Measurements in High Void-Fraction Bubbly Wakes Created by Ventilated Supercavitation

2013 ◽  
Vol 135 (1) ◽  
Author(s):  
Martin Wosnik ◽  
Roger E. A. Arndt
Keyword(s):  
Void Fraction ◽  
High Speed ◽  
Bubble Velocity ◽  
Time Resolved ◽  
Stability And Control ◽  
Ventilated Supercavity ◽  
High Reynolds ◽  
Similarity Scaling ◽  
Interdisciplinary Study ◽  
And Control

A study of ventilated supercavitation in the reentrant jet regime has been carried out in the high-speed water tunnel at St. Anthony Falls Laboratory as the hydrodynamics part of an interdisciplinary study on stability and control of high-speed cavity-running bodies. The work is aimed at understanding the interaction between a ventilated supercavity and its turbulent bubbly wake, with the goal to provide the information needed for the development of control algorithms. Particle image velocimetry (PIV) measurements in high-void fraction bubbly wakes created by the collapse of ventilated supercavities are reported. Bubble velocity fields are obtained and are shown to submit to the same high Reynolds number similarity scaling as the single-phase turbulent axisymmetric wake. A grayscale technique to measure local average void fraction is outlined. Results of a time-resolved PIV experiment at 2000 Hz, using an adaptive masking scheme based on a sliding intensity threshold filter, are also presented.

Measurements in High Void-Fraction Bubbly Wakes Created by Ventilated Supercavitation

2005 ◽  
Author(s):  
Martin Wosnik ◽  
Lucas Gomez Fontecha ◽  
Roger E. A. Arndt
Keyword(s):  
Void Fraction ◽  
High Speed ◽  
Bubble Velocity ◽  
Time Resolved ◽  
Stability And Control ◽  
Ventilated Supercavity ◽  
High Reynolds ◽  
Similarity Scaling ◽  
Interdisciplinary Study ◽  
And Control

A detailed study of ventilated supercavitation in the reentrant jet regime is being carried out in the high-speed water tunnel at St. Anthony Falls Laboratory, as the hydrodynamics part of an interdisciplinary study on stability and control of high-speed cavity-running bodies. It is aimed at understanding the interaction between a ventilated supercavity and its turbulent bubbly wake, with the goal to provide the information needed for the development of control algorithms. Here Particle Image Velocimetry (PIV) measurements in high void fraction bubbly wakes created by the collapse of ventilated supercavities are reported. Bubble velocity fields are obtained, and shown to submit to the same high Reynolds number similarity scaling as the single-phase turbulent axisymmetric wake. A grayscale technique to measure local average void fraction is outlined. Initial results of a time-resolved PIV experiment (2000 Hz) are also presented.

Stability and control of high-speed flows

2001 ◽  
Author(s):  
Helen Reed ◽  
William Saric ◽  
Ian Lyttle ◽  
Yasutoshi Asada
Keyword(s):  
High Speed ◽  
Stability And Control ◽  
And Control ◽  
High Speed Flows

Spinning gasodynamic projectile system identification experiment design

2020 ◽  
Vol 92 (3) ◽  
pp. 452-459 ◽  
Author(s):  
Piotr Lichota ◽  
Mariusz Jacewicz ◽  
Joanna Szulczyk
Keyword(s):  
System Identification ◽  
High Speed ◽  
Content Type ◽  
Stability And Control ◽  
Novel Approach ◽  
Control Derivatives ◽  
Designed Experiment ◽  
Regions Of Stability ◽  
Short Time ◽  
And Control

Purpose The purpose of this paper is to present the methodology that was used to design a system identification experiment of a generic spinning gasodynamic projectile. For this object, because the high-speed spinning motion, it was not possible to excite the aircraft motion along body axes independently. Moreover, it was not possible to apply simultaneous multi-axes excitations because of the short time in which system identification experiments can be performed (multi-step inputs) or because it is not possible to excite the aircraft with a complex input (multi-sine signals) because of the impulse gasodynamic engines (lateral thrusters) usage. Design/methodology/approach A linear projectile model was used to obtain information about identifiability regions of stability and control derivatives. On this basis various sets of lateral thrusters’ launching sequences, imitating continuous multi-step inputs were used to excite the nonlinear projectile model. Subsequently, the nonlinear model for each excitation set was identified from frequency responses, and the results were assessed. For comparison, the same approach was used for the same projectile exited with aerodynamic controls. Findings It was found possible to design launching sequences of lateral thrusters that imitate continuous multi-step input and allow to obtain accurate system identification results in specified frequency range. Practical implications The designed experiment can be used during polygonal shooting to obtain a true projectile aerodynamic model. Originality/value The paper proposes a novel approach to gasodynamic projectiles system identification and can be easily applied for similar cases.

Paper 2. Problems and Requirements of Directional Stability, Control and Manoeuvrability; High-Speed Craft

1972 ◽  
Vol 14 (7) ◽  
pp. 6-13
Author(s):  
M. C. Eames
Keyword(s):  
High Speed ◽  
Stability Control ◽  
Paper Briefly ◽  
Planing Craft ◽  
Stability And Control ◽  
Directional Stability ◽  
Air Cushion ◽  
And Control ◽  
Air Cushion Vehicles

The problems of stability and control of high-speed craft are somewhat different for the various vehicle types. The first part of this paper briefly compares characteristics of air-cushion vehicles and planing craft. This is followed by a more detailed discussion of the problems and requirements of hydrofoil craft.

scholarly journals Bubbly shock propagation as a mechanism for sheet-to-cloud transition of partial cavities

2016 ◽  
Vol 802 ◽  
pp. 37-78 ◽  
Author(s):  
Harish Ganesh ◽  
Simo A. Mäkiharju ◽  
Steven L. Ceccio
Keyword(s):  
Mach Number ◽  
Void Fraction ◽  
High Speed ◽  
Large Scale ◽  
Dynamic Pressure ◽  
Cavity Flow ◽  
Laboratory Frame ◽  
Shock Propagation ◽  
Time Resolved ◽  
Cloud Cavitation

Partial cavitation in the separated region forming from the apex of a wedge is examined to reveal the flow mechanism responsible for the transition from stable sheet cavity to periodically shedding cloud cavitation. High-speed visualization and time-resolved X-ray densitometry measurements are used to examine the cavity dynamics, including the time-resolved void-fraction fields within the cavity. The experimentally observed time-averaged void-fraction profiles are compared to an analytical model employing free-streamline theory. From the instantaneous void-fraction flow fields, two distinct shedding mechanisms are identified. The classically described re-entrant flow in the cavity closure is confirmed as a mechanism for vapour entrainment and detachment that leads to intermittent shedding of smaller-scale cavities. But, with a sufficient reduction in cavitation number, large-scale periodic cloud shedding is associated with the formation and propagation of a bubbly shock within the high void-fraction bubbly mixture in the separated cavity flow. When the shock front impinges on flow at the wedge apex, a large cloud is pinched off. For periodic shedding, the speed of the front in the laboratory frame is of the order of half the free-stream speed. The features of the observed condensation shocks are related to the average and dynamic pressure and void fraction using classical one-dimensional jump conditions. The sound speed of the bubbly mixture is estimated to determine the Mach number of the cavity flow. The transition from intermittent to transitional to strongly periodic shedding occurs when the average Mach number of the cavity flow exceeds that required for the generation of strong shocks.

Identification of gyroplane lateral/directional stability and control characteristics from flight test

1998 ◽  
Vol 212 (4) ◽  
pp. 271-285 ◽  
Author(s):  
S S Houston
Keyword(s):  
High Speed ◽  
Degrees Of Freedom ◽  
Flight Test ◽  
Accident Rate ◽  
Stability And Control ◽  
Directional Stability ◽  
Control Derivatives ◽  
Limited Application ◽  
And Control ◽  
Rotary Wing

This paper presents an analysis of test data recorded during flight trials of a gyroplane. This class of rotary-wing aircraft has found limited application in areas other than sport or recreational flying. However, the accident rate is such that a study of the configuration's stability and control characteristics is timely, and in addition substantive data are required for a new airworthiness and design standard that is under development. The paper complements previous work on the longitudinal degrees of freedom and, as a consequence, serves to consolidate the understanding of gyroplane stability and control. The identified derivatives are related to specific aspects of the layout of the gyroplane, and hence the influence of design on the static and dynamic behaviour is quantified. It is concluded that robust estimates of the lateral and directional stability and control derivatives have been identified. This analysis has focused on ‘high-speed’ flight, and the identified derivatives highlight benign and ‘conventional’ characteristics in this part of the flight envelope.

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