Vehicle Wake Research Articles

Optical Detection of Underwater Propeller Wake Based on a Position-Sensitive Detector

The study of underwater vehicle wake detection is of significant importance within the field of target detection, localisation, and tracking of underwater vehicles. Given that propellers are the propellers of modern ships and underwater vehicles, the propeller wake field represents the principal target source for wake detection in underwater vehicles. The objective of this paper is to propose a method for measuring the wake of an underwater propeller based on a position-sensitive detector. A theoretical model of the relationship between the laser spot displacement and the change in the refractive index of the wake field is established on the basis of the principle of laser beam deflection. A prototype experimental setup for underwater propeller wake measurement was constructed based on the aforementioned optical measurement method. Furthermore, the simulation of the propeller wake flow field with strong density stratification and linear density stratification was conducted based on the experimental setup. Furthermore, experiments were conducted to detect the flow field of a propeller wake. The experimental results indicate that the wake dissipation times of the propeller in a strong density-stratified water environment are approximately 800 s and 750 s. Following the stabilisation of the wake field density, the laser spot position is observed to be stable at 0.341 mm and 0.441 mm, respectively, with a corresponding refractive index change of 2.99 × 10−6 RIU (refractive index unit) and 3.87 × 10−6 RIU, respectively. These experimental results are found to be in general agreement with the simulation results of the propeller wake field. A comparison of the experimental wake measurements based on the device with the wake measurements based on a CTD (conductivity–temperature–depth) device reveals a consistent trend. The realisation of this detection technique is of great significance for the advancement of research in the field of optical detection of underwater vehicle wake streams.

Influence of Vehicle Wake on the Control of Towed Systems

Influence of Vehicle Wake on the Control of Towed Systems

Influence of inflow conditions on simplified heavy vehicle wake

In the current study, the impact of various inflow conditions, including turbulent wind profiles and turbulent intensity, on the wake flow topology of a simplified ground transportation system (GTS) model was investigated using the improved delayed detached eddy simulation. The reliability and accuracy of the numerical method adopted in this paper were verified against the results comprising the aerodynamic drag and the wake flow structure of the GTS model obtained from the large eddy simulation and the experimental data. The research results indicate that turbulent winds characterized by logarithmic and uniform velocity profiles resulted in significantly different wake flow topologies yet exhibit the same dominant frequency. The turbulent intensity also plays a crucial role in the wake of the GTS model. It is observed that an increase in turbulence intensity corresponds with a rise in the aerodynamic drag. Specifically, when the turbulence intensity is set at 15%, there is a 3.68% increase in the aerodynamic drag of the GTS model compared to a case where the turbulence intensity was only 5%. In addition, the turbulent intensity is critical to the dominant frequency characteristics of the wake region of the GTS model. These results demonstrate that both the velocity profiles and the turbulence intensities significantly influence the wake flow topology and aerodynamic drag of the GTS model, providing a valuable reference for establishing appropriate inflow conditions and exploring the formation mechanism of flow topology in the wake of the GTS model.

High-Sensitivity Seawater Refraction Index Optical Measurement Sensor Based on a Position-Sensitive Detector.

The refractive index of seawater is one of the essential parameters in ocean observation, so it is necessary to achieve high-precision seawater refractive index measurements. In this paper, we propose a method for measuring the refractive index of seawater, based on a position-sensitive detector (PSD). A theoretical model was established to depict the correlation between laser spot displacement and refractive index change, utilizing a combination of a position-sensitive detector and laser beam deflection principles. Based on this optical measurement method, a seawater refractive index measurement system was established. To effectively enhance the sensitivity of refractive index detection, a focusing lens was incorporated into the optical path of the measuring system, and simulations were conducted to investigate the impact of focal length on refractive index sensitivity. The calibration experiment of the measuring system was performed based on the relationship between the refractive index of seawater and underwater pressure (depth). By measuring laser spot displacement at different depths, changes in displacement, with respect to both refractive index and depth, were determined. The experimental results demonstrate that the system exhibits a sensitivity of 9.93×10-9 RIU (refractive index unit), and the refractive index deviation due to stability is calculated as ±7.54×10-9 RIU. Therefore, the feasibility of this highly sensitive measurement of seawater refractive index is verified. Since the sensitivity of the refractive index measurement of this measurement system is higher than the refractive index change caused by the wake of underwater vehicles, it can also be used in various applications for underwater vehicle wake measurement, as well as seawater refractive index measurement, such as the motion state monitoring of underwater navigation targets such as AUVs and ROVs.

Effect of underwater vehicle wake on sound propagation characteristics in stratified medium

Due to the uneven distribution of seawater temperature and salinity, the density distribution at different depths is different, thus forming a density step layer with a certain gradient. Acquiring the wake internal wave field generated by underwater vehicles passing through this layered structure and mastering its modulation characteristics for the sound field can provide new technical support for the tracking and identification of underwater vehicles. In this paper, the real size model of a certain type of underwater vehicle is taken as the research object to explore the characteristics of its wake internal wave field, and the influence of navigation parameters on the wake field and the change of winning characteristics under the influence of internal waves are simulated and analyzed. The results show that the navigation parameters of underwater vehicles have obvious influence on the wake field, and then have specific influence on the sound field structure in a certain range, especially on the sound signal of the sound field.

STUDY OF AERODYNAMIC WAKE ANALYSIS OF SUV CARS FOR IMPROVING FUEL CONSUMPTION

SUV cars are known to be some of the most fuel-inefficient vehicles on the road. This is due in part to their large size and shape, which create a lot of aerodynamic drag. The wake region behind an SUV car is particularly turbulent, which further increases drag. The aim of this study of aerodynamic wake analysis of SUV cars for improving fuel consumption is to identify and quantify the factors that contribute to aerodynamic drag in SUV cars, and to develop strategies for reducing drag and improving fuel economy. Identify the factors that contribute to aerodynamic drag in SUV cars. This will involve understanding the flow dynamics of the wake region behind SUV cars and identifying the key features of the wake that contribute to drag. Develop strategies for reducing the size and strength of the wake. This will involve developing methods for modifying the shape of the SUV car or the flow around it in order to reduce drag. Assess the impact of wake reduction on fuel economy. This will involve conducting wind tunnel tests or CFD simulations to determine how changes in the wake affect the overall drag of the SUV car. This study researches the streamlined wake of SUV vehicles to distinguish amazing open doors for diminishing drag. Wind tunnel tests and CFD analysis are utilized to examine the stream designs around and behind an assortment of SUV models. The outcomes show that the streamlined wake of SUV vehicles is described by two enormous vortices. These incorporate diminishing the detachment point at the back of the vehicle, streamlining the backside of the vehicle, and utilizing streamlined gadgets like spoilers and diffusers. In this comparative study we designed and developed a prototype of a conventional SUV body with square back to analyse the actual drag and wake behind the vehicle using CFD analysis and Wind Tunnel test. After performing all the tests for conventional SUV, results are documented to compare the results determined with modified body. KEYWORDS: SUV; CFD; CAD Model; Drag; Base Bleed;

Large Eddy Simulation for Empirical Modeling of the Wake of Three Urban Air Mobility Vehicles

Recent advances in urban air mobility have driven the development of many new vertical take-off and landing (VTOL) concepts. These vehicles often feature original designs departing from the conventional helicopter configuration. Due to their novelty, the characteristics of the supervortices forming in the wake of such aircraft are unknown. However, these vortices may endanger any other vehicle evolving in their close proximity, owing to potentially large induced velocities. Therefore, improved knowledge about the wakes of VTOL vehicles is needed to guarantee safe urban air mobility operations. In this work, we study the wake of three VTOL aircraft in cruise by means of large eddy simulation. We present a two-stage numerical procedure that enables the simulation of long wake ages at a limited computational cost. Our simulations reveal that the wakes of rotary vehicles (quadcopter and side-by-side helicopter) feature larger wake vortex cores than an isolated wing. Their decay is also accelerated due to self-induced turbulence generated during the wake roll-up. A tilt-wing wake, on the other hand, is moderately turbulent and has smaller vortex cores than the wing. Finally, we introduce an empirical model of the vortex circulation distribution that enables fast prediction of wake-induced velocities, within a 2% error of the simulation results on average.

Adjoint shape optimization of Ahmed body to improve aerodynamics

Analyses are done on the bluff body of a simple ground vehicle's wake structure. A 4 million Reynolds number depending on model length. Results for various geometric configurations of the Ahmed body's flow visualization were achieved. There was a flexible geometric element called the base slant angle. Drag research found that body drag makes up about 85% of all drag. The body's rear end is where most drag is created or developed. Horseshoe vortices build a three-deck structure in wake flow. The base slant angle affects these vortices' strength, existence, and merging. Examined is the applicability of these phenomena to actual ground vehicles. To reduce drag and enhance aerodynamics, the body's shape was modified using the adjoint approach and the adjoint shape optimization tool in ANSYS Fluent. In this study, we found that by changing the tail-end vortex structure and flow separation at the rear part of the vehicle, the optimized back shape or rear slant design of the body provides better flow separation that results in better pressure recovery and reduces drag by roughly 7 to 10 percent, respectively. The comparison of experimental CD values for the Ahmed body at different rear slant angles, including 12.5o, 25o, and 30o. Since it had less variance from empirical data, the computationally computed CD for a 30° base slant angle was chosen to do adjoint shape optimization. Mesh cells of less than three lakhs were used in the CFD process, and skewness quality was checked. 60 m/s of velocity was the boundary condition for the velocity inlet.

Coupling effect of vehicle wake and jet flow on the dispersion characteristics and dilution efficiency of pollutants in urban highway tunnels

The pollutants emitted by traveling vehicles are prone to accumulation inside urban highway tunnels, which poses a serious threat to the driving safety and health of passengers. This study employed the dynamic mesh method to simulate a traveling vehicle and investigated the coupling effect of vehicle wake and jet flow on the dispersion characteristics of pollutants in urban highway tunnels. To ensure the accuracy of the numerical simulation results, the turbulence model (realizable k–ε model) and dynamic mesh model were validated through field tests. The results revealed that jet flow can disrupt the large-scale longitudinal vortices pattern in the wake region, whereas vehicle wake can simultaneously weaken the entrainment strength of jet flow. The jet flow was found to be decisive in the space with a height greater than 4 m, whereas the vehicle wake intensity was considerably stronger at the bottom space of the tunnel, leading to the accumulation of pollutants in the passenger breathing zone. To evaluate the effect of jet fans on pollutants in the breathing zone, an innovative dilution efficiency was proposed. The dilution efficiency can be significantly affected by the intensity of vehicle wake and turbulence. Moreover, the dilution efficiency of alternative jet fans was better than that of traditional jet fans.

Aeroacoustic Vehicle Development Method Considering Realistic Wind Conditions

The aeroacoustic development of vehicles is still mainly carried out in wind tunnels under steady flow conditions, although the real situation is different. However, as discussed in several earlier publications, a vehicle experiences unsteady, turbulent flow on road, which results for example from natural wind, wakes of other vehicles, or obstacles at the roadside in combination with side wind. The resulting temporal variations of the wind noise inside the cabin affect the passengers' comfort and safety through fatigue. To be able to also consider the unsteady aeroacoustics in the vehicle development process, a comprehensive method has been developed that is presented in full for the first time in this paper. The on-road situation is simulated in a realistic and reproducible manner in the full-scale wind tunnel of the University of Stuttgart by means of an active turbulence generator, developed by FKFS. The turbulence generator allows to dynamically vary the flow angle with frequency components of up to 10 Hz. By comparing the unsteady wind noise for different flow situations and different vehicles, a flow scenario has been derived which leads to representative and meaningful aeroacoustic results. The measured temporal wind noise variations are investigated using modulation analysis, which has been adapted to show only relevant information in a comprehensible way. Finally, a psychoacoustic metric for rating the annoyance of unsteady, as well as steady, wind noise has been developed based on listening studies. The metric describes the subjective perception and allows evaluation and optimization of the aeroacoustic behavior specifically regarding the passengers' comfort. With this new method all wind noise aspects, steady as well as unsteady, can be determined and taken into account for vehicle development. The evaluation and comparison of vehicles and variants is comprehensive and is focused on the passengers' comfort.

Salient features of wheel-vehicle aerodynamic interactions: Consequences for drag

Salient features of wheel–vehicle interactions and their consequences for drag are investigated experimentally based on a simplified square-back vehicle with different distances l between the rear wheels and the base of the vehicle. Two different mechanisms responsible for a base drag increase of up to 12% are distinguished. At the scale of the vehicle, whatever the distance l, wheels perturb the underflow and induce a global variation of the vertical balance of the vehicle wake. According to the state of the initial wake, significant base drag increase or decrease are observed. Considering the scale of the wheels, if the wheel-to-base distance l/w (w being the width of the wheels) is smaller than a threshold of order 3 in the present configuration, the base drag increases and is very sensitive to l/w. In this situation, a mean mass transfer from the vehicle wake to the wake of the rear wheels is observed. Based on these observations, a physical model is then proposed to explain this high-sensitivity regime.

Excitation and power spectrum analysis of electromagnetic radiation for the plasma wake of reentry vehicles

The plasma wake of reentry vehicles has the advantages of extensive space range and long traceability, which provides new possibilities for the detection and monitoring of reentry vehicles. Based on the Zakharov model, this work investigates the excitation and power spectrum characteristics of electromagnetic radiation for the plasma wake of a typical reentry vehicle. With the aid of parametric decay instability, the excitation condition of electromagnetic radiation for a typical plasma wake is evaluated first. The power spectrum characteristics of electromagnetic radiation, including the effects of both the flight parameters and incident wave parameters are analyzed in detail. The results show that when the phenomenon of excited electromagnetic radiation occurs, plasma wakes closer to the bottom of the vehicle and with faster speeds require higher incident frequencies and thresholds of the electric field. As the frequency of the incident wave increases, peaks appear in the power spectra of plasma wakes, and their magnitudes increase gradually. The frequency shifts of the secondary peaks are equal, whereas, the peaks of the downshifted spectral lines are generally larger than those of the upshifted spectral lines. The work in this paper provides a new idea and method for the tracking of reentry vehicles, which has potential application value in the field of reentry vehicle detection.

Evaluation of the Relationship between Meteorological Variables and NOx Emission Factors Based on Plume-Chasing Measurements

A relationship that links the accuracy of nitrogen oxide emission factors (NOx EFs) calculated from chasing measurements (EFchasing) to meteorological variables was developed. To quantitatively evaluate this relationship, we postulated an “effective ratio” concept based on the momentum wake theory. The effective ratio is considered a function of meteorological variables in the vehicle wake. A mobile platform was used to characterize NOx EFs by following tested vehicles that were installed with a portable emission measuring system (PEMS) on a restricted driving track. The relationship was evaluated based on 172 plume-chasing measurements that were conducted under various operating scenarios such as different tested vehicle speeds and vehicle types. Two calculation approaches (i.e., baseline vs rolling minimum) were used to calculate EFchasing and benchmark against NOx EF from PEMS (EFPEMS). A consistent positive linear relationship (slope ∼28, p < 0.01) is found between the effective ratio and the relative error of EFchasing under all operating scenarios and is independent of calculation approaches. This is evidence that the effective ratio could be a good parameter that quantifies the relative deviation of EFchasing and is independent of calculation approaches. Based on this relationship, the effective ratio can be further used to identify erroneous chasing measurements and improve the accuracy of EFchasing.

Thermal characteristics of vehicle wake induced by the interaction between hydrodynamic wake and cold skin

The wake temperature signal generated by the motion of an underwater vehicle can be captured by infrared detectors, threatening the concealment of the vehicle. To clarify the formation mechanism and physical phenomena of thermal wake, detached-eddy simulations are conducted to establish a thermal wake calculation model, and the volume-of-fluid model is employed to capture the thermal wake characteristics of the water–air interface. Based on the interface heat diffusion and transfer, a high-resolution cold skin boundary layer is established to study the interaction between hydrodynamic wake and temperature boundary layer. The numerical results show that the surface thermal wake presents a long regular strip-shaped characteristic with eddy current structure, which is basically consistent with the results of outdoor wake infrared test in phenomenon and overall intensity. The wake thermal signature originates from the modulation of the cold skin microstructure at the water surface by the wake vorticity. By applying the proposed evaluation method for the thermal characteristics of water surface wakes, the influence of navigation parameters and cold skin parameters on the thermal characteristics of water surface wakes is systematically discussed, and the thermal characteristics of wakes and their influencing factors are summarized.

Research on Key Technologies of Super-Resolution Reconstruction of Medium and Long Wave Maritime Infrared Image

Complex illumination, solar flares and heavy smog on the sea surface have caused difficulties to accurately obtain high-quality imaging and multi-dimensional information of marine monitoring targets, such as oil spill, red tide and underwater vehicle wake. The principle of existing imaging mechanism is complex, and thus it is not practical to capture high-resolution infrared images efficiently. To combat this challenge by utilizing new infrared optical materials and single point diamond-turning technology, we designed and processed a simple, light and strong condensing ability medium and long wavelength infrared imaging optical system with large relative aperture, which can obtain high-quality infrared images. On top of this, with the training from a combination of infrared and visible light images, we also proposed a super-resolution network model, which is composed of a feature extraction layer, an information extraction block and a reconstruction block. The initial features of the input images are recognized in feature extraction layer. Next, to supply missing feature information and recover more details on infrared image extracted from a dense connection block, a feature mapping attention mechanism is introduced. Its main function is to transfer the important feature information of the visible light images in the information extraction block. Finally, the global feature information is integrated in the reconstruction block to reconstruct the high-resolution infrared image. We experimented our algorithm on both of the public Kaist datasets and self-collected datasets, and then compared it with several relevant algorithms. The results showed that our algorithm can significantly improve the reconstruction performance and reveal more detail information, and enhance the visual effect. Therefore, it brings excellent potential in dealing with the problem of low resolution of optical infrared imaging in complex marine environment.

Numerical Simulation of Wake Flow Field in Pitch Motion of Underwater Vehicle

The frequent pitching motion of underwater vehicle during the mission will produce a more complex hydrodynamic wake, which is important for the detection and tracking of underwater vehicles. In this paper, a numerical method is presented to simulate the wake field during the pitching motion of an underwater vehicle by combining the dynamic overset grid method. The evolution law of the wake field is analyzed based on the DARPA SUBOFF simplified model. The effects of underwater vehicle speed on the velocity and turbulent kinetic energy of the wake field and the effects of the longitudinal inclination of the underwater vehicle on the extent of the wake field are discussed.It is found that the wake velocity is positively correlated with the sailing speed of the underwater vehicle, the turbulent kinetic energy of the wake field is directly proportional to the 1.75 power of the sailing speed of the underwater vehicle, and the range of wake field is positively correlated with the pitch angle of underwater vehicle. The larger the pitch angle is, the larger the intensity and size of vortex formed in the flow field are, and the farther the vortex can propagate to the rear of underwater vehicle wake.

Comprehensive Study of the Aerodynamic Influence of Ground and Wheel States on the Notchback DrivAer

This paper conducts an analysis of the aerodynamic influence of different ground and wheel states on the Notchback DrivAer by numerical simulation. The effects of the moving ground and rotating wheels are investigated individually and comprehensively. Experimental data are also included for validation. Through this study, a unique and important low-drag state is observed, in which the vehicle wake near the center region becomes more symmetrical, the pressure on the upper middle base is recovered and the total aerodynamic drag decreases significantly. Furthermore, the formation of this state is determined by the flow rate near the surface of the rear underbody. When the wheels are rotating, the wheel wakes are weakened. On one hand, the drag of wheels and the two sides of the base region is reduced. On the other hand, the boundary layer near the underbody is thinned and the flow near the underbody surface is accelerated, transforming the wake to the low-drag state. Moreover, the moving ground can enhance the wheel wake but its effect on the flow rate near the underbody is complicated. This may be one of the important reasons why the aerodynamic effects of wheel &amp; ground states depend on the vehicle model. Finally, the global effects of wheel rotation and ground movement can affect each other so they should be analyzed together in the vehicle design process.

Evaluation of CFD methodologies for prediction of flows around simplified and complex automotive models

A comprehensive evaluation of the predictive capability and computational costs of Reynolds Averaged Navier–Stokes (RANS), Unsteady RANS (URANS), Delayed Detached-Eddy Simulation (DDES), and Lattice-Boltzmann Method (LBM) methodologies was carried out for flow around the SAE notchback and the DrivAer fastback models. From the comparison, all methods predicted drag within roughly 10% of experimental values. However, this accuracy was misleading for RANS as the predicted flowfield deviated from both the unsteady methods and experiments in regions where flow separation was developing. This was especially true around the rotating wheel flows of the DrivAer model, where RANS predicted extensive separation around the rear wheels to the point that it changed the structure of the vehicle wake. In these regions of highly separated flow, the unsteady methods proved to be much more accurate and robust, although comparisons of the flow around the rotating wheels proved inconclusive as to which methods provided suitable predictive capabilities. Despite improved flow predictions, URANS and DDES proved to be significantly more expensive than RANS, while LBM provided comparable accuracy to URANS/DDES with substantially reduced costs.

Coagulation patterns and the impacts on traffic-related ultrafine particle dispersion in road tunnels employing dynamic mesh algorithms.

.In this study, we continue to analyze the diffusion mechanism of ultrafine particles and the particle coagulation phenomenon with a size range of 26-287 nm exhausted from vehicles during the process of passing through a 100-m-long tunnel using the realizable k-ε model and dynamic grid technique. A three-dimensional model consisting of a 100-m highway tunnel and four side-by-side gasoline vehicles (L × W × H = 4.5 m × 1.8 m × 1.5 m) was established in the STAR-CCM+ computational fluid dynamics software. The gasoline vehicles traveled simultaneously under different situations of three driving speeds of 60 km h-1, 40 km h-1, and 20 km h-1 during the simulation. Through data analysis and research, it was found that the coagulation process of particles is very complicated, especially at low speeds. When the vehicle speed is 20 km h-1, the variation in particle concentration at the vehicle wake near the tailpipe (at the vertical plane located 0.1 m behind the exhaust pipe) causes a large error if the coagulation action is not considered. The relative error of the average particle concentration at 0.5 s of the vertical section 0.1 m away from the exhaust pipe is as high as 193.51%. The relative error in the entire tunnel is only 2.82%, which is less than 5%. Thus, it is recommended that particle coagulation should be considered when analyzing particle dispersion in the near-wake region behind the vehicle and the breathing areas, especially when the vehicle travels slowly inside the tunnel. However, when evaluating the particle concentration and exposure levels for the entire tunnel, coagulation can be ignored without significant errors, especially at a high vehicle speeds. This study clarified the importance of coagulation in different areas and its influence on the diffusion of particulate matter. This is conducive to further analysis of the diffusion characteristics of particulate matter and can appreciably reduce the pollution degree in a tunnel by changing the coagulation efficiency of particulate matter in the future.

Assessment of RANS and DES turbulence models for the underwater vehicle wake flow field and propeller excitation force

Assessment of RANS and DES turbulence models for the underwater vehicle wake flow field and propeller excitation force