The Experts below are selected from a list of 264 Experts worldwide ranked by ideXlab platform
Allan Paull - One of the best experts on this subject based on the ideXlab platform.
-
Skin-Friction measurements in high-enthalpy hypersonic boundary layers
Journal of Fluid Mechanics, 2003Co-Authors: Christopher P. Goyne, Raymond J. Stalker, Allan PaullAbstract:Skin-Friction measurements are reported for high-enthalpy and high-Mach-number laminar, transitional and turbulent boundary layers. The measurements were performed in a free-piston shock tunnel with air-flow Mach number, stagnation enthalpy and Reynolds numbers in the ranges of 4.4-6.7, 3-13 MJ kg(-1) and 0.16 x 10(6)-21 x 10(6), respectively. Wall temperatures were near 300 K and this resulted in ratios of wall enthalpy to flow-stagnation enthalpy in the range of 0.1-0.02. The experiments were performed using rectangular ducts. The measurements were accomplished using a new Skin-Friction gauge that was developed for impulse facility testing. The gauge was an acceleration compensated piezoelectric transducer and had a lowest natural frequency near 40 kHz. Turbulent Skin-Friction levels were measured to within a typical uncertainty of +/-7%. The systematic uncertainty in measured Skin-Friction coefficient was high for the tested laminar conditions; however, to within experimental uncertainty, the Skin-Friction and heat-transfer measurements were in agreement with the laminar theory of van Driest (1952). For predicting turbulent Skin-Friction coefficient, it was established that, for the range of Mach numbers and Reynolds numbers of the experiments, with cold walls and boundary layers approaching the turbulent equilibrium state, the Spalding & Chi (1964) method was the most suitable of the theories tested. It was also established that if the heat transfer rate to the wall is to be predicted, then the Spalding & Chi (1964) method should be used in conjunction with a Reynolds analogy factor near unity. If more accurate results are required, then an experimentally observed relationship between the Reynolds analogy factor and the Skin-Friction coefficient may be applied.
-
Skin-Friction Measurements in a Supersonic Combustor with Crossflow Fuel Injection
Journal of Propulsion and Power, 2001Co-Authors: Haruto Tanno, Allan Paull, Raymond J. StalkerAbstract:Shock-tunnel experiments have been performed to measure the effect on Skin-Friction drag in a supersonic combustor of flow disturbances induced by hydrogen fuel injection transverse to the airstream. Constant-area, circular cross section combustors of lengths varying up to 0.52 m were employed. The experiments were done at a stagnation enthalpy of 7.2 MJ . kg(-1) and a Mach number of 4.3, with a boundary layer that was turbulent downstream of the 0.14-m station in the combustors. Combustor Skin-Friction drag was measured by a method based on the stress wave force balance, the method being validated by agreement between fuel-off Skin-Friction drag measurements and predictions using existing Skin-Friction theories. When fuel was injected, it was found that the drag remained at fuel-off values. Thus, the streamwise vortices and other flow disturbances induced by the fuel injection, mixing, and combustion, which are expected to be present in a scramjet combustor, did not influence the Skin-Friction drag of the combustors.
-
hypervelocity Skin Friction reduction by boundary layer combustion of hydrogen
Journal of Spacecraft and Rockets, 2000Co-Authors: Christopher P. Goyne, Raymond J. Stalker, Allan Paull, C BrescianiniAbstract:Shock-tunnel measurements of Stanton number and Skin-Friction coefficient are reported for the injection of hydrogen through a 1.6-mm slot into a turbulent boundary layer in a l-m-long duct. The mainstream Mach number of 4.5, stagnation enthalpy of 7.8 MJ/kg, pressure of 50 kPa, and temperature of 1500 K provided a combination of flow variables that was sufficient to ensure boundary-layer combustion of the hydrogen. The experiments were also simulated by a numerical mode). The experiments and the numerical model indicated that the Stanton number was only slightly affected by boundary-layer combustion. However, the numerical simulation indicated that injection with combustion caused a reduction of approximately 50% in the Skin Friction coefficient, whereas the experiments yielded an even greater effect, with the reduction in Skin-Friction coefficient reaching 70-80% of the values of Skin Friction with no injection. Numerical simulation of a constant pressure flow indicated that boundary-layer combustion caused the Skin-Friction reduction to persist for at least 5 m downstream.
-
Shock-tunnel Skin-Friction measurement in a supersonic combustor
Journal of Propulsion and Power, 1999Co-Authors: Christopher P. Goyne, Raymond J. Stalker, Allan PaullAbstract:Shock-tunnel measurements are reported of Skin Friction with supersonic hydrogen-air combustion in a constant area duct. A floating-element Skin-Friction gauge was used, in which the shear force was applied directly to a piezoceramic measuring element. The experiments were conducted at stagnation enthalpies of 5.7 and 6.8 MJ kg(-1), a precombustion Mach number of similar to 4.5, and with a maximum duct Reynolds number of 1.3 x 10(7). The measurements showed that, although supersonic combustion caused the Skin Friction to fluctuate with time, it did not affect the mean value of the Skin Friction coefficient, and this mean value could be predicted using existing turbulent: boundary-layer theory. Measurements of heat transfer also established that Reynolds analogy could be used in both the fuel-off and fuel-on flows.
-
Shock tunnel Skin Friction measurement in a supersonic combustor
36th AIAA Aerospace Sciences Meeting and Exhibit, 1998Co-Authors: Christopher P. Goyne, Raymond J. Stalker, Allan PaullAbstract:Shock tunnel measurements are reported of Skin Friction with supersonic hydrogen-air combustion in a constant area duct. A floating element Skin Friction gauge was used, in which the shear force was applied directly to a piezoceramic measuring element. The experiments were conducted at stagnation enthalpies of 5.7 and 6.8 MJ kg, a precombustion Mach number of approximately 4.5, and with a maximum duct Reynolds number of 1.3x10. The measurements showed that the Skin Friction coefficient was unaffected by supersonic combustion, and could be predicted by the correlation of Spalding and Chi. Measurements of heat transfer also established that Reynolds analogy could be used in both the fuel-off and fuel-on flows.
Raymond J. Stalker - One of the best experts on this subject based on the ideXlab platform.
-
Control of Hypersonic Turbulent Skin Friction by Boundary-Layer Combustion of Hydrogen
Journal of Spacecraft and Rockets, 2020Co-Authors: Raymond J. StalkerAbstract:Shvab-Zeldovich coupling of flow variables has been used to extend Van Driest's theory of turbulent boundary-layer Skin Friction to include injection and combustion of hydrogen in the boundary layer. The resulting theory is used to make predictions of Skin Friction and heat transfer that are found to be consistent with experimental and numerical results. Using the theory to extrapolate to larger downstream distances at the same experimental conditions, it is found that the reduction in Skin-Friction drag with hydrogen mixing and combustion is three times that with mixing alone. In application to flow on a flat plate at mainstream velocities of 2, 4, and 6 knits, and Reynolds numbers from 3 X 10(6) to 1 x 10(8), injection and combustion of hydrogen yielded values of Skin-Friction drag that were less than one-half of the no-injection Skin-Friction drag, together with a net reduction in heat transfer when the combustion heat release in air was less than the stagnation enthalpy. The mass efficiency of hydrogen injection, as measured by effective specific impulse values, was approximately 2000 s.
-
Scramjets, sub-orbital flight and Skin Friction
14th AIAA AHI Space Planes and Hypersonic Systems and Technologies Conference, 2006Co-Authors: Raymond J. StalkerAbstract:The use of a shock tunnel in developing concepts for penetrating the sub-orbital flight regime with a scramjet powered vehicle is described. An experimental comparison with flight, the scaling of shock tunnel experimental results, modes of hydrogen fuel injection, and the thrust performance of a simple combustion-thrust nozzle configuration are discussed. Analysis of the operation of an axi-symmetric scramjet powered model then directs attention to the importance of wave analysis, and of Skin Friction drag. Wave analysis emphasizes the importance of slender configurations at high sub-orbital velocities, with an attendant increased emphasis on Skin Friction drag. Combustion of hydrogen in turbulent boundary layers is offered as a means of reducing Skin Friction. When applied to a simplified scramjet flowpath in flight at 4.3km/s (Mach 14), the use of boundary layer combustion doubles the net hydrogen fuel specific impulse for the scramjet.
-
Skin-Friction measurements in high-enthalpy hypersonic boundary layers
Journal of Fluid Mechanics, 2003Co-Authors: Christopher P. Goyne, Raymond J. Stalker, Allan PaullAbstract:Skin-Friction measurements are reported for high-enthalpy and high-Mach-number laminar, transitional and turbulent boundary layers. The measurements were performed in a free-piston shock tunnel with air-flow Mach number, stagnation enthalpy and Reynolds numbers in the ranges of 4.4-6.7, 3-13 MJ kg(-1) and 0.16 x 10(6)-21 x 10(6), respectively. Wall temperatures were near 300 K and this resulted in ratios of wall enthalpy to flow-stagnation enthalpy in the range of 0.1-0.02. The experiments were performed using rectangular ducts. The measurements were accomplished using a new Skin-Friction gauge that was developed for impulse facility testing. The gauge was an acceleration compensated piezoelectric transducer and had a lowest natural frequency near 40 kHz. Turbulent Skin-Friction levels were measured to within a typical uncertainty of +/-7%. The systematic uncertainty in measured Skin-Friction coefficient was high for the tested laminar conditions; however, to within experimental uncertainty, the Skin-Friction and heat-transfer measurements were in agreement with the laminar theory of van Driest (1952). For predicting turbulent Skin-Friction coefficient, it was established that, for the range of Mach numbers and Reynolds numbers of the experiments, with cold walls and boundary layers approaching the turbulent equilibrium state, the Spalding & Chi (1964) method was the most suitable of the theories tested. It was also established that if the heat transfer rate to the wall is to be predicted, then the Spalding & Chi (1964) method should be used in conjunction with a Reynolds analogy factor near unity. If more accurate results are required, then an experimentally observed relationship between the Reynolds analogy factor and the Skin-Friction coefficient may be applied.
-
Skin-Friction Measurements in a Supersonic Combustor with Crossflow Fuel Injection
Journal of Propulsion and Power, 2001Co-Authors: Haruto Tanno, Allan Paull, Raymond J. StalkerAbstract:Shock-tunnel experiments have been performed to measure the effect on Skin-Friction drag in a supersonic combustor of flow disturbances induced by hydrogen fuel injection transverse to the airstream. Constant-area, circular cross section combustors of lengths varying up to 0.52 m were employed. The experiments were done at a stagnation enthalpy of 7.2 MJ . kg(-1) and a Mach number of 4.3, with a boundary layer that was turbulent downstream of the 0.14-m station in the combustors. Combustor Skin-Friction drag was measured by a method based on the stress wave force balance, the method being validated by agreement between fuel-off Skin-Friction drag measurements and predictions using existing Skin-Friction theories. When fuel was injected, it was found that the drag remained at fuel-off values. Thus, the streamwise vortices and other flow disturbances induced by the fuel injection, mixing, and combustion, which are expected to be present in a scramjet combustor, did not influence the Skin-Friction drag of the combustors.
-
hypervelocity Skin Friction reduction by boundary layer combustion of hydrogen
Journal of Spacecraft and Rockets, 2000Co-Authors: Christopher P. Goyne, Raymond J. Stalker, Allan Paull, C BrescianiniAbstract:Shock-tunnel measurements of Stanton number and Skin-Friction coefficient are reported for the injection of hydrogen through a 1.6-mm slot into a turbulent boundary layer in a l-m-long duct. The mainstream Mach number of 4.5, stagnation enthalpy of 7.8 MJ/kg, pressure of 50 kPa, and temperature of 1500 K provided a combination of flow variables that was sufficient to ensure boundary-layer combustion of the hydrogen. The experiments were also simulated by a numerical mode). The experiments and the numerical model indicated that the Stanton number was only slightly affected by boundary-layer combustion. However, the numerical simulation indicated that injection with combustion caused a reduction of approximately 50% in the Skin Friction coefficient, whereas the experiments yielded an even greater effect, with the reduction in Skin-Friction coefficient reaching 70-80% of the values of Skin Friction with no injection. Numerical simulation of a constant pressure flow indicated that boundary-layer combustion caused the Skin-Friction reduction to persist for at least 5 m downstream.
Christopher P. Goyne - One of the best experts on this subject based on the ideXlab platform.
-
Skin-Friction measurements in high-enthalpy hypersonic boundary layers
Journal of Fluid Mechanics, 2003Co-Authors: Christopher P. Goyne, Raymond J. Stalker, Allan PaullAbstract:Skin-Friction measurements are reported for high-enthalpy and high-Mach-number laminar, transitional and turbulent boundary layers. The measurements were performed in a free-piston shock tunnel with air-flow Mach number, stagnation enthalpy and Reynolds numbers in the ranges of 4.4-6.7, 3-13 MJ kg(-1) and 0.16 x 10(6)-21 x 10(6), respectively. Wall temperatures were near 300 K and this resulted in ratios of wall enthalpy to flow-stagnation enthalpy in the range of 0.1-0.02. The experiments were performed using rectangular ducts. The measurements were accomplished using a new Skin-Friction gauge that was developed for impulse facility testing. The gauge was an acceleration compensated piezoelectric transducer and had a lowest natural frequency near 40 kHz. Turbulent Skin-Friction levels were measured to within a typical uncertainty of +/-7%. The systematic uncertainty in measured Skin-Friction coefficient was high for the tested laminar conditions; however, to within experimental uncertainty, the Skin-Friction and heat-transfer measurements were in agreement with the laminar theory of van Driest (1952). For predicting turbulent Skin-Friction coefficient, it was established that, for the range of Mach numbers and Reynolds numbers of the experiments, with cold walls and boundary layers approaching the turbulent equilibrium state, the Spalding & Chi (1964) method was the most suitable of the theories tested. It was also established that if the heat transfer rate to the wall is to be predicted, then the Spalding & Chi (1964) method should be used in conjunction with a Reynolds analogy factor near unity. If more accurate results are required, then an experimentally observed relationship between the Reynolds analogy factor and the Skin-Friction coefficient may be applied.
-
hypervelocity Skin Friction reduction by boundary layer combustion of hydrogen
Journal of Spacecraft and Rockets, 2000Co-Authors: Christopher P. Goyne, Raymond J. Stalker, Allan Paull, C BrescianiniAbstract:Shock-tunnel measurements of Stanton number and Skin-Friction coefficient are reported for the injection of hydrogen through a 1.6-mm slot into a turbulent boundary layer in a l-m-long duct. The mainstream Mach number of 4.5, stagnation enthalpy of 7.8 MJ/kg, pressure of 50 kPa, and temperature of 1500 K provided a combination of flow variables that was sufficient to ensure boundary-layer combustion of the hydrogen. The experiments were also simulated by a numerical mode). The experiments and the numerical model indicated that the Stanton number was only slightly affected by boundary-layer combustion. However, the numerical simulation indicated that injection with combustion caused a reduction of approximately 50% in the Skin Friction coefficient, whereas the experiments yielded an even greater effect, with the reduction in Skin-Friction coefficient reaching 70-80% of the values of Skin Friction with no injection. Numerical simulation of a constant pressure flow indicated that boundary-layer combustion caused the Skin-Friction reduction to persist for at least 5 m downstream.
-
Shock-tunnel Skin-Friction measurement in a supersonic combustor
Journal of Propulsion and Power, 1999Co-Authors: Christopher P. Goyne, Raymond J. Stalker, Allan PaullAbstract:Shock-tunnel measurements are reported of Skin Friction with supersonic hydrogen-air combustion in a constant area duct. A floating-element Skin-Friction gauge was used, in which the shear force was applied directly to a piezoceramic measuring element. The experiments were conducted at stagnation enthalpies of 5.7 and 6.8 MJ kg(-1), a precombustion Mach number of similar to 4.5, and with a maximum duct Reynolds number of 1.3 x 10(7). The measurements showed that, although supersonic combustion caused the Skin Friction to fluctuate with time, it did not affect the mean value of the Skin Friction coefficient, and this mean value could be predicted using existing turbulent: boundary-layer theory. Measurements of heat transfer also established that Reynolds analogy could be used in both the fuel-off and fuel-on flows.
-
Shock tunnel Skin Friction measurement in a supersonic combustor
36th AIAA Aerospace Sciences Meeting and Exhibit, 1998Co-Authors: Christopher P. Goyne, Raymond J. Stalker, Allan PaullAbstract:Shock tunnel measurements are reported of Skin Friction with supersonic hydrogen-air combustion in a constant area duct. A floating element Skin Friction gauge was used, in which the shear force was applied directly to a piezoceramic measuring element. The experiments were conducted at stagnation enthalpies of 5.7 and 6.8 MJ kg, a precombustion Mach number of approximately 4.5, and with a maximum duct Reynolds number of 1.3x10. The measurements showed that the Skin Friction coefficient was unaffected by supersonic combustion, and could be predicted by the correlation of Spalding and Chi. Measurements of heat transfer also established that Reynolds analogy could be used in both the fuel-off and fuel-on flows.
Sudesh Woodiga - One of the best experts on this subject based on the ideXlab platform.
-
Skin-Friction topology of wing–body junction flows
European Journal of Mechanics B-fluids, 2015Co-Authors: Hongjie Zhong, Sudesh Woodiga, Peng Wang, Jinkui Shang, Jianming WangAbstract:Abstract High-resolution time-averaged Skin-Friction fields in wing–body junction flows are extracted from luminescent oil-film visualization images taken at different viewing angles and positions in a wind tunnel. The complete Skin-Friction topology on the wing–body junction surface is reconstructed, and isolated singular points and separation and attachment lines are identified. The evolution of the topological structures is discussed as the angle of attack of the wing changes. The topological consistency of the extracted Skin-Friction fields is examined by applying the Poincare–Bendixson index formula. The relationship between the Skin-Friction topological features and flow structures like the horseshoe vortex, secondary separation, separation bubble and wingtip vortex is explored.
-
Effects of pitch, yaw, and roll on delta wing Skin Friction topology
Proceedings of the Institution of Mechanical Engineers Part G: Journal of Aerospace Engineering, 2015Co-Authors: Sudesh Woodiga, Rs Vewen Ramasamy, Sai Kumar KodeAbstract:High-resolution Skin Friction fields in separated flows over a 65° delta wing and a 76/40° double-delta wing with different junction fillets are obtained by using quantitative global Skin Friction diagnostics based on luminescent oil visualizations. The topological features such as separation and attachment lines on these delta wings are identified, and the effects of the pitch, yaw, and roll angles on the Skin Friction topology are studied systematically. The topological consistency of the measured Skin Friction fields on the delta wings is examined by using the Poincare–Bendixson index formula.
-
Effects of yaw and roll angles on Skin Friction topology on delta wings
50th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 2012Co-Authors: Sudesh Woodiga, Rs Vewen RamasamyAbstract:High-resolution Skin Friction fields in separated flows on delta wings are measured using quantitative global Skin Friction diagnostics based on luminescent oil visualizations. The effects of the yaw and roll angles on the Skin Friction topology on delta wings are studied systematically. The topological features like separation and attachment lines and isolated singular points are identified. The conservation law given by the Poincare-Bendixson index formula for the numbers of the isolated singular points and the boundary switch points is used as a general approach to analyze the Skin Friction topology.
-
Feasibility of global Skin Friction diagnostics using temperature sensitive paint
Measurement Science and Technology, 2011Co-Authors: Sudesh WoodigaAbstract:This paper develops the principle of global Skin Friction diagnostics based on temperature sensitive paint (TSP) measurements in flows. The asymptotic form of the energy equation at a wall is derived, and its inverse solution is sought by using the variational method to extract a relative or normalized Skin Friction field from TSP-measured surface temperature fields. The selection of the relevant parameters (the Lagrange multiplier and the standard deviation of a Gaussian filter) and the intrinsic limitations of this method are discussed in the light of uncertainty analysis. Experimental implementation of this method is described, and the feasibility of TSP-based global Skin Friction diagnostics is examined in impinging jet experiments. The normalized Skin Friction distributions extracted by using this method are in fairly good agreement with hot-film Skin Friction measurements and the theoretical solutions in the normal and oblique impinging jets.
-
Skin Friction topology in a region enclosed by penetrable boundary
Experiments in Fluids, 2011Co-Authors: Sudesh Woodiga, Tian MaAbstract:High-resolution Skin Friction fields in separated flows on a low-aspect-ratio rectangular wing are obtained by using quantitative global Skin Friction diagnostics based on surface luminescent oil visualizations. The topological features like the isolated singular points and the boundary switch points in regions enclosed by penetrable boundaries are identified. The conservation law given by the Poincare–Bendixson index formula for the numbers of the isolated singular points and the boundary switch points is used as a general approach to analyze the topological structure of a Skin Friction field in a singly connected region enclosed by a penetrable boundary in the separated flows.
Haecheon Choi - One of the best experts on this subject based on the ideXlab platform.
-
Skin Friction generation by attached eddies in turbulent channel flow
Journal of Fluid Mechanics, 2016Co-Authors: Matteo De Giovanetti, Yongyun Hwang, Haecheon ChoiAbstract:Despite a growing body of recent evidence on the hierarchical organization of the self-similar energy-containing motions in the form of Townsend’s attached eddies in wall-bounded turbulent flows, their role in turbulent Skin-Friction generation is currently not well understood. In this paper, the contribution of each of these self-similar energy-containing motions to turbulent Skin Friction is explored up to $Re_{\unicode[STIX]{x1D70F}}\simeq 4000$ . Three different approaches are employed to quantify the Skin-Friction generation by the motions, the spanwise length scale of which is smaller than a given cutoff wavelength: (i) FIK (Fukagata, Iwamoto, Kasagi) identity in combination with the spanwise wavenumber spectra of the Reynolds shear stress; (ii) confinement of the spanwise computational domain; (iii) artificial damping of the motions to be examined. The near-wall motions are found to continuously reduce their role in Skin-Friction generation on increasing the Reynolds number, consistent with the previous finding at low Reynolds numbers. The largest structures given in the form of very-large-scale and large-scale motions are also found to be of limited importance: due to a non-trivial scale interaction process, their complete removal yields only a 5–8 % Skin-Friction reduction at all of the Reynolds numbers considered, although they are found to be responsible for 20–30 % of total Skin Friction at $Re_{\unicode[STIX]{x1D70F}}\simeq 2000$ . Application of all the three approaches consistently reveals that the largest amount of Skin Friction is generated by the self-similar motions populating the logarithmic region. It is further shown that the contribution of these motions to turbulent Skin Friction gradually increases with the Reynolds number, and that these coherent structures are eventually responsible for most of turbulent Skin-Friction generation at sufficiently high Reynolds numbers.
