First Experiments and Commissioning of the ORCHID Nozzle Test Section

Abstract

This paper reports one of the initial NICFD experiments in the nozzle test section of the ORCHID aimed at providing accurate data for the validation of flow solvers, albeit, at this stage of the research, the focus is limited to inviscid phenomena. Notably, a series of schlieren photographs displaying Mach waves in the supersonic flow of the dense vapor of siloxane MM were obtained and are documented here for the commissioning experiment, namely, for inlet conditions corresponding to a stagnation temperature and pressure of T 0 = 252 • C and P 0 = 18.4 bara. At these inlet conditions the compressibility factor of the fluid is Z 0 = 0.58. The digital processing of the schlieren images allowed to estimate multiple angles formed by the Mach waves stemming from the upper and lower nozzle surfaces because of the infinitesimal density perturbations generated by the, albeit small, roughness of the metal surfaces. These values are related to the local Mach number by a simple geometric relation. Moreover, the total expanded uncertainty in the Mach number was computed. This information together with the estimate of the average Mach number was used for a first assessment of the capability of evaluating NICFD effects occurring in a dense organic vapor flow of MM by comparison with the results of CFD simulations. The outcome of the comparison was satisfactory. It can thus be inferred that the nozzle test section has been commissioned and it is ready for experimental campaigns in which its full potential in terms of measurements accuracy, repeatability, and operational flexibility will be exploited.

Mach Number Estimation and Pressure Profile Measurements of Expanding Dense Organic Vapors

“…The Mach number distribution along the midplane and its total expanded uncertainty values can then be calculated. For more details on the line extraction algorithm and the uncertainty quantification procedure the reader is referred to [1,5]. Regarding the pressures acquired with the Scanivalve, the statistical averages and standard deviations are directly computed from the measurements obtained in steady conditions.…”

“…The exact same equipment, i.e. light source, pinhole, lenses and camera, employed in the experiment reported in [1] is adopted to visualize gradients of density. In the experiment described in this paper, an additional camera (BOBCAT IGV-B1610 16bit CCD) is used to image the nozzle profile geometry, allowing to track changes owing to thermal expansion and, hence, determine the nozzle throat size at various operating conditions.…”

“…Their values are P 0 (PT011) = 18.36 ± 0.0229 bar, T 0 (TT015) = 253.7 ± 0.66 • C. The pressure measured at the nozzle outlet is P b (PT004) = 2.21 ± 0.0416 bar. 1 The nozzle profiles considered in the CFD model accounts for the thermal expansion of the nozzle housing. Notably, by analyzing with a dedicated camera the position of markers on the lateral surface of the nozzle profiles, the throat height was determined as H th = 7.73 mm.…”

Nitrogen Experiments on a Supersonic Linear Cascade For ORC Applications

“…In this context, experiments are further complicated by the need of instrumentation requiring fluid-specific and condition-specific calibration. Consequently, experiments conceived and performed up to date, with the aim of validating CFD tools [1], typically employed simplified flow configurations, such as either isentropic expansions within planar converging-diverging nozzles [2,3,4] or supersonic flows over aerodynamic bodies [5]. Such experiments entail the indubitable advantage of providing nearly isentropic flows in large portions of the domain (typically upstream/downstream of shock structures); this greatly simplifies the measurement system, since it allows resorting to measurement techniques that do not require aerodynamic calibration.…”