Characterizing and Contrasting Flow Separation on Steady and Maneuvering Bodies of Revolution at High Reynolds Numbers
Abstract
Underwater vehicles (UVs) will play an essential role in subsea and seabed warfare where they are increasingly required to perform precise, low-speed maneuvers such as station keeping, dynamic positioning, and loitering. These vehicles often have smoothly-curved geometries making their hydrodynamics challenging to predict and operate effectively at various flow angles, sometimes utilizing auxiliary propulsion devices. Accurate prediction of forces and moments is crucial for designing these devices, developing operational concepts, and validating control systems. Flow separations on the surfaces of UVs are a major contributor to hydrodynamic behavior and depend on various factors like flow history, laminar-turbulent transitions, streamline curvature, pressure gradients, hull roughness, and external variables such as body motions and changing incidence angles due to currents. Intrinsic flow forcing can also occur in steady flows due to large-scale shedding phenomena. Similar challenges are faced in the aircraft industry, for example during military transport aircraft short take-off and landing as well as high- and low-altitude unloading or on aft sections of helicopter fuselage and short-length s-shaped engine intakes of (stealth) fighters.For this project, an investigation and physical description of the flow separation process on smooth, double-curved convex bodies of revolution, such as the canonical 6:1 prolate spheroid geometry using recent advances in measurement techniques is proposed. Detailed measurement campaigns shedding light on the wall-shear stress distribution and near-wall vorticity distribution will help to understand how upstream parameters, along with time-varying boundary conditions, affect the onset and evolution of the flow separation process both in time and space. In parallel, these detailed measurement campaigns will provide baseline data needed in order to support model development in RANS and wall-modeled LES. The investigation will be conducted at the GWB water-tunnel facility located at the Institute of Fluid Mechanics (TU Braunschweig). These measurements will allow us to address the following objectives in a systematic manner:- Characterize the competing effects of streamwiseversus circumferential pressure gradients on the flow-separation process at high Reynolds numbers by systematically varying the stern geometry from 3:1 down to 1:1 ratio, while keeping the forward geometry constant at 3:1;- By introducing axial accelerations to the model, we will characterize the influence of time varying boundary conditions (memory effects) on the flow-separation process while matching the steady pressure gradients obtained in the initial study with stern-geometry modifications; and- Develop a low-order representation (i.e. scaling) for the flow-separation process by contrasting data obtained in both the steady and dynamic experiments with the goal to determine whether, and if so by how much, memory effects play a role in the ensuing flow-separation.We will specifically integrate replaceable stern geometries of varying aspect ratios constructed specifically to enable time-resolved pressure sensing as well as time resolved temperature-sensitive paint (TSP) measurements. In parallel Lagrangian particle tracking (LPT) in theform of Shake-the-Box measurements will be conducted in order to extract and also link the vorticity formation in the separation region. In the second portion of the research project we will introduce the time-varying boundary condition, as a generalization for maneuvering, via an axial (streamwise) acceleration or deceleration overtop of the baseline tunnel flow. By introducing forcing into the flow field via model acceleration we intend to not only shed light on the modification of the flow-separation process and hence the importance of memory effects on surfaces but to also contrast these dynamic results against the steady-separation data obtained earlier on.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 09, 2024
- Source ID
- N629092412115
Entities
People
- David E. Rival
Organizations
- Office of Naval Research
- TU Braunschweig
- United States Navy