Experimental investigations on transient dynamics of cryogenic cavitating flows under different free-stream conditions

2021 ◽  
Vol 178 ◽  
pp. 121537
Author(s):  
Wendong Liang ◽  
Tairan Chen ◽  
Guoyu Wang ◽  
Biao Huang
Keyword(s):  
Free Stream ◽  
Transient Dynamics ◽  
Experimental Investigations ◽  
Cavitating Flows

The influence of background turbulence on Ahmed-body wake bistability

2021 ◽  
Vol 926 ◽  
Author(s):  
D. Burton ◽  
S. Wang ◽  
D. Tudball Smith ◽  
H. N. Scott ◽  
T. N. Crouch ◽  
...  
Keyword(s):  
Experimental Study ◽  
Turbulence Intensity ◽  
Free Stream ◽  
Wind Tunnels ◽  
Experimental Investigations ◽  
Switching Rate ◽  
Free Stream Turbulence ◽  
Background Turbulence ◽  
Ahmed Body

The discovery of wake bistability has generated an upsurge in experimental investigations into the wakes of simplified vehicle geometries. Particular focus has centred on the probabilistic switching between two asymmetrical bistable wake states of a square-back Ahmed body; however, the majority of this research has been undertaken in wind tunnels with turbulence intensities of less than $1\,\%$ , considerably lower than typical atmospheric levels. To better simulate bistability under on-road conditions, in which turbulence intensities can easily reach levels of $10\,\%$ or more, this experimental study investigates the effects of free-stream turbulence on the bistability characteristics of the square-back Ahmed body. Through passive generation and quantification of the free-stream turbulent conditions, a monotonic correlation was found between the switching rate and free-stream turbulence intensity.

Leading-edge receptivity of a hypersonic boundary layer on a flat plate

2001 ◽  
Vol 426 ◽  
pp. 73-94 ◽  
Author(s):  
A. A. MASLOV ◽  
A. N. SHIPLYUK ◽  
A. A. SIDORENKO ◽  
D. ARNAL
Keyword(s):  
Boundary Layer ◽  
Acoustic Waves ◽  
Free Stream ◽  
Three Dimensional ◽  
Leading Edge ◽  
Experimental Investigations ◽  
Two Dimensional ◽  
Inclination Angles ◽  
Tollmien Schlichting ◽  
Radiation Conditions

Experimental investigations of the boundary layer receptivity, on the sharp leading edge of a at plate, to acoustic waves induced by two-dimensional and three- dimensional perturbers, have been performed for a free-stream Mach number M∞ = 5.92. The fields of controlled free-stream disturbances were studied. It was shown that two-dimensional and three-dimensional perturbers radiate acoustic waves and that these perturbers present a set of harmonic motionless sources and moving sources with constant amplitude. The disturbances excited in the boundary layer were measured. It was found that acoustic waves impinging on the leading edge generate Tollmien–Schlichting waves in the boundary layer. The receptivity coefficients were obtained for several radiation conditions and intensities. It was shown that there is a dependence of receptivity coefficients on the wave inclination angles.

Experimental Investigations Concerning Erosive Aggressiveness of Cavitation at Different Test Configurations

Volume 3 ◽  
2004 ◽  
Author(s):  
B. Bachert ◽  
M. Dular ◽  
S. Baumgarten ◽  
G. Ludwig ◽  
B. Stoffel
Keyword(s):  
Mass Loss ◽  
Cavitation Erosion ◽  
Evaluation Method ◽  
Experimental Investigations ◽  
Cavitating Flows ◽  
Test Rig ◽  
The Third ◽  
Long Duration ◽  
Initial Stage ◽  
Test Objects

The experimental results, which will be presented in this paper, demonstrate the significant influence of the flow velocity, respectively the rotational speed, on the erosive aggressiveness of cavitating flows. On two of the three investigated test objects, cavitation erosion can only be observed in the initial stage by the so-called pit-count evaluation method. Developed erosion with mass loss is impossible to measure because of the very long duration until mass loss appears. The third test rig generates a very aggressive type of cavitation, so that mass loss, depending on the tested material, will appear after relatively short durations. In addition, the initial stage of cavitation erosion can be observed. Three different techniques were applied to investigate cavitation erosion in the initial and developed stage. Thereby, the capability of methods to quantify erosive effects in dependence of influencing operating parameters has been proven.

Study on tip leakage vortex cavitating flows using a visualization method

2018 ◽  
Vol 32 (01) ◽  
pp. 1850003
Author(s):  
Yu Zhao ◽  
Yutong Jiang ◽  
Xiaolong Cao ◽  
Guoyu Wang
Keyword(s):  
High Speed ◽  
Continuous Process ◽  
Great Influence ◽  
Rapid Onset ◽  
Experimental Investigations ◽  
Gap Size ◽  
Visualization Method ◽  
Cavitating Flows ◽  
Tip Leakage Vortex ◽  
Tip Leakage

Experimental investigations of unsteady cavitating flows in a hydrofoil tip leakage region with different gap sizes are conducted to highlight the development of gap cavitation. The experiments were taken in a closed cavitation tunnel, during which high-speed camera had been used to capture the cavitation patterns. A new visualization method based on image processing was developed to capture time-dependent cavitation patterns. The results show that the visualization method can effectively capture the cavitation patterns in the tip region, including both the attached cavity in the gap and the tip leakage vortex (TLV) cavity near the trailing edge. Moreover, with the decrease of cavitation number, the TLV cavity develops from a rapid onset-growth-collapse process to a continuous process, and extends both upstream and downstream. The attached cavity in the gap develops gradually stretching beyond the gap and combines with the vortex cavity to form the triangle cavitating region. Furthermore, the influences of gap size on the cavitation are also discussed. The gap size has a great influence on the loss across the gap, and hence the locations of the inception attached cavity. Besides, inception locations and extending direction of the TLV cavity with different gap sizes also differ. The TLV in the case with [Formula: see text] = 0.061 is more likely to be jet-like compared with that in the case with [Formula: see text] = 0.024, and the gap size has a great influence on the TLV strength.

Influence of Turbulent Wake Upon Flow Separation on a Wing Model

2011 ◽  
Vol 6 (1) ◽  
pp. 50-59
Author(s):  
Mikhail V. Mikhaelis ◽  
Boris Yu. Zanin ◽  
Mikhail M. Katasonov
Keyword(s):  
Flow Separation ◽  
Free Stream ◽  
Leading Edge ◽  
Turbulent Wake ◽  
Experimental Investigations ◽  
High Angle ◽  
External Disturbances ◽  
Wing Model ◽  
Subsonic Wind Tunnel ◽  
Straight Wing

The experimental investigations results of the flow over a straight wing model, placed at the subsonic wind tunnel are presented. The model was installed at high angle of attack so that the flow separation have place near the leading edge. An influence of external disturbances on such flow is studied. Free stream disturbances were generated by thin wire stretched in front of wing model. It is found that the separation can be completely removed when the wire wake achieve a wing upper surface

Intermittency Transport Modeling of Separated Flow Transition

2003 ◽  
Author(s):  
J. Vicedo ◽  
S. Vilmin ◽  
W. N. Dawes ◽  
A. M. Savill
Keyword(s):  
Free Stream ◽  
Transport Model ◽  
Separation Bubble ◽  
Separated Flow ◽  
Intermittent Flow ◽  
Experimental Investigations ◽  
Turbulence Characteristic ◽  
Flow Transition ◽  
Bypass Transition ◽  
Free Stream Turbulence

An intermittency transport model is proposed for modeling separated-flow transition. The model is based on earlier work on prediction of attached flow bypass transition and is applied for the first time to model transition in a separation bubble at various degrees of free-stream turbulence. The model has been developed so that it takes into account the entrainment of the surrounding fluid. Experimental investigations suggest that it is this phenomena which ultimately determines the extent of the separation bubble. Transition onset is determined via a boundary layer correlation based on momentum thickness at the point of separation. The intermittent flow characteristic of the transition process is modeled via an intermittency transport equation. This accounts for both normal and streamwise variation of intermittency and hence models the entrainment of surrounding flow in a more accurate manner than alternative prescribed intermittency models. The model has been validated against the well established T3L semicircular leading edge flat plate test case for three different degrees of free-stream turbulence characteristic of turbomachinery blade applications.

Wave Packet Excitation and its Development in Supersonic Boundary Layer

2013 ◽  
Vol 8 (2) ◽  
pp. 70-78
Author(s):  
Alex Yatskih ◽  
Yuri Yermolaev ◽  
Aleksandr Kosinov ◽  
Nikolay Semionov
Keyword(s):  
Boundary Layer ◽  
Glow Discharge ◽  
Wave Packet ◽  
Free Stream ◽  
Supersonic Boundary Layer ◽  
Low Noise ◽  
Experimental Investigations ◽  
Mean Flow ◽  
Supersonic Wind Tunnel ◽  
Discharge Ignition

A method of exciting of artificial disturbances localized in space and time (wave packets) in a supersonic boundary layer is developed. Experimental investigations are carried out in the low noise supersonic wind tunnel T-325 at Mach M = 2. A model of a flat steel plate with a sharp leading edge is used. Measurements of mean flow and fluctuations are performed by using a constant temperature anemometer. To generate controlled fluctuations the short time surface glow discharge is used. Measurements of controlled disturbances are synchronized in time with glow discharge ignition. To increase the signal-to-noise ratio the time trace averaging technique is applied. Electrical power and polarity of the glow discharge initiation are changed to see their influence on the initial wave packet amplitude. Optimal glow discharge parameters for generation of artificial disturbances are found. The experimental data on the localized disturbances evolution in boundary layer are received. It is obtained that the velocity of the wave packet propagation has speed close to the free stream for the leading wave edge. The trailing edge of the wave packet spreads with subsonic speed relatively the supersonic flow. The wave packet propagates in both the streamwise and spanwise directions. Half-angle of this spreading is approximately equal to 10 degrees relative to the free stream direction. It has been found, that the wave packet is developed inside the boundary layer near of the artificial pulsations source. However the evolution of controlled disturbances leads to their radiation into free flow

Influence of Viscous Effects on Impact Tubes

1953 ◽  
Vol 20 (2) ◽  
pp. 253-256
Author(s):  
C. W. Hurd ◽  
K. P. Chesky ◽  
A. H. Shapiro
Keyword(s):  
Reynolds Number ◽  
Free Stream ◽  
Pressure Coefficient ◽  
Pressure Rise ◽  
Experimental Investigations ◽  
Stream Velocity ◽  
Fluid Density ◽  
Viscous Effects ◽  
Point Pressure ◽  
The Impact

Abstract Experiments were conducted to determine the effect of viscosity on the pressure rise recorded by a blunt-nosed impact tube in incompressible flow. The results are presented in terms of the pressure coefficient (Cp ≡ 2Δp/ρV∞2) as a function of Reynolds number (Rey ≡ V∞α/ν), where Δp is the excess of stagnation-point pressure over free-stream static pressure, V∞ is the free-stream velocity, α is the radius of the impact tube, ρ is the fluid density, and ν is the kinematic viscosity of the fluid. Above Reynolds numbers of 1000, there is no effect of viscosity, and Cp is equal to unity. Between Rey ≌ 50 and Rey ≌ 1000, Cp is slightly less than unity, but has a minimum value of 0.99. For values of Rey less than 50, Cp is always greater than unity. When the Reynolds number is below unity, the pressure rise is independent of the fluid density, and the data may be represented approximately by the formula Cp ≌ 5.6/Rey. The results are compared with the experimental investigations of Barker and of Homann, and with the theoretical studies of Stokes and of Homann.

Numerical/Experimental Investigations on Inlet Back Flow in a Helical Inducer in Partial Flow Conditions

2007 ◽  
Author(s):  
Satoshi Watanabe ◽  
Jun-Ho Kim ◽  
Koichi Ishizaka ◽  
Akinori Furukawa
Keyword(s):  
Flow Rate ◽  
Experimental Investigations ◽  
Cavitating Flows ◽  
Flow Conditions ◽  
Detailed Structure ◽  
Flow Rates ◽  
Back Flow ◽  
Effective Suppression ◽  
Basic Characteristics ◽  
Suction Performance

The attachment of inducer upstream of main impeller is an effective method to improve the suction performance of turbopumps. However, the various types of cavitation instabilities are known to occur even at the designed flow rate as well as in the partial flow rate conditions. The cavitation surge is a viciously unstable phenomenon occurring at partial flow rates, in which all blade cavities are periodically and synchronously elongated and shortened, leading the strong vibration in pump systems. Because the cavitation surge is strongly associated with the inlet back flow of inducer, it is desirable to know the detailed structure of back flow for the development of its effective suppression methods/devices. Then, in the present study, we carried out the numerical and experimental investigations of non-cavitating flows in a two bladed helical inducer with/without an inlet ring plate, which has been found to be effective for the suppression of cavitation surge. The basic characteristics of the inlet back flow structure are obtained and discussed in terms of the occurrence/suppression mechanisms of cavitation surge.

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