Passive Control of Base Pressure in a Converging-Diverging Nozzle with Area Ratio 2.56 at Mach 1.8

In this study,a duct is considered and special attention is paid to a passive method for the control of the base pressure relying on the use of a cavity with a variable aspect ratio.The Mach number considered is 1.8,and the area ratio of the duct is 2.56.In particular,two cavities are examined,their sizes being 3:3 and 6:3.The used L/D spans the interval 1–10 while the NPRs(nozzle pressure ratio)range from 2 to 9.The results show that the control becomes effective once the nozzles are correctly expanded or under-expanded.The pressure contours at different NPR and L/D are presented.It is shown that the NPR and cavity location strongly influence the base pressure.The NPR,Mach number,and cavity aspect ratio have a strong effect on the base pressure in the wake region.

Numerical Analysis of a Microjet-Based Method for Active Flow Control in Convergent-Divergent Nozzles with a Sudden Expansion

A method based on microjets is implemented to control the flow properties in a convergent-divergent nozzle undergoing a sudden expansion.Three different variants of this active control technique are explored numerically by means of a finite-volume method for compressible fluid flow:with the first one,the control is implemented at the base,with the second at the wall,while the third one may be regarded as a combination of these.When jets are over-expanded,the control is not very effective.However,when a favourable pressure gradient is established in the nozzle,the control becomes effective,leading to an increase in the base pressure.

Calculating the Climatology and Anomalies of Surface Cloud Radiative Effect Using Cloud Property Histograms and Cloud Radiative Kernels

Cloud radiative kernels(CRK)built with radiative transfer models have been widely used to analyze the cloud radiative effect on top of atmosphere(TOA)fluxes,and it is expected that the CRKs would also be useful in the analyses of surface radiative fluxes,which determines the regional surface temperature change and variability.In this study,CRKs at the surface and TOA were built using the Rapid Radiative Transfer Model(RRTM).Longwave cloud radiative effect(CRE)at the surface is primarily driven by cloud base properties,while TOA CRE is primarily decided by cloud top properties.For this reason,the standard version of surface CRK is a function of latitude,longitude,month,cloud optical thickness(τ)and cloud base pressure(CBP),and the TOA CRK is a function of latitude,longitude,month,τand cloud top pressure(CTP).Considering that the cloud property histograms provided by climate models are functions of CTP instead of CBP at present,the surface CRKs on CBP-τhistograms were converted to CTP-τfields using the statistical relationship between CTP,CBP andτobtained from collocated CloudSat and MODIS observations.For both climate model outputs and satellites observations,the climatology of surface CRE and cloud-induced surface radiative anomalies calculated with the surface CRKs and cloud property histograms are well correlated with those calculated from surface radiative fluxes.The cloud-induced surface radiative anomalies reproduced by surface CRKs and MODIS cloud property histograms are not affected by spurious trends that appear in Clouds and the Earth's Radiant Energy System(CERES)surface irradiances products.

Real-time human blood pressure measurement based on laser self-mixing interferometry with extreme learning machine

In this paper, we present a method based on self-mixing interferometry combing extreme learning machine for real-time human blood pressure measurement. A signal processing method based on wavelet transform is applied to extract reversion point in the self-mixing interference signal, thus the pulse wave profile is successfully reconstructed. Considering the blood pressure values are intrinsically related to characteristic parameters of the pulse wave, 80 samples from the MIMIC-II database are used to train the extreme learning machine blood pressure model. In the experiment, 15 measured samples of pulse wave signal are used as the prediction sets. The results show that the errors of systolic and diastolic blood pressure are both within 5 mm Hg compared with that by the Coriolis method.

Computational study on flow through truncated conical plug nozzle with base bleed

Conical plug nozzle and truncated conical plug nozzle are advanced rocket nozzles suitable for use as altitude compensating nozzles.In this study flow through the conical plug and truncated conical plug nozzles are numerically simulated to first validate with experimental data and then to compare the performance when a base bleed is introduced.The numerical analysis has considered two-dimensional axisymmetric models.Reynolds-averaged NavierStokes equations are solved with two equation shear stress transport k-ω turbulence model.For the validation of the plug nozzle,flow features and wall pressure along the length of the nozzle is taken for different nozzle pressure ratios.For the validation of truncated plug nozzle,flow features and base pressures at various nozzle pressure ratios are compared.The base bleed is taken as 2%of the inlet mass flow rate.The comparison of results shows that the introduction of base bleed helps to compensate for the loss of thrust due to conical plug nozzle truncation.