Browsing by Author "Prince, Simon"

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    Air jet flow control on pitching aerofoils
    (Cranfield University, 2019-07-08 09:09) Prince, Simon; Green, Richard; Khodaglian, Vahik
    Experimental data on the effect of steady and pulsed air jet vortex generator blowing on a RAE9645 aerofoil section in dynamic stall.
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    Assessment of Turbulence Models for Transonic / Supersonic Smooth Surface Separation
    (Cranfield University, 2021-06-21 13:14) Prince, Simon; González caballero, Roberto; Di Pasquale, Davide
    A systematic comparison of the principle modern turbulence prediction methods for the solution of the Navier-Stokes equations for the calculation of high speed flows about slender forebodies at low to moderate angle of attack is presented. This class of flow involves smooth surface turbulent boundary layer separation resulting in steady symmetric leeside vortices, and also the formation of embedded shock waves from the displacement effect of the large vortices in supersonic flow. As such this flow is both complex and highly sensitive to the state of the boundary layers on the body. This study revealed that the method which most consistently provides accurate predictions of the overall forces and moments on the body, the most accurate distribution of surface pressure and can most accurately resolve the flow features, including leeside vortices and embedded shock wave features, is the Solution Adaptive Simulation method. Detached Eddy Simulation and the Reynold Stress Model, which would be expected to provide superior accuracy over the RANS based linear eddy viscosity models, on the whole, failed to provide better predictions. In fact, the k-omega Realizable and k-omega SST turbulence models provided data which was almost as consistently accurate as the Solution Adaptive Simulation method. The standard k-omega turbulence model appears to be completely unsuitable for the computation of this class of high speed flow problem, and this may be associated with the poor initial / default prescription of the value of omega at the far-field boundary.
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    Base flow characteristics for a sub-scale high-speed exhaust at over-expanded mode
    (ICAS - International Council of the Aeronautics Sciences, 2024-10-07) Tsentis, Spyros; Goulos, Ioannis; Prince, Simon; Pachidis, Vassilios; Zmijanovic, Vladeta
    This paper presents a numerical investigation on the base flow characteristics of a sub-scale, high-speed exhaust system at over-expanded state. The geometry is representative of future, advanced propulsion concepts. It features a truncated, ideal-contoured (TIC) nozzle and an axisymmetric cavity embedded at the base. Scale resolving simulations are performed using the Delayed Detached Eddy Simulation (DDES) turbulence modelling approach. The configuration is mounted on the test section of a wind tunnel through a wing-pylon to facilitate ongoing experiments. The proper orthogonal decomposition (POD) method is employed to identify the salient flow features at the base in terms of energy content. Time-averaged base pressure results show slightly reduced levels of pressure behind the pylon by approximately 1.2%. Additionally, reduced levels of pressure fluctuations in the region directly downstream of the pylon are identified, suggesting a severe impact on the base flow. This is further confirmed through the modal decomposition of the base flow. The first two most energetic modes of the flow exhibit strong spatial asymmetry in the intensity of velocity fluctuations, the latter being significantly reduced in the region behind the pylon. This is important for future, high-speed vehicles, which typically employ wingtip mounted nacelles and could exhibit increased levels of side loads as a result of this azimuthal asymmetry in the flow development.
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    Cavity impact on the base flow unsteadiness for a high-speed exhaust system
    (American Society of Mechanical Engineers, 2024-06-24) Tsentis, Spyros; Goulos, Ioannis; Prince, Simon; Pachidis, Vassilios; Zmijanovic, Vladeta
    Future propulsion systems will be essential to enable sustainable high-speed flight and routine space access. Such concepts usually employ base-embedded, convergent-divergent nozzles and cavity regions to facilitate their mission, thus altering the flow dynamics at the base notably in comparison to contemporary launch vehicles. This paper presents a numerical investigation on the impact of a cavity region on the base flow unsteadiness for a sub-scale, high-speed exhaust system at over-expanded mode. The fully-installed model in the test section of a wind tunnel is employed to facilitate an ongoing experimental campaign. The Delayed Detached Eddy Simulation turbulence modeling approach is utilized to investigate the flow at the base. The configuration featuring the cavity is directly compared to a baseline apparatus, where the cavity has been removed, thus allowing for the impact of the cavity to be identified. Results show that the cavity region can reduce the base pressure fluctuations up to 20% and acts in a damping-like manner for the base flow unsteadiness. The total energy of the pressure fluctuations spectrum at the base can be reduced by as much as 38% compared to the baseline configuration. However, the impact of the cavity on the time-averaged pressure distribution at the base is negligible. Finally, the cavity is found to have a notable effect on the nozzle side loads, which are are reduced by an order of magnitude compared to the baseline case, and behave in an axisymmetric manner. This indicates that the cavity could act as a passive flow control mechanism for side loads reduction.
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    Data for: The use of range-resolved interferometry for multi-parameter sensing in a wind tunnel
    (Cranfield University, 2023-12-12 14:59) Barrington, James; James, Stephen; Kissinger, Thomas; Staines, Stephen; Alcusa Saez, Erica; Lawson, Nicholas; Tatam, Ralph; Prince, Simon
    Each data set relates to the data displayed in Figure 2 of the conference paper. The 1st column in each file outlines the data type and unit.
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    Data supporting "Optical Fibre Pressure Sensing Using a Frequency Modulated Laser-Based Signal Processing Technique"
    (Cranfield University, 2023-04-21 12:36) Barrington, James; James, Stephen; Kissinger, Thomas; Staines, Stephen; Prince, Simon; Alcusa Saez, Erica; Lawson, Nicholas; Tatam, Ralph
    Each file contains the relevant data to the figure as stated in its name. Column headers within the file outline the variable and its associated unit. The authors, where possible, have tried to keep the data in its rawest, useable form in order to provide the greatest flexibility for future manipulation. All data files are formatted as csv for accessibility.
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    Optical fibre pressure sensing using a frequency modulated laser-based signal processing technique
    (IOP Publishing, 2023-04-21) Barrington, James; James, Stephen; Kissinger, Thomas; Staines, Stephen; Prince, Simon; Alcusa Saez, Erica; Lawson, Nicholas J.; Tatam, Ralph P.
    Range resolved interferometry (RRI) applied to the interrogation of an extrinsic Fabry–Perot based pressure sensor in laboratory and wind tunnel environments is presented. A simple, compact sensor head design was fabricated and subsequently characterised using RRI, which was shown to have a sensitivity of 1.627x10-3 rad Pa−1 with a noise standard deviation of 9 Pa over a data rate of 1.5 kHz. When installed in a high-lift wing for surface pressure evaluation during wind tunnel testing, the approach outlined here was able to perform as well as a conventionally employed commercial device for relative static pressure measurements.
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    Passive transonic shock control on bump flow for wing buffet suppression
    (MDPI, 2023-06-20) Di Pasquale, Davide; Prince, Simon
    Since modern transport aircraft cruise at transonic speeds, shock buffet alleviation is one indispensable challenge that civil transport research needs to be addressed. Indeed, in the transonic flow regime shock-induced separation and transonic buffet compromise the flight envelope of an aircraft, and therefore its operational safety and structural integrity. One possible solution is to control and delay the boundary layer separation. The aim of this work was to study whether sub-boundary layer scale period roughness, which locally increases the boundary layer displacement thickness, can act as a virtual shock bump, with aim of bifurcating the foot of the shock wave to reduce the shock’s adverse effect on the boundary layer in the same way as solid shock bumps are known to act. This passive approach can then enhance the buffet margin, consequently extending the safe flight envelope. An experimental investigation was performed, applying this passive technique on a wind tunnel wall bump model which simulated the flow over the upper surface of an aerofoil. The results, in terms of surface pressure distribution and corresponding shadowgraph flow visualisation, showed that such periodic roughness can, indeed, bifurcate the shock wave and delay shock-induced separations, depending on the orientation of the roughness and its periodicity. A virtual shock bump effect can be produced using the displacement effect of periodic sub-boundary layer scale roughness.
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    Propulsion aerodynamics for a novel high-speed exhaust system
    (American Society of Mechanical Engineers (ASME), 2023-09-28) Tsentis, Spyros; Goulos, Ioannis; Prince, Simon; Pachidis, Vassilios; Zmijanovic, Vladeta
    A key requirement to achieve sustainable high-speed flight and efficiency improvements in space access, lies in the advanced performance of future propulsive architectures. Such concepts often feature high-speed nozzles, similar to rocket engines, but employ different configurations tailored to their mission. Additionally, they exhibit complex interaction phenomena between high-speed and separated flow regions at the base, which are yet not well understood, but are critical in terms of pressure and viscous forces. This paper presents a numerical investigation on the aerodynamic performance of a representative novel exhaust system, which employs a high-speed, truncated, ideal contoured nozzle and a complex-shaped cavity region at the base. Reynolds-Averaged Navier-Stokes computations are performed for a number of Nozzle Pressure Ratios (NPRs) and free stream Mach numbers in the range of 2.7 < NPR < 24 and 0.7 < M∞ < 1.2 respectively. The corresponding Reynolds number lies within the range of 1.06 · 106 < Red < 1.28 · 106 based on the maximum diameter of the configuration. A decomposition of the drag domain forces exposes the major trends between the constituent elements. The impact of the cavity on the aerodynamic characteristics of the apparatus is revealed by direct comparison to an identical non-cavity configuration. Results show a consistent trend of increasing base drag with increasing NPR for all examined M∞ for both configurations. This is attributed to the jet entrainment effect and to the lower base pressure imposed by the higher jet flow expansion. The cavity region is found to have almost no impact on the incipient separation location of the nozzle flow. At low supersonic speeds of M∞ = 1.2 and high NPRs, the cavity has a significant effect on the aerodynamic performance, transitioning nozzle operation to under-expanded conditions. This results in approximately 12% higher drag coefficient compared to the non-cavity case and shifts the minimum NPR for which the system produces positive gross propulsive force to higher values.
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    Propulsion aerodynamics for a novel high-speed exhaust system
    (American Society of Mechanical Engineers, 2023-12) Tsentis, Spyros; Goulos, Ioannis; Prince, Simon; Pachidis, Vassilios; Zmijanovic, Vladeta
    A key requirement to achieve sustainable high-speed flight and efficiency improvements in space access, lies in the advanced performance of future propulsive architectures. Such concepts often feature high-speed nozzles, similar to rocket engines, but employ different configurations tailored to their mission. This paper presents a numerical investigation on the aerodynamic performance of a representative novel exhaust system, which employs a high-speed, truncated, ideal contoured nozzle and a complex-shaped cavity region at the base. Reynolds-Averaged Navier-Stokes computations are performed for a number of Nozzle Pressure Ratios (NPRs) and free stream Mach numbers in the range of 2.7 < NPR < 24 and 0.7 < M∞ < 1.2 respectively. The corresponding Reynolds number lies within the range of 1.06 · 106 < Red < 1.28 · 106 based on the maximum diameter of the configuration. The impact of the cavity on the aerodynamic characteristics is revealed by direct comparison to an identical non-cavity configuration. Results show a consistent trend of increasing base drag with increasing NPR for all examined M∞ for both configurations, owing to the jet entrainment effect. Cavity is found to have no impact on the incipient separation location of the nozzle flow. At conditions of M∞ = 1.2 and high NPRs, the cavity has a significant effect on the aerodynamic performance, transitioning nozzle operation to under-expanded conditions. This results in approximately 12% higher drag coefficient compared to the non-cavity case and shifts the minimum NPR for which the system produces positive gross propulsive force to higher values.
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    The use of range-resolved interferometry for multi-parameter sensing in a wind tunnel
    (SPIE, 2023-05-23) Barrington, James; James, Stephen; Kissinger, Thomas; Staines, Stephen; Prince, Simon; Alucsa-Saeza, Erica; Lawson, Nicholas J.; Tatam, Ralph P.
    The work presented demonstrates that key parameters in aerodynamic structural characterisation of pressure, strain, and structural dynamics, can be all measured via optical fibre sensors interrogated using the principles of range-resolved interferometry (RRI). When used to interrogate sensors simultaneously deployed on a high lift wind in a wind tunnel, the approach yielded resolutions of 31 μPa/ √ Hz and 1 nε/ √ Hz at a bandwidth of 1526 Hz for pressure and strain, respectively, demonstrating the accuracy and versatility of the RRI signal processing technique.
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    Wind tunnel installation effects on the base flow for a high-speed exhaust system
    (AIAA, 2024-01-04) Tsentis, Spyros; Goulos, Ioannis; Prince, Simon; Pachidis, Vassilios; Zmijanovic, Vladeta; Saavedra, Josè
    It is envisaged that future propulsion concepts will enable high-speed flight and improve space access. However, their aerodynamic behavior is not yet well understood, especially at the base where severe flow separation occurs, requiring further analyses using both numerical and experimental techniques. This paper presents a numerical investigation of the wind tunnel installation effects on a representative, sub-scale, high-speed exhaust system. The analysis facilitates an ongoing design of experiments and de-risking activity. The apparatus features a truncated, ideal-contoured nozzle and an axially symmetric cavity region embedded at the base. The viable design space owing to high blockage is identified in terms of maximum approach Mach number. A systematic jet vectoring effect is observed in all cases examined. The origins of this effect are investigated and attributed solely to the pressure distribution asymmetry caused by the existence of the wing-pylon. Additionally, local flow similarity at the base of the tunnel-installed model with respect to unconstrained flow is investigated and presented, along with a proposed methodology to establish comparability. This analysis is of increased practical importance, due to the size range of most closed transonic tunnels found in academic research facilities. Results show that the pressure distribution at pre-choking tunnel conditions agrees within less than 1.5% and 0.1% for the base and cavity wall surfaces, respectively. At post-choking tunnel operation, the base pressure distribution of the model exhibits increased deviations in the azimuthal direction of up to 7.5%. The base pressure distribution in the corresponding unconstrained flow case falls within the observed pressure range of the tunnel-installed model, while the pressure distribution along the cavity wall agrees within less 1%. The findings of this study suggest that a jet vectoring effect could potentially manifest to wingtip mounted nacelles, usually incorporated in future, high-speed vehicles. Finally, it is demonstrated, that local flow similarity exists at the base with respect to unbounded flow, even for post-choking tunnel conditions, which is critical in base flows and base drag reduction analyses.