1. Flow control using electromagnetic fields is one of the options to reduce aerothermal loads to the spacecraft structures in ionized high enthalpy flows. Resler and Sears1,2,3performedseveralcomputationalinvestigationsof ionized super- and hypersonic flow fields in the presence of electromagnetic fields. In turn, the proliferation of computational investigations made immediately evident the necessity of well designed and cleanly performed experiments whose findings could serve the important task of flow-solver validation. Indeed, shortly after the appearance of Ref 1, Ziemer and Bush4investigated computationally and experimentally the influence of an externally applied magnetic-induction field on the shock stand-off distance in ionized air flowing at M=4.5 past a hemispherical cylinder in a shock tube. In September 1959, Ziemer5published a detailed description of the experiment. It turnedoutthatwhen thepulsed electric current in the coaxialcoils inside the cylinderproduced an external magnetic induction of 4 T in the vicinity of the stagnation point, the shock-wave standoff distance increased by a factor of 7.5 with respect to the situation without magnetic induction. The increase in shock-layer volume evidenced in Ziemer's flow-field photographs suggested a relief of the heat-flux distribution on the hemispherical-cylinder wall
2. yet Ziemer did not measure the heat flux. In 1962, Wilkinson6investigated the influence of an externally applied magnetic-induction field on the heat flux in the stagnation point of a blunt cone in ionized argon flowing at M=3 from the supersonic nozzle of an arc jet. The measurement technique consisted of monitoring the time history of the stagnation-point temperature and, then, of deriving the heat flux on the basis of the thin-wall model. The results, although somewhat scattered, indicated a monotonous decrease of the stagnation-point heat flux, down to almost 30%, with increasing magnetic-induction (squared) intensity (polarity NORTH). He investigated the influence of the magnetic-induction polarity on the flow field, remarked the inadequacy of short-duration facilities for heat-flux measurements in the presence of electromagnetic fields, indicated the shortcomings of thermocouples in electromagnetic environments due to the appearance of stray electromotive forceswhich falsify temperature readings.
3. Other heat-flux targeted experiments have been performed in more recent years. In Japan, Abe and collaborators12-14have been and are still working on the subject matter, although they have provided only temperature measurements. Several Russian experimental activities have been reviewed by Bityurin et alii15. In 2007, Bobashev and collaborators16performedaratherinterestingexperimentwithnitrogenflowingatM=4past a sharp-cone/cylinder. The configuration features a pointed electrode at the cone tip and a ring electrode at the cone base; therefore, electric currents can be passing between nitrogen flow and body. The heat flux was measured in two points of the cylindrical part via bismuth-monocrystal sensors based on transversal Seebeck effect17. Although the data are still being processed and interpreted, the heat flux seems to increase when the electric current is allowed to pass, similarly to what was found by Nowak and Yuen9. This experiment is very challenging for flow-solver validation because the correct implementation of the electromagnetic boundary conditions for even the case of non-conducting body are not yet fully mastered and the boundary conditions for conducting body introduce a level of complexity that is still beyond computational reach and, perhaps, physical understanding.