Dissecting the Pressure Field in Tidal Flow past a Headland: When Is Form Drag “Real”?

Abstract In the few previous measurements of topographic form drag in the ocean, drag that is much larger than a typical bluff body drag estimate has been consistently found. In this work, theory combined with a numerical model of tidal flow around a headland in a channel gives insight into the mechanisms that create form drag in oscillating flow situations. The total form drag is divided into two parts: the inertial drag, which is derived from a local potential flow solution, and the separation drag, which accounts for flow features such as eddies. The inertial drag can have a large magnitude, yet it cannot do work on the flow because its phase is in quadrature with the velocity. The separation drag has a magnitude that is nearly equal to the bluff body drag and accounts for all of the energy removed from the flow by the topography. In addition, the dependence of the form drag on the tidal excursion distance and the aspect ratio of the headlands were determined with a series of numerical experiments. This theory explains why form drag can be so large in the ocean, and it provides a method for separating the pressure field into the parts that can and cannot extract energy from the flow.

Download Full-text

Effect of splitter plate on bluff body drag

AIAA Journal ◽

10.2514/3.14297 ◽

1999 ◽

Vol 37 ◽

pp. 1125-1126 ◽

Cited By ~ 1

Author(s):

E. Rathakrishnan

Keyword(s):

Bluff Body ◽

Splitter Plate ◽

Body Drag

Download Full-text

Detection of Anomalous Diffusion with Deep Residual Networks

Entropy ◽

10.3390/e23060649 ◽

2021 ◽

Vol 23 (6) ◽

pp. 649

Author(s):

Miłosz Gajowczyk ◽

Janusz Szwabiński

Keyword(s):

Image Classification ◽

Anomalous Diffusion ◽

Numerical Experiments ◽

Driving Forces ◽

Living Cells ◽

Diffusion Type ◽

Training Time ◽

Initial Network ◽

Unseen Data ◽

Insight Into

Identification of the diffusion type of molecules in living cells is crucial to deduct their driving forces and hence to get insight into the characteristics of the cells. In this paper, deep residual networks have been used to classify the trajectories of molecules. We started from the well known ResNet architecture, developed for image classification, and carried out a series of numerical experiments to adapt it to detection of diffusion modes. We managed to find a model that has a better accuracy than the initial network, but contains only a small fraction of its parameters. The reduced size significantly shortened the training time of the model. Moreover, the resulting network has less tendency to overfitting and generalizes better to unseen data.

Download Full-text

Effects of the Main Gas Path Pressure Field on Rim Seal Flows in a Stationary Linear Cascade

Volume 5C: Heat Transfer ◽

10.1115/gt2015-43517 ◽

2015 ◽

Cited By ~ 2

Author(s):

Jeffrey Gibson ◽

Karen Thole ◽

Jesse Christophel ◽

Curtis Memory

Keyword(s):

Bluff Body ◽

Pressure Field ◽

Turbine Engines ◽

Gas Turbine Engines ◽

Baseline Design ◽

Linear Cascade ◽

Blade Row ◽

High Degree ◽

Effectiveness Data ◽

Computational Predictions

Rim seals in the turbine section of gas turbine engines aim to reduce the amount of purge air required to prevent the ingress of hot mainstream gas into the under-platform space. A stationary, linear cascade was designed, built, and benchmarked to study the effect of the interaction between the pressure fields from an upstream vane row and downstream blade row on hot gas ingress for engine-realistic rim seal geometries. The pressure field of the downstream blade row was modeled using a bluff body designed to produce the pressure distortion of a moving blade. Sealing effectiveness data for the baseline seal indicated that there was little to no ingress with a purge rate greater than 1% of the main gas path flow. Adiabatic endwall effectiveness data downstream in the trench between the vane and blade showed a high degree of mixing. Extending the seal feature associated with the vane endwall indicated better sealing than the baseline design. Steady computational predictions were found to overpredict the sealing effectiveness due to underpredicted mixing in the trench.

Download Full-text

Endwall Blockage in Axial Compressors

Journal of Turbomachinery ◽

10.1115/1.2841344 ◽

1999 ◽

Vol 121 (3) ◽

pp. 499-509 ◽

Cited By ~ 97

Author(s):

S. A. Khalid ◽

A. S. Khalsa ◽

I. A. Waitz ◽

C. S. Tan ◽

E. M. Greitzer ◽

...

Keyword(s):

Tip Clearance ◽

Design Parameters ◽

Tip Clearance Flow ◽

Axial Compressors ◽

Clearance Flow ◽

Flow Features ◽

Physical Insight ◽

Level Loading ◽

Stagger Angle ◽

Insight Into

This paper presents a new methodology for quantifying compressor endwall blockage and an approach, using this quantification, for defining the links between design parameters, flow conditions, and the growth of blockage due to tip clearance flow. Numerical simulations, measurements in a low-speed compressor, and measurements in a wind tunnel designed to simulate a compressor clearance flow are used to assess the approach. The analysis thus developed allows predictions of endwall blockage associated with variations in tip clearance, blade stagger angle, inlet boundary layer thickness, loading level, loading profile, solidity, and clearance jet total pressure. The estimates provided by this simplified method capture the trends in blockage with changes in design parameters to within 10 percent. More importantly, however, the method provides physical insight into, and thus guidance for control of, the flow features and phenomena responsible for compressor endwall blockage generation.

Download Full-text

Experimental investigation of isothermal and reacting flow characteristics downstream of axisymmetric bluff body stabilizers under stratified or fully premixed inlet mixture conditions

10.12681/eadd/48856 ◽

2020 ◽

Author(s):

Γεώργιος Πατεράκης

Keyword(s):

Experimental Investigation ◽

Turbulent Flow ◽

Bluff Body ◽

Operating Conditions ◽

Reacting Flow ◽

Wide Range ◽

Flow Features ◽

Air Mixing ◽

The Impact ◽

Stratified Flames

The current work describes an experimental investigation of isothermal and turbulent reacting flow field characteristics downstream of axisymmetric bluff body stabilizers under a variety of inlet mixture conditions. Fully premixed and stratified flames established downstream of this double cavity premixer/burner configuration were measured and assessed under lean and ultra-lean operating conditions. The aim of this thesis was to further comprehend the impact of stratifying the inlet fuelair mixture on the reacting wake characteristics for a range of practical stabilizers under a variety of inlet fuel-air settings. In the first part of this thesis, the isothermal mean and turbulent flow features downstream of a variety of axisymmetric baffles was initially examined. The effect of different shapes, (cone or disk), blockage ratios, (0.23 and 0.48), and rim thicknesses of these baffles was assessed. The variations of the recirculation zones, back flow velocity magnitude, annular jet ejection angles, wake development, entrainment efficiency, as well as several turbulent flow features were obtained, evaluated and appraised. Next, a comparative examination of the counterpart turbulent cold fuel-air mixing performance and characteristics of stratified against fully-premixed operation was performed for a wide range of baffle geometries and inlet mixture conditions. Scalar mixing and entrainment properties were investigated at the exit plane, at the bluff body annular shear layer, at the reattachment region and along the developing wake were investigated. These isothermal studies provided the necessary background information for clarifying the combustion properties and interpreting the trends in the counterpart turbulent reacting fields. Subsequently, for selected bluff bodies, flame structures and behavior for operation with a variety of reacting conditions were demonstrated. The effect of inlet fuel-air mixture settings, fuel type and bluff body geometry on wake development, flame shape, anchoring and structure, temperatures and combustion efficiencies, over lean and close to blow-off conditions, was presented and analyzed. For the obtained measurements infrared radiation, particle image velocimetry, laser doppler velocimetry, chemiluminescence imaging set-ups, together with Fouriertransform infrared spectroscopy, thermocouples and global emission analyzer instrumentation was employed. This helped to delineate a number of factors that affectcold flow fuel-air mixing, flame anchoring topologies, wake structure development and overall burner performance. The presented data will also significantly assist the validation of computational methodologies for combusting flows and the development of turbulence-chemistry interaction models.

Download Full-text

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

Volume 6: Fluids and Thermal Systems; Advances for Process Industries, Parts A and B ◽

10.1115/imece2011-62673 ◽

2011 ◽

Cited By ~ 2

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.

Download Full-text

Oscillatory flow regimes around four cylinders in a diamond arrangement

Journal of Fluid Mechanics ◽

10.1017/jfm.2019.609 ◽

2019 ◽

Vol 877 ◽

pp. 955-1006 ◽

Cited By ~ 2

Author(s):

Chengjiao Ren ◽

Liang Cheng ◽

Feifei Tong ◽

Chengwang Xiong ◽

Tingguo Chen

Keyword(s):

Oscillatory Flow ◽

Bluff Body ◽

Substantial Reduction ◽

Period Doubling ◽

Flow Regimes ◽

Mode Competition ◽

Single Type ◽

Phase Dynamics ◽

Flow Features ◽

Four Cylinders

Oscillatory flow around a cluster of four circular cylinders in a diamond arrangement is investigated using two-dimensional direct numerical simulation over Keulegan–Carpenter numbers (KC) ranging from 4 to 12 and Reynolds numbers (Re) from 40 to 230 at four gap-to-diameter ratios (G) of 0.5, 1, 2 and 4. Three types of flows, namely synchronous, quasi-periodic and desynchronized flows (along with 14 flow regimes) are mapped out in the (G, KC, Re)-parameter space. The observed flow characteristics around four cylinders in a diamond arrangement show a few unique features that are absent in the flow around four cylinders in a square arrangement reported by Tong et al. (J. Fluid Mech., vol. 769, 2015, pp. 298–336). These include (i) the dominance of flow around the cluster-scale structure at $G=0.5$ and 1, (ii) a substantial reduction of regime D flows in the regime maps, (iii) new quasi-periodic (phase trapping) $\text{D}^{\prime }$ (at $G=0.5$ and 1) and period-doubling $\text{A}^{\prime }$ flows (at $G=1$) and most noteworthily (iv) abnormal behaviours at ($G\leqslant 2$) (referred to as holes hereafter) such as the appearance of spatio-temporal synchronized flows in an area surrounded by a single type of synchronized flow in the regime map ($G=0.5$). The mode competition between the cluster-scale and cylinder-scale flows is identified as the key flow mechanism responsible for those unique flow features, with the support of evidence derived from quantitative analysis. Phase dynamics is introduced for the first time in bluff-body flows, to the best knowledge of the authors, to quantitatively interpret the flow response (e.g. quasi-periodic flow features) around the cluster. It is instrumental in revealing the nature of regime $\text{D}^{\prime }$ flows where the cluster-scale flow features are largely synchronized with the forcing of incoming oscillatory flow (phase trapping) but are modulated by localized flow features.

Download Full-text

Aerodynamic Behavior of Asymmetric Jets in 3-D Furnaces

Volume 3: Coal, Biomass and Alternative Fuels; Combustion and Fuels; Oil and Gas Applications; Cycle Innovations ◽

10.1115/94-gt-441 ◽

1994 ◽

Author(s):

F. M. El-Mahallawy ◽

M. A. Hassan ◽

M. A. Ismail ◽

H. Zafan

Keyword(s):

Numerical Simulation ◽

Flow Pattern ◽

Numerical Experiments ◽

Recirculation Zone ◽

Reverse Flow ◽

Three Dimensional ◽

Flow Region ◽

Stabilization Method ◽

Flow Features

The purpose of this paper is to present and evaluate numerical experiments illustrating the flow features in a 3-D furnace utilizing unconventional asymmetrical jet that creates natural recirculation zone. The numerical simulation of this aerodynamic stabilization method have unveiled the three-dimensional nature of the flow pattern which possesses a quite large reverse flow region. The size and strength of the built recirculation zone would be capable of stabilizing the burning of low-quality fuels.

Download Full-text