An annular plenum is integrated downstream of six pulse detonation combustors arranged in a can-annular configuration. The primary purpose of the plenum is the mitigation of pressure and velocity fluctuations, which is crucial for operation with a downstream turbine. The flow inside the plenum is investigated by means of flush-mounted pressure transducers arranged in axial and circumferential directions. The test rig is operated in different firing patterns at frequencies up to 16.7 Hz per tube. Two firing patterns are studied to characterize the shock dynamics inside the plenum. The obtained data allow for a better understanding of shock interaction and attenuation inside the plenum as well as the quantification of pressure fluctuations at the plenum outlet. Furthermore, a comparison is made between piezoresistive and piezoelectric pressure transducers showing the capability of piezoresistive transducers for high frequency pressure measurements.

Non-intrusive temporally and spatially resolved measurements of dynamic phenomena are heavily reliant on high-speed (>1 kHz) digital scientific cameras. The cost of these cameras is a major constraint on the operation of many experimental and educational research facilities. In this paper we present a performance analysis of a low-cost high-speed CMOS camera, the Chronos 1.4. Developed for consumer use, we investigate its potential as a scientific camera. It uses a 12 bit Luxima LUX1310 CMOS sensor with 1280 × 1024 px at 6.6 µm pitch and 1 µs minimum global shutter. It is capable of recording at 1057 Hz at full frame and up to 38 kHz with a reduced field of view. It provides a number of features not typically found in low-cost consumer cameras, such as external triggering and shutter gating control, clock outputs, and raw binary data output. We test the linearity of the sensor response using a pulsed LED source and analyse the sensor performance in terms of noise, jitter and intensity lag. A quantitative demonstration of the camera's performance under realistic experimental conditions is demonstrated with an image correlation velocimetry measurement in a high-speed propellant spray. The camera compares favourably against several scientific high speed cameras from major manufacturers. The camera is well suited for high resolution forward-scattering and in-line imaging techniques such as schlieren, shadowgraphy, holography and bright-field microscopy. Spatial bias in the dark field noise floor makes it generally unsuitable for lowlight measurement conditions. However, the small footprint and low cost make it ideal as an educational tool and for multi-camera experiments. These tests were conducted independently of the manufacturer and the authors have no conflicts of interest to disclose.

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Mitigation of pressure pulsations in the exhaust of a pulse detonation combustor is crucial for operation with a downstream turbine. For this purpose, a device termed the shock divider is designed and investigated. The intention of the divider is to split the leading shock wave into two weaker waves that propagate along separated ducts with different cross sections, allowing the shock waves to travel with different velocities along different paths. The separated shock waves redistribute the energy of the incident shock wave. The shock dynamics inside the divider are investigated using numerical simulations. A second-order dimensional split finite volume MUSCL-scheme is used to solve the compressible Euler equations. Furthermore, low-cost simulations are performed using geometrical shock dynamics to predict the shock wave propagation inside the divider. The numerical simulations are compared to high-speed schlieren images and time-resolved total pressure recording. For the latter, a high-frequency pressure probe is placed at the divider outlet, which is shown to resolve the transient total pressure during the shock passage. Moreover, the separation of the shock waves is investigated and found to grow as the divider duct width ratio increases. The numerical and experimental results allow for a better understanding of the dynamic evolution of the flow inside the divider and inform its capability to reduce the pressure pulsations at the exhaust of the pulse detonation combustor.

This note investigates how small changes in the protrusion depth of a pressure transducer affect the pressure measurement of a moving shock wave. Measurements are undertaken with Kistler, Kulite, and PCB sensors in flush, recessed, and protruded sensor positions. Measurements of both absolute pressure and Mach number are shown to be insensitive to sensor protrusion depth. An assessment of sensor response time indicates a significantly shorter reaction time for the Kulite and PCB sensors compared with the Kistler sensor.

Time-resolved visualisation of shock wave motion within a powered resonant tube (PRT) is presented for the regurgitant mode of operation. Shock position and velocity are measured as functions of both time and space from ultra-high-speed schlieren visualisations. The shock wave velocity is seen to vary across the resonator length for both the incident and reflected waves. Three mechanisms are explored as explanations for the variation in velocity: change in local fluid velocity, variation in shock strength and variations in local temperature. For the incident wave, local fluid velocity and shock strength are extracted from the data and both are demonstrated to contribute to the observed variation, with a non-trivial remainder likely explained by variation in temperature.

An investigation of shock diffraction through a non-quiescent background medium is presented using both experimental and numerical techniques. Unlike diffracting shocks in quiescent media, a spatial distortion of the shock front occurs, producing a region of constant shock angle. An example of this process arises in the exhaust from a pulse-detonation combustor. As the background velocity is increased, such as through the inclusion of a converging nozzle at the exhaust, the spatial distortion becomes more apparent. Numerical simulations using a compressible Euler solver demonstrate that the distortion is not due to the geometrical influence of the nozzle, but rather is a function of the magnitude of the background flow velocity. The distortion is studied using a modified geometrical shock dynamics formulation which includes the background flow and is validated against experiments. A simple model is presented to predict the shock distortion angle in the weak-shock limit. Finally, the axial decay behaviour of the shock is investigated and it is shown that the advection of the shock by the background flow delays the arrival of the head and tail of the expansion characteristic at the centreline. This leads to an increase in the rate of decay of the shock Mach number as the background flow velocity is increased.

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