On the Stability of Supercavitating Projectiles Based on Lagrangian Analysis

2005 ◽  
Author(s):  
Yasmin Khakpour ◽  
Miad Yazdani
Keyword(s):  
Numerical Simulation ◽  
Drag Reduction ◽  
High Speed ◽  
The Body ◽  
Cavity Surface ◽  
Lagrangian Analysis ◽  
The Stability ◽  
Stability Enhancement

In this work, numerical simulation is used to study the stability enhancement of high speed supercavitating Shkval missile. Although supercavitation is known as one of the most effective methods for drag reduction, producing the cavity, either by ventilation or by cavitator at front of the body, may cause some instabilities on cavity surface and thus on the projectile’s motion. Therefore removing these instabilities comes as an important point of discussion. First of all, we calculate the sources of instabilities and measure respective forces and then present some approaches that significantly reduce these instabilities. One of these methods that could produce more stable supercavities is injecting of the air into the cavity unsteadily which varies through the projectile’s surface. This approach is provided by arrays of slots distributed on the projectile’s surface and unsteady injection is modeled over the surface. Furthermore, the position of ventilation, dramatically affects the stability like those in aerodynamics. In all approaches it is assumed that the supercavity covers the whole of the body, however the forces caused by the wakes, formed behind the body are taken into account. The calculation is performed at three cavitation numbers with respective velocities of 100 m/s, 150 m/s, 200 m/s.

Stability Enhancement of Supercavitating Projectiles by Unsteady Air Injection

2005 ◽  
Author(s):  
Yasmin Khakpour ◽  
Miad Yazdani
Keyword(s):  
Numerical Simulation ◽  
Drag Reduction ◽  
High Speed ◽  
The Body ◽  
Air Injection ◽  
Cavity Surface ◽  
The Stability ◽  
Stability Enhancement

In this work, numerical simulation is used to study the stability enhancement of high speed supercavitating hydrofoils. Although supercavitation is known as one of the most effective methods for drag reduction, producing the cavity, either by ventilation or by cavitator at front of the body, may cause some instabilities on cavity surface and thus on the projectile’s motion. Therefore removing these instabilities comes as an important point of discussion. First of all, we calculate the sources of instabilities and measure respective forces and then present some approaches that significantly reduce these instabilities. One of these methods that could produce more stable supercavities is injecting of the air into the cavity unsteadily which varies through the projectile’s surface. This approach is provided by arrays of slots distributed on the projectile’s surface and unsteady injection is modeled over the surface. Furthermore, the position of ventilation, dramatically affects the stability like those in aerodynamics. In all approaches it is assumed that the supercavity covers the whole of the body, however the forces caused by the wakes, formed behind the body are taken into account. The calculation is performed at three cavitation numbers with respective velocities of 40 m/s, 50 m/s, 60 m/s.

scholarly journals Improving the Stability of the Passenger Vehicle by Using an Active Stabilizer Bar Controlled by the Fuzzy Method

Complexity ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-20
Author(s):  
Tuan Anh Nguyen
Keyword(s):  
High Speed ◽  
Control Method ◽  
Spatial Dynamics ◽  
The Body ◽  
Vertical Force ◽  
Dynamics Model ◽  
Track Dynamics ◽  
The Difference ◽  
Lift Off ◽  
The Stability

The rollover phenomenon is a particularly dangerous problem. This phenomenon occurs when the driver travels at high speed and suddenly steers. Under the influence of centrifugal force, the body vehicle will be tilted and cause the wheels to lift off the road. To solve this problem, the method of using an active stabilizer bar has been proposed. The active stabilizer bar is controlled automatically by a previously designed controller. The performance of the active stabilizer bar depends on the selected control method. Previous research often only used a half-car dynamics model combined with a linear single-track dynamics model to simulate the vehicle’s oscillation. In addition, most of the research focuses only on the use of linear control methods for the active stabilizer bar. Therefore, the performance of the stabilizer bar is not guaranteed. This paper focuses on establishing the model of spatial dynamics combined with the nonlinear double-track dynamics model that fully describes the vehicle’s oscillation most accurately. Besides, the fuzzy control method is proposed to control the operation of the hydraulic stabilizer bar. This is a completely novel model, and it is suitable for the actual traveling conditions of the vehicle. Also, simulations are done based on different scenarios. The results of the paper showed that the values of the roll angle, the difference in the vertical force at the wheels, and the displacement of the unsprung mass were significantly reduced when the vehicle used the active stabilizer bar, which is controlled by an intelligent control method. Therefore, the stability and safety of the vehicle have been guaranteed. This result will be the basis for performing other more complex research in the future.

Effect of Jet Hole Size on Drag Reduction Performance of Bionic Jet Surface

2014 ◽  
Vol 1022 ◽  
pp. 87-90
Author(s):  
Zhao Gang ◽  
Fang Li ◽  
Wei Xin Liu ◽  
Shu Zhang ◽  
Hong Shi Bi ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Drag Reduction ◽  
High Speed ◽  
Reduction Rate ◽  
Surface Model ◽  
Surface Boundary ◽  
Hole Size ◽  
Friction Resistance ◽  
Rectangular Jet ◽  
Flow Length

According to the problem of drag reduction on bionic jet surface, a rectangular jet surface model which is similar to shark branchial shape was built, and numerical simulation was processed by using SST k-ω turbulence model, moreover, influence of jet hole size on the drag reduction performance of jet surface was studied. The results show that: the effect of flow length of rectangular jet hole on the drag reduction is remarkable, with the increase of flow length, fluid friction resistance of the jet surface decreases, the maximum drag reduction rate was 14.38%, and the results of numerical simulation was verified by carrying out experiments. The jet fluid decreases the sweep on the wall of mainstream high speed fluid, which increases the thickness of jet surface boundary layer, thereby reducing the surface friction of the jet hole downstream.

scholarly journals Effects of Heat Addition on Wave Drag Reduction of a Spiked Blunt Body

2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Hongyu Wang ◽  
Yanguang Yang ◽  
Langquan Li ◽  
Gang Wang ◽  
Qinghu Zhang
Keyword(s):  
Drag Reduction ◽  
High Speed ◽  
Blunt Body ◽  
Wave Drag ◽  
The Body ◽  
Continuous Heating ◽  
Heat Addition ◽  
Reduction Coefficient ◽  
Wave Drag Reduction ◽  
High Speed Vehicle

Drag reduction technology plays a significant role in extending the flight range for a high-speed vehicle. A wave drag reduction strategy via heat addition to a blunt body with a spike was proposed and numerically validated. The heat addition is simulated with continuous heating in a confined area upstream of the blunt body. The effects of heat addition on drag reduction in three flow conditions ( M = 3.98 , 5 , 6 ) were compared, and the influence of power density q h ( q 1 = 2.0 × 10 8   W / m 3 , q 2 = 5.0 × 10 8   W / m 3 , and q 3 = 1.0 × 10 9   W / m 3 ) of heating was evaluated. Results show that the heat addition has a positive way to reduce the drag of the body with a spike alone, and more satisfactory drag reduction effectiveness can be achieved at a higher Mach number. The drag reduction coefficient increases with q h in the same flow condition, with a maximum of 38.9% ( M = 6 ) as q 3 = 1.0 × 10 9   W / m 3 . The wave drag reduction principle was discussed by a transient calculation, which indicates that the separation region has entrainment of the heated air and expanded with its sonic line away from the blunt cone, which results in an alleviation of the pressure load caused by shock/shock interaction.

Full Annulus Simulation of a High-Speed Centrifugal Compressor Using an Unstructured RANS Flow Solver

2004 ◽  
Author(s):  
Chunhua Sheng
Keyword(s):  
Centrifugal Compressor ◽  
High Speed ◽  
Three Dimensional ◽  
Air Injection ◽  
Governing Equations ◽  
Flow Solver ◽  
The Stability ◽  
Sliding Technique ◽  
Stability Enhancement ◽  
Air Streams

This paper presents numerical simulations for a high-speed centrifugal compressor using an unstructured Reynolds averaged Naiver-Stokes flow solver U2NCLE. It solves three-dimensional compressible governing equations using an arbitrary Mach number solution algorithm. The stability enhancement for a centrifugal compressor was achieved by injecting air streams into the vaneless region of the diffuser. Numerical prediction of the stabilizing effect of air injection in the centrifugal compressor requires full annulus simulations of the compressor system. This work presents numerical procedures for simulating full annulus centrifugal compressor, including air injection modeling. A sliding technique is employed to handle relative motion grids for impeller and diffuser interactions. Computed results for the centrifugal compressor are analyzed and assessed with the experiment.

Direct Numerical Simulation of Turbulent Friction Drag Reduction by Traveling Wave-Like Blowing Using Plasma Actuators

2011 ◽  
Author(s):  
Yasuhito Murai ◽  
Koji Fukagata
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Drag Reduction ◽  
Traveling Wave ◽  
Body Force ◽  
Phase Speed ◽  
The Body ◽  
Plasma Actuators ◽  
Friction Drag ◽  
Friction Drag Reduction

We numerically investigated the effects of friction drag reduction and energy gain by traveling wave-like blowing using plasma actuators arrayed on channel walls. Wall-normal flow is induced by opposed arrangement of plasma actuators. We used Shyy et al.’s model [1] to compute the body force of plasma actuators, which is added to the Navier-Stokes equation. With this model, the body force distribution is simplified as compared to the actual one, which is quite complicated. We perform direct numerical simulation under several parameter sets: the wavenumber, the amplitude, and the phasespeed of body forces. The obtained maximum friction drag reduction rate is 37% as compared to the uncontrolled case. Under the same phase speed and amplitude of body force, the friction drag is found to be reduced more with larger wavenumber. Under the same phase speed and wavenumber, the friction drag reduction is found to be larger with stronger body force. In the drag reducing cases, formation of spanwise vortices leads to reduction of the Reynolds sheer stress near the wall as well as the friction drag. Although net energy saving is acheived in some parameter sets, it is not achieved in most cases. This means that the reduced pumping power is generally smaller than the power input of plasma actuators.

Numerical Simulation of Body Heat Transfer Coefficient Test of a Railway Vehicle

2011 ◽  
Vol 291-294 ◽  
pp. 1713-1721
Author(s):  
Jian Bin Zang ◽  
Ming Wei Cai ◽  
Nai Ping Gao
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Cross Sections ◽  
High Speed ◽  
Mean Value ◽  
The Body ◽  
Railway Vehicle ◽  
Body Heat

The body heat transfer coefficient of a railway vehicle is an essential parameter for designing vehicle. The proposed method in this paper could be used to simulate the test conditions of body heat transfer coefficient of a railway vehicle. The simulated object was a middle of high speed train and the numerical simulation was two-dimensional due to the limitation of RAM capacity of PC computers. Simulation results with five different meshing showed body heat transfer coefficient was affected greatly by the amount of grids. Existence of thermal bridge would increase body heat transfer coefficient significantly, which was concluded by the simulation of two models. Three typical cross sections of a middle were used for simulation of the body heat transfer coefficient and the weighted mean value was 1.30 W/m2•K. The difference was only 7% compared with the actual test value of 1.215 W/m2•K, which indicated the advantage of this method.

scholarly journals How seabirds plunge-dive without injuries

2016 ◽  
Vol 113 (43) ◽  
pp. 12006-12011 ◽  
Author(s):  
Brian Chang ◽  
Matthew Croson ◽  
Lorian Straker ◽  
Sean Gart ◽  
Carla Dove ◽  
...  
Keyword(s):  
High Speed ◽  
Elastic Beam ◽  
The Body ◽  
Neck Length ◽  
Anatomical Features ◽  
Fluid Forces ◽  
High Speed Impact ◽  
Physical Experiments ◽  
Geometric Factors ◽  
The Stability

In nature, several seabirds (e.g., gannets and boobies) dive into water at up to 24 m/s as a hunting mechanism; furthermore, gannets and boobies have a slender neck, which is potentially the weakest part of the body under compression during high-speed impact. In this work, we investigate the stability of the bird’s neck during plunge-diving by understanding the interaction between the fluid forces acting on the head and the flexibility of the neck. First, we use a salvaged bird to identify plunge-diving phases. Anatomical features of the skull and neck were acquired to quantify the effect of beak geometry and neck musculature on the stability during a plunge-dive. Second, physical experiments using an elastic beam as a model for the neck attached to a skull-like cone revealed the limits for the stability of the neck during the bird’s dive as a function of impact velocity and geometric factors. We find that the neck length, neck muscles, and diving speed of the bird predominantly reduce the likelihood of injury during the plunge-dive. Finally, we use our results to discuss maximum diving speeds for humans to avoid injury.

Kinematics of the knee joint

2012 ◽  
Vol 2 (3) ◽  
pp. 353-359
Author(s):  
W. Sampers ◽  
T. Sierens
Keyword(s):  
High Speed ◽  
Degrees Of Freedom ◽  
The Body ◽  
Linear Actuator ◽  
Test Rig ◽  
Q Angle ◽  
The Stability ◽  
Near Future ◽  
Patella Tracking ◽  
Knee Rig

In 2006 a test rig was built by Ghent University to measure patellofemoral pressures. The maingoal of the current study is to improve and upgrade the Ghent Knee Rig (GKR). The improvement consistsof a better approach of the Q angle. The mechanical connection between the linear actuator and the rectusfemoris tendon represents the force of the quadriceps. To validate the results of measurement, it isnecessary the connection approaches the direction of the real muscle. The patella is bond with the body byuse of ligaments and retinacula, which have a unknown influence on the stability of the patella. Alsoquadriceps and the trochlea are important stabilizers. The upgrade of the GKR is a tool to measure thepatella stability, which is done by pulling the patella out of the trochlea and measure the force needed for acertain displacement. It is important the patella has five degrees of freedom (DOF) so no extra force but thestability is measured and the effect of dysplasia and trochleoplasty can be examined. In the near future theGKR will be expanded to the possibility of measuring patella tracking. The relative movements of thedifferent components of the knee will be followed by high speed cameras.

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