.

Heat transfer and skin-friction in a turbulent boundary layer under a non-equilibrium longitudinal adverse pressure gradient

The experimental data on the effect of weak and moderate non-equilibrium adverse pressure gradients (APG) on the parameters of dynamic and thermal boundary layers are presented. The Reynolds number based on the momentum thickness at the beginning of the APG region was Re** = 5500. The APG region was a slot channel with upper wall expansion angles from 0 to 14°. The profiles of the mean and fluctuation velocity components were measured using a single-component hot-wire anemometer. The friction coefficients were determined using two methods, namely, the indirect Clauser method and the direct method of weighting the lower wall region on a single-component strain-gage balance. The heat transfer coefficients were determined by a transient method using an IR camera. It is noticed that in the pressure gradient range realized the universal logarithmic region in the boundary layer profile is conserved. The values of the relative (divided by the parameters in zero gradient flow at the same value of Re**) friction and heat transfer coefficients, together with the Reynolds analogy factor, are determined as functions of the longitudinal pressure gradient. The values of the relative friction coefficient reduced to cf/cf0 = 0.7 and those of the heat transfer to St/St0 = 0.9. A maximum value of the Reynolds analogy factor (St/St0)/(cf/cf0) = 1.16 was reached for the pressure gradient parameter β = 2.9.

Studies on six-component rotating strain-gauge balance calibration for aircraft propellers testing

Studies on six-component rotating strain-gauge balance calibration for aircraft propellers testing

Study on six-component rotating strain-gauge balance development for helicopter tail rotor testing

Study on six-component rotating strain-gauge balance development for helicopter tail rotor testing

Static component of the temperature error of the strain-gauge balance: determination of the temperature sensitivity coefficient

Static component of the temperature error of the strain-gauge balance: determination of the temperature sensitivity coefficient