Surface Pressure Measurements Research Articles

Short-term wind forecasting via surface pressure measurements: Stochastic modeling and sensor placement

We propose a short-term wind forecasting framework for predicting real-time variations in atmospheric turbulence based on nacelle-mounted anemometer and ground-level air-pressure measurements. Our approach combines linear stochastic estimation and Kalman filtering algorithms to assimilate and process real-time field measurements with the predictions of a stochastic reduced-order model that is confined to a two-dimensional plane at the hub height of turbines. We bridge the vertical gap between the computational plane of the model at hub height and the measurement plane on the ground using a projection technique that allows us to infer the pressure in one plane from the other. Depending on the quality of this inference, we show that customized variants of the extended and ensemble Kalman filters can be tuned to balance estimation quality and computational speed 1–1.5 diameters ahead and behind leading turbines. In particular, we show how synchronizing the sign of estimates with that of velocity fluctuations recorded at the nacelle can significantly improve the ability to follow temporal variations upwind of the leading turbine. We also propose a convex optimization-based framework for selecting a subset of pressure sensors that achieve a desired level of accuracy relative to the optimal Kalman filter that uses all sensing capabilities.

Dynamic calibration of a high-resolution wind tunnel model for ultra-low-range fluctuating surface pressure measurement

Abstract Measuring surface pressures in a low-speed wind tunnel which are well-resolved in both space and time can be particularly challenging. A technique has therefore been developed for the simultaneous dynamic calibration of large numbers of pressure tappings on a wind tunnel model. A portable, variable-volume plenum is used to calibrate the model \textit{in situ}. A forcing function consisting of sequential sinusoids at varying frequencies is used to obtain the spectral responses, with feedback control implemented to ensure consistent amplitudes independent of the plenum's own dynamics. This discrete calibration technique is shown to significantly reduce uncertainty propagation compared to white noise, chirp or step functions. The effectiveness of the dynamic calibration is validated against laser diagnostics in turbulent flow. As a demonstration of the capability of this technique, spatially-resolved surface pressure statistics are then presented for the five wetted faces of a cube in an atmospheric wind tunnel turbulent boundary layer.

Learning Airfoil Flow Field Representation via Geometric Attention Neural Field

Numerical simulation in fluid dynamics can be computationally expensive and difficult to achieve. To enhance efficiency, developing high-performance and accurate surrogate models is crucial, where deep learning shows potential. This paper introduces geometric attention (GeoAttention), a method that leverages attention mechanisms to encode geometry represented by point cloud, thereby enhancing the neural network’s generalizability across different geometries. Furthermore, by integrating GeoAttention with neural field, we propose the geometric attention neural field (GeoANF), specifically for learning representations of airfoil flow fields. The GeoANF embeds observational data independently of the specific discretization process into a latent space, constructing a mapping that relates geometric shape to the corresponding flow fields under given initial conditions. We use the public dataset AirfRANS to evaluate our approach, GeoANF significantly surpasses the baseline models on four key performance metrics, particularly in volume flow field and surface pressure measurements, achieving mean squared errors of 0.0038 and 0.0089, respectively.

Flow topology and turbulent characteristics of cross flow over a wall bounded inline tube bundle with small pitch to diameter ratio

The characteristics of cross flow over tube bundles with small pitch to diameter ratios (S/D) are preferable for intermediate heat exchangers (IHXs) of High Temperature Gas-cooled Reactors (HTGRs) due to they can further improve the compactness of such heat exchangers. However, small S/D usually introduces more complex flow phenomena, such as biased wakes, main frequency disappearing in velocity spectrum, as well as the quasi-stable phenomenon. In the current investigation, the cross flow over an inline tube bundle (8 columns and 20 rows) with S/D = 1.25 was experimentally investigated in a low-speed wind tunnel using various measurement techniques including two-dimensional, two-component (2D2C) Particle Image Velocimetry (PIV), split hot film anemometry, surface pressure measurements and wind tunnel balances. Firstly, PIV was used to obtain the time averaged streamwise and transverse velocity fields (in z-normal plane). The direction of the turbulent wakes and transverse flows behind the tubes were investigated. It was found that at the middle spanwise plane (z = 0 mm), the wakes and transverse flows are both towards the nearby bounding wall. However, at planes closer to the end of the tubes, the directions of the wakes and transverse flows are away from the bounding walls (z=±200 mm). To further confirm this phenomenon, split hot films are used to measure the transverse flow direction at different streamwise and spanwise positions, revealing that the direction of the wakes and transverse flows remained consistent at different streamwise positions. Streamwise and spanwise velocity fields (in y-normal planes) measured using PIV demonstrates that there exists spanwise flow (z direction) in different transverse planes (y-normal planes) within the tube bundle. The spanwise and transverse flows form secondary flows in the plane normal to the flow direction (x-normal plane). The secondary flows are symmetrical about the z = 0 mm plane and y = 0 plane. Therefore, the streamlines within the tube bundle are in a helical shape. In the current surface pressure measurement, two sets of main frequencies corresponding to Sr = 0.047 and 0.112 were identified in the surface pressure spectrum. Moreover, transverse velocity sudden jumps were observed in specific regions from the reconstructed PIV results using Proper Orthogonal Decomposition (POD). This phenomenon was particularly prominent at the plane (z = 150 mm) where the wake and transverse flow directions transition.

UN ESTUDIO EXPERIMENTAL DE PROPIEDADES FÍSICAS DE SAPONINAS Y SU INTERACCIÓN CON UN MODELO DE MEMBRANA DE BACTERIAS GRAM-NEGATIVAS EMPLEANDO PELÍCULAS LANGMUIR-BLODGETT Y MICROSCOPÍA DE FUERZA ATÓMICA

Saponins are non-ionic biosurfactants that exhibit antifungal, antiviral and antibacterial properties. However, the mechanisms by which saponins exhibits these properties are not well understood. In the present work, Langmuir and atomic force microscopy (AFM) techniques were employed to investigate the interactions of saponins with a model of Gramnegative bacterial membranes. The lipid films contained extracts of phosphatidylethanolamine and phosphatidylglycerol from Escherichia coli bacteria. The results suggest that saponins repel phospholipids, thereby increasing membrane fluidity. They also showed evidence of adsorption of the saponin by the membrane model. These results were cross-checked with AFM images. A mechanism for how saponin alters the phospholipid membrane is proposed. Langmuir technique and atomic force microscopy proved to be useful tools to investigate the interaction of biologically relevant compounds with cell membrane models. The results of the surface pressure measurements, combined with those obtained from AFM, provided evidence for the susceptibility of membranes to the insertion of saponins and their possible modes of action. The results of this study may contribute to a better understanding of the mechanisms of antifungal, antiviral and antibacterial activity of saponins

Boundary sources of velocity gradient tensor and its invariants

The present work elucidates the boundary behaviors of the velocity gradient tensor (A≡∇u) and its principal invariants (P, Q, R) for compressible flow interacting with a stationary rigid wall. First, it is found that the boundary value of A exhibits an inherent physical structure being compatible with the normal-nilpotent decomposition, where both the strain-rate and rotation-rate tensors contain the physical contributions from the spin component of the vorticity. Second, we derive the kinematic and dynamical forms of the boundary A flux from which the known boundary fluxes can be recovered by applying the symmetric–antisymmetric decomposition. Then, we obtain the explicit expression of the boundary Q flux as a result of the competition among the boundary fluxes of squared dilatation, enstrophy and squared strain-rate. Importantly, we find that both the coupling between the spin and surface pressure gradient, and the spin-curvature quadratic interaction (sw·K·sw), are not responsible for the generation of the boundary Q flux, although they contribute to both the boundary fluxes of enstrophy and squared strain-rate. Moreover, we prove that the boundary R flux must vanish on a stationary rigid wall. Finally, the boundary fluxes of the principal invariants of the strain-rate and rotation-rate tensors are also discussed. It is revealed that the boundary flux of the third invariant of the strain-rate tensor is proportional to the wall-normal derivative of the vortex stretching term (ω·D·ω), which serves as a source term accounting for the spatiotemporal evolution rate of the wall-normal enstrophy flux. As an example, several relevant surface quantities to the surface curvature are calculated based on global skin friction and surface pressure measurements in a flow over a National Advisory Committee for Aeronautics Fundamental Aeronautics Investigates The Hill model. These theoretical results provide a unified description of boundary vorticity and vortex dynamics, which could be valuable in understanding the formation mechanisms of complex near-wall coherent structures and the boundary sources of flow noise.

Spontaneous Laminar Separation Bubble Bursting on an Airfoil

An experimental investigation was conducted on a NACA 0018 airfoil at near-stall conditions, with stalled, stable laminar-separation bubble, and intermediate flow conditions were considered. Planar particle image velocimetry and surface pressure measurements were used to quantify the flow development at the midspan of the model. For the intermediate conditions, the airfoil is stalled in the time-average sense. However, conditionally averaged velocity field measurements reveal that reattachment of the separated flow and laminar separation bubble formation occur intermittently on the suction surface. The characteristics of the intermittently forming separation bubble and fully separated flow are analyzed based on conditional statistics, revealing variations in the transition process that may underpin the observed low-frequency flow oscillations. The growth rates of the most amplified wavenumbers in the separated shear layer vary with the angle between the separation streamline and the suction surface, leading to earlier transition when the separation angle increases. This change in transition location may play a role in spontaneous changes between fully separated and reattaching flow states.

Drag Reduction of Truck and Trailer Combination with Different Passive Flow Control Methods

In this study, drag force and surface pressure measurements were conducted on a 1/32 scaled truck-trailer combination model. The experimental tests were carried out between the ranges of 312×103- 844×103 Reynolds Numbers in a suction type wind tunnel. The aerodynamic drag coefficient (CD) and distribution of pressure coefficient (CP) were experimentally determined on the truck and trailer combination. The regions where has big pressure coefficients were determined on the truck-trailer by using flow visualizations. The aerodynamic structure of truck-trailer combination models was improved by passive flow control methods on 4 different models. By using newly designed spoiler on the model 1, drag coefficient was reduced 10.01 %. On the model 2, adding trailer rear extension with a spoiler, the reduction was obtained as 11.35 %. For the model 3 which is obtained adding side skirt to model 2, the improvement reached 18.85 %. The model 4 was composed of model 2 and a bellow between the truck and trailer. The drag force improvement was obtained as 22.80 % for model 4.

Analysis of wind vibration characteristics of a slab‐type high‐rise residential building

AbstractA slab‐type high‐rise residential building with a depth‐to‐width ratio exceeding 6 was studied. Multi‐point surface pressure measurements and high‐frequency force balance (HFFB) wind tunnel tests were conducted to investigate the wind‐induced dynamic characteristics of the building. The dynamic responses, especially accelerations closely related to serviceability performance, were determined and examined in both time and frequency domains. The spectral properties of the time‐history acceleration responses were compared with frequency‐domain results. Analyses showed acceleration responses were amplified when along‐wind or across‐wind directions aligned with the shorter building axis. The slab‐type cross‐section reduced vortex shedding in the across‐wind direction. As a result, peak accelerations were often dominated by along‐wind excitations. Torsional accelerations approached those induced by along‐wind winds, likely due to both fundamental and higher modes.

Blade Surface Pressure Measurements in the Field and Their Usage for Aerodynamic Model Validation

ABSTRACTThis study presents results from a long‐term measurement campaign on a research wind turbine in the field. Pressure measurements are conducted at 25% blade radius over several months. Together with inflow measurements provided by a LiDAR system, they form an extensive dataset, which is used in the validation of numerical aerodynamic models. The model validation is conducted based on both ten‐minute average data as well as time‐resolved unsteady data. Initially, it is investigated how representative ten‐minute average pressure measurements are of the underlying unsteady aerodynamics. Binned ten‐minute average pressure distributions are then analysed together with their numerical counterpart, consisting of a combination of rotor and airfoil level aerodynamic/aeroelastic simulation results using average environmental and operating conditions as input. Finally, time‐resolved measurements and simulation results are compared, validating the aeroelastic tools' capability to reproduce unsteady aerodynamics.Overall, reasonable agreement is found between numerical simulations and field experiment data showcasing two aspects: Numerical tools based on blade element momentum theory and panel methods with viscous‐inviscid interaction remain relevant for simulating modern multi‐megawatt wind turbines, and long‐term pressure measurements provide invaluable means for validating such tools.

Unsteady Loads of a Scaled Rotor on and Near the Landing Deck of the NATO Generic Destroyer with Concurrent Stereo PIV and Surface Pressure Measurements

Rotorcraft shipboard operations are risky and demand high piloting skills. To gain further understanding and familiarize pilots with these complicated scenarios, various methods of computational simulations have been used in the past decades. Yet, some simulation methods may not capture a realistic response of the rotorcraft due to simplified modeling of the interactional aerodynamics in order to achieve real-time capability for pilot training. Thus, improvements to these simulations are required, and experimental data that unveil the interactional aerodynamics and dynamics between the rotor and ship are needed for computational validation efforts. In this study, an extensive experimental investigation of the ship???rotor dynamic interface problem was conducted to gain a general understanding of the interactional aerodynamics between a 1:100 wind-tunnel-scale NATO Generic Destroyer and a representative single main rotor, operating both stationary and dynamically moving in space in the vicinity of the landing deck. Data obtained through simultaneous measurements of rotor hub loads, ship deck surface pressures, and stereoscopic particle image velocimetry flow fields gave valuable insight into the highly coupled aerodynamic phenomena. Results showed that the rotor hub loads exhibited a high dependency on both the wind direction and also the position of the rotor relative to the landing deck. A bifurcation in the regions of high unsteady thrust was observed under certain wind conditions due to the ship airwake, impacting different portions of the rotor disk. The inflow angles across the rotor disk were estimated and assessed through flow field measurement, revealing how the ship airwake altered the rotor inflow and wake structure that contributed to the unique change in rotor loads under various hovering conditions.

Observing System Simulation Experiments Exploring Potential Spaceborne Deployment Options for a Differential Absorption Radar Measuring Marine Surface Pressures

AbstractA new technology for remote measurements of marine surface pressure has been proposed, employing a V‐band differential absorption radar and a radiometric temperature sounder to calculate the total column atmospheric mass. Observing System Simulation Experiments (OSSEs) are performed to evaluate the potential impact of Spaceborne Marine Surface Pressure (SMSP) on Numerical Weather Prediction. These experiments build on prior efforts (Privé, McLinden, et al., 2023, https://doi.org/10.16993/tellusa.3254), but with an updated version of the OSSE framework and with more sophisticated simulation of the SMSP observations and a longer experiment period. Several different instrument configurations are compared, including both scanning and non‐scanning orbits. SMSP impacts are calculated for analysis quality and forecast skill, and a forecast sensitivity observation impact tool is employed to place SMSP observations in context with the global observing network. The effects of rain contamination on observation quality are explored. Different magnitudes of simulated SMSP observation error are tested in the context of data assimilation to show the range of potential behaviors. Overall, SMSP observations are found to be most beneficial in the southern hemisphere extratropics, with statistically significant forecast improvements for the first 72 hr of the forecast. A constellation of four non‐scanning SMSP satellites is found to outperform a single scanning instrument with a 250 km wide swath.

Investigation of streamwise streak characteristics over a compression ramp at Mach 4

Experiments of shock wave/boundary layer interactions over a nominally two-dimensional compression ramp are conducted in a Mach 4 Ludwieg tube tunnel. Measurements of Schlieren, Rayleigh scattering, and surface pressure are performed to present the relevant flow features. The effects of two parameters, namely the Reynolds number based on the length of the flat plate and the ramp angle, on the flow stabilities are focused on. Four ramp angles of 6°, 8°, 10°, and 12° are tested under a Reynolds number of 7.22 × 105, while two other Reynolds numbers (3.66 × 105 and 9.19 × 105) are investigated with a ramp angle of 10°. Streamwise streaks are observed downstream of the reattachment point. The spanwise wavelength of the streaks remains unchanged with different ramp angles, whereas it slightly decreases as the Reynolds number increases. Power spectral density results show that the flow is transitional in the streak region and becomes turbulent where streaks break down. When increasing the ramp angle or the Reynolds number, the streamwise length of streaks shrinks. Two different patterns are distinguished at the breakdown, resembling the two unstable modes observed in the breakdown of Görtler vortices. To clarify the underlying physics of the formation of streaks, global stability analysis and resolvent analysis are carried out. Two regions of maximum optimal gain are identified, which are associated with Mack's first mode and streaks. The former can serve as an initial seed of Görtler instability via nonlinear interaction, while the latter can be associated with transient growth due to the lift-up mechanism and Görtler instability.

Flow over two inline rough cylinders in the postcritical regime

This study investigates the flow behavior over roughened inline cylinders for postcritical flow, a parameter space with relatively little prior scrutiny. Two cylinders of the same relative surface roughness, ks/D=1.9×10−3, separated by a pitch (i.e., L, distance between the centers of two cylinders) between 1.175≤L/D≤10 are studied at Reynolds numbers from 3×105 to 6×105 using unsteady surface pressure measurements. As pitch ratio is increased from L/D=1.175, CD of the downstream cylinder increases sharply at (L/D)c=3.25. This critical pitch ratio (L/D)c is toward the lower end of the reported range for subcritical smooth cylinders. Asymmetric mean gap flow along with alternating reattachment is found for 1.5≤L/D<2.25 (i.e., two asymmetric modes in the gap, mode 1 and mode 2, that are the reflections of each other), and symmetric gap flow with a continuous reattachment is found for 2.25<L/D≤3. The gap flow is also symmetric for the closest pitch ratio tested of L/D=1.175. While the change in upstream cylinder drag coefficient with Reynolds number broadly follows that of an isolated cylinder, for the downstream cylinder, it is approximately independent. The critical separation is also insensitive to Reynolds number within 3×105≤Re≤6×105. Transitions between the reattachment and the co-shedding flow are predominantly continuous over the spanwise planes tested. On the other hand, alternating reattachment occurs in spanwise cells, where one sectional measurement exhibits the asymmetric mode 1 while a spanwise-adjacent section exhibits the asymmetric mode 2 or even symmetric flow. Previously reported maxima in the fluctuating lift and drag coefficients of the downstream cylinder at L/D≈2.4 at subcritical Reynolds numbers are absent in the current investigation.

Exploring the role of aspartic acid in modulating micellization behavior of cationic cetyltrimethylammonium bromide

The study of the interaction between aspartic acid (Asp) and cetyltrimethylammonium bromide (CTAB) reveals important information about surfactant organization, surface tension, critical micelle concentration (CMC), and surface pressure. Because of enhanced surfactant solubility brought about by electrostatic interactions, Asp’s ionization lowers CTAB’s CMC. The maximal surface excess concentration falls with increasing Asp concentration, suggesting competition for surface adsorption. The minimum occupied area per surfactant molecule increases at the same time, indicating changed surfactant activity at the interface between air and water. Higher CTAB concentrations are associated with a decrease in surface tension, which suggests that when Asp concentration rises, micelle formation would be promoted. Saturation effects, on the other hand, happen at high Asp concentrations and interfere with micelle formation. These tendencies are supported by surface pressure measurements, highlighting the significance of ionic interactions in micelle behavior.Moreover, surfactant structuring is impacted by the packing parameter decreasing as Asp concentration increases. The changing balance between hydrophilic and hydrophobic interactions within the CTAB/Asp micellar complexes is further explained by variations in degree of counterion dissociation of micelles (α) values. The complex dynamics of ionic interactions and their impact on surfactant behavior in CTAB/Asp systems are highlighted by these studies.

Quantifying the aerodynamic admittance and spanwise coherence functions of buffeting lift for bridge decks through the measurement of segmental forces

The assessment of buffeting response of long span bridges relies significantly on the aerodynamic admittance and spanwise coherence functions of buffeting forces acting on bridge decks. This study presents a novel approach to derive admittance and coherence functions of buffeting lift on bridge decks, utilizing wind tunnel measurement of forces on spanwise distributed segments. The approach is developed by establishing connections of the power spectrum and coherence function of segmental lift with the admittance and coherence functions of strip lift. This study also explores the direct estimation of the generalized buffeting forces on long span bridges from the segmental force, eliminating the need of extracting admittance and coherence functions of strip force. The methodology is firstly validated for a thin plate with theoretical force information, follow by its application to a twin-box bridge deck using wind tunnel data. The investigation assesses the influence of a pre-assumed coherence model on the identified admittance and coherence functions and its consequential impact on the generalized buffeting forces of long span bridges. The proposed approach offers a practical and efficient means to quantify buffeting forces acting on bridge decks with intricate configurations, such as truss sections, where surface pressure measurement may pose challenges.

Streamline curvature effects generated by tornado-like flows on the aerodynamics of a low-rise structure

This paper examines the streamline curvature effects on the aerodynamic pressure patterns induced by tornado-like flows on a low-rise structure. The analysis derives from the detailed scrutiny of a wind tunnel test campaign carried out at the WindEEE Dome tornado simulator. The simulated tornado-like flows were characterized by a swirl ratio such that the cores were characterized by multiple vortices. The tornado-like vortex was slowly translated across the chamber of the simulator. Surface pressure measurements were acquired on both the building model surface and on a circular ground plate around it, and synchronized with velocity measurements gathered from four Cobra probes installed in the proximity of the corners of the structure. These Cobra probes allowed the definition of the tornadic streamlines. Multiple nominally identical repeats were carried out to gather a robust estimation of conditionally-averaged pressure and velocity measurements based on the position of the tornado-like vortex. When comparing different cases characterized by similar conditions of upstream wind direction, the mean aerodynamic pressure patterns were revealed to be sensitive to the streamline curvature. Moreover, these are distinct than those generated from straight-line ABL winds, consistently calibrated upon the measurements from the Cobra probes in the upstream proximity of the building.

Static pressure response model of fluorescent pressure-sensitive film for underwater surface pressure measurement

The fluorescent pressure-sensitive film (FPSF) is a non-contact, deformation-based optical pressure sensor with high spatial resolution. The pressure response principle of FPSF is to convert pressure change into variations in fluorescent intensity through the deformation of fluorescent microspheres embedded within the film. To quantitatively analyze the pressure–deformation–intensity mechanism, a static pressure response model was established in this study. First, a finite element model was developed to predict the deformation of microspheres within the film under pressure. Second, the deformation-induced variation in fluorescent intensity was modeled with consideration of the light path blockage effect. The pressure calibration curve of the FPSF predicted by the proposed model was noted to be consistent with the experimental results of underwater calibration. In addition, the relationship between pressure sensitivity and the structural parameters of the FPSF were investigated using the pressure response model.

Simulation of Hypersonic Shock-Boundary Layer Interaction Using Shock-Strength Dependent Turbulence Model

Shock-induced flow separation is important in hypersonic intake unstart and for unsteady aero-thermal loads. This work presents a computational study of shock-boundary layer interaction (SBLI) at hypersonic Mach numbers. The objective is to accurately predict the separation bubble size for oblique shock impingement on a turbulent boundary layer and for two-dimensional axisymmetric cone-flare SBLI cases. We use the Reynolds-averaged Navier Stokes method with an advanced shock-strength-dependent turbulence model. A recently developed transport equation-based shock sensor is employed to identify the location and strength of shock waves. The computational results are found to match experimental measurements of surface pressure and skin-friction coefficient for a series of test cases, highlighting the effects of Mach number, shock generator angle, and wall cooling on the size of the separation bubble. Results are also found to conform to the scaling of SBLI separation size found in the literature. This is one of the few such corroborations for hypersonic axisymmetric SBLI.

Surface Pressure Measurement of Truncated, Linear Aerospike Nozzles Utilising Secondary Injection for Aerodynamic Thrust Vectoring

A cold-gas test campaign has been conducted at the DLR’s P6.2 test bench in Lampoldshausen, with the objective of investigating the linear aerospike nozzle flow in interaction with secondary injection thrust vector control (SITVC). In this campaign, the influence of nozzle truncation, injection position and injection pressure on the nozzle surface and base pressure is analysed using pressure probes and Schlieren flow-visualisation techniques. The effects of injection position and truncation on the nozzle surface pressure development are comparable for all geometric variations, resulting in a locally increased static pressure upstream and a locally decreased static pressure downstream of the injection. The magnitude and dimension of these high- and low-pressure regions are correlated with the injection pressure. However, the influence of injection position and truncation on the base pressure is not entirely predictable by the named parameters, indicating an interdependence between both geometric parameters. Finally, the required pressure ratio of injection to the primary flow to ensure sonic injection has been analysed on TUD’s cold-gas test bench. This allows the respective injection position-dependent threshold to be identified. The analysis reveals that these experiments have been conducted under transsonic injection conditions.