Eugene Timofeev

Pressure measurements in laboratory-scale blast wave flow fields.

The present study examines the effects that temporal and spatial averagings due to finite size and finite response time of pressure transducers have on the pressure measurements in blast wave flow fields generated by milligram charges of silver azide. In such applications, the characteristic time and length scales of the physical process are of the same order of magnitude as the temporal and spatial characteristics of the transducer. The measured pressure values will then be spatially and temporally averaged, and important parameters for the assessment of blast effects may not be properly represented in the measured trace. In this study, face-on and side-on pressure transducer setups are considered. In the experiments, face-on and side-on readings at the same distance from the charge as well as time-resolved optical visualization of the whole flow field are obtained simultaneously for the same explosive event. The procedure of data extraction from the experimental pressure traces is revisited and discussed in detail. In the numerical modeling part of the study, numerical blast flow fields are generated using an Euler flow solver. A numerical pressure transducer model is developed to qualitatively simulate the averaging effects. The experimental and numerical data show that the results of pressure measurements in experiments with small charges must be used with great caution. The effective averaging of the pressure signal may lead to a significant underestimation of blast wave intensities. The side-on setup is especially prone to this effect. The face-on setup provides results close to those obtained from optical records only if the pressure transducer is sufficiently remote from the charge.

Reflection of blast waves from straight surfaces

This paper presents the results of an ongoing experimental and numerical investigation into the unsteady process of blast wave reflection from straight smooth surfaces. Basic blast wave phenomena such as the transition from regular to irregular wave reflection can be adequately and conveniently studied in a laboratory environment by using small charges with masses in the milligram range. Previous work [1] has already revealed considerable discrepancies between numerical and experimental results for the location xtr of the transition from regular to irregular wave reflection. Further experiments with improved diagnostics confirm that the experimental determination of the transition point is rather difficult and possibly inaccurate because of the initially minuscule size and gradual growth of the Mach stem.

On the Influence of Reynolds Number on the Mach Stem Height at Shock Reflection from a Circular Cylinder

The transition from so-called regular to irregular shock wave reflection has been the subject of considerable research effort over the last seven decades [1]. The most thoroughly investigated case is that of the straight wedge

On the Self-starting Constraints for Busemann Intakes with Overboard Spillage

The air intake is an important component of hypersonic airbreathing engines. It is essentially a converging duct decelerating and compressing airflow and supplying the compressed air to the engine’s combustor. Molder and Szpiro [1] proposed to use the Busemann flow [2] as the basis for hypersonic air intake design.

Startability analysis of Busemann intakes with overboard spillage

In this work quasi-steady starting of Busemann intakes with overboard mass spillage is considered analytically and simulated numerically using 2D and 3D unstructured adaptive Euler finite-volume flow solvers. Two designs of Busemann intakes are under consideration: the conventional one based on Busemann flow with a weak conical shock and a newly proposed one based on Busemann flow with a strong conical shock. For both designs, the overboard spillage is achieved by cutting out an angular section of the full Busemann intake and covering the cuts with flat plates allowing for overboard spillage and maintaining the Busemann flow in the started mode. The theory predicting the self-starting (spontaneous starting) area ratios for Busemann intakes with overboard spillage is outlined. Methodology of finding the self-starting area ratios for a given free-stream Mach number via numerical experiments is discussed and applied to Busemann intakes with different capture angles. The numerical findings confirm the theoretical predictions of self-starting boundaries. It is demonstrated that overboard spillage significantly improves the starting characteristics of Busemann intakes. Furthermore, the strong-shock design leads to markedly better starting characteristics.

Visual determination of the onset of irregular blast wave reflection

This paper presents further results of an ongoing experimental and numerical investigation into the unsteady process of blast wave reflection from straight smooth surfaces. It is shown that basic blast wave phenomena such as the transition from regular to irregular wave reflection can be adequately and conveniently studied in a laboratory environment by using small charges with masses in the milligram range. While the laboratory scale generally provides greater accessibility, it also imposes more stringent conditions on the diagnostics than the large-scale environment. The paper reviews the previously found considerable discrepancies between numerical and experimental results for the location xtr of the transition from regular to irregular wave reflection. These are caused by the initially minuscule size and gradual growth of the Mach stem and the limited resolution of the recording material. Different techniques are used to improve the accuracy of the experimental determination of the transition point, and a new combination of modern high-speed photography with the traditional soot technique is shown to be the most promising tool for this purpose.