No abstract

An active flow control concept using counterflowing jets to significantly modify the external flowfields and strongly weaken or disperse the shock-waves of supersonic and hypersonic vehicles to reduce the aerothermal loads and wave drag was investigated. Experiments were conducted in a trisonic blow-down wind-tunnel, complemented by pre-test computational fluid dynamics (CFD) analysis of a 2.6% scale model of Apollo capsule, with and without counterflowing jets, in Mach 3.48 and 4.0 freestreams, to assess the potential aerothermal and aerodynamic benefits of this concept. The model was instrumented with heat flux gauges, thermocouples and pressure taps, and employed five counterflowing jet nozzles (three sonic and other two supersonic with design Mach numbers of 2.44 and 2.94) and nozzle exit diameters ranging from 0.25 to 0.5 inch. Schlieren data show that at low jet flow rates of 0.05 and 0.1 lb,/sec, the interactions result in a long penetration mode (LPM) jet, while the short penetration mode (SPM) jet is observed at flow rates greater than 0. Ilb,/sec., consistent with the pre-test CFD predictions. For the LPM, the jet appears to be nearly hlly-expanded, resulting in a very unsteady and oscillatory flow structure in which the bow shock becomes highly dispersed such that it is no longer discernable. Higher speed camera Schlieren data reveal the shock to be dispersed into striations of compression waves, which suddenly coalesce to a weaker bow shock with a larger standoff distance as the flow rate reached a critical value. The pronounced shock dispersion could significantly impact the aerodynamic performance (L/D) and heat flux reduction of spacecrafk in atmospheric entry and re-entry, and could also attenuate the entropy layer in hypersonic blunt body flows. For heat transfer, the results show significant reduction in heat flux, even giving negative heat flux for some of the SPM interactions, indicating that the flow wetting the model is cooling, instead of heating the model, which could significantly impact the requirements and design of thermal protection system. These findings strongly suggest that the application of counterflowing jets as active flow control could have strong impact on supersonic and hypersonic vehicle design and performance. IntroductionOne of the technical challenges in space exploration and interplanetary missions is controlled entry and re-entry into planetary and Earth atmospheres, which requires the dissipation of considerable kinetic energy as the spacecrafk decelerates and penetrates the atmosphere. As such, effective heat load management of stagnation points and acreage heating remain a technological challenge and pose significant risk, especially for human missions.

The confluence of societally impacting forces such as climate change, overpopulation, and overdevelopment are stressing freshwater reserves (see figure 1) [1,2]. Beyond issues of scarcity, fresh water quality is increasingly affected by pollution derived from agriculture and industry. Water reuse addresses water scarcity [3][4][5][6]. By water reuse, we refer to the use of technology to directly or indirectly recycle treated wastewater effluent for potable and non-potable applications, thereby augmenting existing water supplies. In the US alone, water reuse, if implemented, could meet up to 30% of the current public water supply demand [7]. Advanced water treatment technologies are required to reduce contaminant levels in reused water to acceptable values [8]. These same technologies have the potential to also remove those contaminants not addressed by conventional water treatment systems. Advanced oxidation processes (AOPs) have been identified as the basis for the treatment of difficult water, addressing contaminants that are difficult to strip, absorb or biodegrade conventionally

We apply the Space-Time Conservation Element and Solution Element (CESE) method to solve the ideal MHD equations with special emphasis on satisfying the divergence free constraint of magnetic field, i.e., ∇⋅B = 0. In the setting of the CESE method, four approaches are employed: (i) the original CESE method without any additional treatment,(ii) a simple corrector procedure to update the spatial derivatives of magnetic field B after each time marching step to enforce ∇⋅B = 0 at all mesh nodes, (iii) an constraint-transport method by using a special staggered mesh to calculate magnetic field B, and (iv) the projection method by solving a Poisson solver after each time marching step. To demonstrate the capabilities of these methods, two benchmark MHD flows are calculated (i) a rotated one-dimensional MHD shock tube problem, and (ii) a MHD vortex problem.The results show no differences between different approaches and all results compare favorably with previously reported data.3

An active flow control concept using counterflowing jets to significantly modify the external flowfields and strongly weaken or disperse the shock-waves of supersonic and hypersonic vehicles to reduce the aerothermal loads and wave drag was investigated. Experiments were conducted in a trisonic blow-down wind-tunnel, complemented by pre-test computational fluid dynamics (CFD) analysis of a 2.6% scale model of Apollo capsule, with and without counterflowing jets, in Mach 3.48 and 4.0 freestreams, to assess the potential aerothermal and aerodynamic benefits of this concept. The model was instrumented with heat flux gauges, thermocouples and pressure taps, and employed five counterflowing jet nozzles (three sonic and other two supersonic with design Mach numbers of 2.44 and 2.94) and nozzle exit diameters ranging from 0.25 to 0.5 inch. Schlieren data show that at low jet flow rates of 0.05 and 0.1 lb,/sec, the interactions result in a long penetration mode (LPM) jet, while the short penetration mode (SPM) jet is observed at flow rates greater than 0. Ilb,/sec., consistent with the pre-test CFD predictions. For the LPM, the jet appears to be nearly hlly-expanded, resulting in a very unsteady and oscillatory flow structure in which the bow shock becomes highly dispersed such that it is no longer discernable. Higher speed camera Schlieren data reveal the shock to be dispersed into striations of compression waves, which suddenly coalesce to a weaker bow shock with a larger standoff distance as the flow rate reached a critical value. The pronounced shock dispersion could significantly impact the aerodynamic performance (L/D) and heat flux reduction of spacecrafk in atmospheric entry and re-entry, and could also attenuate the entropy layer in hypersonic blunt body flows. For heat transfer, the results show significant reduction in heat flux, even giving negative heat flux for some of the SPM interactions, indicating that the flow wetting the model is cooling, instead of heating the model, which could significantly impact the requirements and design of thermal protection system. These findings strongly suggest that the application of counterflowing jets as active flow control could have strong impact on supersonic and hypersonic vehicle design and performance. IntroductionOne of the technical challenges in space exploration and interplanetary missions is controlled entry and re-entry into planetary and Earth atmospheres, which requires the dissipation of considerable kinetic energy as the spacecrafk decelerates and penetrates the atmosphere. As such, effective heat load management of stagnation points and acreage heating remain a technological challenge and pose significant risk, especially for human missions.