Generalizing Prediction of Bluff Body Aerodynamic Load Maps

2015 ◽  
Author(s):  
Sorin Pirau ◽  
Brandon Liberi ◽  
Natasha Barbely ◽  
Narayanan Komerath
Keyword(s):  
Aspect Ratio ◽  
Bluff Body ◽  
Navier Stokes ◽  
Gradual Transition ◽  
Aerodynamic Load ◽  
Rotation Method ◽  
Continuous Rotation ◽  
Rate Effects ◽  
Body Shapes ◽  
Definition Of

The Continuous Rotation method enables efficient definition of all aerodynamic load components on bodies of arbitrary shape for arbitrary attitudes. This is applied to several bluff body shapes including cylinders, a cuboid, a flat plate and a porous box. Rate effects and unsteadiness are shown to be negligible using a cylinder of aspect ratio 1. The genesis of the side force on the yawed cylinder, and the differences between rough and smooth cylinders, are derived from comparisons between experiments and diagnostic computations with an unsteady Navier-Stokes solver. Interpolating Fourier coefficients of the azimuthal load variation appears to be viable to generalize loads on cylinders of varying aspect ratio. A large variation is seen for aspect ratio 0.5 to 1, with a more gradual transition to ‘high aspect ratio’ features beyond aspect ratio 2.

Generalized Airloads Prediction for Bluff Bodies Transported as Slung Loads

2015 ◽  
Author(s):  
Nicholas Motahari ◽  
Nandeesh Hiremath ◽  
Dhwanil Shukla ◽  
Brandon Liberi ◽  
Nikolaus Thorell ◽  
...  
Keyword(s):  
Aspect Ratio ◽  
Bluff Body ◽  
Flight Speed ◽  
Navier Stokes ◽  
Bluff Bodies ◽  
Aerodynamic Loads ◽  
Rotation Method ◽  
Continuous Rotation ◽  
Speed Prediction ◽  
Body Shapes

Objects of arbitrary shapes have to be carried as slung loads under aircraft, particularly rotorcraft. The flight speed is limited by the possibility of slung loads going into divergent oscillations. In 2014 we presented a testing-based approach to predict the safe flight speed, applicable to bluff bodies of arbitrary shape. Since then, an extensive variety of bluff-body shapes has been tested, and we venture further towards generalized airload prediction, required for generalized divergence speed prediction. Extending recent work, the Continuous Rotation method is applied to obtain aerodynamic loads on generic shapes: a circular cylinder and a rectangular prism, both with aspect ratio varied systematically. The genesis of the side force on the yawed cylinder, and the differences between rough and smooth cylinders, have been derived from comparisons between experiments and diagnostic computations with an unsteady Navier-Stokes solver. Interpolating Fourier coefficients of the azimuthal load variation appears to be viable to generalize loads on cylinders of varying aspect ratio for both the generic shapes.

Divergence Prediction for Practical Helicopter Slung Loads

2016 ◽  
Author(s):  
Nicholas Motahari ◽  
Thomas Kim ◽  
Dhwanil Shukla ◽  
Nandeesh Hiremath ◽  
Narayanan Komerath
Keyword(s):  
Bluff Body ◽  
General Pattern ◽  
Oscillation Amplitude ◽  
Flight Test ◽  
Scale Model ◽  
Aerodynamic Load ◽  
Stable Operation ◽  
Rotation Method ◽  
Angle Data ◽  
Continuous Rotation

Certifying the highest safe speed for an aircraft with a slung load, is life-critical yet daunting. Two flight cases are considered, to test an iterative procedure that predicts the divergence speed from experimental scale model data and simulations. The first is an empty engine canister. The second is a segment of a water-floatable military Ribbon Bridge. In each case, mass, geometry, tether length from a single rotation-bearing attachment, and moments of inertia, come from flight preparations. An initial aerodynamic load map is interpolated and synthesized from a growing library on bluff body aerodynamics. Dynamic simulation with these data predict maximum roll, pitch and yaw angles reached as functions of freestream speed. This yieldw a good initial estimate of critical speeds and dynamics. Model-scale wind tunnel data using our Continuous Rotation method about the required axes, refine simulation. For the engine canister, simulations matched detailed flight test data on maximum trailing and rolling amplitudes over the operational speed range. Trail angle data showed that Reynolds number errors are not significant. In this paper, model-based results explained the correct speed where the ribbobn bridge flight test was stopped. While flight test oscillation amplitude histories depend on initial perturbations of the load, a 15-degree initial amplitude gives conservative results. Ribbon bridge airloads resemble those on a long container but with asymmetries. Dynamic behavior follows the general pattern of an intermediate hump in roll amplitude followed by stable operation at higher speeds until divergence occurs.

Aerodynamic Load Mapping of Bluff Bodies: An Update and Summary

2016 ◽  
Author(s):  
Nicholas Motahari ◽  
Dhwanil Shukla ◽  
Nandeesh Hiremath ◽  
Narayanan Komerath
Keyword(s):  
Aspect Ratio ◽  
Rectangular Prism ◽  
Circular Cylinders ◽  
Aerodynamic Load ◽  
Bluff Bodies ◽  
Aerodynamic Loads ◽  
Bridge Model ◽  
Rotation Method ◽  
Continuous Rotation ◽  
Large Interaction

Measurements of 6-DOF aerodynamic loads on bluff bodies using the continuous rotation method are summarized. New results are presented on two rectangular prisms and on three practical shapes — an Engine Canister model, a Ribbon Bridge model, and a model of a standardized aerodynamic container to carry automobiles. Efforts are described, to relate the aerodynamic loads on the practical shapes, to weighted combinations of aerodynamic loads on interpolated canonical shapes. The Engine Canister aerodynamic loads are obtained to good approximation from those on an interpolated cylinder of aspect ratio 1.9. Likewise, the Ribbon Bridge aerodynamic loads are approximated from loads on rectangular prisms and circular cylinders. An attempt is made to predict the load variation on a rectangular prism, from those measured on a prism 1/3 as long using topological arguments; this attempt shows the large interaction effects on such a shape.

Pressure Field of a Yawed Aspect Ratio 1 Circular Cylinder

2017 ◽  
Author(s):  
Nandeesh Hiremath ◽  
Dhwanil Shukla ◽  
Anshuman Pandey ◽  
James W. Gregory ◽  
Narayanan Komerath
Keyword(s):  
Aspect Ratio ◽  
Circular Cylinder ◽  
Sensor Data ◽  
Navier Stokes ◽  
Windward Side ◽  
Test Case ◽  
Single Shot ◽  
Aerodynamic Loads ◽  
Streamline Curvature ◽  
Continuous Rotation

The aerodynamic loads and the flow around an Aspect Ratio 1 circular cylinder in the range of 300K to 400K Reynolds number, pose a surprisingly rich fundamental problem. This aspect ratio demonstrates features from the ‘coin’ limit as well as the high aspect ratio limit. Well-resolved measurements of all 6 components of aerodynamic loads became possible with the Continuous Rotation method. The genesis of the side loads, drag and yawing moment on a yawed aspect ratio 1 cylinder, is examined using 3 different methods. The first is direct pressure sensing on the flat side surface using pressure taps and individual sensors, done on similar setups at two different facilities. This is of course sparse but gives direct quantitative measures for validation. The second is pressure-sensitive paint (PSP), which provides a full distribution of pressure across the surface, with high spatial resolution that is limited only by the optics of the setup. The third is to extract the surface pressure using an algorithm that uses measured three-dimensional velocity data, along with the continuity and Navier-Stokes equations with a streamline-curvature model used to obtain the initial estimate. As possible, the measurements are compared with those computed from first principles using a Navier-Stokes solver. The streamline curvature method is validated against a numerical test case for an infinite cylinder, operated in the Foppl regime. It is then applied to the AR1 cylinder test case, and found to yield satisfactory comparison with interpolated surface plots from point measurements. The single-shot/transient PIV technique is applied to obtain the pressure map on the leeside and windward side of the yawed cylinder. The results are compared to point sensor data and PSP data. Comparisons of all these are shown, and linked to prior aerodynamic load measurements and computations. Agreement is good, with reasons for disagreement and uncertainty identified.

scholarly journals A multivariate intersection over union of SiamRPN network for visual tracking

2021 ◽  
Author(s):  
Zhihui Huang ◽  
Huimin Zhao ◽  
Jin Zhan ◽  
Huakang Li
Keyword(s):  
Aspect Ratio ◽  
Visual Tracking ◽  
Target Location ◽  
Coincidence Degree ◽  
Distance Ratio ◽  
Geometric Factors ◽  
Fast Motion ◽  
Definition Of ◽  
Overlap Area ◽  
Center Distance

AbstractSiamPRN algorithm performs well in visual tracking, but it is easy to drift under occlusion and fast motion scenes because it uses $$\ell _1$$ ℓ 1 -smooth loss function to measure the regression location of bounding box. In this paper, we propose a multivariate intersection over union (MIOU) loss in SiamRPN tracking framework. Firstly, MIOU loss includes three geometric factors in regression: the overlap area ratio, the center distance ratio, and the aspect ratio, which can better reflect the coincidence degree of target box and prediction box. Secondly, we improve the definition of aspect ratio loss to avoid gradient explosion, improve the optimization performance of prediction box. Finally, based on SiamPRN tracker, we compared the tracking performance of $$\ell _1$$ ℓ 1 -smooth loss, IOU loss, GIOU loss, DIOU loss, and MIOU loss. Experimental results show that the MIOU loss has better target location regression than other loss functions on the OTB2015 and VOT2016 benchmark, especially for the challenges of occlusion, illumination change and fast motion.

Numerical study of the flow over the modified simple frigate shape

2020 ◽  
pp. 095441002097775
Author(s):  
Tong Li ◽  
Yibin Wang ◽  
Ning Zhao
Keyword(s):  
Bluff Body ◽  
Recirculation Zone ◽  
Numerical Study ◽  
Reference Value ◽  
Flow Fields ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation ◽  
Simulation Results

The simple frigate shape (SFS) as defined by The Technical Co-operative Program (TTCP), is a simplified model of the frigate, which helps to investigate the basic flow fields of a frigate. In this paper, the flow fields of the different modified SFS models, consisting of a bluff body superstructure and the deck, were numerically studied. A parametric study was conducted by varying both the superstructure length L and width B to investigate the recirculation zone behind the hangar. The size and the position of the recirculation zones were compared between different models. The numerical simulation results show that the size and the location of the recirculation zone are significantly affected by the superstructure length and width. The results obtained by Reynolds-averaged Navier-Stokes method were also compared well with both the time averaged Improved Delayed Detached-Eddy Simulation results and the experimental data. In addition, by varying the model size and inflow velocity, various flow fields were numerically studied, which indicated that the changing of Reynolds number has tiny effect on the variation of the dimensionless size of the recirculation zone. The results in this study have certain reference value for the design of the frigate superstructure.

Large Eddy Simulation of the Flow Around a Diffuser-Equipped Bluff Body in Ground Effect

2011 ◽  
Author(s):  
Lara Schembri Puglisevich ◽  
Gary Page
Keyword(s):  
Large Eddy Simulation ◽  
Bluff Body ◽  
Vortex Formation ◽  
Ground Effect ◽  
Vortical Flow ◽  
Navier Stokes ◽  
Flow Structures ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Flow Features

Unsteady Large Eddy Simulation (LES) is carried out for the flow around a bluff body equipped with an underbody rear diffuser in close proximity to the ground, representing an automotive diffuser. The goal is to demonstrate the ability of LES to model underbody vortical flow features at experimental Reynolds numbers (1.01 × 106 based on model height and incoming velocity). The scope of the time-dependent simulations is not to improve on Reynolds-Averaged Navier Stokes (RANS), but to give further insight into vortex formation and progression, allowing better understanding of the flow, hence allowing more control. Vortical flow structures in the diffuser region, along the sides and top surface of the bluff body are successfully modelled. Differences between instantaneous and time-averaged flow structures are presented and explained. Comparisons to pressure measurements from wind tunnel experiments on an identical bluff body model shows a good level of agreement.

Some Elements of Functional Analysis

2006 ◽  
Author(s):  
Jean-Yves Chemin ◽  
Benoit Desjardins ◽  
Isabelle Gallagher ◽  
Emmanuel Grenier
Keyword(s):  
Functional Analysis ◽  
Weak Solutions ◽  
Vector Fields ◽  
Stokes Equations ◽  
Stokes Operator ◽  
Navier Stokes ◽  
Navier Stokes Equations ◽  
Dual Spaces ◽  
Type Spaces ◽  
Definition Of

Before introducing the concept of Leray’s weak solutions to the incompressible Navier–Stokes equations, classical definitions of Sobolev spaces are required. In particular, when it comes to the analysis of the Stokes operator, suitable functional spaces of incompressible vector fields have to be defined. Several issues regarding the associated dual spaces, embedding properties, and the mathematical way of considering the pressure field are also discussed. Let us first recall the definition of some functional spaces that we shall use throughout this book. In the framework of weak solutions of the Navier– Stokes equations, incompressible vector fields with finite viscous dissipation and the no-slip property on the boundary are considered. Such H1-type spaces of incompressible vector fields, and the corresponding dual spaces, are important ingredients in the analysis of the Stokes operator.

Partially-averaged Navier–Stokes simulations of two bluff body flows

2016 ◽  
Vol 272 ◽  
pp. 692-706 ◽  
Author(s):  
Siniša Krajnović ◽  
Guglielmo Minelli ◽  
Branislav Basara
Keyword(s):  
Bluff Body ◽  
Navier Stokes ◽  
Bluff Body Flows
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