Analysis of the Flow Around Supercavitating Hydrofoils with Midchord and Face Cavity Detachment

1991 ◽  
Vol 35 (03) ◽  
pp. 198-209
Author(s):  
Spyros A. Kinnas ◽  
Neal E. Finer
Keyword(s):  
Pressure Distribution ◽  
Integral Equations ◽  
Inviscid Flow ◽  
Panel Method ◽  
Pressure Side ◽  
Flow Conditions ◽  
Trailing Edge ◽  
Pressure Distributions ◽  
Work First ◽  
Flow Criterion

In this work, first the linearized supercavitating hydrofoil problem with arbitrary cavity detachment points is formulated in terms of unknown source and vorticity distributions. The corresponding integral equations are inverted analytically and the results are expressed in terms of integrals of quantities which depend only on the hydrofoil shape. These integrals are computed numerically, in an accurate and efficient way, to produce cavity shapes and pressure distributions on the foil and cavity. The effect of the cavity detachment points on the shape of the cavity and the foil pressure distribution is investigated. An inviscid flow criterion for the cavity detachment point is derived for the case where the cavity detaches in front of the trailing edge on the pressure side of the hydrofoil. Finally, the accuracy of the linearized cavity theory is assessed for different foils and flow conditions, by analyzing the produced cavity shapes with a nonlinear panel method.

Improvement of Cooled Turbine Airfoils by Special Cutback

2010 ◽  
Author(s):  
Boris I. Mamaev ◽  
Mikhail M. Petukhovskiy ◽  
Alexander V. Pozdnyakov ◽  
Marat R. Valeev
Keyword(s):  
Substantial Reduction ◽  
Reynolds Numbers ◽  
Pressure Side ◽  
Trailing Edge ◽  
Turbine Efficiency ◽  
Flow Parameters ◽  
Pressure Distributions ◽  
Turbine Airfoils ◽  
Bend Angles ◽  
Cooling Air

A substantial reduction in high temperature turbine efficiency due to a thickening trailing edge on the blades can be compensated by ejection of cooling air on the airfoil pressure side near the edge, which is made thinner at the expense of a pressure-side contour bend. A blade-row midspan section of the aircraft high-pressure turbine was chosen for investigations. Flow parameters of the section: inlet and outlet angles were 36° and 65°, respectively (axial reference), outlet isentropic Mach number was 0.94. Four linear cascades were examined. They differed mainly in the airfoil trailing edge geometry. Three airfoils had the same thin trailing edges and contour bend angles ε = 10, 15 and 20°; one airfoil with a thick round edge had no bend. Widths of the slot for cooling air ejection were the same for all airfoils tested. Measurements were made for exit Mach numbers from 0.6 to 0.95 and relative cooling mass flows from 0 to 1.5%. The respective Reynolds numbers varied from 7.5·106 to 9·106. The incidence value was 2°. Pressure distributions along profiles, outlet total and static pressures, back pressures for cooling air with gas-outlet angles were measured. The experiments showed streamlining of all cascades were favorable. For the airfoils with ε = 10 and 15° the profile losses were low and normal for uncooled cascades with thin trailing edge. Hence, for such bends losses due to a step on the airfoil pressure side were negligible. As expected, the losses in the cascade with the thick rounding edge were significantly higher. The losses in the cascade with ε = 20° were the greatest. The coolant exit had no distinct influence on streamlining airfoils. The back-pressure for cooling air was approximately equal to the outlet static pressure. For cascades with ε = 10 and 15° the ejection of coolant led to a small increase of losses due to additional mixing losses. Thus, the airfoil contour bend is a powerful tool for the aerodynamic improvement of cooled turbines. It may lead to gains in stage efficiency of 1…1.5%. It should be noted that this tool has already been used successfully for several aircraft and industrial turbines of recent design.

A wake singularity potential flow model for airfoils experiencing trailing-edge stall

1993 ◽  
Vol 251 ◽  
pp. 203-218 ◽  
Author(s):  
W. W. H. Yeung ◽  
G. V. Parkinson
Keyword(s):  
Potential Flow ◽  
Inviscid Flow ◽  
Near Wake ◽  
Trailing Edge ◽  
Pressure Distributions ◽  
Free Streamlines ◽  
Potential Flow Model ◽  
Theoretical Pressure ◽  
Simple Sequence ◽  
Good Agreement

An incompressible inviscid flow theory for single and two-element airfoils experiencing trailing-edge stall is presented. For the single airfoil the model requires a simple sequence of conformal transformations to map a Joukowsky airfoil, partially truncated on the upper surface, onto a circle over which the flow problem is solved. Source and doublet singularities are used to create free streamlines simulating shear layers bounding the near wake. The model's simplicity permits extension of the method to airfoil-flap configurations in which trailing-edge stall is assumed on the flap. Williams’ analytical method to calculate the potential flow about two lifting bodies is incorporated in the Joukowsky-arc wake-singularity model to allow for flow separation. The theoretical pressure distributions from these models show good agreement with wind-tunnel measurements.

Passive Effusion Cooling in a Rectangular S-Bend Diffuser

2012 ◽  
Author(s):  
B. C. N. Ng ◽  
A. M. Birk
Keyword(s):  
Experimental Study ◽  
Pressure Distribution ◽  
Back Pressure ◽  
Wall Pressure ◽  
Flow Conditions ◽  
Complex Flow ◽  
Atmospheric Flow ◽  
Pressure Distributions ◽  
Outlet Flow ◽  
Recovery Performance

The experimental study considered passive effusion cooling in an S-bend diffusing passage in which ambient cool air was drawn naturally into the S-duct passage with sub-atmospheric flow distributions. Seven-hole pressure probes were used to measure the test section’s inlet and outlet flow conditions that were used to evaluate the performance of the S-bend diffuser. Back-pressure, outlet flow-fields and wall pressure distributions were investigated to study the effects of effusion cooling on the pressure recovery performance of the S-bend diffuser. The study revealed a substantial back-pressure penalty and wall pressure distribution alteration in the S-bend passage with full coverage effusion cooling. The outlet diffuser was shown to be not as effective with effusion cooling. The findings highlighted the importance of the design of effusion holes locations in complex flow passages.

Passive Effusion Cooling in a Rectangular S-Bend Diffuser

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
B. C. N. Ng ◽  
A. M. Birk
Keyword(s):  
Experimental Study ◽  
Pressure Distribution ◽  
Back Pressure ◽  
Wall Pressure ◽  
Flow Conditions ◽  
Complex Flow ◽  
Hole Pressure ◽  
Pressure Distributions ◽  
Outlet Flow ◽  
Recovery Performance

The experimental study considered passive effusion cooling in an S-bend diffusing passage in which ambient cool air was drawn naturally into the S-bend passage with subatmospheric flow distributions. Seven-hole pressure probes were used to measure the test section’s inlet and outlet flow conditions which were used to evaluate the performance of the S-bend diffuser. Back-pressure, outlet flow-fields, and wall pressure distributions were investigated to study the effects of effusion cooling on the pressure recovery performance of the S-bend diffuser. The study revealed a substantial back-pressure penalty and wall pressure distribution alteration in the S-bend passage with full coverage effusion cooling. The outlet diffuser was shown to be not as effective with effusion cooling. The findings highlighted the importance of the design of effusion holes locations in complex flow passages.

Sensitivity of Cascade Pressure Distribution for Inverse Design of Turbine Blade

2019 ◽  
Author(s):  
R. Nanthini ◽  
B. V. S. S. S. Prasad ◽  
Y. V. S. S. Sanyasiraju
Keyword(s):  
Pressure Distribution ◽  
Turbine Blade ◽  
Wedge Angle ◽  
Leading Edge ◽  
Small Variation ◽  
Suction Side ◽  
Inviscid Flow ◽  
Initial Guess ◽  
Inverse Design ◽  
Trailing Edge

Abstract In an iterative inverse design of a turbine blade, choice of initial guess profile is crucial. As the pressure distribution is very sensitive to the leading and trailing edge shapes and the profile slope and curvature, a good initial guess profile will help in faster convergence. In this paper, the sensitivity of the pressure distribution is determined by carrying out numerical simulations with ANSYS Fluent 17.2 for the inviscid flow. The flow domain comprises of a two dimensional transonic turbine cascade. It consists of a turbine blade enclosed by inlet, outlet and periodic boundaries. Inlet total pressure, total temperature and inlet angle are given as the boundary conditions at the inlet and static pressure is imposed at the outlet boundary. The flow is solved for continuity, momentum and energy equations. Sensitivity of different parameters — leading edge thickness, trailing edge thickness, leading edge shape, inlet and outlet wedge angle on the pressure distribution is demonstrated for VKI blade cascade. It is found that the pressure side of the profile is less sensitive and that even a small variation in suction side of the profile geometry can affect the performance of the blade significantly. It is shown that, with the proposed methodology and sequence of steps, the final guess blade is quite close to the original blade.

Experimental and numerical investigations of hole injection on the suction side throat of transonic turbine vanes in a cascade with trailing edge injection

2017 ◽  
Vol 232 (8) ◽  
pp. 1454-1466 ◽  
Author(s):  
Jie Gao ◽  
Ming Wei ◽  
Yunning Liu ◽  
Qun Zheng ◽  
Ping Dong
Keyword(s):  
Shock Wave ◽  
Mass Flow ◽  
Suction Side ◽  
Hole Injection ◽  
Pressure Side ◽  
Trailing Edge ◽  
Transonic Flows ◽  
Pressure Distributions ◽  
Numerical Predictions ◽  
Mach Numbers

Trailing-edge mixing flows associated with coolant injection are complex, in particular at transonic flows, and result in significant aerodynamics losses. The objective of this paper is to evaluate the impacts of hole injection near the suction side throat on shock wave control and aerodynamic losses. A series of tests and calculations on effects of hole injection on the suction-side throat of a high-pressure turbine vane cascade with and without trailing-edge injection were conducted. Wake traverses with a five-hole probe and tests of pressure distributions on the turbine profile were taken for total injection mass flow ratios of 0% and 1.2% under test Mach numbers of 0.7, 0.78, and 0.87. Meantime, numerical predictions are carried out for exit isentropic Mach numbers of 0.7, 0.78, 0.87, and 1.1 and hole-injection mass flow ratios of 0%, 0.17%, 0.3%, and 0.89%. Numerical predictions show a reasonable agreement with the experimental data, and wake total pressure losses and flow angles as well as pressure distributions on the turbine profile were compared to calculations without hole injection, indicating a significant effect of hole injection on the profile wake development and its blockage effect on the shock-wave flow in the vane cascade passage. At subsonic flows, the hole injection on the suction side throat thickens the suction-side boundary layer, and increases the flow mixing, thus causing increased wake losses and flow angles. At transonic flows, while the trailing-edge injection reduces the strength of the shock wave at the trailing-edge pressure side, the hole injection on the suction side throat alters the local pressure fields, and then tends to enhance the shock-wave at the trailing-edge pressure-side; however, it seems to reduce the strength of the shock-wave at the trailing-edge suction side.

A Surface Panel Method for Design of Hydrofoils

1994 ◽  
Vol 38 (03) ◽  
pp. 175-181
Author(s):  
Chang-Sup Lee ◽  
Young-Gi Kim ◽  
Jung-Chun Suh
Keyword(s):  
Integral Equation ◽  
Boundary Value Problem ◽  
Pressure Distribution ◽  
Three Dimensional ◽  
Panel Method ◽  
Simultaneous Equations ◽  
Surface Panel Method ◽  
Total Potential ◽  
Pressure Distributions

A surface panel method treating a boundary-value problem of the Dirichlet type is presented to design a hydrofoil corresponding to a prescribed pressure distribution. An integral equation is derived from Green's theorem, giving a relation between the total potential of known strength and the unknown local flux. Upon discretization, a system of linear simultaneous equations is formed and solved for an assumed geometry. The pseudo local flux, present due to the incorrect positioning of the assumed geometry, plays a role of the geometry corrector, with which the new geometry is computed for the next iteration. Sample designs for a series of pressure distributions of interest are performed to demonstrate the fast convergence, effectiveness and robustness of the procedure. The method is shown equally applicable to designing two- and three-dimensional hydrofoil geometry.

scholarly journals Effect of Pressure Distribution on the Energy Dissipation of Lap Joints under Equal Pre-tension Force

Open Physics ◽  
2019 ◽  
Vol 17 (1) ◽  
pp. 320-328
Author(s):  
Delin Sun ◽  
Minggao Zhu
Keyword(s):  
Energy Dissipation ◽  
Pressure Distribution ◽  
Theoretical Basis ◽  
Lap Joints ◽  
Power Exponent ◽  
Lap Joint ◽  
Stick Slip ◽  
Pressure Distributions ◽  
Hysteretic Characteristics ◽  
Effective Use

Abstract In this paper, the energy dissipation in a bolted lap joint is studied using a continuum microslip model. Five contact pressure distributions compliant with the power law are considered, and all of them have equal pretension forces. The effects of different pressure distributions on the interface stick-slip transitions and hysteretic characteristics are presented. The calculation formulation of the energy dissipation is introduced. The energy dissipation results are plotted on linear and log-log coordinates to investigate the effect of the pressure distribution on the energy distribution. It is shown that the energy dissipations of the lap joints are related to the minimum pressure in the overlapped area, the size of the contact area and the value of the power exponent. The work provides a theoretical basis for further effective use of the joint energy dissipation.

scholarly journals Dynamic flight load measurements with MEMS pressure sensors

2021 ◽  
Author(s):  
Christian Raab ◽  
Kai Rohde-Brandenburger
Keyword(s):  
Pressure Distribution ◽  
Pressure Sensors ◽  
Flow Characteristics ◽  
Flight Test ◽  
Measurement Technology ◽  
Test Program ◽  
Aerodynamic Pressure ◽  
Pressure Distributions ◽  
Time Histories ◽  
Mems Pressure Sensors

AbstractThe determination of structural loads plays an important role in the certification process of new aircraft. Strain gauges are usually used to measure and monitor the structural loads encountered during the flight test program. However, a time-consuming wiring and calibration process is required to determine the forces and moments from the measured strains. Sensors based on MEMS provide an alternative way to determine loads from the measured aerodynamic pressure distribution around the structural component. Flight tests were performed with a research glider aircraft to investigate the flight loads determined with the strain based and the pressure based measurement technology. A wing glove equipped with 64 MEMS pressure sensors was developed for measuring the pressure distribution around a selected wing section. The wing shear force determined with both load determination methods were compared to each other. Several flight maneuvers with varying loads were performed during the flight test program. This paper concentrates on the evaluation of dynamic flight maneuvers including Stalls and Pull-Up Push-Over maneuvers. The effects of changes in the aerodynamic flow characteristics during the maneuver could be detected directly with the pressure sensors based on MEMS. Time histories of the measured pressure distributions and the wing shear forces are presented and discussed.

scholarly journals Influence of the Spatial Pressure Distribution of Breaking Wave Loading on the Dynamic Response of Wolf Rock Lighthouse

2021 ◽  
Vol 9 (1) ◽  
pp. 55
Author(s):  
Darshana T. Dassanayake ◽  
Alessandro Antonini ◽  
Athanasios Pappas ◽  
Alison Raby ◽  
James Mark William Brownjohn ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Pressure Distribution ◽  
Distinct Element ◽  
Breaking Waves ◽  
Breaking Wave ◽  
Wave Loading ◽  
Wave Impact ◽  
Pressure Distributions ◽  
Impact Area ◽  
The Impact

The survivability analysis of offshore rock lighthouses requires several assumptions of the pressure distribution due to the breaking wave loading (Raby et al. (2019), Antonini et al. (2019). Due to the peculiar bathymetries and topographies of rock pinnacles, there is no dedicated formula to properly quantify the loads induced by the breaking waves on offshore rock lighthouses. Wienke’s formula (Wienke and Oumeraci (2005) was used in this study to estimate the loads, even though it was not derived for breaking waves on offshore rock lighthouses, but rather for the breaking wave loading on offshore monopiles. However, a thorough sensitivity analysis of the effects of the assumed pressure distribution has never been performed. In this paper, by means of the Wolf Rock lighthouse distinct element model, we quantified the influence of the pressure distributions on the dynamic response of the lighthouse structure. Different pressure distributions were tested, while keeping the initial wave impact area and pressure integrated force unchanged, in order to quantify the effect of different pressure distribution patterns. The pressure distributions considered in this paper showed subtle differences in the overall dynamic structure responses; however, pressure distribution #3, based on published experimental data such as Tanimoto et al. (1986) and Zhou et al. (1991) gave the largest displacements. This scenario has a triangular pressure distribution with a peak at the centroid of the impact area, which then linearly decreases to zero at the top and bottom boundaries of the impact area. The azimuthal horizontal distribution was adopted from Wienke and Oumeraci’s work (2005). The main findings of this study will be of interest not only for the assessment of rock lighthouses but also for all the cylindrical structures built on rock pinnacles or rocky coastlines (with steep foreshore slopes) and exposed to harsh breaking wave loading.

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