High-speed Underwater Vehicle Research Articles

High-fidelity simulations of boundary layer transition on an underwater axisymmetric body with stability theory

During the cruise status of an underwater high-speed vehicle, the flow around the vehicle's head typically transitions from a laminar to a turbulent state, triggering flow noise that can interfere with the normal operation of sonar. In order to accurately investigate this flow noise through numerical simulation, a high-fidelity turbulent flow field solution is essential. Common traditional turbulence numerical simulation methods, such as unsteady Reynolds-averaged simulation and large eddy simulation (LES), struggle to capture high-frequency turbulent fluctuations accurately due to their inability to directly resolve small-scale eddy structures, which results in compromising the simulation accuracy of high-frequency flow noise. To address this issue, this paper employs direct numerical simulation (DNS) to achieve high-fidelity resolution of the turbulent flow field, thereby enabling a more accurate assessment of flow noise distribution on the vehicle's surface. Meanwhile, considering significant computational resources required to solve the entire flow field in an underwater high Reynolds number environment, this study also incorporates the fixed transition modeling method and stability theory to confine the DNS computational domain to the vicinity of the transitional zone to improve simulation efficiency. Comparative analysis of flow noise monitoring results in the laminar, transitional, and turbulent zones revealed that the flow noise source in the laminar zone exhibits the lowest amplitude across all frequencies, while the flow noise source in the transitional zone features the highest amplitude, approximately 10 dB higher than that in the turbulent zone. Moreover, significant amplitudes in high-frequency components (above 30 kHz) are detected in both the transition and turbulent zones. Additionally, this study employs LES with the Smagorinsky model to simulate the flow field within the same computational domain as DNS, demonstrating the limitations of the Smagorinsky model-based LES in capturing high-frequency flow noise.

High-fidelity simulations of boundary layer transition on an underwater axisymmetric body with stability theory

During the cruise status of an underwater high-speed vehicle, the flow around the vehicle's head typically transitions from a laminar to a turbulent state, triggering flow noise that can interfere with the normal operation of sonar. In order to accurately investigate this flow noise through numerical simulation, a high-fidelity turbulent flow field solution is essential. Common traditional turbulence numerical simulation methods, such as unsteady Reynolds-averaged simulation and large eddy simulation (LES), struggle to capture high-frequency turbulent fluctuations accurately due to their inability to directly resolve small-scale eddy structures, which results in compromising the simulation accuracy of high-frequency flow noise. To address this issue, this paper employs direct numerical simulation (DNS) to achieve high-fidelity resolution of the turbulent flow field, thereby enabling a more accurate assessment of flow noise distribution on the vehicle's surface. Meanwhile, considering significant computational resources required to solve the entire flow field in an underwater high Reynolds number environment, this study also incorporates the fixed transition modeling method and stability theory to confine the DNS computational domain to the vicinity of the transitional zone to improve simulation efficiency. Comparative analysis of flow noise monitoring results in the laminar, transitional, and turbulent zones revealed that the flow noise source in the laminar zone exhibits the lowest amplitude across all frequencies, while the flow noise source in the transitional zone features the highest amplitude, approximately 10 dB higher than that in the turbulent zone. Moreover, significant amplitudes in high-frequency components (above 30 kHz) are detected in both the transition and turbulent zones. Additionally, this study employs LES with the Smagorinsky model to simulate the flow field within the same computational domain as DNS, demonstrating the limitations of the Smagorinsky model-based LES in capturing high-frequency flow noise.

Dynamic Testing of a Hybrid-Propellant Water-Breathing Ram Rocket in Underwater Cruise Conditions

High-speed submerged marine vehicles, such as torpedoes, traveling at velocities of an order of 100 m/s and above, require powerful propulsion to overcome the tremendous hydrodynamic drag. This paper aims to investigate a marine hybrid-propellant water-breathing ram rocket (marine ramjet or ducted rocket) under various underwater cruise conditions. At high underwater cruise speeds, the ram rocket outperforms regular rocket motors, substantially increasing its specific impulse and thrust. This investigation utilized a unique test facility capable of dynamically testing the marine ramjet. Over 20 dynamic experiments have been conducted, revealing the submerged motor characteristics at different cruise speeds, water-to-propellant mass ratios, and oxidizer-to-fuel mass ratios, thereby creating a performance map of the marine ramjet. The results were compared with static firing data and theoretical calculations, showing a good agreement with standard specific impulse improvement of about 55% compared to a regular hybrid rocket, reaching a maximum value of 380 s. The significant increase in performance demonstrates the potential of the water-breathing ramjet for propelling high-speed underwater vehicles.

Structural Stability Analysis of Underwater High-Speed Moving Vehicles in Supercavity Flow Velocity

The purpose of this paper is to analyze the structural stability of an underwater high-speed vehicle. The drag characteristics of a moving body moving at high speed in water were analyzed, and a stability analysis of the structure was performed by applying the non-conservative property according to the driven force in a rocket propulsion environment. To this end, the fluid characteristics that enable high-speed maneuvering in an underwater environment were described, and the structural stability was analyzed by simplifying modeling by increasing the resulting drag. In addition, for high-speed underwater movement, an analysis of the following force according to drag and axial load and the effect on structural stability was conducted by simplifying the structure attached to a specific location when a supercavitation occurs.

Optimized design of the overall shapes of supercavitating vehicles based on a multi-objective adaptive genetic algorithm

The supercavitating vehicle is a new generation of high-speed underwater vehicles enveloped by a large bubble of gas or vapor (i.e., a supercavity) to reduce navigation resistance by an order of magnitude, except for the head and tail. However, due to the limited hydrodynamic forces, it is difficult to ensure stable motion. The overall shape of the vehicle is not only the critical factor to ensure a suitable relative position between the vehicle and its supercavity for stable motion, but also directly affects the ease of generation and development of the supercavity. Therefore, this study focuses on the characteristic parameters of the overall shape of the vehicle and first establishes a multi-objective optimization model based on the dynamic model of the supercavitating vehicle with the incipient supercavitation number and the vehicle volume as the optimization objectives. Then, given the relatively good global, robust and universal characteristics of the adaptive genetic algorithm compared to other algorithms, a multi-objective optimization algorithm is developed and improved using the subsection optimization method for the main optimization variable. The characteristic parameters of the overall shapes are optimized for natural and ventilated supercavitating vehicles using the algorithm based on the multi-objective optimization model so that it is easier to create a supercavity under the conditions of the same flow and force equilibrium and the vehicle has a larger volume. By optimizing the vehicles under different navigation depths and slenderness ratios, the design rules for the characteristic parameters of the overall shape and the control surface parameters are obtained based on the optimization objectives, and the motion state and hydrodynamic characteristics of the optimized vehicles are revealed.

Experimental Investigation on Aluminum-Based Water Ramjet for Propelling High-Speed Underwater Vehicles

Major challenges in developing and realizing a novel aluminum–water reaction-based water ramjet propulsion system for high-speed underwater vehicles and demonstration of a water-breathing jet propulsion test facility are investigated. Two stages of combustion, propellant grain combustion and subsequent water combustion, with primary combustion products are adopted. High-pressure-molded propellant grains up to 45% of micro–nano () aluminum were prepared and combusted in the primary chamber, which exhibits mild ignition delay, and a residue of 4–6% was retained. Once water is injected into the secondary chamber, the net thrust generation is increased more than twice from the exhaust jet and improves the specific impulse by 40%. The lean fuel conditions in the secondary chamber lead to reduction in combustion propensity, which causes drop in efficiency. The ultrafine iron-oxide-catalyzed micro–nano blended propellants marginally improved the propulsive performance than the uncatalyzed compositions. The efficiency of the catalyzed propellants was enhanced up to 38.6%. Aluminum agglomeration in primary combustion considerably occurred; apparently, only a fraction of aluminum particles or agglomerates are completely burnt within the secondary chamber, and the remaining aluminum particles are either partially burnt or go unreacted.

Numerical investigation of ventilated cavitating flow from high to low cavitation numbers

Cavitation occurs when an underwater vehicle moves at a high speed, causing the water to change from the liquid phase into the vapour phase in the low-pressure region. As one of the most efficient drag reduction technologies for high-speed underwater vehicles, the artificially ventilated cavitation flow needs to be studied. In this paper, the ventilated cavitating flow over a high-speed underwater vehicle is analysed with a multi-phase solver from high to low natural cavitation numbers. The large eddy simulation turbulence model, volume of fluid method and Kunz cavitation model are used in the numerical calculation to simulate and capture the three-phase (air, liquid water, and vapour) cavitation flow. The miscibility of the air and vapour phases inside the cavity is also considered in the simulation. To validate the solver, two benchmark cases with air ventilated into a cavitating flow are simulated. Then the characteristics of the ventilated cavitating flows from a high to low natural cavitation number are analysed to study the development of the ventilated cavity with miscible air and vapour inside it. The results show that air ventilation can prevent pressure fluctuations at the surface of an underwater vehicle caused by cloud cavitating flow at a moderate natural cavitation number. Compared to no ventilation, drag reduction of ventilated cavitating flow can reach up to about 85% at a low cavitation number.

Data Enhancement of Underwater High-Speed Vehicle Echo Signals Based on Improved Generative Adversarial Networks

Underwater target recognition is currently one of the hottest topics in computational intelligence research. However, underwater target recognition tasks based on deep learning techniques are difficult to conduct due to the shortage of acoustic echo signal samples, which results in poor training performance for existing deep learning models. Generative adversarial networks (GANs) have been widely used in data enhancement and image generation, providing a novel strategy for dealing with challenges in the research field mentioned above. To address the insufficiency of echo signal data for underwater high-speed vehicles, this paper proposes an underwater echo signal data enhancement method that uses an improved GAN based on convolution units for small sample sizes. First, we take pool test data as the training sample input and carry out data standardization, data interception, and copy-related processing work. Secondly, this paper proposes an improved generative adversarial network underwater (IGAN-UW) model to generate underwater echo signals. Finally, a CNN model combines the generated data with the original data to conduct classification training for underwater targets. Experimental results show that the IGAN-UW model is suitable for the generation of highly realistic original echo signals in cases with small sample sizes, providing a new approach to the active detection and recognition of underwater targets.

Adaptive Controller Design for Dynamic Maneuvers of High Speed Underwater Vehicles

Adaptive Controller Design for Dynamic Maneuvers of High Speed Underwater Vehicles

Computational investigation on ventilated supercavitating flows and its hydrodynamic characteristics around a high-speed underwater vehicle

Notwithstanding the effectiveness of ventilated cavitation as a safe way to accelerate and achieve natural supercavitation, detailed physics of ventilated cavitating flows and hydrodynamic effects on underwater vehicles have been rarely explored. The present work deals with computational investigation on ventilated supercavitating flows around a high-speed underwater vehicle and its hydrodynamic characteristics. The homogeneous mixture model is adopted for describing the cavitating flow field composed of water, water vapor, and a ventilated gas. After extensively validating the flow solver with experiments of ventilated cavitating flows, we carry out a series of computations of supercavitating flows around a high-speed underwater vehicle with four control fins, and investigate the flow physics and the vehicle’s hydrodynamic characteristics. The computations are performed under different freestream velocities, ventilation rates, and angles of attack. Furthermore, the unsteady effects of turbulence are examined by comparing the computed results based on unsteady Reynolds-Averaged Navier–Stokes (URANS) simulation and Detached Eddy Simulation (DES).The computational results show that the cavitating flows cause substantial nonlinear characteristics in cavity shapes and hydrodynamic forces such as lift, drag, and pitching moment, due to the presence of natural and ventilated cavitations and their interaction. This can be beneficially exploited in understanding and predicting ventilated supercavitating flows around a high-speed underwater vehicle, and establishing an accurate dynamic model of the vehicle’s motion.

Investigation of a Marine Water-Breathing Hybrid Ram-Rocket Motor

This work presents theoretical and experimental performance studies and a general scheme of an innovative concept for propelling marine high-speed underwater vehicles, a water-breathing hybrid ram rocket. The water-augmented hybrid ram rocket enables obtaining superior performance relatively to a standard rocket and improved performance relatively to a parallel water–augmented solid ram rocket. In addition, it demonstrates improved safety and controllability due to the hybrid motor characteristics. The theoretical model incorporated data from a thermochemical program. The experimental investigation was based on static firing tests of hybrid rocket motors augmented by the addition of water during combustion. The study focused on the use of a non-water-reactive propellant combination, cured polyester as fuel and gaseous oxygen as oxidizer. Wide ranges of oxidizer-to-fuel and water-to-propellant ratios were considered. The experimental results showed a significant improvement (up to 70%) in specific impulse, relatively to a non-water-augmented hybrid rocket, in good accordance with the theoretical results. It is concluded that for standard chamber pressure of 6.9 MPa, corresponding to the ram pressure for cruising at , a specific impulse greater than 400 s can be achieved by a water-augmented hybrid ram rocket using a non-hydro-reactive fuel.

Free surface and near-wall effects on the cloud cavitating flow over an axisymmetric projectile

For high-speed underwater vehicles, cavitation can be one of the most important speed barriers. The cavitating flow can be even complex when an underwater vehicle is sailing close to the free surface/wall. In this study, the mutual effects of the free surface and near-wall on the cloud cavitating flow that surrounds an axisymmetric projectile are investigated by water tank experiment and the computational fluids dynamics (CFD). The Split-Hopkinson pressure bar (SHPB) technology is applied in the experiment to accelerate the projectile in a short time. In our numerical approach, the volume of fluid (VOF) method, the large eddy simulation (LES) turbulence model, and the Zwart-Gerber-Belamri (ZGB) cavitation model are used. The cloud cavitating flow under the free surface/wall effect is investigated by changing the distance between the projectile and free surface (df) or wall (dw). Both the experiment and the simulation show that the unstable cavity evolution includes four stages induced by the re-entrant jet: cavity growth, re-entrant jet, cavity shedding and collapsing. The results further show that as df decreases, the cavity length is shorter and the cavity becomes more stable; as dw decreases, the cavity length is longer and the cavity becomes less stable. By understanding the free surface/wall effect on the stability of the cloud cavitating flow, the parameters space spanned by df and dw can be divided into several distinct flow regimes, in which the entire shedding cavity (symmetry/asymmetry), steady and non-shedding cavity, partial cavity shedding, and ventilated cavity are identified.

Dynamics modeling and motion control for high-speed underwater vehicles using H-infinity synthesis with anti-windup compensator

The control synthesis of a high-speed supercavitating vehicle (HSSV) faces many difficulties such as the stability, control, and maneuvering with dynamical uncertainties due to parameter perturbations, external disturbances, unmodeled dynamics, measurement noises, and actuator constraints. Inspired by the HSSV dynamical analysis, this paper proposes the H∞ (i.e. "H-infinity") robust control synthesis to generate a robust low-order controller, which is intended for real implementations to ensure active control actions. Particularly, the presented control scheme includes a feedback component and an anti-windup compensator. The anti-windup synthesis is to provide system stability under actuator saturations. Extensive simulations show that the designed controller provides good performances with high robustness for vertical plane manoeuver while effectively eliminating planning forces, exogenous disturbances and noises as well as overcoming cavitator saturations.

Investigation of ventilation demand variation in unsteady supercavitation

Understanding the air injection strategy of a ventilated supercavity is important for designing high-speed underwater vehicles wherein an artificial gas pocket is created behind a flow separation device to reduce skin friction. Our study systematically investigates the effect of flow unsteadiness on the ventilation requirements to form (CQf) and collapse (CQc) a supercavity. Imposing flow unsteadiness on the incoming flow has shown an increment in higher CQf at low free stream velocity and lower CQf at high free stream velocity. High-speed imaging reveals distinctly different behaviors in the recirculation region for low and high freestream velocity under unsteady flows. At low free stream velocities, the recirculation region formed downstream of a cavitator shifted vertically with flow unsteadiness, resulting in lower bubble collision and coalescence probability, which is critical for the supercavity formation process. The recirculation region negligibly changed with flow unsteadiness at high free stream velocity and less ventilation is required to form a supercavity compared to that of the steady incoming flow. Such a difference is attributed to the increased transverse Reynolds stress that aids bubble collision in a confined space of the recirculation region. CQc is found to heavily rely on the vertical component of the flow unsteadiness and the free stream velocity. Interfacial instability located upper rear of the supercavity develops noticeably with flow unsteadiness and additional bubbles formed by the distorted interface shed from the supercavity, resulting in an increased CQc. Further analysis on the quantification of such additional bubble leakage rate indicates that the development and amplitude of the interfacial instability accounts for the variation of CQc under a wide range of flow unsteadiness. Our study provides some insights on the design of a ventilation strategy for supercavitating vehicles in practice.

Analysis of Motion Characteristics of a Controllable Ventilated Supercavitating Vehicle Under Accelerations

Abstract The development of a maneuverable underwater high-speed vehicle is worthy of attention and study using supercavitation drag reduction theory and technology. The supercavity shape determines the hydrodynamics of the vehicle, and especially during a maneuver, its unsteady characteristics have a significant impact on the motion stability of the vehicle. The three-dimensional dynamic model of a ventilated supercavitating vehicle is established using the unsteady supercavity dynamic model based on the rigid body dynamics theory as an extension of the vehicle's longitudinal dynamic model in our recent work. The vehicle's accelerating and decelerating motions are simulated in the straight flight state using a self-developed numerical method based on the vehicle's dynamic model with the designed control law. Motion characteristics are analyzed on the evolution laws of the vehicle's motion state variables and control variables and the supercavity's characteristic parameters (i.e., ventilation cavitation number, supercavity maximum diameter, and supercavity length) in the acceleration motions. The evolution laws in the accelerating and decelerating motions are compared, and the effects of the acceleration on the laws are further analyzed. This study lays the foundation for the in-depth study of the hydrodynamic characteristics and motion stability of ventilated supercavitating vehicles in maneuvering states.

Experimental Study on the Unsteady Natural Cloud Cavities: Influence of Cavitation Number on Cavity Evolution and Pressure Pulsations

High-speed underwater vehicles are subjected to complex multiphase turbulent processes, such as the growth, development, shedding, and collapse of cavitation bubbles. To study the cavity evolution and pressure pulsation characteristics, in this paper, cloud cavitation over a conical axisymmetric test body with four pressure sensors is investigated. A multi-field simultaneous measurement experiment method for the natural cavitation of underwater vehicles is proposed to understand the relationship between cavity evolution and instantaneous pressure. The results show that the evolution of cloud cavitation can be mainly divided into three stages: (I) the growth process of the attached cavity, (II) the shedding process of the attached cavity, and (III) the collapse of detached cavities. The evolution of the attached cavity and collapse of the large-scale shedding cavity will cause strong pressure pulsations. It is found that the cavitation number plays an important role in cavitation evolution and pressure pulsation. Interestingly, as the cavitation number decreases, the fluctuation intensity of cavitation increases significantly and gradually presents obvious periodicity. Moreover, the unstable cavitating flow patterns are highly correlated with the time domain and frequency domain characteristics of pressure. Especially, as the cavitation number decreases, the main frequency becomes lower and the pressure band becomes more concentrated.

Study of the Operating Characteristics for the High-Speed Water Jet Pump Installed on the Underwater Vehicle with Different Cruising Speeds

Due to the higher propulsive efficiency, lesser vibration, and better maneuverability, the water jet pump is widely applied to high-speed underwater vehicles. By taking a newly developed water jet pump system as the object, the corresponding underwater vehicle’s operating characteristics affected by different cruising speeds (15.43, 30.86, and 52.47 m/s) were investigated. The steady results reply that the cruising speed increase will result in the decline of the overall performances comprised of the head, the efficiency, the thrust, and the power. While, by using different analyzing methods, the unsteady results are listed as follows: (1) The energy loss theory denotes that the increasing cruising speed promoted the kinetic energy diffusion from the Reynolds stress and viscous stress and depress the turbulent kinetic energy production and the viscous dissipation. (2) The statistical PLS method reveals that the tip load effect on the leakage flow becomes weaker when the cruising speed becomes larger, while the effect from the scraping pressure has a completely opposite trend. (3) Further unsteady analysis implies that the increasing cruising speed makes the pressure pulsation larger and makes the radial force, the axial force, and the cloudy cavity size smaller.

Effect of Acoustic Shock on Submarine

The carried-out analysis of the dynamics of a submarine body’s translational motion affected by an acoustic shock in the ideal medium provides for the possibility to evaluate the physical properties of the medium and elastic properties of the external body of the submarine to the value of limited motion of a submersible vehicle. The results of analysis provide for the possibility to conduct a comparative analysis of the submersible vehicle’s translational motion affected by an acoustic shock, taking into account the peculiarities of the motion medium, or rather taking into account the viscosity of the real medium. In this work, evaluative measurements of the features of moving the layout of the submarine were carried out. The limiting values of the displacement of the layout of the submarine are established for the case of the presence of an external artificial diffuse disturbance. A fluid with air bubbles from a compressed air cylinder was used to create an artificial diffuse perturbation. Such conditions are possible with intensive local bombardment or the presence of other high-speed underwater vehicles involved in local underwater operations.

Signal synchronization method for depth information transmission of high-speed underwater vehicle

Signal synchronization method for depth information transmission of high-speed underwater vehicle

Theoretical analysis and experimental research of non-cavitation noise on underwater counter-rotation propellers

The non-cavitation noise of counter-rotation propeller is a key factor for detection and recognition of underwater high-speed vehicles. This paper presents a theoretical analysis and a hybrid numerical simulation method of underwater counter-rotation propeller non-cavitation noise. An experimental verification is also included. The sound pressure spectrum model is presented to describe the non-cavitation noise of a counter-rotation propeller with application of generalised acoustic analogy method. The counter-rotation propeller noise is predicted using the frequency-domain acoustic analogy. The flow field is analysed by computational fluid dynamics based on the viscous flow theory. The flow field pressure is used for the acoustic spectrum prediction. The numerical simulation results are verified by a cavitation-tunnel experiment. Throughout the study, the counter-rotation propeller non-cavitation noise is analysed. The overall results indicate that the numerical approach is reliable for predicting non-cavitation noise of counter-rotation propeller, which is beneficial for characteristics extraction and identification of underwater high-speed vehicles.