Wall Pressure Measurements Research Articles

Generalized, Three-Dimensional Wind Tunnel Wall Correction Using Nonlinear Least-Squares Optimization

A novel three-dimensional technique for correcting wind tunnel measurements for wall interference has been developed. The flow around the test body and its wake is approximated as a series of inviscid singularities, while the wind tunnel walls and model support are approximated using a panel method. A nonlinear least-squares approach with trust-region reflective optimization is then used to obtain the strength and locations of singularities together with the domain boundary panel strengths by fitting to measured wall pressures. The technique is demonstrated using computational fluid dynamics for the test case of a well-documented slender delta wing body with high blockage and validated against both experiments and legacy data. The nonlinear least-squares wall correction method is shown to demonstrate a significant improvement in wall corrections compared to the classical two-variable technique.

Predicting Wall Pressure in Shock Wave/Boundary Layer Interactions with Convolutional Neural Networks

Within the dynamic realm of variable-geometry shock wave/boundary layer interactions, the wall parameters of the flow field undergo real-time fluctuations. The conventional approach to sensing these changes in wall pressure through sensor measurements is encumbered by a cumbersome process, leading to diminished efficiency and an inability to provide swift predictions of wall parameters. This paper introduces a data-driven methodology that leverages non-contact schlieren imaging to predict wall pressure within the flow field, a technique that holds promise for informing the optimized design of variable-geometry systems. A sophisticated deep learning framework, predicated on Convolutional Neural Networks (CNN), has been engineered to anticipate alterations in wall pressure stemming from high-speed shock wave/boundary layer interactions. Utilizing an impulsive wind tunnel with a Mach number of 6, we have procured a sequence of schlieren images and corresponding wall pressure measurements, capturing the continuous variations induced by an attack angle from a shock wave generator. These data have been instrumental in compiling a comprehensive dataset for the training and evaluation of the CNN. The CNN model, once trained, has adeptly deduced the distribution of wall pressure from the schlieren imagery. Notwithstanding, it was observed that the CNN’s predictive prowess is marginally diminished in regions where pressure variations are most pronounced. To assess the model’s generalization capabilities, we have segmented the dataset according to different temporal intervals for network training. Our findings indicate that while the generalization of all models crafted was less than optimal, Model 4 demonstrated superior generalization. It is thus suggested that augmenting the training set with additional samples and refining the network architecture will be a worthwhile endeavor in subsequent research initiatives.

Experimental Investigation Of The Flow-Acoustic Interaction In Human Phonation

In the human phonation process, acoustic standing waves in the vocal tract can influence the fluid flow through the glottis. To investigate the amount of two-way coupling between the flow field and the acoustics, the supraglottal flow field has been recorded via high-speed particle image velocimetry (PIV) in a synthetic larynx model for several configurations with different vocal tract lengths. Based on the obtained velocity fields, aeroacoustic source terms were computed. Furthermore, the hydrodynamic pressure in the vocal tract was recorded via wall pressure measurements. The recordings revealed that near a vocal tract resonance frequency, the focal fold oscillation frequency jumps onto the resonance. This is accompanied by a substantial relative increase in aeroacoustic sound generation efficiency. At the same time, the glottal volume flow needed for stable vocal fold oscillation decreases strongly. The pressure measurements showed that acoustic anti-resonances of the vocal tract directly dampen the harmonic content of the hydrodynamic pressure field when matching frequencies. This result shows that back-coupling of the acoustics onto the flow field does not only occur in the case where the vocal fold oscillation frequency and a resonance frequency of the vocal tract match, but also under more other conditions.

Using Ultrasound Imaging To Identify Flow Reattachment In Shear-Thinning Suspensions

The current study explores ultrasound imaging velocimetry (UIV) as an alternative method for capturing flow fields in shear-thinning suspensions. In particular, UIV is used here together with pressure measurements to identify the reattachment point and to correlate the point's location with the pressure recovery downstream of an axisymmetric expansion. Four fluids are investigated: pure water, as well as three 1750ppm xanthum-gum-in-water solutions mixed with non-reactive mineral micro-particles at 0%, 15% and 30% volume fractions. Wall-pressure measurements were collected through taps located at 0 to 13 throat diameters downstream of the expansion with subsequent UIV measurements collected from 0.5 to 5 throat diameters downstream of the expansion. Pressure-tap measurements for the tested suspensions demonstrate 80% to 100% total pressure recovery achieved at approximately 4 to 5 throat diameters downstream from the throat. Furthermore, all four fluids exhibit total pressure recoveries within 10% of Borda-Carnot prediction. Despite similar pressure recoveries, UIV revealed different reattachment lengths for the tested fluids. Water exhibited a reattachment length of approximately four throat diameters, which is expected within the tested turbulent regime, while the xanthum-gum solution exhibited a delayed reattachment beyond the field-of-view when the effective Reynolds number is O(100). Pipe-wall velocity measurements suggest that the dense suspensions exhibit similar reattachment lengths to that of water despite expectations that the dense suspensions would behave similar to the pure xanthum-gum solution given: the similar Reynolds number between the pure xanthum-gum solution and the tested dense suspensions; and previous work done by Barnes et al. (2024) and others revealing shear-layer stabilization within dense suspensions. It is suspected that increased diffusion within the suspension mitigates the shear layer's ability to convect downstream, but improved measurements are required to state this conclusively.

Reconstruction Of Time-Averaged 3D Pressure Fields In The Wake Of An Ahmed Body With Pressure From PIV

In this contribution, we present and compare time-averaged pressure fields reconstructed from scanned stereoscopic 2D3C-PIV data and volumetric 3D-PTV data (Shake-The-Box) with classic pointwise surface pressure tap measurements. Measurements were conducted in the near-wake region of an one-quarter scaled Ahmed body (Ahmed 1984) with 25° slant angle at height-based Reynolds numbers of Re = 5.06 · 10^4 and 1.13 · 10^5, respectively, i.e. free-stream velocities of 10.5 m/s and 23.5 m/s. The measurements are a continuation of previous measurements (Gericke et al. 2023, Ladwig et al. 2023) with a focus on the more complex flow topology concerning the wake flow structure. Measurements were conducted in a low-speed wind tunnel of Göttinger design with a semi-closed test section at Bochum University of Applied Sciences. The investigated flow field in the near wake region is dominantly characterized by a strongly three-dimensional flow field based on a mutually influenced vortex system in the wake, which challenges the utilized pressure reconstruction algorithm based on the Reynolds-averaged Navier-Stokes equations. The present study addresses challenges in pressure reconstruction due to the presence of highly transient rotational and shearing flow in the context of a practical application. The results show good agreement between reconstructed PIV/PTV-based pressure fields and reference pressure measurements using classic wall pressure measurements. The global characteristics of the pressure distributions are correctly reproduced. The agreement is particularly good in areas of unidirectional flow and local smaller velocity gradients. In shear zones as well as separation and, e.g., recirculation areas, larger deviations are clearly visible, as the velocity gradients present near the surface are not sufficiently captured at all.

An Experimental Investigation of Low-Frequency Active Excitation in Scramjet Combustor Using a Micro-Pulse Detonation Engine

A micro-pulse detonation engine (μPDE) was designed and installed to a direct-connect scramjet combustor of Pusan National University (PNU-DCSC). The active excitation on the scramjet combustor was experimentally studied using the μPDE operating at frequencies of 10–20 Hz. A vitiation air heater (VAH) was used to supply high-enthalpy vitiated air to the isolator and the scramjet combustor at a Mach number of 2.0, with a total temperature of 1600 K and a total pressure of 1.68 MPa. The exit of μPDE was located at the center of the cavity of the scramjet combustor. Active excitation was performed at equivalence ratios of 0.111 and 0.163, and characteristics were analyzed through Schlieren recording and bottom wall pressure measurement. As a result, when the detonation emitted from the μPDE entered the scramjet combustor, it instantly formed a shock train and moved forward within the scramjet combustor. The flame instantaneously changed from the cavity shear layer flame to the cavity flame. Through bottom wall pressure measurement, it was also observed that active excitation resulted in a significant pressure increase near the cavity compared to when active excitation was not performed. This revealed combustion characteristics, indicating improved combustion efficiency from the pressure increase in the scramjet combustor.

ML for fast assimilation of wall-pressure measurements from hypersonic flow over a cone

Data assimilation (DA) integrates experimental measurements into computational models to enable high-fidelity predictions of dynamical systems. However, the cost associated with solving this inverse problem, from measurements to the state, can be prohibitive for complex systems such as transitional hypersonic flows. We introduce an accurate and efficient deep-learning approach that alleviates this computational burden, and that enables approximately three orders of magnitude computational acceleration relative to variational techniques. Our method pivots on the deployment of a deep operator network (DeepONet) as an accurate, parsimonious and efficient meta-model of the compressible Navier–Stokes equations. The approach involves two main steps, each addressing specific challenges. Firstly, we reduce the computational load by minimizing the number of costly direct numerical simulations to construct a comprehensive dataset for effective supervised learning. This is achieved by optimally sampling the space of possible solutions. Secondly, we expedite the computation of high-dimensional assimilated solutions by deploying the DeepONet. This entails efficiently navigating the DeepONet’s approximation of the cost landscape using a gradient-free technique. We demonstrate the successful application of this method for data assimilation of wind-tunnel measurements of a Mach 6, transitional, boundary-layer flow over a 7-degree half-angle cone.

Effect of Gas Addition on Liquid Kerosene Combustion in a Scramjet Combustor

Experiments were conducted at Mach 2.52 to investigate the effect of gas addition on the mixing and combustion characteristics of the liquid kerosene in a scramjet combustor. Two different combustion modes (scram mode and ram mode) were achieved by varying the equivalence ratio. Flowfield diagnostic techniques, such as shadow visualization and wall pressure measurement, and Proper Orthogonal Decomposition analysis were employed to investigate the complex supersonic gas– liquid two-phase combustion flowfield. It is found that, compared to the pure high-pressure kerosene, the gas-added kerosene can achieve better combustion performance at low injection pressure. The gas addition increases the fuel-jet penetration depth and promotes flowfield fluctuations. The gas–liquid two-phase instability induces large-scale vortices within the fuel-jet shear layer. The diffusion and mixing of kerosene are enhanced by the large-scale vortices, and the rapid and intense combustion of kerosene is realized.

Fluid and Combustion Dynamics in Axisymmetric and Perisymmetric Supersonic Combustion Flowpaths

An experimental comparison of the fluid and combustion dynamics between axisymmetric and perisymmetric ethylene-fueled supersonic flowpaths was made in a Mach 4.5 high-enthalpy flow. The perisymmetric shape can be characterized as roughly elliptical, with sharp corners at its major axis vertices. High-speed imaging of the flow luminescence and wall pressure measurements were performed simultaneously. Four different combustion modes (scram mode, scram-ram transition, ram mode, and unstart) were observed by altering the global equivalence ratio. Time-resolved measurements revealed that the mode transitions for the perisymmetric model occurred earlier than the axisymmetric model. The instantaneous data showed transient phenomena such as upstream flame propagation in the combustor, reverse flame propagation into the isolators, and the propagation of the pseudo-shock. In addition, an inlet buzz was observed for the perisymmetric model. The time-resolved high-speed images and the pressure data revealed that inlet unstart and restart repeatedly occurred during the inlet buzz. The results of a Fourier transform analysis indicated that acoustic resonance within the flowpath was the primary mechanism for the inlet buzz of the perisymmetric model.

Reynolds-number scaling of wall-pressure–velocity correlations in wall-bounded turbulence

Wall-pressure fluctuations are a practically robust input for real-time control systems aimed at modifying wall-bounded turbulence. The scaling behaviour of the wall-pressure–velocity coupling requires investigation to properly design a controller with such input data so that it can actuate upon the desired turbulent structures. A comprehensive database from direct numerical simulations (DNS) of turbulent channel flow is used for this purpose, spanning a Reynolds-number range $Re_\tau \approx 550\unicode{x2013}5200$ . Spectral analysis reveals that the streamwise velocity is most strongly coupled to the linear term of the wall pressure, at a Reynolds-number invariant distance-from-the-wall scaling of $\lambda _x/y \approx 14$ (and $\lambda _x/y \approx 8$ for the wall-normal velocity). When extending the analysis to both homogeneous directions in $x$ and $y$ , the peak coherence is centred at $\lambda _x/\lambda _z \approx 2$ and $\lambda _x/\lambda _z \approx 1$ for $p_w$ and $u$ , and $p_w$ and $v$ , respectively. A stronger coherence is retrieved when the quadratic term of the wall pressure is concerned, but there is only little evidence for a wall-attached-eddy type of scaling. An experimental dataset comprising simultaneous measurements of wall pressure and velocity complements the DNS-based findings at one value of $Re_\tau \approx 2$ k, with ample evidence that the DNS-inferred correlations can be replicated with experimental pressure data subject to significant levels of (acoustic) facility noise. It is furthermore shown that velocity-state estimations can be achieved with good accuracy by including both the linear and quadratic terms of the wall pressure. An accuracy of up to 72 % in the binary state of the streamwise velocity fluctuations in the logarithmic region is achieved; this corresponds to a correlation coefficient of $\approx$ 0.6. This thus demonstrates that wall-pressure sensing for velocity-state estimation – e.g. for use in real-time control of wall-bounded turbulence – has merit in terms of its realization at a range of Reynolds numbers.

On low-frequency unsteadiness of single-incident and dual-incident shock waves/turbulent boundary layer interactions with large-scale separations

Interactions between turbulent boundary layer and single-incident or dual-incident shock waves are commonly observed in supersonic inlets. To provide novel insights into the unsteadiness of these interactions, six incident shock wave/turbulent boundary layer interactions (ISWTBLIs), including both single-ISWTBLIs and dual-ISWTBLIs, are experimentally investigated using dynamic wall-pressure measurements at Mach 2.73 flow conditions. Through spectral analysis and correlation analysis, the unsteadiness characteristics of single-ISWTBLIs and dual-ISWTBLIs are comparatively examined, revealing significant influences of shock-wave strength and shock-wave distance on low-frequency unsteadiness. Specifically, both regions near the separation and reattachment points exhibit distinct low-frequency unsteadiness in single-ISWTBLIs and dual-ISWTBLIs with relatively strong separations. An increase in the deflection angle from 10° to 12° in single-ISWTBLIs extends the streamwise separation length, while causing a dramatic decrease in both characteristic frequency and normalized characteristic frequency (Strouhal number) of low-frequency unsteadiness. However, for dual-ISWTBLIs, as the shock-wave distance increases, there is an initial increase followed by a subsequent decrease in the separation length accompanied by a continuously increasing characteristic frequency, thus indicating a different relationship between separation length and characteristic frequency of unsteadiness in dual-ISWTBLIs in comparison with that observed in single-ISWTBLIs. Moreover, correlation analysis revealed that the pressure signals in the reattachment region are of strong negative correlation with those near the separation-shock foot, and the correlation increases with increasing shock-wave strength in single-ISWTBLIs and decreasing shock-wave distance in dual-ISWTBLIs.

Experimental and Numerical Investigations of Steam Expansion Rate in Low Pressure Steam Turbine

Abstract This study focused on the expansion rate of steam; the effect on efficiency was investigated experimentally and numerically by varying the expansion rate of steam in the stage, where condensation occurs by varying the flowrate and inlet temperature using a five-stage model steam turbine. The steam expansion rate of the stator blades in each stage was evaluated from the measured wall pressure and total pressure. In addition, the turbine efficiency was evaluated from the measured torque and mass flowrate, and the effect of flowrate and condensing stage can be taken into account for losses caused by condensation. In addition, numerical calculations to account for the effects of nonequilibrium condensation were performed using ANSYS CFX. The numerical calculations were able to show the details of the nucleation situation and the resulting changes in flow patterns. Numerical evaluation of the subcooling loss showed that there was no difference in subcooling loss between different mass flow rates. The steam expansion rate was evaluated from the measurement results, and it was found that there was no difference in the steam expansion rate due to differences in mass flowrate. This corresponds to the numerical result that the subcooling loss does not vary with flowrate.

An Optimized Pressure-Based Method for Thrust Vectoring Angle Estimation

This research developed a pressure-based thrust vectoring angle estimation method for fluidic thrust vectoring nozzles. This method can accurately estimate the real-time in-flight thrust vectoring angle using only wall pressure information on the inner surface of the nozzle. We proposed an algorithm to calculate the thrust vectoring angle from the wall pressure inside the nozzle. Non-dominated sorting genetic algorithm II was applied to find the optimal sensor arrays and reduce the wall pressure sensor quantity. Synchronous force and wall pressure measurement experiments were carried out to verify the accuracy and real-time response of the pressure-based thrust vectoring angle estimation method. The results showed that accurate estimation of the thrust vectoring angle can be achieved with a minimum of three pressure sensors. The pressure-based thrust vectoring angle estimation method proposed in this study has a good prospect for engineering applications; it is capable of accurate real-time in-flight monitoring of the thrust vectoring angle. This method is important and indispensable for the closed-loop feedback control and aircraft attitude control of fluidic thrust vectoring control technology.

Unsteady loads on circular cylinder in cross-flow: An observation in natural wind and comparison with wind tunnel experiments

We present the synchronized unsteady wall pressure measurements performed at the circumference of a full scale 35 m circular chimney submitted to natural wind. The atmospheric turbulent boundary layer generates a turbulence intensity of 15 % at the altitude of the measurements and the corresponding Reynolds number is 1.13 106. For the first time, the steady and unsteady pressure distributions around the circumference are presented, despite large difficulties in the measuring process. The analysis of the pressure distribution using the bi-orthogonal decomposition (BOD) is a key factor in the success of the processing. By comparison with wind tunnel similar measurements, with 2D cylinders, the time-averaged pressure distribution is found between the one of a subcritical regime and a supercritical regime, slightly closer to the subcritical regime notably because the base pressure coefficients are similar. The atmospheric turbulence is an essential ingredient for the unsteady pressure response on the chimney, which generates high levels of RMS pressure, much higher than all those measured in wind tunnel, even under the turbulent flow generated by a grid. The analysis by BOD allowed the extraction of a term which is mainly generated by alternate vortex shedding. Despite a very noisy signal, the Strouhal number is determined to be 0.20–0.24. The corresponding shape of the pressure distribution is compared with those found in wind tunnel: it is shown that the full scale field measurements are close, but not identical, to the small scale measurements in wind tunnel on a rough cylinder submitted to a grid generated turbulent flow.

Interaction and breakdown induced by multiple optimal disturbances in hypersonic boundary layer

The present paper finds that the coexistence of multiple primary instability waves may cause a non-trivial nonlinear interaction and breakdown process, which has not been reported before. In the considered Mach 6 flat-plate boundary layer, a global resolvent analysis reports three optimal disturbances (local maxima): a high-frequency planar wave, a low-frequency oblique wave and a stationary streak. For the dominant planar and oblique waves, a parabolised stability equation analysis identifies the initial non-modal transient growth and downstream modal growth. Initiated by these two optimal disturbances jointly, the complete linear and nonlinear instability processes until breakdown to turbulence are shown with direct numerical simulation. Owing to the transient growth, the oblique wave may be more significant than the planar wave in the breakdown. The oblique wave and scales of nonlinear interactions are pronounced in the outer layer, whose significance may not be comprehensively characterised by the wall pressure measurement. Fourier modes characterising the oblique-wave oblique breakdown, the planar-wave fundamental resonance, the planar-wave subharmonic resonance and the combination resonance related to a detuned mode are observed successively. The detuned mode seems to dominate the near-wall dynamics in the late nonlinear stage, characterised by $\varLambda$ -like structures. Meanwhile, the existence of this detuned mode is independent of the initial amplitude ratio and the absolute amplitude of the oblique and planar waves. Weakly nonlinear stability analyses demonstrate that the detuned mode is mainly a consequence of the secondary instability under the combination of planar and oblique primary waves. Wave vector plots reveal the resonant state of multiple triads. Energy budget and amplitude-correction analyses provide a clear physical image of energy transfer.

Flow enhancement from wall pressure observations: A compressible continuous adjoint data assimilation model

This study establishes a compressible continuous adjoint data assimilation (C2ADA) approach for reproducing a complete mean flow from sparse wall pressure observations. The model-form error induced by the Boussinesq approximation is corrected by the addition of a spatially varying additive forcing term. The linear part of the eddy viscosity, computed using the conventional Reynolds-averaged Navier–Stokes model, is incorporated for ensuring the well-posedness of the optimization. The model is derived theoretically to minimize discrepancies between the wall pressure measurements and the numerical predictions of the primary-adjoint system, thereby enabling determination of the optimal contribution of the Reynolds force vector. The effects of divergence schemes and turbulence models are investigated by examining flow over a 30P30N airfoil. The C2ADA model, employing two distinct schemes, demonstrates significant improvements in velocity estimation, but the first-order scheme introduces excessive dissipation, resulting in an under-prediction of spanwise vorticity. The C2ADA model combined with different eddy-viscosity models uniquely recovers the Reynolds force vectors and obtains mean fields that outperform those achieved solely through conventional eddy viscosity models. The practicability of the C2ADA model for capturing complex flow phenomena is confirmed by applying it to study three-dimensional flow over a 65° delta wing. Despite limited wall pressure observations, the C2ADA model has shown a notable improvement in accurately estimating the intensity and location of both the primary and secondary vortices. Recovery errors in the apex region are significantly diminished by incorporating a paucity of observations account for the effect of inboard vortex. The study broadens the applicability of continuous adjoint-based approaches for modeling compressible flow, as our C2ADA approach is easily implemented in existing computational fluid dynamics solvers and has significantly higher computational efficiency than other approaches.

Investigation of shock/shock interferences on the aerodynamics of a fragment in the wake of debris in a rarefied regime/at high altitude

This work presents an experimental investigation focused on the analysis of aerodynamic properties between two interacting spheres in a supersonic rarefied flow. Atmospheric re-entries of space debris, whether natural or man-made, begin at altitude 120 km, and observations of historical re-entries have shown that fragmentation occurs between 90 and 50 km. The resulting fragments interact with each other, altering their own trajectories while traversing the different flow regimes between the free molecular and continuum regimes. This study focuses on the intermediate slip regime, where viscous effects of varying magnitude can influence the nature of the interactions of the shocks and modify them from the already known behaviour in the continuum regime. Specifically, this study examines how two spheres interact with each other upon re-entry into the atmosphere, focusing particularly on the six types of shock/shock interactions identified by Edney. The experiments were performed in the MARHy wind tunnel, in a steady Mach 4 laminar flow with static pressure 2.67 Pa. To highlight the differences between the six types of interferences, a variety of set-ups and devices were used: flow-field visualization, aerodynamic forces (through two diagnoses, aerodynamic balance and the swinging sphere technique) and wall pressure measurements. Results demonstrate the identification of differences according to the type of interference observed, showing in particular the viscous effect of rarefied flows by making a comparison with the continuum regime.

The impacts of material acoustic impedance and thickness on single laser-induced bubble dynamics and determining factors in resulting pressure

The objective of this paper is to experimentally identify the primary sources of pressure when a laser-induced cavitation bubble is collapsing to a wall with specific emphases on the material acoustic impedance and thickness. Both high-speed videos and local wall pressure measurements were performed for various standoff ratios γ, bubble diameters, and wall materials. In the case of a rigid wall, in addition to the known high pressure for γ<0.6 where the bubble attaches and collapses on the wall (ring collapse), at γ≈1.12 where the jet is dominant, and low pressure obtained at γ≈0.913, where neither effect is significant, we further captured similar pressure profiles during the collapse after the first rebound at γ≈1.16 for the ring collapse, γ≈1.79 for the jet, and γ≈1.41 for the minimal, respectively. This indicates a strong jet is typically followed by a strong ring collapse. Generally, the pressure from the second collapse increases faster with the bubble size than that of the first collapse. For walls featuring smaller acoustic impedance or thickness, which cannot be approximated as rigid bodies or accessed by pressure sensor, our unique bubble edge analyzing tool shows that the ring collapse and jet effects are moved to smaller values of γ. The maximum pressure exerted on the wall in these cases is smaller than that on the rigid wall. Finally, we summarized the asymptotic evolution curves of each edge which bound the bubble dynamics at different standoff ratios.

Experimental study of load characteristics caused by underwater explosion bubble collapsing in the neighborhood of a rigid wall

In this paper, a series of underwater explosion (UNDEX) experiments were carried out in a cubical explosion tank, to investigate the complex behaviors of one bubble collapsing near a vertical rigid wall. The evolution of the bubble was captured by a high-speed camera and the pressure caused by both the primary shock wave and the bubble collapse on the surface of the wall was measured by several sensors installed on the wall surface. Experimental results of the measured wall pressure and the resultant load impulse are compared with theoretical results that are calculated from the corrected empirical formula. A good agreement between the experimental and theoretical results is achieved. On this basis, the effects of the bubble-wall distance on the bubble behaviors and the corresponding explosion load characteristics on the rigid surface are analyzed and discussed. The result aims to provide a feasible reference for the study of near-field UNDEX bubble dynamics and the resultant load on structures nearby.

Combustion characteristics of a dual-mode ramjet engine with a supersonic aerodynamic ramp injector

The combustion characteristics of a liquid-hydrocarbon-fueled dual-mode ramjet combustor with a new injector, including a cavity-type flame holder, were investigated under inflow conditions of M 1.8, total pressure of 590 kPa, and total temperature of 930 K. The newly proposed injector uses various injection methods, such as an aerodynamic ramp, pre-mixing chamber, barbotage gas, and supersonic nozzle. The aerodynamic ramp injection method consists of four injectors with inclination angles of 40° and 80° and toe-in angles of 30° and 60°. This was adopted to increase the penetration height of the fuel while minimizing the total pressure loss. A pre-mixing chamber with a barbotage gas injection device was employed to enhance atomization and fuel–air mixing. In addition, a contoured Mach 3 supersonic nozzle was used to obtain a higher momentum through acceleration. For performance comparison, a combustor with a pre-mixing chamber and barbotage gas was used in the same manner, but injected by a cylindrical nozzle with a 15-degree of transverse angle. The ignition was initiated by a torch ignitor installed on the cavity floor with hydrogen pilot fuel. Once combustion stabilized, only the main liquid fuel was supplied. The Mach number was calculated using quasi-one-dimensional analysis based on the measured wall pressures and inlet conditions. The results showed that the model combustor with two types of injectors operated in the ramjet mode, which was subsonic near the flame holder and supersonic at the exit of the combustor. At the combustor outlet, the total pressure according to the equivalence ratio of 0.25 to 0.56, the newly proposed injector case showed a higher pressure level, steep increase, and more uniform pressure distribution than the baseline injector from the measurement result of the pitot pressure rake at the combustor exit.